ප්ලාස්මා (භෞතික විද්‍යාව)

භෞතික විද්‍යාවෙහි සහ රසායන විද්‍යාවෙහි, ප්ලාස්මා  යනු වායුවක අංශු කිසියම් ප්‍රමාණයක්  අයනීකෘත වූ විට නිමැවෙන පදාර්ථයේ අවස්ථාවකි. 

ප්ලාස්මා අවස්ථාවේදී  අයනීකෘත වායුවක් වන අතර ඉලෙක්ට්රෝනයක යම් අනුපාතයක් නිදහස් වන අතර ඒවා පරමාණුවකට හෝ අණුවක් වෙතට බැඳී ඇත. ධනාත්මක හා සෘණ ආරෝපණ තරමක් ස්වාධීනව ගමන් කිරීමට හැකියාව ඇති විද්යුත් චුම්බක ක්ෂේත්රයට දැඩි ලෙස ප්රතිචාර දැක්වීමට ප්ලාස්මා විදුලිය සන්නායක වේ. එබැවින් ප්ලාස්මා ඝන ද්රව්ය, ද්රව හෝ වායූන් මෙන් නොව එහි ද්රව්යමය තත්වයක් ලෙස සැලකේ. ප්ලාස්මා සාමාන්යයෙන් උදාසීන වායු වළාකුළු ආකාරයක් (උදා. තරු) උදා වේ.

ඉතිහාසය

මෙම පදාර්ථය පළමු වරට ක්ෲක්ස් නලයක් තුළ මුලින්ම හදුනාගත් අතර 1879 දී ශ්රීමත් විලියම් ක්රූකොස් විසින් විස්තර කරන ලදී (ඔහු එය "විකිරණමය පදාර්ථයයි" ලෙස හැඳින්වේ.) [1] ක්රූකොස් නාලය "කැතෝඩ කිරණ" යන පදාර්ථයේ ස්වභාවය බ්රිතාන්ය විද්යාඥ ශ්රීමත් ජේ. ජේ. 1897 දී තොම්සන් [2] සහ 1928 දී අර්වින්ග් ලන්ග්මීර් විසින් "ප්ලාස්මා" ලෙස නම් කරන ලදී. සමහරවිට එය රුධිර ප්ලාස්මා මත ඔහුට මතක් කළ නිසාය. ලන්ග්මියර් මෙසේ ලිවීය:

ඉලෙක්ට්රෝන කිහිපයක් අඩංගු කොපුවල ඇති ඉලෙක්ට්රෝඩයන් ආසන්නයේ හැරුණු විට, අයනීකෘත වායුව නිසා සමාන අයුරින් අයන සහ ඉලෙක්ට්රෝන අඩංගු වන අතර එහි ප්රතිඵලයක් ලෙස අභ්යවකාශ ආරෝපණ ඉතා කුඩා වේ. අයන සහ ඉලෙක්ට්රෝන වල සමබර ආරෝපනයක් සහිත මෙම කලාපය විස්තර කිරීමට නම් ප්ලාස්මා නාමය භාවිතා කළ යුතුය. "[1]

ප්ලාස්මා යනු ස්කන්ධය හා පරිමාව අනුවය. විශ්වයේ බහුලම දෙය වන්නේ සංයුතියයි. [1] තාරකා සියල්ලම ප්ලාස්මා වලින් සෑදූ අතර තාරකා අතර අවකාශය පවා ප්ලාස්මා සමග පිරවිය හැකි නමුත් ඉතා විරල වේ (තාරකාභෞතික ප්ලාස්මා, අන්තර්ගෝලීය මාධ්ය සහ අන්තර්ගෝලීය අවකාශය බලන්න). සූර්ය පද්ධතියේ දී ග්රහ මණ්ඩලයේ නොවන බොහෝ ප්ලූටෝ ග්රහයන්ගෙන් ග්රහයන්ගෙන් සියයට 0.1 ක් හා ප්ලූටෝ කක්ෂය තුල පරිමාව 10-15% ක් පමණ වේ. වායුමය ප්ලාස්මා ඇතුලත ඉතා කුඩා ධාන්ය වර්ගයක් ද සෘණ ආරෝපණ ආරෝපණයක් ලබා ගනී. එසේ කිරීමෙන් ප්ලාස්මා හි ඉතා විශාල සෘණ අයන සංරචකයක් ලෙස ක්රියා කළ හැකි නිසා (ධූලි ප්ලාස්මා බලන්න).

