Makoto Toda

High power test of MA cavity for J-PARC RCS

We have been testing the RF cavities for the J-PARC RCS, so that we can operate the cavities without severe problems. Before some MA cores were damaged, then we found such cores have low ribbon resistance. After that we have tested the cavities loaded with cores which have improved ribbon resistance.

RF Acceleration in KEK Booster

The KEK booster synchrotron is a rapid-cycling machine with a repetition rate of 20 Hz. The rf system was designed for accelerating the proton beam injected at 20 MeV up to its final energy of 500 MeV. The booster succeeded in accelerating 8 x 10/sup 10/ protons/pulse to the designed energy on Dec. 12, 1974. Since then the beam intensity was steadily increased to 5.7 x 10/sup 11/ protons/pulse with adjustments and improvements of the machine components, especially of the rf system. An outline of the rf system and the present status of its operation are presented. Main parameters characterizing the rf system are listed, and accelerating parameters and the estimated beam characteristics are shown.

The Second Harmonic RF System for J-PARC MR Upgrade

Power upgrade scenario of J-PARC Main Ring includes replacement of RF cavities with higher field gradient using magnetic alloy, Finemet ®-FT3L, cores than the present ones. It also needs to install the second harmonic RF cavity in the other section where dedicated water system for RF cavities is not available. Installation scenario of the second harmonic RF will be presented.

Simulation of Phase Modulation for Longitudinal Emittance Blow-Up in J-PARC MR

The J-PARC MR provides a coasting proton beam for nuclear physics experiments by slow extraction. The longitudinal emittance should be enlarged until the MR flat top to mitigate the microwave instability. We have investigated a Phase Modulation (PM) method[1,2,3,4] by using a High Frequency Cavity (HFC) to increase the emittance. We have performed extensive simulation studies to find the appropriate parameters of the PM through the particle tracking simulation. We found that the effective HFC frequency has linear dependence with the PM frequency as shown in Fig. 1, where the emittance is smoothly enlarged. Furthermore, we found that the required HFC voltage is inverse proportional to the square root of the duration time of the PM as shown in Fig. 2. These PM properties will be used for the design of the HFC. We describe the particle tracking simulation results of controlled emittance blow-up by the PM.

Simulation of Debunching for Slow Extraction in J-PARC MR

The J-PARC MR delivers a proton beam for nuclear physics experiments with slow extraction. The beam is debunched at flat top to obtain a coasting beam by turning off the rf voltage. The beam loading effect can disturb the uniformity of the debunching at the flat top. We describe the results of the particle tracking simulation including the beam loading effect.

RF Acceleration in KEK Main Ring

A description of the RF system and measurements of some longitudinal phenomena of the KEK Main Ring are presented. The beam loss at the phase transition has been reduced by the improvement of the radial position detector and by the stabilization of quadrupole oscillations. The debunching for slow beam extraction is done by two successive frequency jumps with simultaneous reduction of the RF voltage.