Blood plasma: constituent elements (substances, proteins), functions in the body, use. What is Plasma? For those who do not understand physics
PLASMA - partially or fully ionized gas formed from neutral atoms (or molecules) and charged particles (ions and electrons). The most important feature of a plasma is its quasineutrality, which means that the volumetric densities of positive and negative charged particles from which it is formed are almost the same. Gas transforms into a plasma state if some of its constituent atoms (molecules) for some reason have lost one or more electrons, i.e. turned into positive ions. In some cases, negative ions can also arise in plasma as a result of the "attachment" of electrons to neutral atoms. If no neutral particles remain in the gas, the plasma is called fully ionized.There is no sharp boundary between gas and plasma. Any substance that is initially in a solid state begins to melt as the temperature rises, and evaporates with further heating, i.e. turns into gas. If it is a molecular gas (for example, hydrogen or nitrogen), then with a subsequent increase in temperature, the gas molecules decompose into individual atoms (dissociation). At an even higher temperature, the gas ionizes, and positive ions and free electrons appear in it. Freely moving electrons and ions can carry electric current, so one of the definitions of plasma is that plasma is a conductive gas. Heating a substance is not the only way to obtain plasma.
Plasma is the fourth state of matter, it obeys the laws of gas and in many ways behaves like a gas. At the same time, the behavior of plasma in a number of cases, especially when exposed to electric and magnetic fields, turns out to be so unusual that it is often spoken of as a new fourth state of matter. In 1879 the English physicist W. Crookes, who studied the electric discharge in tubes with rarefied air, wrote: "The phenomena in evacuated tubes open up a new world for physical science in which matter can exist in the fourth state." Ancient philosophers believed that the basis of the universe is made up of four elements: earth, water, air and fire. . In a sense, this corresponds to the currently accepted division into the aggregate states of matter, and the fourth element is fire and, obviously, plasma corresponds.
The very term "plasma" in relation to a quasineutral ionized gas was introduced by the American physicists Langmuiry Tonks in 1923 when describing the phenomena in a gas discharge. Until that time, the word "plasma" was used only by physiologists and denoted a colorless liquid component of blood, milk or living tissues, but soon the concept of "plasma" was firmly included in the international physical vocabulary, becoming widespread.
Plasma production . The method of creating plasma by means of conventional heating of a substance is not the most common one. In order to thermally obtain complete ionization of the plasma of most gases, it is necessary to heat them up to temperatures of tens and even hundreds of thousands of degrees. Only in vapors of alkali metals (such as, for example, potassium, sodium or cesium), the electrical conductivity of the gas can be seen already at 2000–3000 ° C, this is due to the fact that in the atoms of monovalent alkali metals an electron outer shell much weaker bound to the nucleus than in the atoms of other elements periodic system elements (i.e. has a lower ionization energy). In such gases at the temperatures indicated above, the number of particles whose energy is higher than the ionization threshold is sufficient to create a weakly ionized plasma.The generally accepted method of obtaining plasma in laboratory conditions and technology is the use of an electric gas discharge. A gas discharge is a gas gap to which a potential difference is applied. In the gap, charged particles are formed that move in an electric field, i.e. create a current. To maintain the current in the plasma, it is necessary for the negative electrode (cathode) to emit electrons into the plasma. The emission of electrons from the cathode can be achieved in various ways, for example, by heating the cathode to sufficiently high temperatures (thermal emission), or by irradiating the cathode with any short-wavelength radiation (X-rays,
g radiation), capable of knocking electrons out of the metal (photoelectric effect). Such a discharge, created by external sources, is called non-self-sustaining.To independent Discharges include spark, arc and glow discharges, which are fundamentally different from each other in the way electrons are generated at the cathode or in the interelectrode gap. The spark discharge is usually intermittent even with a constant voltage across the electrodes. During its development, thin spark channels (streamers) appear, penetrating the discharge gap between the electrodes and filled with plasma. An example of one of the most powerful spark discharges is lightning.
In an ordinary arc discharge, which is realized in a rather dense gas and at a sufficiently high voltage on the electrodes, thermal emission from the cathode occurs most often from the fact that the cathode is heated by gas ions incident on it. An arc discharge arising in the air between two incandescent carbon rods, to which a corresponding electric voltage was supplied, was first observed at the beginning of the 19th century. Russian scientist V.V. Petrov. The brightly glowing discharge channel takes the shape of an arc due to the action of Archimedean forces on a highly heated gas. An arc discharge is also possible between refractory metal electrodes, this is associated with numerous practical applications of arc discharge plasma in powerful light sources, in electric arc furnaces for melting high-quality steels, in electric welding of metals, as well as in generators of a continuous plasma jet - the so-called plasmatrons. . The temperature of the plasma jet can reach 7000-10000 TO.
Various forms of cold or glow discharge are created in the discharge tube at low pressures and not very high voltages. In this case, the cathode emits electrons through the mechanism of the so-called field emission, when the electric field at the cathode surface simply pulls electrons out of the metal. The gas-discharge plasma extending from the cathode to the anode sections and at some distance from the cathode forms a positive column, which differs from the rest of the discharge sections by the relative constancy along the length of the parameters characterizing it (for example, the electric field strength). Glowing advertising tubes, fluorescent lamps, internally coated with complex phosphors, represent numerous applications of glow discharge plasma. A glow discharge in a plasma of molecular gases (for example, CO and CO 2) is widely used to create an active medium for gas lasers based on vibrational-rotational transitions in molecules.
The very process of ionization in the plasma of a gas discharge is inextricably linked with the passage of current and has the character of an ionization avalanche . This means that the electrons appearing in the gas gap are accelerated by the electric field during the free path and, before colliding with the next atom, gain energy sufficient to ionize the atom, i.e. knock out another electron). In this way, the multiplication of electrons in the discharge and the establishment of a stationary current take place.
In low-pressure glow gas discharges, the degree of plasma ionization (i.e., the ratio of the density of charged particles to the total density of particles constituting the plasma) is usually small. This plasma is called weakly ionized. Controlled thermonuclear fusion (CTF) installations use a high-temperature fully ionized plasma of hydrogen isotopes: deuterium and tritium. At the first stage of research on CTF, the plasma was heated to high temperatures of the order of millions of degrees by the electric current itself in the so-called self-compressible conducting plasma filaments (ohmic heating) ( cm... NUCLEAR FUSION). In toroidal tokamak-type plasma magnetic confinement devices, it is possible to to heat the plasma to temperatures of the order of tens and even hundreds of millions of degrees by injecting (injecting) high-energy beams of neutral atoms into the plasma. Another way is to use powerful microwave radiation, the frequency of which is equal to the ion cyclotron frequency (i.e., the frequency of rotation of ions in a magnetic field) - then heating the plasma by the method of the so-called cyclotron resonance.
Plasma in space. Under terrestrial conditions, due to the relatively low temperature and high density of terrestrial matter, natural plasma is rare. In the lower layers of the Earth's atmosphere, the only exceptions are lightning strikes. In the upper layers of the atmosphere, at altitudes of the order of hundreds of kilometers, there is an extended layer of partially ionized plasma, called the ionosphere. , which is created by the ultraviolet radiation of the sun. The presence of the ionosphere provides the possibility of long-range radio communication at short waves, since electromagnetic waves are reflected at a certain height from the layers of the ionospheric plasma. In this case, radio signals, due to multiple reflections from the ionosphere and from the Earth's surface, are able to bend around the convex surface of our planet.In the Universe, the bulk of matter (about 99.9%) is in the state of plasma. The sun and stars are formed from plasma, the ionization of which is caused by high temperatures. So, for example, in the inner region of the Sun, where thermonuclear fusion reactions take place, the temperature is about 16 million degrees. A thin region of the Sun's surface with a thickness of about 1000 km, called the photosphere, from which most of the solar energy is emitted, forms plasma at a temperature of about 6000 TO... In rarefied nebulae and interstellar gas, ionization occurs under the influence of ultraviolet radiation from stars.
