Abstract
A prototype cavity for the annular-ring coupled structure (ACS) for use in the Japan Proton Accelerator Research Complex (J-PARC) linac has been developed to confirm the feasibility of achieving the required performance. This prototype cavity is a buncher module, which includes ten accelerating cells in total. The ACS cavity is formed by the silver brazing of ACS half-cell pieces stacked in a vacuum furnace. The accelerating cell of the ACS is surrounded by a coupling cell. We, therefore, tuned the frequencies of the accelerating and coupling cells by an ultraprecision lathe before brazing, taking into account the frequency shift due to brazing. The prototype buncher module was successfully conditioned up to 600 kW, which corresponds to an accelerating field that is higher than the designed field of $4.1\text{ }\text{ }\mathrm{MV}/\mathrm{m}$ by 30%. We describe the frequency-tuning results for the prototype buncher module and its high-power conditioning.
Highlights
Several types of biperiodic =2-mode structures [1] have been developed for roomtemperature high-energy proton linacs: an on-axis coupled structure [2], a side-coupled structure (SCS) [3], a diskand-washer structure [4], and an annular-ring coupled structure (ACS) [4].Geometrically, the ACS can be considered as an axially symmetric version of the SCS
The accelerating-cell frequency of the SCS can be tuned by deforming the structure from the outside, whereas that of the ACS is surrounded by its coupling cell
The purpose of the present study is to demonstrate the feasibility of achieving the required performance from a newly designed ACS
Summary
Several types of biperiodic (alternating periodic) =2-mode structures [1] have been developed for roomtemperature high-energy proton linacs: an on-axis coupled structure [2], a side-coupled structure (SCS) [3], a diskand-washer structure [4], and an annular-ring coupled structure (ACS) [4]. The asymmetry possibly gives rise to emittance growth and/or halo formation, which has not been fully studied, partly because of a lack of experimental data Under this circumstance, it is preferable to improve the axial symmetry of the accelerating field, if it can be done without any cost. The smooth surface of the ACS obtained by ultraprecision machining guarantees a high Q value and high discharge limit The latter is important for realizing a stable operation as well as short conditioning. The accelerating-cell frequency of the SCS can be tuned by deforming the structure from the outside, whereas that of the ACS is surrounded by its coupling cell. This report describes the fabrication of the ACS prototype cavity and the results of a high-power test of this cavity for using it in the J-PARC linac
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