C. Ohmori

A 150 MeV FFAG synchrotron with "Return-Yoke Free" magnet

The 150 MeV proton FFAG (Fixed Field Alternating Gradient) synchrotron is under construction at KEK to investigate the possibilities of various applications such as proton beam therapy after the success of the POP FFAG synchrotron. One of distinguished features of this machine compared with the PoP FFAG is to use a new type of magnet, Return-Yoke Free magnet. Because there is no return-yoke in the median plane in this magnet, the beam injection and extraction become easier.

High field-gradient cavities loaded with magnetic alloys for synchrotrons

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. 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 an electron beam and MA-loaded cavity installed in the AGS for the barrier bucket experiment. A new development for high-Q HGC using a cut core configuration will be also reported.

Magnetic alloy loaded RF cavity for barrier bucket experiment at the AGS

A magnetic alloy (MA) loaded cavity which was developed by KEK was used for the barrier bucket experiment at the AGS. The MA loaded cavity could generate a single sine-wave of 40 kV with less RF power than a ferrite loaded cavity because of its broad-band impedance. In order to reduce the voltage induced by beam, the feedforward system was applied and the beam loading was compensated. With the barrier bucket scheme, five bunches were transferred successfully. Total of 3/spl times/10/sup 13/ protons were accumulated without beam loss. They were re-bunched by the accelerating cavities and accelerated.

Recent beam studies of the PoP FFAG proton synchrotron

The PoP (Proof of Principle) FFAG accelerator, which was the world first FFAG proton synchrotron, was constructed at KEK. After the first proton beam acceleration of FFAG, we studied various aspects of the PoP FFAG. The observed beam orbit shift during the acceleration was consistent with the simulation result. It was confirmed that the beam intensity increased about five times with multi-bunch injection. The horizontal acceptance of the PoP FFAG was estimated at about 4000 /spl pi/ mm.mrad experimentally.

Barrier cavities in the Brookhaven AGS

In collaboration with KEK two barrier cavities, each generating 40 kV per turn have been installed in the Brookhaven AGS. Machine studies are described and their implications for high intensity operations are discussed.

Multi-orbit synchrotron with FFAG focusing for acceleration of high intensity hadron beams

A multi-orbit synchrotron (MOS) with fixed field alternating gradient (FFAG) focusing is attractive for acceleration of high intensity hadron beams because acceleration cycle could be increased. The magnetic field of MOS is static, therefore, the repetition rate of acceleration could be increased more than 10 times larger than that of ordinary rapid cycling synchrotron (RCS) if an efficient high voltage RF accelerating system becomes available. Recently, a new type of high gradient RF cavity (HGC) using high permeability magnetic alloy (MA) has been developed and MOS with FFAG focusing becomes very promising. In order to clarify the feasibility of rapid cycling MOS (RCMOS) experimentally, proof-of-principle (POP) machine, which accelerates protons up to 1 MeV with 1 kHz repetition, is under development. We have also made several designs on high intensity proton accelerators with RCMOS for various applications such as an accelerator driven system (ADS) as an energy breeder, a spallation neutron source and a proton driver for a muon collider.

Longitudinal impedance tuner using high permeability material

We have succeeded in canceling longitudinal space charge effects using the impedance tuner at the KEK-PS. The impedance tuner consists of the new material, FINEMET which has large permeability over the beam spectrum region. A frequency shift of coherent quadrupole mode is measured to infer the modified impedance. It turns out that nonlinearity unavoidable in a longitudinal RF bucket has to be treated carefully in order to digest observed beam signals. We describe how to measure the impedance from the beam signal, how to analyze the effect of impedance tuner, and how to succeed in canceling space charge effects.