Above the surface of the Sun is a rarefied, highly heated region (at a temperature of about one million degrees), which is called the solar corona. The stationary flux of nuclei of hydrogen atoms (protons) emitted by the solar corona is called solar wind . Plasma streams from the surface of the Sun create interplanetary plasma. The electrons of this plasma are captured by the Earth's magnetic field and form radiation belts around it (at a distance of several thousand kilometers from the Earth's surface). Plasma streams resulting from powerful solar flares change the state of the ionosphere. Fast electrons and protons, entering the Earth's atmosphere, cause the appearance of auroras in northern latitudes.
Plasma properties. Quasineutrality. One of important features plasma is that the negative charge of the electrons in it almost exactly neutralizes the positive charge of the ions. Under any influences on it, the plasma tends to maintain its quasi-neutrality. If in some place a random displacement (for example, due to density fluctuations) of part of the electrons occurs, creating an excess of electrons in one place and a deficiency in another, a strong electric field arises in the plasma, which prevents the separation of charges and quickly restores quasineutrality. The order of magnitude of such a field can be estimated as follows. Let in a layer of plasma with a thickness of D x a space charge is created with a density q ... According to the laws of electrostatics, at a length D x it creates an electric field E = 4 p q D x (The absolute system of units of the CGSE is used. In practical units - volts per centimeter - this field is 300 times larger). Let there be in 1 cm 3 D n e excess electrons in excess of those that precisely neutralize the ion charge. Then the space charge density q = e D n e, where e = 4.8 · 10 –10 units. СГС - electron charge. The electric field arising from the separation of charges is equal to E = 1.8 · 10 -6 D x in / cmAs a specific example, we can consider a plasma with the same concentration of particles as atmospheric air at the Earth's surface - 2.7 · 10 19 molecules / cm 3 or 5.4 · 10 19 atoms / cm 3. Let all atoms become singly charged ions as a result of ionization. The corresponding concentration of plasma electrons in this case is
n e = 5.4 10 19 electron / c m 3. Let the electron concentration change by 1% over a length of 1 cm. Then D n e = 5.4 10 17 electron / cm 3, D x = 1 cm and, as a result of charge separation, an electric field appears E " 10 12 in / cm.It would take enormous energy to create such a strong electric field. This suggests that for the considered example of a sufficiently dense plasma, the actual charge separation will be negligible. For a typical case of a thermonuclear plasma (
n e ~ 10 12 - 10 14 cm –3), the field that prevents charge separation for the above example remains very large ( E ~ 10 7 10 9 v / cm). Debye length and radius. Spatial scale of charge separation or that characteristic length below which (in order of magnitude) the separation of charges becomes noticeable can be estimated by calculating the work of separating charges over a distance d , which is accomplished by the forces arising along the length x electric field E = 4 p n e ex .Taking into account that the force acting on the electron is equal to
eE , the work of this force isThis work cannot exceed the kinetic energy of the thermal motion of plasma particles, which for the case of one-dimensional motion is equal to (1/2)
kT, where k - Boltzmann constant, T - temperature, i.e. A Ј (1/2) k T .This condition gives an estimate of the maximum scale of charge separation
This quantity is called the Debye length after the scientist who introduced it for the first time, investigating the phenomenon of electrolysis in solutions, where a similar situation occurs. For the above example of plasma under atmospheric conditions (
n e = 5.4 · 10 19 cm –3 T= 273 K, k = 1.38 · 10 –16 erg / K) we obtain d = 1.6 · 10 -19 cm, and for thermonuclear plasma conditions ( n e = 10 14 cm –3, T = 10 8 K) value d = 7 · 10 –3 cm.For a much more rarefied plasma, the Debye length may turn out to be more sizes the plasma volume itself. In this case, the condition of quasineutrality is violated, and it makes no sense to call such a system a plasma.
Length
d (or Debye radius) is the most important characteristic of the plasma. In particular, the electric field created by each individual charged particle in the plasma is screened by particles of opposite sign and actually disappears at a distance of the order of the Debye radius from the particle itself. On the other hand, the quantity d determines the depth of penetration of the external electric field into the plasma. Noticeable deviations from quasineutrality can occur near the boundaries of a plasma with a solid surface just at distances of the order of the Debye length.Plasma Oscillations . One more important characteristic plasma is the plasma (or Langmuir) oscillation frequency w p ... Plasma fluctuations are fluctuations in charge density (eg, electron density). They are caused by the action on the charge of an electric field arising from the violation of the quasineutrality of the plasma. This field seeks to restore the disturbed balance. Returning to the equilibrium position, the charge by inertia "skips" this position, which again leads to the appearance of a strong restoring field.Thus, Langmuir oscillations of the charge density in the plasma arise. The electron plasma oscillation frequency is determined in this case by the expression
For thermonuclear plasma, for example, (
n e = 10 14 cm –3) the electron plasma frequency turns out to be w p = 10 11 s –1. Plasma ideality. By analogy with an ordinary gas, a plasma is considered ideal if the kinetic energy of motion of its constituent particles is significantly greater than the energy of their interaction. A noticeable difference between plasma and gas is manifested in the nature of the interaction of particles. The interaction potential of neutral atoms and molecules in an ordinary gas is short-range. Particles have a noticeable effect on each other only when they come close to each other at distances of the order of the molecular diameter a ... Average distance between particles at gas density n defined as n –1/3 ( cm. GAS). In this case, the gas ideality condition has the form: a n –1/3. The Coulomb potential of interaction of charged particles in plasma turns out to be long-range, i.e. charged particles create extended electric fields around themselves, slowly decreasing with distance. The energy of the Coulomb interaction of two particles with a charge e at a distance R from each other is equal to e 2 / R ... Substituting instead of R average distance b between particles and assuming the average kinetic energy of particles equal to kT , the condition for the ideality of the plasma can be represented in the form: kT ... To assess the deviation of plasma from ideality, the parameter of plasma imperfection is usually introducedObviously, the plasma is ideal if
g 1.The condition of plasma ideality can be given a clearer meaning by introducing the concept of the so-called Debye sphere. A sphere with a radius equal to the Debye radius is allocated in the plasma volume, and the number of particles is counted
N D contained in this ball,~ g –3/2Comparison with criterion (3) shows that the condition of plasma ideality is reduced to the requirement that a sufficient number of particles appear in the Debye sphere (
N D >> 1).For the conditions of thermonuclear plasma considered above (
n e = 10 14 cm –3, T = 10 8 K ) it turns out that N D "10 8 ... For plasma generated in a lightning discharge ( n e = 5 10 19, T = 10 4), the quantity N D " 0.1. Such a plasma turns out to be weakly imperfect.Plasma thermodynamics. If a plasma satisfies the ideality condition, then in thermodynamic terms it behaves like an ideal gas, which means that its behavior obeys the usual gas laws ( cm... GAS). Since plasma is a mixture of particles of different types (including ions and electrons), the application of Dalton's law allows us to write the equation of state of an ideal plasma, which relates the plasma pressurewith the densities of each of the types of particles in the mixture, in the form p = p 1 + p 2 +… = ( n 1 + n 2 + ...) kTHere
T - the temperature common for all components of the mixture, corresponding to the establishment of complete thermodynamic equilibrium in the plasma. The real plasma of many experimental installations, as a rule, is not in a state of thermal equilibrium. Thus, a gas-discharge plasma is heated by the energy that is released during the passage of an electric current in the gas and is transmitted mainly to the light component of the plasma - electrons. When colliding with heavy particles (ions and atoms), electrons give up only a small part of their energy. If there are enough electrons in the plasma to provide an intense exchange of energy between them, a quasi-equilibrium is established in the plasma, corresponding to the establishment of an electron temperature that differs from the temperature of ions and atoms. ( T e> T ). This plasma is called non-isothermal. In gas-lit advertising tubes or in fluorescent lamps, for example, the electron temperature is usually tens of thousands of Kelvin, while the ion temperature and the temperature of the neutral gas are no higher than 1000-2000 TO... For a fully ionized plasma of thermonuclear installations, the plasma equation of state is written in the form p = k ( n e T e + n i T i )In this case, in contrast to a conventional gas-discharge plasma, the ion temperature may turn out to be noticeably higher than the electron temperature.