ප්ලාස්මා ගුණ හා පැරාමිතිය

අර්ථ දැක්වීම 
Although a plasma is loosely described as an electrically neutral medium of positive and negative particles, a definition can have three criteria:

 The plasma approximation: Charged particles must be close enough together that each particle influences many nearby charged particles, rather than just interacting with the closest particle (these collective effects are a distinguishing feature of a plasma). The plasma approximation is valid when the number of charge carriers within the sphere of influence (called the Debye sphere whose radius is the Debye screening length) of a particular particle ae higher than unity to provide collective behavior of the charged particles. The average number of particles in the Debye sphere is given by the plasma parameter, "Λ" (the Greek letter Lambda).
 Bulk interactions: The Debye screening length (defined above) is short compared to the physical size of the plasma. This criterion means that interactions in the bulk of the plasma are more important than those at its edges, where boundary effects may take place. When this criterion is satisfied, the plasma is quasineutral.
Plasma frequency: The electron plasma frequency (measuring plasma oscillations of the electrons) is large compared to the electron-neutral collision frequency (measuring frequency of collisions between electrons and neutral particles). When this condition is valid, electrostatic interactions dominate over the processes of ordinary gas kinetics.

Ranges of plasma parameters

Plasma parameters can take on values varying by many orders of magnitude, but the properties of plasmas with apparently disparate parameters may be very similar (see plasma scaling). The following chart considers only conventional atomic plasmas and not exotic phenomena like quark gluon plasmas:

Degree of ionization 
For plasma to exist, ionization is necessary.  The term "plasma density" by itself usually refers to the "electron density", that is, the number of free electrons per unit volume.  The degree of ionization of a plasma is the proportion of atoms which have lost (or gained) electrons, and is controlled mostly by the temperature. Even a partially ionized gas in which as little as 1% of the particles are ionized can have the characteristics of a plasma (i.e. respond to magnetic fields and be highly electrically conductive). The degree of ionization, α is defined as α = ni/(ni + na) where ni is the number density of ions and na is the number density of neutral atoms.  The electron density is related to this by the average charge state <Z> of the ions through ne=<Z> ni where ne is the number density of electrons.

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 ප්ලාස්මා උෂ්ණත්වය සාමාන්‍යයෙන් මනිනු ලබන්නේ [[[]] හෝ ඉලෙක්ට්‍රෝන වෝල්ට් වල වන අතර එය අංශුවකට තාප චාලක ශක්තියේ අවිධිමත් මිනුමකි.   මැක්ස්වෙලියන් ශක්තියෙන් [[බෙදා හැරීමේ කාර්යය] සැලකිය යුතු ලෙස අපගමනය වූ විට පවා ඉලෙක්ට්‍රෝන තාප සමතුලිතතාවයට ආසන්නව පිහිටා ඇත.  ]], උදාහරණයක් ලෙස පාරජම්බුල කිරණ, ශක්තිජනක අංශු හෝ ශක්තිමත් විද්‍යුත් ක්ෂේත්‍ර හේතුවෙන්.  ස්කන්ධයේ විශාල වෙනස නිසා ඉලෙක්ට්‍රෝන අයන හෝ උදාසීන පරමාණු සමඟ සමතුලිතතාවයට පැමිණීමට වඩා වේගයෙන් තාප ගතික සමතුලිතතාවයට පැමිණේ.  මේ හේතුව නිසා "අයන උෂ්ණත්වය" "ඉලෙක්ට්‍රෝන උෂ්ණත්වය ට වඩා බෙහෙවින් වෙනස් විය හැකිය.  දුර්වල අයනීකෘත තාක්‍ෂණික ප්ලාස්මා වල මෙය විශේෂයෙන් සුලභ වේ, අයන බොහෝ විට පරිසර උෂ්ණත්වය අසල ඇත.

