Coupled Dynamics of Neutrals and Plasma

Summary form only given. Space and laboratory plasmas can be dramatically affected by neutral depletion. We focus on laboratory low-temperature plasmas in steady-state in which volume ionization is balanced by wall recombination. For collisional plasma that is in pressure balance with the neutral gas we showed that because of the inherent coupling of ionization and transport, an increase of the energy invested in ionization can nonlinearly enhance the transport process. Such an enhancement of the plasma transport due to neutral depletion was shown to result in an unexpected decrease of the plasma density when power is increased; despite the increase of the flux of generated plasma. Unexpected steady-state has also been found for collisionless plasma due to neutral depletion. For collisionless neutral-gas the strong ionization resulted in an expected neutral-gas minimum at the center of the chamber. However, if the neutral-gas is collisional so that its pressure increases with density, strong ionization results in a maximum of the neutral-gas density surprisingly located at the center of the chamber. The effect of neutral gas heating is also analyzed. It is shown that this neutral gas heating can affect the plasma steady-state even if the plasma pressure is much lower than the neutral gas pressure.