Particle collisions in plasma . In an ordinary gas, the processes of interaction (collisions) of particles are mainly elastic in nature. This means that in such collisions, the total momentum and energy of each interacting pair of particles remain unchanged. If the gas or plasma is not very rarefied, particle collisions quickly enough lead to the establishment of the known Maxwellian velocity distribution of particles ( cm... MOLECULAR KINETIC THEORY), which corresponds to the state of thermal equilibrium. Plasma differs from gas in a much wider variety of particle collision processes. In a weakly ionized plasma, a special role is played by elastic interactions of electrons with neutral atoms or molecules, such processes as, for example, ion charge exchange on atoms. As the degree of plasma ionization increases, long-range Coulomb interactions of charged plasma particles are added to the usual elastic short-range interactions of neutral atoms and molecules and electrons with neutral particles. At sufficiently high temperatures or in the presence of high-energy electrons, which they acquire, for example, in the electric field of a gas discharge, many collisions are inelastic. These include processes such as the transition of atoms and molecules to an excited state, ionization of atoms, recombination of electrons and ions with the participation of a third particle, etc.Coulomb interactions of charged particles play a special role in plasma. If in a neutral ideal gas the particles are in free motion most of the time, sharply changing their speed only at the moments of short-term collisions, the forces of Coulomb attraction or repulsion between electrons and ions retain a noticeable value even at a relatively large distance of particles from each other. At the same time, this interaction is limited by a distance of the order of the Debye radius, beyond which the interaction of the separated charged particle with other charged particles is screened . The trajectory of charged particles can no longer be represented as a zigzag line consisting of short path segments, as is done when considering elastic collisions in an ordinary gas. In plasma, each charged particle is always in the field created by the rest of the electrons and ions. The effect of a plasma microfield on particles is manifested in a smooth continuous change in the magnitude and direction of the particle velocity (Fig. 1). Theoretical analysis shows that the resulting effect of weak collisions, due to their multiplicity, turns out to be much larger than the effect due to rare collisions, as a result of which there is a sharp change in the magnitude and direction of the particle velocity.
In describing particle collisions, an important role is played by the so-called collision cross section or scattering cross section. For atoms interacting as solid elastic balls, the cross section
s = 4 p a 2, where a Is the diameter of the ball. It can be shown that in the case of interactions of charged particles, the Coulomb collision cross section consists of two factors that take into account short-range and long-range interactions. Close interaction responds a sharp turn in the direction of movement of the particles. The particles approach each other to the smallest distance between them if the potential energy of the Coulomb interaction is compared with the kinetic energy of the relative motion of the particles, e 1, e 2 - charges of particles, r - the distance between them, v - relative speed, m Is the reduced mass (for an electron m equal to the mass of an electron m e ). For the interaction between an electron and a singly charged ion, the distance of short-range interaction b = r min defined asThe effective cross section of the interaction is the area of a circle of radius
b, i.e. p b 2. However, the direction of motion of the particle also changes due to long-range interactions, leading to a gradual curvature of the path. Calculations show that the total cross section for Coulomb scattering is obtained by multiplying the cross section for short-range interaction by the so-called Coulomb logarithm s = p b 2 s = p b 2 ln LThe magnitude
L under the sign of the logarithm is equal to the ratio of the Debye radius(formula (1)) to the parameter of short-range interaction b ... For ordinary plasma (for example, fusion plasma), the Coulomb logarithm varies within 10–20. Thus, long-range interactions contribute to the scattering cross section, which is an order of magnitude larger than short-range ones.Average mean free path of particles between collisions in gas
l is defined by the expression.
The average time between collisions is
, 7 b v с = (8 kT / p m ) 1/2 is the average thermal velocity of particles.By analogy with gas, one can introduce the concepts of the mean free path and mean time between collisions and in the case of Coulomb collisions of particles in a plasma, using as
s expression (8). Since the value s in this case, it depends on the particle velocity; to pass to the values averaged over the Maxwellian velocity distribution of particles, one can approximately use the expression for the mean square of the particle velocity b v 2 с = (3 kT / m e ). As a result, an approximate estimate for the mean time of electron-ion collisions in plasma is obtained
which turns out to be close to the exact value. The mean free path of electrons in a plasma between their collisions with ions is determined as
For electron-electron collisions
... The average time of ion-ion collisions turns out to be many times longer: t ii = (2 m i/ m e) 1/2 t ei .Thus, due to the small electron mass in the plasma, a certain hierarchy of characteristic collision times is established. Analysis shows that the times given above correspond to the average characteristic times of momentum transfer of particles during their collisions. As noted earlier, when an electron interacts with a heavy particle, a very small (proportional to the ratio of their masses) energy transfer occurs electron. Due to this, the characteristic time of energy transfer
turns out to be the smallest in this hierarchy of times: t E = (m i/ 2 m e) t ei .For the conditions of a thermonuclear plasma with ions of a heavy isotope of hydrogen (deuterium)
n e = 10 14 cm –3, T = 10 8 K, m D / m e = 3.7 10 3) the estimates give t ei "2 · 10 –4 c, t ee "3 · 10 –4, t ii "10 –2 c, t E "0.3 cThe characteristic average mean free paths for electrons and ions under these conditions are close (~ 106 cm), which is many times greater than the mean free paths in gases under normal conditions.
