Ion energy measurements at the surface of an ion cyclotron range of frequencies antenna faraday shield

Abstract

The effects of rf fields on the energy of ions hitting the surface of an ion cyclotron range of frequencies (ICFR) antenna exposed to a plasma must be investigated to provide an understanding of the impurity generation from the antenna. A resonant loop antenna with a two-tier Faraday shield, installed on the Radio Frequency Test Facility at Oak Ridge National Laboratory, was used to study these effects. Samples of silicon were placed below the antenna and on the Faraday shield surface, facing the plasma, to measure incident ion energy. The samples were exposed to electron cyclotron heated plasmas without rf power and with 22 kW of rf power at antenna currents of up to 400 A. The fluence of—5 X 1017D/cm2from deuterium plasmas was near the saturation level of the samples. The energy of the incident ions was estimated by measuring the amount of deuterium trapped in the samples with D3He, p)4He nuclear reaction analysis. The results obtained from the trapped deuterium measurements are compared with ion energies measured directly with a gridded energy analyzer located near the antenna. They show that the rf-enhanced ion energy distribution measured in the plasma is proportional to the impact energies on the surface of the Faraday shield and increases with antenna current. © 1990, American Vacuum Society. All rights reserved.