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What is a cryogenic plasma

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08 Sep,2020

What is a cryogenic plasma:

99.9% of the matter in the universe is in a plasma state. Our planet is the exception to the rule. In addition, for plasma in nature, we can also list the sun, ionosphere, auroras, lightning, and so on. In the artificial plasma generation methods, gas discharge method is more simple and efficient than heating method, such as fluorescent lamp, neon lamp, arc welding, corona discharge and so on. The density and temperature values of the various major types of plasma generated naturally and artificially span nearly 20 orders of magnitude from a density of 106 (units/m3) of rarefied interstellar plasma to a density of 1025 of arc discharge plasma. Its temperature distribution ranges from 100K low temperature to 108-109K (100-1 billion degrees) of ultra-high temperature fusion plasma. The electron Volt (ELECTRON Volt) of the temperature axis is a common temperature unit in the plasma field, 1eV=11600K.

Plasmas usually contain three kinds of particles: electrons, positive ions and neutral particles (including uncharged particles such as atoms or molecules and atomic groups). Let their densities be ne, Ni,nn respectively. Since the gas is quasi-neutral, the molecular density before ionization is NE ≈ NN. Therefore, we define the ionization degree =ne/(ne+nn) to measure the ionization degree of the plasma. Both the corona and the hot plasma in fusion are 100% ionized, and a plasma like this =1 is called a fully ionized plasma. Ionization degrees greater than 1%(≥10-2) are called strongly ionized plasma, like the flame plasma is mostly neutral particles (<10-3), called weak ionization plasma.

If the discharge is carried out under the condition of high pressure close to atmospheric pressure, then electrons, ions and neutral particles will exchange kinetic energy fully through intense collision, so that the plasma reaches the thermal equilibrium state. If the temperature of the electron, ion and neutral particles respectively to Te, Ti, Tn, we put the three particle temperature approximately equal (Te material Ti material Tn) thermal equilibrium plasma called hot plasma, in the actual thermal plasma generator, arc discharge between cathode and anode effect makes the work flow of gas ionization occurs, it is the output of the plasma jet, can be used as a plasma jet, plasma spray flame, etc.

On the other hand, low-pressure plasmas below a few hundred palas are often in non-thermal equilibrium. Now, electrons lose almost no energy when they collide with ions or neutral particles, so they have Te, >, >, Ti, Te, >, >, Tn. We call such plasmas cold plasmas. Of course, even at high pressure, the low-temperature plasma can be generated by short pulse discharge modes with no thermal effect, namely corona discharge or arc sliding jet discharge. At present, the glow discharge technology under atmospheric pressure has become a research hotspot in the world. The mechanism of producing non-equilibrium plasma at atmospheric pressure is not clear, and the research on the transport characteristics of plasma at high pressure has just begun, which has formed a new research hotspot.

crf plasma

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