The average time of energy exchange between electrons and ions can be of the same order of magnitude as the usual macroscopic time characteristic of experiments carried out with plasma. This means that during a time of the order of magnitude
t E , a stable temperature difference between the electronic and ionic components of the plasma can be maintained in the plasma.Plasma in a magnetic field. At high temperatures and low plasma densities, charged particles spend most of their time in free motion, weakly interacting with each other. This allows in many cases to consider plasma as a collection of charged particles that move almost independently of each other in external electric and magnetic fields.The movement of a charged particle with a charge
q in an external electric field with an intensity E occurs under the action of a force F = qE , which leads to the motion of the particle with constant acceleration. If a charged particle moves with speedin a magnetic field, then the magnetic field acts on it with the Lorentz force F = qvB sin a, B - magnetic field induction in teslas ( Tl ) (in the international system of units SI), a - the angle between the direction of the lines of magnetic induction and the direction of the particle velocity. When the particle moves parallel to the lines of induction ( a = 0 or a = 180 ° ) the Lorentz force is zero, i.e. the magnetic field does not affect the motion of the particle, and it maintains its speed in this direction. The greatest force acts on a charged particle in the perpendicular direction ( a = 90 ° ), while the Lorentz force acts perpendicular to both the direction of the particle velocity and the direction of the magnetic induction vector. This force does not perform work and therefore can only change the direction of the velocity, but not its magnitude. It can be shown that the trajectory of the particle in this case is a circle (Fig. 2). The radius of the circle is easy to find if we write down Newton's second law for this case, according to which the product of mass and centripetal acceleration is equal to the force acting on the particle, mv 2 / R) = qvB, whence it followsThe magnitude
R called the Larmor radius after the English physicist Larmor, who at the end of the 19th century. studied the movement of charged particles in a magnetic field. The angular velocity of rotation of the particle w H = v / R defined asand is called the Larmor (or cyclotron) rotation. This name arose because it is with such a frequency that charged particles circulate in special accelerators - cyclotrons.
Since the direction of the Lorentz force depends on the sign of the charge, electrons and positive ions rotate in opposite directions, while the Larmor radius of singly charged ions is (
M / m ) times the radius of rotation of electrons ( M Is the mass of the ion, m Is the mass of an electron). For hydrogen ions (protons), for example, this ratio is almost 2000.When a charged particle moves uniformly along the lines of force of the magnetic field and simultaneously rotates around it, the trajectory of the particle is a helical line. The helical trajectories of the ion and electron are shown in Fig. 3.
In those cases when, in addition to the magnetic field, some other fields act on the charged particle (for example, gravity or an electric field) or when the magnetic field is inhomogeneous, the nature of the particle's motion becomes more complex. Detailed analysis shows that under such conditions the center of the Larmor circle (it is often called the leading center) begins to move in the direction perpendicular to the magnetic field. This movement of the leading center is called drift. Drift motion differs from the free motion of charged particles in that under the action of a constant force it does not occur uniformly accelerated, as follows from Newton's second law, but at a constant speed. It follows from the calculations that in the case of a uniform magnetic field (such a field is obtained, for example, between the flat poles of a large electromagnet or inside a solenoid - a uniformly wound long coil with current), the absolute value of the drift velocity is determined by the expression
, F ^ - the component of the force perpendicular to the lines of force of the magnetic field. Forces such as gravity and centrifugal force, which in the absence of a magnetic field act equally on all particles (regardless of their charge), cause electrons and ions to drift in opposite directions, i.e. in this case, a nonzero drift electric current appearsIn the case when, along with a uniform magnetic field, a uniform electric field acts perpendicular to its lines of force, the expression for the drift velocity takes the form:
The strength of the electric field is itself proportional to the charge of the particle; therefore, in expression (17), the charge was reduced. The drift of particles in this case leads only to the motion of the entire plasma, i.e. does not excite current (Fig. 4). A drift, the speed of which is determined by expression (17), is called electrical drift.
Various specific types of drift occur in an inhomogeneous magnetic field. So, as a result of the curvature of the lines of force (longitudinal inhomogeneity of the magnetic field), a centrifugal force acts on the center of the cyclotron circle, which causes the so-called centrifugal drift. The transverse inhomogeneity of the field (condensation or rarefaction of lines of force) leads to the fact that the cyclotron circle is, as it were, pushed out across the field with a force proportional to the change in the magnitude of the magnetic field induction per unit length. This force causes the so-called gradient drift.
Plasma magnetic confinement. The study of the peculiarities of plasma behavior in magnetic fields came to the fore when the problem of implementing controlled thermonuclear fusion (CTF) arose. The essence of the problem is to carry out on Earth the same nuclear fusion reactions (conversion of hydrogen into helium) that serve as sources of energy for the Sun and other stars. These reactions themselves can proceed only at ultra-high temperatures (of the order of hundreds of millions of degrees), therefore the substance in a thermonuclear reactor is a completely ionized plasma. Obviously, the main difficulty is to isolate this high-temperature plasma from the walls of the reactor.In 1950, Soviet physicists I.E. Tamm and A.D. Sakharov and, independently of them, a number of foreign scientists put forward the idea of magnetic thermal insulation of plasma. This idea can be illustrated by the following simple example. If you create a uniform magnetic field inside a straight pipe filled with plasma, then charged particles will twist around the magnetic field lines, moving only along the pipe (Fig. 5), in order to avoid particles escaping through the ends of the pipe, you can connect both its ends, i.e. ... bend the pipe into a "donut". A pipe of this shape is a torus, and the corresponding device is called a toroidal magnetic trap. . The magnetic field inside the torus is created by a wire coil wound around it, through which a current is passed.
However, this simple idea immediately runs into a number of difficulties, which are associated, first of all, with the drift motion of the plasma. Since the lines of force of the magnetic field in a toroidal trap are circles, centrifugal drift of particles towards the walls of the trap can be expected. In addition, due to the adopted geometry of the installation, the coils with current are located on the inner circumference of the torus closer to each other than on the outer one, therefore, the magnetic field induction increases in the direction from the outer wall of the torus to the inner one, which obviously leads to a gradient drift of particles to the walls traps. Both types of drift of particles cause the movement of charges of the opposite sign in different directions, as a result, an excess of negative charges is formed at the top, and positive charges at the bottom. (fig. 6). This results in an electric field that is perpendicular to the magnetic field. The resulting electric field causes an electric drift of particles and the plasma as a whole rushes to the outer wall.
The idea of magnetic thermal insulation of plasma in a toroidal trap can be saved if a special type of magnetic field is created in it, so that the magnetic induction lines are not circles, but helical lines winding onto the toroidal surface (Fig. 7). Such a magnetic field can be created either using a special coil system, or by twisting the torus into a figure that resembles the number eight ("eight"). The corresponding devices are called stellarators (from the word "stellar" - stellar). Another method, which also makes it possible to compensate for the plasma drift in a toroidal trap, is to excite an electric current along the torus directly along the plasma. The ring current system was named tokamak (from the words "current chamber", "magnetic coils").
There are other ideas for magnetic plasma confinement. One of them consists, for example, in the creation of traps with magnetic "plugs" or the so-called "mirror cells". In such devices, the lines of force of the longitudinal magnetic field are condensed towards the ends of the cylindrical chamber in which the plasma is located, resembling in its shape the neck of a bottle (Fig. 8). The escape of charged particles to the walls across the longitudinal magnetic field is prevented by their twisting around the lines of force. An increase in the magnetic field towards the ends ensures the pushing of the cyclotron circles into the region of a weaker field, which creates the effect of magnetic "mirrors". Magnetic "plugs" are sometimes called magnetic mirrors; charged particles are reflected from them, like from a mirror.
