Design and high-power testing of offline conditioning cavity for CiADS RFQ high-power coupler

To validate the design rationality of the power coupler for the RFQ cavity and minimize cavity contamination,we designed a low-loss offline conditioning cavity and conducted high-power testing.This offline cavity features two coupling ports and two tuners,operating at a frequency of 162.5 MHz with a tuning range of 3.2 MHz.Adjusting the installation angle of the coupling ring and the insertion depth of the tuner helps minimize cavity losses.We performed electromagnetic structural and multiphysics simulations,revealing a minimal theoretical power loss of 4.3%.However,when the cavity frequency varied by110 kHz,theoretical power losses increased to10%,necessitating constant tuner adjustments during conditioning.Multiphysics simulations indicated that increased cavity temperature did not affect frequency variation.Upon completion of the offline high-power conditioning platform,we measured the transmission performance,revealing a power loss of 6.3%,exceeding the theoretical calculation.Conditioning utilized efficient automatic range scanning and standing wave resonant methods.To fully condition the power coupler,a 15°phase difference between two standing wave points in the condition-ing system was necessary.Notably,the maximum continuous wave power surpassed 20 kW,exceeding the expected target.

Design study of a radio-frequency quadrupole for high-intensity beams

The Rare isotope Accelerator Of Newness（RAON） heavy-ion accelerator has been designed for the Rare Isotope Science Project（RISP） in Korea. The RAON will produce heavy-ion beams from 660-MeV-proton to200-MeV/u-uranium with continuous wave（CW） power of 400 k W to support research in various scientific fields.Its system consists of an ECR ion source, LEBTs with 10 ke V/u, CW RFQ accelerator with 81.25 MHz and 500 ke V/u, a MEBT system, and a SC linac. In detail, the driver linac system consists of a Quarter Wave Resonator（QWR） section with 81.25 MHz and a Half Wave Resonator（HWR） section with 162.5 MHz, Linac-1, and a Spoke Cavity section with 325 MHz, Linac-2. These linacs have been designed to optimize the beam parameters to meet the required design goals. At the same time, a light-heavy ion accelerator with high-intensity beam, such as proton,deuteron, and helium beams, is required for experiments. In this paper, we present the design study of the high intensity RFQ for a deuteron beam with energies from 30 ke V/u to 1.5 MeV/u and currents in the m A range. This system is composed of an Penning Ionization Gauge ion source, short LEBT with a RF deflector, and shared SC Linac. In order to increase acceleration efficiency in a short length with low cost, the 2nd harmonic of 162.5 MHz is applied as the operation frequency in the D^＋RFQ design. The D^＋RFQ is designed with 4.97 m, 1.52 bravery factor. Since it operates with 2nd harmonic frequency, the beam should be 50% of the duty factor while the cavity should be operated in CW mode, to protect the downstream linac system. We focus on avoiding emittance growth by the space-charge effect and optimizing the RFQ to achieve a high transmission and low emittance growth. Both the RFQ beam dynamics study and RFQ cavity design study for two and three dimensions will be discussed.