 ඉලෙක්ට්රෝන, අයන සහ උදාසීන වල සාපේක්ෂ උෂ්ණත්වය මත පදනම්ව, ප්ලාස්මා "තාප" හෝ "තාප නොවන" ලෙස වර්ගීකරණය කර ඇත.  තාප ප්ලාස්මා වල ඉලෙක්ට්‍රෝන හා බර අංශු එකම උෂ්ණත්වයේ පවතී, එනම් ඒවා එකිනෙකා සමඟ තාප සමතුලිතතාවයේ පවතී.  අනෙක් අතට තාප නොවන ප්ලාස්මා වලට අයන හා උදාසීන වඩා අඩු උෂ්ණත්වයක (සාමාන්‍යයෙන් කාමර උෂ්ණත්වය) ඇති අතර ඉලෙක්ට්‍රෝන බොහෝ “උණුසුම්” වේ.

 උෂ්ණත්වය ප්ලාස්මා අයනීකරණයේ මට්ටම පාලනය කරයි.  විශේෂයෙන්, සහා සමීකරණය නමින් හැඳින්වෙන සම්බන්ධතාවයක අයනීකරණ ශක්තිය (හා වඩා දුර්වල ලෙස ity නත්වය අනුව) සාපේක්ෂව “ඉලෙක්ට්‍රෝන උෂ්ණත්වය” මගින් ප්ලාස්මා අයනීකරණය තීරණය වේ.  ප්ලාස්මා සමහර විට සම්පූර්ණයෙන්ම අයනීකරණය වී ඇත්නම් එය "උණුසුම්" හෝ වායු අණු වලින් කුඩා කොටසක් (උදාහරණයක් ලෙස 1%) අයනීකරණය වී ඇත්නම් "සීතල" ලෙස හැඳින්වේ (නමුත් "උණුසුම් ප්ලාස්මා" යන යෙදුම්වල වෙනත් අර්ථ දැක්වීම්  සහ "සීතල ප්ලාස්මා" පොදු වේ).  “සීතල” ප්ලාස්මා වල වුවද ඉලෙක්ට්‍රෝන උෂ්ණත්වය තවමත් සෙල්සියස් අංශක දහස් ගණනකි.  "ප්ලාස්මා තාක්‍ෂණය" ("තාක්‍ෂණික ප්ලාස්මා") සඳහා භාවිතා කරන ප්ලාස්මා සාමාන්‍යයෙන් මෙම අර්ථයෙන් සීතල වේ.

Potentials 

Since plasmas are very good conductors, electric potentials play an important role. 
The potential as it exists on average in the space between charged particles, independent of the question of how it can be measured, is called the "plasma potential" or the "space potential". If an electrode is inserted into a plasma, its potential will generally lie considerably below the plasma potential due to what is termed a Debye sheath.  The good electrical conductivity of plasmas causes their electric fields to be very small.  This results in the important concept of "quasineutrality", which says the density of negative charges is approximately equal to the density of positive charges over large volumes of the plasma (), but on the scale of the Debye length there can be charge imbalance. In the special case that double layers are formed, the charge separation can extend some tens of Debye lengths.

The magnitude of the potentials and electric fields must be determined by means other than simply finding the net charge density. A common example is to assume that the electrons satisfy the "Boltzmann relation": 
. 

Differentiating this relation provides a means to calculate the electric field from the density: 
.

It is possible to produce a plasma which is not quasineutral. An electron beam, for example, has only negative charges. The density of a non-neutral plasma must generally be very low, or it must be very small, otherwise it will be dissipated by the repulsive electrostatic force.