Plasma diffusion across the magnetic field. Previous analysis of the behavior of charged particles in a magnetic field was based on the assumption that there are no collisions between particles. In reality, the particles, of course, interact with each other, their collisions lead to the fact that they jump from one line of induction to another, i.e. move across the lines of force of the magnetic field. This phenomenon is called transverse plasma diffusion in a magnetic field. Analysis shows that the rate of transverse diffusion of particles decreases with increasing magnetic field (inversely proportional to the square of the magnetic induction B ), as well as with an increase in the plasma temperature. However, in reality, the diffusion process in plasma turns out to be more complicated.The main role in the transverse diffusion of plasma is played by collisions of electrons with ions, while ions that move around the lines of force in circles with a larger radius than electrons, as a result of collisions "more easily" pass to other lines of force, that is, they diffuse across the lines of force faster, than electrons. Due to the different diffusion rate of particles of opposite sign, charge separation occurs, which is impeded by the emerging strong electric fields. These fields practically eliminate the resulting difference in the velocities of electrons and ions, as a result of which a joint diffusion of oppositely charged particles is observed, which is called ambipolar diffusion. Such diffusion across the magnetic field is also one of the important reasons for the escape of particles to the walls in magnetic plasma confinement devices.
Plasma as a conductive liquid. If collisions of particles in plasma play a significant role, consideration of it on the basis of the model of particles moving in external fields independently of each other becomes not entirely justified. In this case, the concept of plasma as a continuous medium, similar to a liquid, is more correct. It differs from a liquid in the compressibility of plasma, and also in the fact that plasma is a very good conductor of electric current. Since the plasma conductivity turns out to be close to the conductivity of metals, the presence of currents in the plasma leads to a strong interaction of these currents with a magnetic field. The movement of plasma, as a conductive liquid, in electric and magnetic fields, is being studied magnetohydrodynamics .In magnetohydrodynamics, the approximation of an ideally conducting plasma is often used: this means that the electrical resistance of the plasma is considered very small (and, conversely, the conductivity of the plasma is infinitely large). When the plasma moves relative to the magnetic field (or the magnetic field relative to the plasma) in the plasma, in accordance with Faraday's law of electromagnetic induction, an EMF of induction should arise. But this EMF would cause an infinitely large current in an ideally conducting plasma, which is impossible. Hence it follows that the magnetic field cannot move relative to such a plasma: the field lines of force turn out to be, as it were, "glued in" or "frozen in" into the plasma, moving along with it.
The concept of "frozen-in" magnetic field plays an important role in plasma physics, making it possible to describe many unusual phenomena observed especially in cosmic plasma . At the same time, if the resistance of the plasma is not equal to zero, then the magnetic field can move relative to the plasma, i.e. there is, as it were, a "seepage" or diffusion of the magnetic field into the plasma. The lower the plasma conductivity, the greater the rate of such diffusion.
If we consider a stationary plasma volume surrounded by an external magnetic field, then in the case of a perfectly conducting plasma this field cannot penetrate into the volume. Plasma, as it were, "pushes" the magnetic field beyond its limits. This property of plasma is spoken of as a manifestation of its diamagnetism. . At finite conductivity, the magnetic field seeps into the plasma and the initially sharp boundary between the external magnetic field and the field in the plasma itself begins to blur.
The same phenomena can be simply explained if we introduce the concept of the forces acting on the plasma from the magnetic field or the value of the magnetic pressure equivalent to these forces. Let the conductor with current be located perpendicular to the lines of force of the magnetic field. According to Ampere's law, for each unit of length of such a conductor from the side of the magnetic field with magnetic induction
B a force equal to IB where I - current strength in the conductor. In a conducting medium (plasma), a single volume element can be distinguished. The strength of the current flowing perpendicular to one of the faces of this volume is equal to the current density in the substance j ... The force acting on a unit volume of a conductor in a direction perpendicular to the lines of force of the magnetic field is determined then as F = j ^ B where j ^ Is the component of the current density vector directed across the magnetic field. An example would be an infinitely long circular plasma cylinder (plasma filament). If the current density is j , then it is easy to verify that any streamline in the plasma cylinder is acted upon from the side of the magnetic field by the force F directed to the axis of the cylinder, the combination of these forces tends to compress the plasma column, as it were. The total force per unit area is called magnetic pressure. The magnitude of this pressure is determined by the expression m - magnetic permeability of the medium, m 0 - magnetic constant (magnetic permeability of vacuum). Let there be a sharp boundary between plasma and vacuum. In this case, the magnetic pressureacting on the plasma surface from the outside is balanced by the gas kinetic pressure of the plasma p and the pressure of the magnetic field in the plasma itselfIt follows from the relation that the magnetic field induction
B less magnetic field induction in plasma B 0 outside the plasma, and this can be regarded as a manifestation of plasma diamagnetism.The magnetic pressure obviously plays the role of some piston compressing the plasma. For an ideally conductive environment (
p m = 0) the action of this piston ensures equilibrium between the magnetic pressure applied from the outside to the plasma and the hydrostatic pressure inside it, i.e. confinement of plasma by a magnetic field. If the plasma conductivity is finite, then the plasma boundary is blurred, the magnetic piston turns out to be "full of holes", after a while the magnetic field completely penetrates into the plasma and nothing prevents the plasma from expanding under the action of its hydrostatic pressure.Plasma waves. If in an ordinary neutral gas in some place there is a rarefaction or compaction of the medium, then it propagates inside the gas from point to point in the form of a so-called sound wave. In a plasma, in addition to the disturbance of the pressure (or density) of the medium, oscillations arise due to the separation of charges (Langmuir or plasma oscillations). The simplest and most important way to excite plasma oscillations is, for example, their excitation by a beam of fast electrons passing through the plasma, which causes the plasma electrons to be displaced from the equilibrium position. Under the combined action of pressure forces and an electric field, plasma oscillations begin to propagate in the medium, so-called Langmuir or plasma waves appear.The propagation of periodic oscillations in a medium is characterized by a wavelength
l , which is associated with the period of oscillations T by the relation l = vT, where v - phase velocity of wave propagation. Along with the wavelength, the wave number is considered k = 2 p / l ... Since the vibration frequency w and period T bound by the condition w T = 2 p, then w = kvThe direction of wave propagation is characterized by a wave vector equal in magnitude to the wave number. If the direction of propagation of the wave coincides with the direction of the oscillations, then the wave is called longitudinal. When vibrations occur perpendicular to the direction of propagation of the wave, it is called transverse. Sound and plasma waves are longitudinal. An example of transverse waves is electromagnetic waves, which represent the propagation of periodic changes in the strength of electric and magnetic fields in a medium. An electromagnetic wave propagates in a vacuum at the speed of light
C .For ordinary sound and electromagnetic waves propagating in a neutral gas, their propagation speed does not depend on the wave frequency. The phase velocity of sound in a gas is determined by the expression
, p - pressure, r - density, g =
c p /
c v Is the adiabatic exponent (
c p and
c v - specific heat capacities of gas at constant pressure and at constant volume, respectively) / On the contrary, waves propagating in plasma are characterized by the presence of this dependence, which is called the dispersion law ... NS electron plasma waves propagate, for example, with the phase velocity
, w 0, is the frequency of electron plasma oscillations,Is the square of the speed of electronic sound. The phase velocity of electronic waves is always greater than the speed of sound waves. For long wavelengths, the phase velocity tends to infinity, which means that the entire plasma volume oscillates with a constant frequency
