ECRIS operation with multiple frequencies

Abstract

The 10.5GHz electron cyclotron resonance ion source (ECRIS) at Argonne National Laboratory has been utilizing a 10.5GHz klystron and an 11–13GHz traveling wave tube amplifier (TWTA) for beam production in two-frequency heating mode. The beam intensities obtained from the source with two-frequency heating have shown a factor of 2 improvement over single-frequency heating for the higher charge states. Following a simple logic that an increased number of resonance zones leads to enhanced source performance, a 14GHz klystron was added to the source configuration enabling the plasma to be simultaneously excited with three discrete frequencies. In studies with three-frequency heating when compared to two-frequency heating, the beam intensity for O7+ increased from 70.4to84.2eμA, Kr23+ (mass 86, 99.9% enriched) increased from 3.5to7.2eμA, and Xe28+ (mass 136, 60% enriched) increased from 7.9to12.2eμA. A rf power combiner was added to the TWTA so that it could be driven simultaneously with two frequencies. With the TWTA operating at 10.85 and 12.66GHz, the intensities of O6+ increased 80% and O7+ doubled compared to single-frequency operation, further demonstrating the multiple frequency heating effect except in this instance with a single transmitter.