Abrupt variation in ion current with biased disk voltage in the electron cyclotron resonance ion source

Abstract

The performance of the biased disk in the 6.4GHz electron cyclotron resonance ion source at VECC, Kolkata was studied at a pressure of ∼1×10−7Torr. We observed an abrupt variation of beam current with bias voltage. For low negative bias voltages (from 0 to −5V) the beam current gradually decreases and then shows a sudden change in magnitude at a voltage of about −6V. The higher the charge state, the higher is the magnitude of this change. For H+ also the current changes abruptly, but the jump is from a higher to a lower current. This indicates a sudden change in the charge-state distribution of the beam, likely corresponding to a suddenly improved confinement.