w 0 .Oscillations of ions in plasma occur at a much lower frequency due to the large mass of ions in comparison with electrons. Electrons with greater mobility, following the ions, almost completely compensate for the electric fields arising from such oscillations, therefore, the propagation of ion waves occurs at the speed of ionic sound. Studies have shown that ion-sound waves in an ordinary equilibrium plasma with an electron temperature
T e , which differs little from the ion temperature T i , decay strongly already at distances of the order of the wavelength. However, practically undamped ion waves exist in a strongly nonisothermal plasma ( T e >> T i ), while the phase velocity of the wave is defined as v = ( kT e / m i ) 1/2. This corresponds to the so-called ionic sound with electronic temperature. In this case, the speedsignificantly exceeds the thermal velocity of ions v t ~ ( kT i / m i ) 1/2 .The propagation of electromagnetic waves in plasma is of particular interest. The dispersion law in this case has the form
Wave propagation is possible only if the wave frequency
w exceeds the electron plasma frequency w 0. If the speed of an electromagnetic wave in a vacuum is equal to c (the speed of light), then in a substance the phase speed of propagation is determined by the formula v = c / n, where n Is the refractive index of the medium. From formulas (19) and (21) it follows w w 0, the refractive index becomes imaginary, which means that under this condition the wave in the plasma cannot propagate. If, after passing through some medium, an electromagnetic wave hits the plasma boundary, then it penetrates only into a thin surface layer of the plasma, since when the condition w w 0 oscillations in an electromagnetic wave are "slow". Over the period of fluctuations T the charged particles of the plasma "have time" to be distributed in such a way that the fields arising in the plasma impede the propagation of the wave. In the case of "fast" oscillations ( w> w 0), such a redistribution does not have time to occur, and the wave freely propagates through the plasma.In accordance with formula (2), the electron plasma frequency. This allows for fixed values
n e find the limiting value of the length of the electromagnetic wave, above which it is reflected from the plasma boundary. To estimate this quantity in the case of the passage of electromagnetic waves in the Earth's ionosphere, the formula is used l pr = 2 p (c / w 0), where w 0 is determined by formula (2). The maximum concentration of electrons in the ionosphere, according to rocket probe measurements, is 10 12 m–3. For the plasma frequency, in this case, we obtain the value w 0 = 6 · 10 –7 s –1, and for the wavelength l pr " 30 m.Consequently, radio waves from l > 30 m will be reflected from the ionosphere, and for distant space communication with satellites and orbital stations, radio waves with a much shorter wavelength must be used.An important method of plasma diagnostics is based on the use of the same theoretical expressions - microwave sounding . Plasma is illuminated with a directed beam of electromagnetic waves. If the wave passes through the plasma and is detected by a receiver placed on the other side, then the plasma concentration is below the limit. A "latching" signal means that the plasma concentration is higher than the limit. So, for the waves usually used in this case with a length
l = 3 cm, the limiting electron density is 10 12 cm –3.The picture of wave propagation in plasma becomes much more complicated in the presence of an external magnetic field. Only in the particular case when the direction of the electric oscillations in the wave occurs along the magnetic field, the electromagnetic wave in the plasma behaves in the same way as in the absence of a magnetic field. The presence of a magnetic field leads to the possibility of propagation of waves of a completely different nature than in the case of ordinary electromagnetic waves. Such waves arise when the direction of electrical vibrations is perpendicular to the external magnetic field. If the frequency of oscillations of the electric field is small in comparison with the cyclotron frequencies in the plasma, then the plasma behaves simply like a conducting liquid, and its behavior is described by the equations of magnetohydrodynamics. In this frequency range, magnetohydrodynamic waves propagate parallel to the magnetic field , and perpendicular to it - magneto-sound . The physical nature of these waves can be visualized using the concept of a frozen-in magnetic field.
In a magneto-acoustic wave, the substance, together with the field frozen into it, moves along the direction of wave propagation. The mechanism of the phenomenon is similar to ordinary sound, only, together with fluctuations in the pressure (density) of the plasma itself along the same direction, condensation and rarefaction of the lines of force of the frozen-in magnetic field appear. The wave propagation speed can be found using the usual formula for the speed of sound, which additionally takes into account the presence of magnetic pressure. As a result, the speed of the wave
(Adiabatic exponent for magnetic pressure
g m = 2). If the ratio of the gas pressure to the magnetic pressure is small, thenThe mechanism of wave propagation in a direction parallel to a magnetic field can be compared to the propagation of a wave along an oscillating string. The speed of movement of the substance is here perpendicular to the direction of propagation. The lines of force of the magnetic field play the role of elastic filaments (strings), and the oscillation mechanism here consists in the "bending" of the magnetic lines of force together with the plasma "glued" to them. Despite the difference in the mechanisms of the phenomenon (in comparison with the previous case), the propagation speed of magnetohydrodynamic waves at low frequencies is exactly equal to the speed of magnetic sound
V A (24). Magnetohydrodynamic waves were discovered by the Swedish astrophysicist Alfvén in 1943 and are named after Alfvén waves.Vladimir Zhdanov
LITERATURE Frank-Kamenetskiy D.A. Plasma is the fourth state of matter... M., Atomizdat, 1963Artsimovich L.A. Elementary Plasma Physics... M., Atomizdat, 1969
Smirnov B.M. Introduction to Plasma Physics... M., Science, 1975
V.P. Milantiev, S.V. Temko Plasma physics... M., Enlightenment, 1983
Chen F. Introduction to Plasma Physics... M., Mir, 1987
The word "plasma" has many meanings, including a physical term. So what is plasma in physics?
Plasma is an ionized gas that is formed by neutral molecules and charged particles. This gas is ionized - at least one electron is separated from the shell of its atoms. Distinctive feature this environment can be called its quasi-neutrality. Quasineutrality means that among all charges per unit volume of plasma, the number of positive charges is equal to the number of negative charges.
We know that matter can be gaseous, liquid or solid - and these states, called aggregate, are capable of flowing into one another. So, plasma is considered the fourth state of aggregation in which the substance can stay.
So, plasma is distinguished by two main properties - ionization and quasineutrality. We will talk about its other features further, and first we will pay attention to the origin of the term.
Plasma: a history of definition
Otto von Guericke began to study the discharges in 1972, however, for the next two and a half centuries, scientists could not identify special properties and distinctive features ionized gas.
The author of the term "plasma" as a physical and chemical definition believe Irving Langmuir. The scientist conducted experiments with partially ionized plasma. In 1923, he and another American physicist, Tonks, coined the term itself.
Plasma physics originated between 1922-1929.
The word "plasma" is of Greek origin and means a plastic sculpted figure.
What is plasma: properties, forms, classification
If a substance is heated, it will become gaseous when it reaches a certain temperature. If you continue heating, then the gas will begin to decay into its constituent atoms. Then they turn into ions: this is plasma.
There are different forms of this state of matter. Plasma manifests itself in terrestrial conditions in lightning discharges. It also forms the ionosphere - a layer in the upper atmosphere. The ionosphere appears under the influence of ultraviolet radiation and makes it possible to transmit radio signals over long distances.
There is much more plasma in the Universe. The baryonic matter of the Universe is almost completely in the state of plasma. Plasma forms stars, including the sun. Other forms of plasma found in space are interstellar nebulae, solar wind (a stream of ionized particles coming from the Sun).
In nature, in addition to lightning and the ionosphere, plasma exists in the form of such interesting phenomena as the lights of St. Elmo, the Northern Lights.
There is artificial plasma - for example, in fluorescent and plasma lamps, in electric arcs of arc lamps, etc.
Plasma classification
Plasmas are:
- perfect, imperfect;
- high-, low-temperature;
- nonequilibrium and equilibrium.
