Masashi Shirakata

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.

Experience of the erosion-corrosion problems in the main ring cooling water system at the KEK-PS

After more than two decades have passed since the KEK-PS construction, water leak accidents in the cooling system have occurred frequently. Low conductivity deionized water, at 20 degrees centigrade, is supplied at the Mechanical support building and circulates in a closed loop. Water flows through the main ring magnets, various magnets for beam injection and extraction, correction magnets and the power supply system, and so on. Recently, various repair works due to the plugged water pipes have been attempted in a high radioactivated area. After several investigations it was concluded that most of the leaks come from erosion-corrosion after long periods of use. We introduce erosion-corrosion problems into future cooling system/material designs.

Observation of Emittance Growth at KEK PS

Emittance growth has been observed in the transverse direction at the injection period of the 12 GeV main ring of the KEK proton synchrotron. Measurement of the beam profiles using flying wires has revealed a characteristic temporal change of the beam profile within a few milliseconds after injection. Horizontal emittance growth was observed when the horizontal tune was close to the integer. The effect was more enhanced for higher beam intensity and could not be explained with the injection mismatch. 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 qualitatively reproduced the beam profiles.

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.

Space charge effects during the injection period of 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 injection. Horizontal emittance growth was observed when the horizontal tune was close to the integer. The effect was more enhanced for higher beam intensity and could not be explained with the injection mismatch. 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 qualitatively reproduced the beam profiles.

Simulations of the Beam Loss Distribution at J-PARC Main Ring

The Japan Proton Accelerator Research Complex (JPARC) is integrated by a set of high intensity proton accelerators. At this operation level, the monitoring and control of the beam losses and residual radiation are priority for its safe performance and maintenance. At Main Ring (MR), a discrepancy appears between the beam loss signal detected by the monitors and the residual dose measured. To understand this difference and the mechanism that produces these losses, a beam simulation study is implemented using the Strategic Accelerator Design (SAD) and Geometry and Tracking (Geant4) code. The first stage of the survey uses SAD to obtain the location of the losses around the lattice per turn. Then, Geant4 produces the secondary showers in the elements. Finally, we make the extrapolation with the residual radiation and compare with the measurements. The description and results of this work are presented in this paper.

Residual Radiation Measurements at J-PARC MR Using the ASTROCAM 7000HS Newly Developed Radioactive Substance Visualization Camera

Mitsubishi heavy Industries, Ltd. (MHI) released the ASTROCAM 7000HS, a radioactive substance visualization camera. The ASTROCAM 7000HS incorporates the technologies for the gamma-ray detector used for the ASTRO-H satellite, which MHI has been developing under entrustment from and together with scientists at the Institute of Space and Astronautical Science (ISAS) at the Japan Aerospace Exploration Agency (JAXA), and the design was modified for use on land to commercialize the product [1]. MHI and Mitsubishi Heavy Industries Mechatronics Systems, Ltd. (MHI-MS) performed on-site residual radiation measurements at the 50 GeV Main Ring (MR) of the Japan Proton Accelerator Research Complex (J-PARC) under collaboration with the High Energy Accelerator Research Organization (KEK) and the Japan Atomic Energy Agency (JAEA) and succeeded visualization of radiation hot spots of the accelerator components. The outline of the ASTROCAM 7000HS, the measurement principle and the first measurement results at the JPARC MR are described.

Optics Tuning for Beam Collimation in the J-PARC 3-50 Beam Transport Line

The Japan Proton Accelerator Research Complex (J-PARC) 3-50 Beam Transport line (3-50BT) is a beam transport line from 3-GeV rapid-cycling synchrotron (RCS) to 50-GeV main ring (MR). The RCS is a high-intensity proton accelerator, where the designed beam power is 1 MW, and has the complex source of space charge effect and beam instability, etc. Therefore, the uncontrolled emittance growth and beam halo increase nonlinearly with the beam power ramp up. Additionally, the physical aperture of 81  mm mrad in the MR is smaller than physical aperture of 486  mm mrad in the RCS. Therefore, the 3-50BT line has the collimators in order to remove the unwanted beam tail or halo from the RCS. The designed collimator aperture is 54  mm mrad. It is required to measure and optimize the optics parameters in the collimator area for taking full advantage of the beam collimation. Especially, it is very important to make the dispersion functions free in the collimator area and optimize the beta function to remove beam tail or halo over predefined transverse emittance. This paper introduces the method of optics measurement and reports the results of the measurement and optimization based on an accelerator model.

Residual Field Correction of Pulsed Bending Magnet

At the J-PARC, to deliver bunches of protons to both of beam transport lines, 3NBT and 3-50BT, a pulsed bending magnet (PB) [1] is operated. Bunches between K1 and K4 timing are bended to 3-50BT, and the other bunches through the PB to 3NBT after the magnetic field is fallen down. The rise and fall time of the pulsed bending magnet was designed as less than 40msec because the interval time of bunches is 40msec. However the residual magnetic field after K4 has been observed as equal to 0.27mrad kick angle at K5 as shown in Fig1. Therefore, bunches at K5, K6 and K7 have not been filled to avoid time depended beam orbit shift at the target of Material and Life Science Experimental Facility (MLF). If the residual field of PB is corrected, the production beam power for the MLF will be higher with K5, K6 and K7 bunches. To reduce the PB residual field, additional coils have been wound to poles of the PB, and a power supply has been installed. Results of the beam study by using the additional correction coil will be reported in this paper.