Charge separation current in a electron cyclotron heated torus plasma

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In plasmas immersed in the toroidal field B, electrons drift downward while ions drift upward due to the field gradient and curvature(B.> 0 assumed). The same amount of current must flow into and out from the conducting vessel walls at the top and bottom, respectively, to realize current circulation via the vacuum vessel. In an ECR plasma in the LATE device radial profiles of vertical charge separation currents have been measured by radially aligned multi-electrodes fabricated at the top and bottom. Both the profiles at the top and bottom are nearly the same as the profile 2pe/RB. in the plasma as theoretically predicted. Current characteristics upon the sweep of external voltage onto the top ion collectors reveal that the current is due to inflow of ions with no secondary electron emission.