Experimental and numerical studies on potential distributions in a plasma

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Abstract
Experimental results on the distribution of the electric potential in a plasma between two grids which are biased at constant potentials are reported. The plasma between the grids was injected from a source located on the low potential grid side. A common feature of the measured potential profile was a sheath near the low potential grid followed by a strong negative potential gradient. The experimental scheme was simulated numerically. The simulated potential profiles were found to be qualitatively similar to the experimental ones. Furthermore, the simulation brought out the plasma processes involved in the formation of the steady state profiles. The important feature during the transient phase in the simulation was seen to be the propagation of a solitary potential pulse, which was identified to be an electron 'hole', which propagated in the direction of electron drift with a velocity of the order of the electron thermal velocity. The reflection of the 'hole' from the high potential grid led to the formation of the steady state profile.