A fast tuning method for a RFQ accelerator with ramped inter-vane voltage

This article is devoted to the study of a fast tuning method for the four-vane RFQ (Radio Frequency Quadrupole) accelerator with ramped-voltage. In the four-vane RFQ accelerator, the field distribution is formed mainly by the field of quadrupole modes and dipole modes. The purpose of tuning is acquiring the operating frequency and adjusting the inter-vane voltage distribution to the designed curve by changing the proportion of these modes. In this article, the transmission-line model of the RFQ is presented to describe the field distribution of all these modes. Then the perturbation theory is applied to calculate the effect of the tuners on the field distributions. On the basis of these analyses, the tuning method has been concluded and a computer program THURT (TsingHua University RFQ Tune) has been composed to perform all the calculations based on matrix operations. The tuning experiment carried out on the RFQ accelerator of the CPHS (Compact Pulsed Hadron Source) project at Tsinghua University is described. The merits and drawbacks of this method are also discussed.