Abstract
We developed a two-beam interdigital-H-type radio frequency quadrupole (IH-RFQ) linac as a prototype of a multibeam IH-RFQ for high intensity heavy ion acceleration in the low energy region. This linac has two sets of RFQ electrodes within an IH-type resonant frequency cavity that is a power-efficient structure for low energy beam acceleration. The linac can accelerate two beams in parallel in one cavity with a reduction in the coulomb repulsive force (the space charge effect) between the accelerated heavy ion particles. The resonance frequency and the Q factor of the linac were found to be 47 MHz and 5900, respectively. We also developed a two-beam laser ion source with a direct plasma injection scheme as an injection system for the two-beam IH-RFQ linac and built a system to demonstrate the use of the two-beam IH-RFQ linac. Using this linac system, we were able to accelerate carbon ions from 5 to 60 keV/u and generate an output beam current of about 108 mA (2×54 mA/channel). A coherency between the two beams, derived from the imbalance of the beam loading, was observed in the acceleration test with carbon ions.
Highlights
Radio frequency quadrupole (RFQ) linacs accelerate beams with strong focusing
We evaluated the advantages of the multibeam interdigital-H-type radio frequency quadrupole (IH-RFQ) linac quantitatively; coherency in each beam channel was observed in this test
In order to estimate changes in the resonance frequency, with respects to the amount of deformation, we assumed that the displacement over the cavity walls is uniform and used these displacements to simulate the changes in the rf properties using MICRO-WAVE STUDIO (MWS)
Summary
Radio frequency quadrupole (RFQ) linacs accelerate beams with strong focusing. It is possible to achieve greater than 90% transmission rates of accelerated particles, the ratio of the number of injected particles to the number of output particles. In order to achieve a higher beam current, such as 100 mA or more, one would need a set of several in parallel-operated linacs Using this acceleration method, the number of peripheral devices, such as the evacuation systems, the ion sources, the rf amplifiers, the control systems, and so on, increase depending on the required output beam. We have studied a multibeam RFQ linac system, with multiple channels accelerating several beams in parallel in one cavity, in order to generate high intensity heavy ion beams without a significant increase in the size of the linac system. With DPIS as the injection system of a multibeam RFQ linac In this scheme, the laser ion source is connected to the RFQ cavity directly without a LEBT. We evaluated the advantages of the multibeam IH-RFQ linac quantitatively; coherency in each beam channel was observed in this test
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