Development and cold-test of an RFQ-DTL coupled cavity

With the continuous strengthening of application requirements, neutron sources are becoming more and more compact, integrated and mobile. There are challenges in two aspects. The first is to achieve high transmission efficiency of high beam current physically, the second is to achieve integration and miniaturization technically. The coupling of RFQ and DTL is a feasible way. A preliminary study on the key physical problems in the RFQ-DTL coupled cavity has been accomplished. For the beam dynamics, the compact matching of RFQ and DTL was studied for the coupled cavity. Taking the compact physical design of the RFQ-DTL for deuterium ion beam of 30 mA with the energy of 11 MeV without MEBT as an example, we studied the smooth transition of the phase advance per unit length, the ability of RFQ transition cell to rotate beam in the transverse phase space, the transverse and longitudinal acceptance optimization of DTL. The RFQ and DTL can be matched transversely and longitudinally after removing MEBT, and the transmission efficiency is 98.7%. For direct coupling of four-vane RFQ and CH-DTL, we studied the realization of the coupling, the factors affecting the field amplitude ratio, the tuning of the cavity, and the influence of the superimposed field on the beam transmission. The field amplitude ratio between RFQ and CH-DTL is from 16.5 to 36.2. Under the influence of the superimposed field, the difference in normalized RMS emittance is less than 1%. We have designed, constructed and cold-test the 750 MHz model cavity. The normalized electric field coefficients measured and simulated are basically in agreement.