Bremen 2017 – scientific programme

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P: Fachverband Plasmaphysik

P 25: Theory and Modeling III

P 25.5: Talk

Thursday, March 16, 2017, 09:45–10:00, HS 2010

Thermodynamics of the ions in the sheath — Uwe Czarnetzki and •Tsanko Tsankov — Institute for Plasma and Atomic Physics, Ruhr-University Bochum, 44780 Germany

Space charge sheaths form where the plasma is in contact with a surface. The high electric field in the sheath strongly accelerates the ions and largely determines the properties of their population reaching the wall. These properties are important for the plasma-wall interaction. One of the prominent parameters that describe the energy spread of the ions is their effective temperature.

Here, through a kinetic approach it will be shown, that in a fully collisionless sheath the effective ion temperature cools down due to an adiabatic expansion. The presence of collisions leads to ion energy flow and heating of the ions. This effect can reverse the trend of a decrease of the effective ion temperature as the ions approach the wall. Experiments and simulations show that even weak collisionality is sufficient for that. The results apply for both stationary and oscillating sheaths, provided the ion transport can be treated as quasi-stationary.