High field-gradient cavities loaded with magnetic alloys for synchrotrons

Abstract

Very high field-gradient has become available by a new Magnetic Alloy (MA)-loaded cavity developed for high intensity proton synchrotrons. The available RF voltage per core is ten times larger than that of the ordinary ferrite core. The maximum voltage of 20 kV has been achieved by the High-Field Gradient Cavity(HGC) of 40 cm in length [1].Because the intrinsic Q-value of the MA core is low, acceleration without any tuning system also becomes possible. The first beam acceleration test using the HGC has been performed successfully at the HIMAC(Heavy Ion Medical Accelerator in Chiba). Furthermore, the dual harmonic RF and barrier bucket experiments have been carried out.Another advantage of the MA-loaded cavity is that it is easy to compensate the beam loading. The feed forward beam compensation was applied for both HGC on the test bench using electron beam and MA-loaded cavity installed in the AGS for the barrier bucket experiment. A new development for high-Q HGC using cut core configuration will be also reported.

Synchrotron RF system for the JAERI-KEK Joint Project

“…The advantage of the scheme is that the shunt impedance is constant for the wide range of Q value (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20). The optimum Q value is between 10 and 20 for the 50 GeV Synchrotron to reduce the transient beam loading and bucket distortion effects, and to sweep the rf frequency without any tuning.…”

“…For 3 GeV Synchrotron, it is 0.5 W/cc There are two different schemes to cool the cores. One is, so called, direct cooling [5,6] and the other is indirect one. In case of direct cooling, the cores are stored in the water tank and cooled by the water directly.…”

The present status of the JAERI/KEK joint project for high-intensity proton accelerators

“…One of the most difficult problems inherent to the highenergy RCS was solved by the innovative development of the accelerating cavity loaded with magnetic alloy(MA) [16][17][18], one of which is FINEMET. This cavity can generate the field gradient of over 50 kV/m (potentially over 100 kV/m) which is several times as high as conventional ferrite-loaded cavities.…”

The first beam acceleration test using high gradient cavity at HIMAC

“…The cavity was driven by a pushpull amplifier using two 150 kW tetrodes. The frequency sweeping from 1 to 5 MHz has been achieved without any tuning circuit because of its broadband characteristics of the MA-loaded cavity [2].…”