In astrophysical plasmas, Debye screening prevents electric fields from directly affecting the plasma over large distances (ie. greater than the Debye length). But the existence of charged particles causes the plasma to generate and be affected by magnetic fields.  This can and does cause extremely complex behavior, such as the generation of plasma double layers, an object which separates charge over a few tens of Debye lengths. The dynamics of plasmas interacting with external and self-generated magnetic fields are studied in the academic discipline of magnetohydrodynamics.

චුම්භකනය ****
A plasma in which the magnetic field is strong enough to influence the motion of the charged particles is said to be magnetized. A common quantitative criterion is that a particle on average completes at least one gyration around the magnetic field before making a collision (ie.  where  is the "electron gyrofrequency" and  is the "electron collision rate"). It is often the case that the electrons are magnetized while the ions are not. Magnetized plasmas are anisotropic, meaning that their properties in the direction parallel to the magnetic field are different from those perpendicular to it. While electric fields in plasmas are usually small due to the high conductivity, the electric field associated with a plasma moving in a magnetic field is given by E = -v x B (where E is the electric field, v is the velocity, and B is the magnetic field), and is not affected by Debye shielding.

Comparison of plasma and gas phases 
Plasma is often called the fourth state of matter. It is distinct from other lower-energy states of matter; most commonly solid, liquid, and gas, although it is closely related to the gas phase in that it also has no definite form or volume. Physicists consider a plasma to be more than a gas because of a number of distinct properties including the following:

Complex plasma phenomena

Although the underlying equations governing plasmas are relatively simple, plasma behaviour is extraordinarily varied and subtle: the emergence of unexpected behaviour from a simple model is a typical feature of a complex system. Such systems lie in some sense on the boundary between ordered and disordered behaviour, and cannot typically be described either by simple, smooth, mathematical functions, or by pure randomness. The spontaneous formation of interesting spatial features on a wide range of length scales is one manifestation of plasma complexity. The features are interesting, for example, because they are very sharp, spatially intermittent (the distance between features is much larger than the features themselves), or have a fractal form. Many of these features were first studied in the laboratory, and have subsequently been recognised throughout the universe. Examples of complexity and complex structures in plasmas include:

Filamentation
Striations or string-like structures are seen in many plasmas, like the plasma ball (image above),  the aurora, lightning, electric arcs, solar flares, and supernova remnants. They are sometimes associated with larger current densities, and the interaction with the magnetic field can form a magnetic rope structure. (See also Plasma pinch)

Shocks or double layers
Plasma properties change rapidly (within a few Debye lengths) across a two-dimensional sheet in the presence of a (moving) shock or (stationary) double layer. Double layers involve localised charge separation, which causes a large potential difference across the layer, but does not generate an electric field outside the layer. Double layers separate adjacent plasma regions with different physical characteristics, and are often found in current carrying plasmas. They accelerate both ions and electrons.

Electric fields and circuits
Quasineutrality of a plasma requires that plasma currents close on themselves in electric circuits. Such circuits follow Kirchhoff's circuit laws, and possess a resistance and inductance. These circuits must generally be treated as a strongly coupled system, with the behaviour in each plasma region dependent on the entire circuit. It is this strong coupling between system elements, together with nonlinearity, which may lead to complex behaviour. Electrical circuits in plasmas store inductive (magnetic) energy, and should the circuit be disrupted,  for example, by a plasma instability, the inductive energy will be released as plasma heating and acceleration. This is a common explanation for the heating which takes place in the solar corona. Electric currents, and in particular, magnetic-field-aligned electric  currents (which are sometimes generically referred to as "Birkeland currents"), are also observed in the Earth's aurora, and in plasma filaments.

Cellular structure
Narrow sheets with sharp gradients may separate regions with different properties such as magnetization, density, and temperature, resulting in cell-like regions. Examples include the magnetosphere, heliosphere, and heliospheric current sheet. Hannes Alfvén wrote: "From the cosmological point of view, the most important new space research discovery is probably the cellular structure of space. As has been seen, in every region of space which is accessible to in situ measurements, there are a number of 'cell walls', sheets of electric currents, which divide space into compartments with different magnetization, temperature, density, etc ."

