Operational Characteristics of a lOO-mA, 2-MeV

A IOO-mA, 2.07-MeV Radio-Frequency Quadruple (RFQ III) has been commissioned and operated routinely on the Accelerator Test Stand (ATS) [l] at Los Alamos National Laboratory. To characterize the RFQ output beam dynamics, measurements were made of the beam transmission and of the transverse and longitudinal phase-space distributions. Data were taken for different RFQ III operating conditions and compared to simulations. I. INTRODUCTION The ATS experimental program had the objective of comparing measured performance of an accelerating structure to predicted performance. The evaluation was made by comparing measured and predicted beam transmission, position and angle centroids, energy and phase centroids, and transverse and longitudinal phase-space distributions. RFQ III was the third RFQ in a series of RFQs [2,3] to be tested on the ATS. Pertinent RFQ III design parameters: frequency is 425 MHz, number of cells is 358, length is 289.23 cm, design vane potential is 111 kV, average radius is 0.4047 cm, final radius is 0.278 cm, final modulation is 1.83, initial synchronous phase is -90°, final synchronous phase is -30”. peak surface field is 32.7 MV/m, nominal current limit is 167 mA, and design acceptance at 100 mA is 0.232 x cm-mradian. This paper presents the RFQ III commissioning results. The RFQ vane potential is the only adjustable variable of the RFQ. It affects the transverse and longitudinal focusing of the beam. The RFQ vane polential was determined from end point measurements of the x-ray energy spectrum generated by electrons accelerated across the vane gap [73. The x-my energy spectra were measured versus cavity rf power and used to calibrate rf pickup loops in the RFQ. The pickup loops were used to set the RFQ vane potential. The RFQ operating voltage range was 95 to 138 kV.