A RFQ injector for EN Tandem Linac heavy ion accelerator

The conceptional design of a RFQ to be used as an injector of heavy ions for the Tandem-Linac system is discussed. Singly charged ions from the negative ion source are to be accelerated to more than 300 Kev by the RFQ at a frequency of 26 MHz. The pulse width of the output beam is designated as < 2ns and the energy dispersion ≤ 2 % with a beam utilization efficiency of > 95 %. The bunching process was carefully studied with a model of a sequence of RF gaps simulating the cells of the RFQ structure so as to optimize the design parameters. A novel structure with variable longitudinal drift space in-between cells was then developed. The result given by the analytic expressions agree well with those computed by the Monte Carlo simulation. The computation also shows that the total length of the RFQ can be shortened by additional double drift harmonic buncher set ahead of it. The profile of the RFQ electrodes was investigated in the light of the above discussion. (author)