Plasma and Gas: Comparison
Plasma and gas are similar in many ways, but there are significant differences in their properties. For example, in terms of electrical conductivity, gas and plasma are different - gas has low values for this parameter, while plasma, on the contrary, is high. Gas consists of similar particles, plasma - of different properties - charge, speed, etc.
At high t-pax, under the influence of an electromagnet. fields of high intensity, when irradiated by streams of charged particles of high energy. A characteristic feature of plasma, which distinguishes it from the usual ionized one, is that the linear dimensions of the volume occupied by the plasma are much larger than the so-called. Debye screening radius D (see). The D value for the i-th with H i and t-th T i is determined by the expression:
where n e and T e - and t-ra, respectively, e i -charge, e-elementary electric. charge (charge), k-. From this expression it follows that in plasma, as a rule, t-ry and differ.
In low-temperature plasma, the average energy or much less than the effective ionization energy of the particles; A high-temperature plasma is considered to be characterized by the inverse ratio of the indicated energies (the contribution to the ionization of different particles is taken into account). Usually a low-temperature plasma has a t-py of particles less than 10 5 K, a high-temperature plasma of the order of 10 -10 8 K. The ratio of charged particles to the total of all particles is called. the degree of plasma ionization.
NS lasma obtained in the lab. conditions, is in thermodynamic. sense and is always thermodynamically nonequilibrium. energy and mass lead to the violation of local thermodynamic. and stationarity (see), Planck's law for the radiation field, as a rule, does not hold. Plasma is called. thermal, if its state is described within the local thermal model. , namely: all particles are distributed in speed in accordance with Maxwell's law; t-ry of all components are the same; the composition of the plasma is determined, in particular, the ionic composition is determined between ionization and (the Eggert-Saha f-la is essentially an expression for these processes); population of energetic. levels of all particles obey the Boltzmann distribution. Thermal plasma is usually characterized by a high degree of ionization and m. B. implemented in with a relatively low effective ionization energy at a sufficiently high optical frequency. density (i.e., plasma radiation is almost entirely absorbed by its own particles). Plasma is usually described by a partial local thermal model. , edges includes all of the above. provisions, but requires obeying the Boltzmann law of the populations of only the excited levels of plasma particles, excluding their ground states. Such a plasma is called. quasi-equilibrium; an example of a quasi-equilibrium plasma-column electric. arcs at atm. ...
Failure to comply with at least one of the conditions of the local thermal. leads to the appearance of a non-equilibrium plasma. Obviously, there is an infinite number of non-equilibrium plasma states. An example of a strongly nonequilibrium plasma is a glow discharge plasma at 10 1 -10 3 Pa, in which the average energy is 3-6 eV, and m-t-ra heavy particles usually does not exceed 1000 K. The existence and stationarity of such a nonequilibrium state of plasma is due to the difficulty energy exchange between and heavy particles. In plasma, they say. , in addition, there may be an ineffective
energy exchange between diff. int. degrees of freedom: electronic, vibrational, rotational. Within each of the degrees of freedom, energy exchange occurs relatively easily, which leads to the establishment of quasi-equilibrium particle distributions over the corresponding energetic. states. In this case, they speak of electronic, vibrate, rotate. t-pax of plasma particles.Main the features of plasma that distinguish it from neutral and allow one to consider plasma as a special, fourth state of matter (fourth matter), are as follows.
1) Collective interaction, i.e. simultaneous interaction. with each other of a large number of particles (under normal conditions, the interaction between the particles, as a rule, is paired), due to the fact that the Coulomb forces of attraction and repulsion decrease with distance much more slowly than the forces of interaction. neutral particles, i.e. interaction in plasma are "long-range".
2) The strong influence of electric. and magn. fields on the Holy Island of the plasma, a cut leads to the appearance of spaces in the plasma. charges and currents and causes a number of specific. sv-in plasma.
One of the most important sv-in plasma is its quasineutrality, i.e. almost complete mutual compensation of charges at distances much larger than the Debye screening radius. Electric. the field of an individual charged particle in the plasma is screened by the fields of particles with a charge of the opposite sign, i.e. practically decreases to zero at distances of the order of the Debye radius from the particle. Any violation of quasineutrality in the volume occupied by the plasma leads to the appearance of strong electric currents. fields of spaces. charges restoring the quasineutrality of the plasma.
In the state of plasma is the overwhelming part of the islands of the Universe - stars, stellar, galactic. nebulae and the interstellar medium. Around the Earth, plasma exists in space in the form of a "solar wind" and fills the Earth's magnetosphere (forming the Earth's radiation belt) and the ionosphere. The processes in the near-earth plasma are caused by the magn. storms and auroras. The reflection of radio waves from the ionospheric plasma provides the possibility of long-distance radio communication on Earth.
To the lab. conditions and at prom. applications, plasma is obtained by means of electric. discharge in
Blood is formed by combining a group of substances - plasma and corpuscles. Each part has distinct functions and performs its own unique tasks. Certain blood enzymes make it red, however, in percentage terms, most of the composition (50-60%) is a light yellow liquid. This plasma ratio is called hematocrine. Plasma gives blood a liquid state, although it is heavier than water in density. Dense plasma is made by the substances it contains: fats, carbohydrates, salts and other components. Human blood plasma can become cloudy after eating fatty foods. And so, what is blood plasma and what are its functions in the body, we will learn about all this further.
Components and composition
More than 90% of the blood plasma is water, the rest of its components are dry substances: proteins, glucose, amino acids, fat, hormones, dissolved minerals.
Proteins account for about 8% of the plasma composition. in turn, they consist of a fraction of albumin (5%), a fraction of globulins (4%), fibrinogens (0.4%). Thus, 1 liter of plasma contains 900 g of water, 70 g of protein and 20 g of molecular compounds.
The most common protein is. It is formed in the bake and occupies 50% of the protein group. The main functions of albumin are transport (transfer of trace elements and drugs), participation in metabolism, protein synthesis, and amino acid reservation. The presence of albumin in the blood reflects the state of the liver - a low albumin index indicates the presence of a disease. Low albumin in children, for example, increases the chance of jaundice.
Globulins are large molecular components of protein. They are produced by the liver and organs of the immune system. Globulins can be of three types: beta, gamma, alpha globulins. They all provide transport and communication functions. also called antibodies, they are responsible for the response of the immune system. With a decrease in immunoglobulins in the body, a significant deterioration in the work of immunity is observed: permanent bacterial and.
Protein fibrinogen is formed in the liver and, becoming fibrin, it forms a clot at the sites of vascular lesions. Thus, the liquid is involved in the process of its coagulation.
Among the non-protein compounds are:
- Organic nitrogen-containing compounds (urea nitrogen, bilirubin, uric acid, creatine, etc.). The increase in nitrogen in the body is called nitrogenomy. It occurs when there is a violation of the excretion of metabolic products with urine or with an excessive intake of nitrogenous substances due to the active breakdown of proteins (starvation, diabetes mellitus, burns, infections).
- Organic nitrogen-free compounds (lipids, glucose, lactic acid). To maintain health, a number of these vital signs must be monitored.
- Inorganic elements (calcium, sodium salt, magnesium, etc.). Minerals are also essential components of the system.
Plasma ions (sodium and chlorine) maintain an alkaline blood level (ph), which ensures the normal state of the cell. They also serve to support osmotic pressure. Calcium ions are involved in muscle contraction reactions and affect the sensitivity of nerve cells.
