K. Koseki

Switching power supply for induction accelerators

A new particle acceleration method using pulsed induction cells was introduced in the super-bunch project at KEK. Unlike conventional RF acceleration, this acceleration method separates functions of acceleration and confinement. As a result, this acceleration method is capable of accelerating a very long bunch of beam or a wide mass range of particles. However, it is necessary to give a very fast pulsed- excitation to the magnetic material to induce an electric field to accelerate particles. Switching power supplies of high voltage output with very fast pulse-operation is one of the most important key technologies for this new acceleration method. Features of switching power supply developed for induction synchrotron is reported. The 31 kW MOSFET switch performed 1 MHz continuous operation with 15 nsec rise time.

A POP experiment scenario of induction synchrotron at the KEK 12 GeV-PS

A scenario for the first POP experiment and crucial issues of accelerator operation with induction acceleration are discussed.

R&D works on 1MHz power modulator for induction synchrotron

A proof of principle experiment of an Induction Synchrotron is scheduled in 2003 at the KEK 12GeV-PS. Proton bunches are accelerated with a 10kV of rectangular shaped induction voltage. An accelerating system consists of four induction cavities capable of individually generating a 2.5kV of output voltage. Each cavity is driven by a solid-state power modulator, which is operated at a revolution frequency of 600-800 kHz. The modulator circuit consists of MOS-FETs as switching element. Uniformity in the voltage waveform is crucial for the stable acceleration. Ringing in the voltage waveform caused by coupling of self-inductance of circuit and output capacitance of MOS-FETs deteriorates the uniformity. With the help of circuit analysis and simulation method of minimizing the self-inductance has been developed. Ratio of numbers of MOS-FETs in series and in parallel which defines the total output capacitance is also important to design the power modulator circuit. Power loss in MOS-FET is also important for stable operation of the power modulator. By the circuit analysis, it is also found that the output capacitance contributes to the power loss.

Induction Acceleration of a Single RF Bunch in the KEK PS

Results of the induction acceleration of a single RF bunch in the KEK PS are reported.

Design study of 1MHz induction cavity for induction synchrotron

An induction cavity was designed for the POP experiment of induction synchrotron using the KEK 12 GeV PS. It must be operated at a repetition rate of 667-882 kHz for acceleration from the injection energy to the flat-top energy. Design issues include handling of heat deposit, minimization of voltage droop and coupling impedance, and tolerable jitter. Its Q-value on the cavity assembled following the design was obtained from the longitudinal coupling impedance measurement. Effects of the droop in the acceleration voltage on the synchrotron motion, which has been estimated from the circuit parameter measurement on R, C, and L, was analysed from a longitudinal beam dynamics point of view. The effect of the droop is given by the square of phase delay.

Space Charge Effects at the KEK PS Main Ring

Space charge effects during the injection period of the 12 GeV main ring of the KEK proton synchrotron have been studied. Measurement of the transverse beam profiles using flying wires has revealed a characteristic temporal change of the beam profile within a few milliseconds after the injection. Horizontal emittance growth was observed when the horizontal tune was close to the integer. The effect was more enhanced for higher beam intensity. Resonance created by the space charge field was the cause of the emittance growth. A multiparticle tracking simulation program, ACCSIM, taking account of space charge effects has successfully reproduced the beam profiles.