Neutral gas depletion in low temperature plasma

Abstract

Neutral depletion can significantly affect the steady state of low temperature plasmas. Processes that lead to neutral depletion and the resulting plasma–neutrals steady state are reviewed. Two such processes are due to collisions of neutrals with plasma. One process is the drag by ions that collide with neutrals and push them towards the wall. Another process is neutral-gas heating by collisions with plasma that makes the gas hotter at the discharge center. These processes, which usually occur under (static) pressure balance between plasma and neutrals, are called here ‘neutral pumping’. When collisions are negligible, neutrals that move ballistically between the chamber walls are depleted through ionization, a process called here ‘ion pumping’. The effect of the magnetic field on neutral depletion is explored in plasma in which the dynamics is governed by cross-field diffusion. Finally, neutral depletion in a flowing plasma is analyzed.

Helicon-type radiofrequency plasma thrusters and magnetic plasma nozzles

“…The neutral heating process is suggested to be used for another type of the electric propulsion device named the 'pocket rocket' . The detailed physical mechanisms of the plasma-neutral interaction in various regimes have been discussed in Fruchtman (2017).…”

1-D Modeling of the Screw-Pinch Plasma in PROTO-SPHERA

“…Results on degree of ionization, azimuthal current density from (8) and azimuthal ion velocity from (9) are shown in Figure 7 for the lowest temperature case and in Figure 8 for the highest temperature case. The degree of ionization in the plasma core is 40 % at T e = 1 eV and 100 % at T e = 2.5 eV, while absolute values of self-generated azimuthal current density and velocity increase substantially at higher temperature.…”

“…The 1-D analysis for ions and electrons is similar to the one developed for magnetized gas discharge plasmas [6,7], but uniform neutral gas density was assumed in those works, while neutral dynamics is kept into account in this work. The effects of decreasing neutral density inside the plasma (neutrals depletion) were reviewed in [8], but without including the confining force that arises from plasma current. On the other hand, screw-pinch analyses including the full electromagnetic force, see for example [9], usually assume fully ionized plasma.…”

Observation of Axial Neutral-Gas Flow Reversal in an ECR Plasma

“…Partially ionized plasma can be ubiquitously found in nature, laboratories, and the edge region of magnetically confined plasmas [1,2], and the neutral gas in plasma plays an important role in the physical processes and the organization of plasma discharges. A plasma fluid is coupled with a neutral fluid via collision and radiation processes, and hence, understanding the characteristics of neutral gas transport is important.…”