During the life of the body, metabolic products, biologically active elements, hormones, nutrients and vitamins enter the bloodstream. It does not change specifically. Regulatory mechanisms provide one of the most important properties of blood plasma - the constancy of its composition.
Plasma functions
The main task and function of plasma is to move blood cells and nutrients. It also performs a bunch of fluids in the body that go outside the circulatory system, since it has the ability to penetrate through.
The most important function of blood plasma is to conduct hemostasis (ensuring the operation of the system in which the fluid is able to stop at and remove the subsequent thrombus involved in coagulation). The task of plasma in the blood also comes down to maintaining a stable pressure in the body.
In what situations and for what purpose? Plasma is most often transfused not entirely of blood, but only its components and plasma liquid. When producing, with the help of special means, the liquid and the shaped elements are separated, the latter, as a rule, are returned to the patient. With this type of donation, the frequency of donation increases up to twice a month, but no more than 12 times a year.
Blood serum is also made from blood plasma: fibrinogen is removed from the composition. At the same time, serum from plasma remains saturated with all antibodies that will resist microbes.
Blood diseases affecting plasma
Human diseases that affect the composition and characteristics of plasma in the blood are extremely dangerous.
There is a list of diseases:
- - occurs when an infection enters the bloodstream directly.
- and adults - a genetic protein deficiency responsible for clotting.
- Hypercoagulant state - too rapid coagulation. In this case, the viscosity of the blood increases and the patients are prescribed drugs to thin it.
- Deep - the formation of blood clots in the deep veins.
- DIC syndrome - the simultaneous occurrence of blood clots and bleeding.
All diseases are associated with the peculiarities of the functioning of the circulatory system. Exposure to individual components in the structure of blood plasma is capable of returning the viability of the organism back to normal.
Plasma is a liquid component of blood with a complex composition. She herself performs a number of functions, without which the vital activity of the human body would be impossible.
For medical purposes, blood plasma is often more effective than a vaccine, since its constituent immunoglobulins reactively destroy microorganisms.
The times when plasma was associated with something unreal, incomprehensible, fantastic are long gone. Nowadays, this concept is actively used. Plasma is used in industry. It is most widely used in lighting engineering. An example is gas discharge lamps that illuminate streets. But it is also present in fluorescent lamps. It is also found in electric welding. After all, the welding arc is a plasma generated by a plasmatron. Many other examples can be cited.
Plasma physics is an important branch of science. Therefore, it is worth understanding the basic concepts related to it. This is what our article is about.
Definition and types of plasma
What is given in physics is quite clear. Plasma is a state of matter when the latter contains a significant (commensurate with the total number of particles) number of charged particles (carriers) that can move more or less freely inside the substance. The following main types of plasma in physics can be distinguished. If the carriers belong to particles of the same type (and particles of opposite sign of charge, which neutralize the system, do not have freedom of movement), it is called one-component. In the opposite case, it is - two- or multicomponent.
Plasma features
So, we have briefly characterized the concept of plasma. Physics is an exact science, therefore one cannot do without definitions. Let us now talk about the main features of this state of matter.
In physics, the following. First of all, in this state, under the influence of already small electromagnetic forces, the movement of carriers arises - a current that flows in this way and until these forces disappear due to the screening of their sources. Therefore, the plasma ultimately passes into a state where it is quasi-neutral. In other words, its volumes, which are larger than a certain microscopic value, have zero charge. The second feature of plasma is associated with the long-range nature of the Coulomb and Ampere forces. It consists in the fact that movements in this state, as a rule, have a collective character, involving big number charged particles. These are the basic properties of plasma in physics. It would be useful to remember them.
Both of these features lead to the fact that plasma physics is unusually rich and varied. Its most striking manifestation is the ease of occurrence of various kinds of instabilities. They are a serious obstacle hindering the practical application of plasma. Physics is a science that is constantly evolving. Therefore, it is hoped that over time these obstacles will be removed.
Plasma in liquids
Moving on to specific examples of structures, we begin by considering plasma subsystems in condensed matter. Among liquids, one should first of all name - an example, which corresponds to the plasma subsystem - a single-component plasma of electron carriers. Strictly speaking, the discharge of interest to us should also include liquids-electrolytes, in which there are carriers - ions of both signs. However, for various reasons, electrolytes are not included in this category. One of them is that there are no light, mobile carriers such as electrons in the electrolyte. Therefore, the properties of plasma indicated above are much less pronounced.
Plasma in crystals
Plasma in crystals has a special name - plasma solid... Although there are charges in ionic crystals, they are immobile. Therefore, the plasma is not there. In metals, on the other hand, there are conductivities that make up a one-component plasma. Its charge is compensated by the charge of stationary (more precisely, unable to move over long distances) ions.
Plasma in semiconductors
Considering the fundamentals of plasma physics, it should be noted that the situation in semiconductors is more varied. Let us briefly describe it. A single-component plasma in these substances can arise if appropriate impurities are introduced into them. If impurities easily donate electrons (donors), then n-type carriers - electrons - appear. If, on the other hand, impurities easily take out electrons (acceptors), then p-type carriers arise - holes ( empty spaces in the distribution of electrons), which behave like particles with a positive charge. A two-component plasma, formed by electrons and holes, arises in semiconductors in an even simpler way. For example, it appears under the action of light pumping, which throws electrons from the valence band into the conduction band. Note that, under certain conditions, electrons and holes that are attracted to each other can form a bound state similar to a hydrogen atom - an exciton, and if the pumping is intense and the exciton density is high, then they merge together and form a droplet of an electron-hole liquid. Sometimes this state is considered a new state of matter.
Gas ionization
The examples given referred to special cases of a plasma state, and plasma in its pure form is called.Many factors can lead to its ionization: electric field (gas discharge, thunderstorm), light flux (photoionization), fast particles (radiation from radioactive sources, cosmic rays, which and were discovered by an increase in the degree of ionization with height). However, the main factor is the heating of the gas (thermal ionization). In this case, the electron is detached from the collision of another gas particle with the latter, which has sufficient kinetic energy due to the high temperature.
High temperature and low temperature plasma
Low-temperature plasma physics is something we come into contact with almost every day. Examples of such a state are flame, matter in a gas discharge and lightning, various types of cold cosmic plasma (ion and magnetospheres of planets and stars), a working substance in various technical devices (MHD generators, burners, etc.). Examples of high-temperature plasma are the matter of stars at all stages of their evolution, except early childhood and old age, working substance in installations for controlled thermonuclear fusion (tokamaks, laser devices, beam devices, etc.).
The fourth state of matter
A century and a half ago, many physicists and chemists believed that matter consists only of molecules and atoms. They come together in combinations, either completely disordered or more or less ordered. It was believed that there are three phases - gaseous, liquid and solid. Substances take them under the influence of external conditions.
However, at present we can say that there are 4 states of matter. It is plasma that can be considered new, the fourth. Its difference from the condensed (solid and liquid) states is that it, like a gas, does not have not only shear elasticity, but also a fixed intrinsic volume. On the other hand, plasma is related to the condensed state by the presence of short-range order, i.e., the correlation of the positions and composition of particles adjacent to a given plasma charge. In this case, such a correlation is generated not by intermolecular, but by Coulomb forces: a given charge repels from itself charges of the same name and attracts opposite charges.
Plasma physics has been briefly reviewed by us. This topic is quite voluminous, so we can only say that we have revealed its foundations. Plasma physics certainly deserves further consideration.
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