Exploring the beam parameter space of a CW RFQ proton accelerator

RFQ1, a 100% duty factor radio-frequency quadrupole (RFQ) to accelerate 75 mA of protons to a final energy of 0.6 MeV, is a testbed for a wide range of high-power RFQ experiments. First beam was accelerated in RFQ1 in July 1988, and an experimental program to investigate the beam parameter space of the machine was started. With the initial three-beamlet ion sources adjusted to deliver 5 mA to the RFQ, only 35% of the beam was captured and accelerated to design energy. Changing to a lower emittance single-beamlet source, transmission improved to almost 80% with over 6 mA CW (continuous wave) accelerated. The realization of the replaceable component design of the RFQ, CW operation of vane coupling rings and the ability of the racetrack seals to maintain vacuum and RF integrity over large temperature gradients were demonstrated. Design deficiencies in the injector that spoil the match to the RFQ have been identified, and TRANSPORT and PARMTEQ were used to examine corrective measures