Response of Currents Circulating in an End Region of a Tandem Mirror to Variation of End Plate Resistance

This paper describes response of currents circulating in an end region of the GAMMA 10 tandem mirror to variation of an end plate resistance R_EP. By changing its value from less than 1 Ω to over 1 MΩ, are examined the variation of the plasma potentials and the current balance at the end plate during fundamental ECRH. Main results are as follows. First, for R_EP ≥ 3 kΩ, the end plate potential as measured from the vacuum vessel is nearly constant and for R_EP ≤ 0.5 kΩ, on the contrary, the current flowing through the resistance is nearly constant. Second, the plasma potentials other than the end plate weakly depends on R_EP. In particular, the plasma potential at the central cell hardly varies with R_EP. Third, with decreasing R_EP, a step-like increase in the net current flowing through the end plate is observed at R_EP ≈ Z_eff. Ion currents are observed on ring electrodes installed in the mirror cell in which ECRH is applied. A part of the ion current is to be connected to the end plate current.