Critical ionization velocity
The Critical ionization velocity is the relative velocity between an (magnetized) ionized plasma and a neutral gas above which a runaway ionization process takes place. The critical ionization process is a quite general mechanism for the conversion of the kinetic energy of a rapidly streaming gas into ionization and plasma thermal energy. Critical phenomena in general are typical of complex systems, and may lead to sharp spatial or temporal features.

Ultracold plasma 
It is possible to create ultracold plasmas, by using lasers to trap and cool neutral atoms to temperatures of 1 mK or lower. Another laser then ionizes the atoms by giving each of the outermost electrons just enough energy to escape the electrical attraction of its parent ion. 

The key point about ultracold plasmas is that by manipulating the atoms with lasers, the kinetic energy of the liberated electrons can be controlled. Using standard pulsed lasers, the electron energy can be made to correspond to a temperature of as low as 0.1 K,­ a limit set by the frequency bandwidth of the laser pulse. The ions, however, retain the millikelvin temperatures of the neutral atoms. This type of non-equilibrium ultracold plasma evolves rapidly, and many fundamental questions about its behaviour remain unanswered. Experiments conducted so far have revealed surprising dynamics and recombination behavior which are pushing the limits of our knowledge of plasma physics.
One of the metastable states of strongly nonideal plasma is Rydberg matter which forms upon condensation of excited atoms.

ආරෝපිත ප්ලැස්මා 
The strength and range of the electric force and the good conductivity of plasmas usually ensure that the density of positive and negative charges in any sizeable region are equal ("quasineutrality"). A plasma which has a significant excess of charge density or which is, in the extreme case, composed of only a single species, is called a non-neutral plasma. In such a plasma, electric fields play a dominant role. Examples are charged particle beams, an electron cloud in a Penning trap, and positron plasmas.

Dusty plasma and grain plasma
A dusty plasma is one containing tiny charged particles of dust (typically found in space) which also behaves like a plasma. A plasma containing larger particles is called a grain plasma.

Mathematical descriptions 
[[Image:Magnetic rope.svg|thumb|256px|The complex self-constricting magnetic field lines and current paths in a field-aligned Birkeland current which may develop in a plasma<ref>See Evolution of the Solar System, 1976)</ref> ]]

To completely describe the state of a plasma, we would need to write down all the 
particle locations and velocities, and describe the electromagnetic field in the plasma region.
However, it is generally not practical or necessary to keep track of all the particles in a plasma.
Therefore, plasma physicists commonly use less detailed descriptions known as models, of which
there are two main types:

 ද්‍රව ආකාතිය 
Fluid models describe plasmas in terms of smoothed quantities like density and averaged velocity around each position (see Plasma parameters). One simple fluid model, magnetohydrodynamics, treats the plasma as a single fluid  governed by a combination of Maxwell's equations and the Navier–Stokes equations. A more general description is the two-fluid picture, where the ions and electrons are described separately. Fluid models are often accurate when collisionality is sufficiently high to keep the plasma velocity distribution close to a Maxwell–Boltzmann distribution. Because fluid models usually describe the plasma in terms of a single flow at a certain temperature at each spatial location, they can neither capture velocity space structures like beams or double layers nor resolve wave-particle effects.

 ගතික ප්ලැස්මා 
Kinetic models describe the particle velocity distribution function at each point in the plasma, and therefore do not need to assume a Maxwell–Boltzmann distribution. A kinetic description is often necessary for collisionless plasmas. There are two common approaches to kinetic description of a plasma. One is based on representing the smoothed distribution function on a grid in velocity and position. The other, known as the particle-in-cell (PIC) technique, includes kinetic information by following the trajectories of a large number of individual particles. Kinetic models are generally more computationally intensive than fluid models. The Vlasov equation may be used to describe the dynamics of a system of charged particles interacting with an electromagnetic field.

