Development of a new type of Cs plasma ion gun for application in a heavy ion beam tokamak diagnostic

Abstract

A new type of high-density caesium plasma ion source is described, which is capable of producing Cs+ beam currents of up to 300 mu A. The ion emitting surface in the caesium plasma conforms automatically to the accelerator geometry to give perveance match, providing that the ion density is correctly adjusted with respect to the required beam energy. Ready operation of the source at different energies with constant perveance is facilitated in this way. Consequently, the beam divergence is practically independent of the beam energy. The plasma density is maintained at the required level by controlling the temperature of the source chamber walls on which atomic caesium is deposited. The ion source and the beam transport line have been developed at Culham and deliver a low-divergence 1.5 mu A Cs+ beam at the gun output, with an energy of up to 25 keV. The apparatus now serves as the injection part of the heavy ion beam deflection analyser of the ISTTOK tokamak in Lisbon.