 කෘතිම ප්ලැස්මා 
Most artificial plasmas are generated by the application of electric and/or magnetic fields. Plasma generated in a laboratory setting and for industrial use can be generally categorized by:
The type of power source used to generate the plasma; DC, RF and microwave.
The pressure at which they operate; vacuum pressure (< 10 mTorr), moderate pressure (~ 1 Torr), and atmospheric pressure (760 Torr). 
The degree of ionization within the plasma; fully ionized, partially ionized, weakly ionized.
The temperature relationships within the plasma; Thermal plasma (Te = Tion = Tgas), Non-Thermal or "cold" plasma (Te >> Tion = Tgas)
The electrode configuration used to generate the plasma.
The magnetization of the particles within the plasma; Magnetized (both ion and electrons are trapped in Larmor orbits by the magnetic field), partially magnetized (the electrons but not the ions are trapped by the magnetic field), non-magnetized (the magnetic field is too weak to trap the particles in orbits but may generate Lorentz forces).
Its application

Examples of industrial/commercial plasma
Low-pressure dischargesGlow discharge plasmas: non-thermal plasmas generated by the application of DC or low frequency RF (<100 kHz) electric field to the gap between two metal electrodes. Probably the most common plasma; this is the type of plasma generated within fluorescent light tubes. Capacitively coupled plasma (CCP): similar to glow discharge plasmas, but generated with high frequency RF electric fields, typically 13.56 MHz. These differ from glow discharges in that the sheaths are much less intense. These are widely used in the microfabrication and integrated circuit manufacturing industries for plasma etching and plasma enhanced chemical vapor deposition.Inductively coupled plasma (ICP): similar to a CCP and with similar applications but the electrode consists of a coil wrapped around the discharge volume which inductively excites the plasma.Wave heated plasma: similar to CCP and ICP in that it is typically RF (or microwave), but is heated by both electrostatic and electromagnetic means.  Examples are helicon discharge, electron cyclotron resonance (ECR), and ion cyclotron resonance (ICR).  These typically require a coaxial magnetic field for wave propagation.

Atmospheric pressureArc discharge: this is a high power thermal discharge of very high temperature ~10,000 K. It can be generated using various power supplies. It is commonly used in metallurgical processes. For example it is used to melt rocks containing Al2O3 to produce aluminium.Corona discharge: this is a non-thermal discharge generated by the application of high voltage to sharp electrode tips. It is commonly used in ozone generators and particle precipitators.Dielectric barrier discharge (DBD):'' this is a non-thermal discharge generated by the application of high voltages across small gaps wherein a non-conducting coating prevents the transition of the plasma discharge into an arc. It is often mislabeled 'Corona' discharge in industry and has similar application to corona discharges. It is also widely used in the web treatment of fabrics. The application of the discharge to synthetic fabrics and plastics functionalizes the surface and allows for paints, glues and similar materials to adhere.

Fields of active research 

This is just a partial list of topics. A more complete and organized list can be found on the Web site for Plasma science and technology.

මේවාත් බලන්න

 Plasma channel
 Plasma parameters
 Plasma nitriding
 Magnetohydrodynamics
 Electric field screening
 List of plasma physicists
 Important publications in plasma physics
 IEEE Nuclear and Plasma Sciences Society
 Free space plasma generator

සටහන්

බාහිරට යොමු 
 Plasmas: the Fourth State of Matter
  Animation on the plasma excitation
 Plasma Science and Technology
 Plasma on the Internet comprehensive list of plasma related links.
 Introduction to Plasma Physics: Graduate course given by Richard Fitzpatrick | M.I.T. Introduction by I.H.Hutchinson
 NRL Plasma Formulary online (or an html version)
 Plasma Coalition page
 Plasma Material Interaction
 How to make a glowing ball of plasma in your microwave with a grape | More (Video)
 How to make plasma in your microwave with only one match (video)
 Plasma Ignition How to make a plasma ignition system (Video)

 U.S. Dept of Agriculture research project "Decontamination of Fresh Produce with Cold Plasma"
 CNRS LAEPT "Electric Arc Thermal Plasmas  (french)

 
Astrophysics
Fundamental physics concepts
Electrical conductors
Phases of matter
භෞතික විද්‍යාව