Tadamichi Kawakubo

Fast data acquisition system of a non-destructive profile monitor for a synchrotron beam by using a microchannel plate with multi-anodes

A microchannel plate (MCP) is a good sensor for the head of a non-destructive profile monitor (NDPM) in a synchrotron ring. The gain of the sensor can be controlled from 1 to 104 by adjusting the bias voltage on the MCP. If the gain of the MCP is not sufficient for observing a polarized beam with an intensity which is about one thousandth of the normal beam intensity, two MCPs in series (tandem type) should be used for the sensor. The conventional type of NDPM takes data by moving an MCP with a narrow window from the end of the beam size to the other end during many acceleration periods. Therefore, the measured beam profile is the average of the beam dynamics over many acceleration periods, and data taking requires a long time. The fast NDPM data acquisition system introduced in this article can obtain a beam profile from injection into a synchrotron to extraction only for one acceleration period. The head of the NDPM is a large rectangular MCP having multi-anodes of a strip line. Each anode has an independent electric system for data taking into a computer. In a parallel data acquisition system, such as this monitor system, the calibration of the whole gain of each channel from the MCP to the analog-to-digital converter (ADC) is the most important. In our system, this is done by longitudinally rotating the MCP by 90° (i.e., the direction of the anode strips is set perpendicular to the beam direction).

Non-destructive emittance measurement of a beam transport line

Abstract In order to measure the transverse beam emittance non-destructively, we have developed a new method using profile monitors. The usual assumption of Gaussian distribution is not necessary for it to measure the percent emittance. So, even if the profile is far from Gaussian, the percent emittance can be measured accurately. This method was applied to the 20 MeV KEK beam transport line and resulted in horizontal and vertical emittances of ϵh = 85 mm mrad and ϵv = 25 mm mrad containing 85% of the particles.

Analysis and measurement of beam dynamics in H− charge-exchange injection

Abstract The beam dynamics during the period of H − charge-exchange injection is analyzed in detail. The formulas to calculate the beam characteristics at the end of this period, such as the hitting probability of protons on the charge-stripping foil, momentum distribution, injection efficiency and emittance are deduced. These formulas include the space charge effect and can be applied to a high intensity beam. The beam characteristics were measured in the KEK Booster Synchrotron by changing the injection energy, thickness of the stripping foil, duration and the injection timing of the chopped H − ion beam. The calculated results are in good agreement with the measurements.

Switching power supply for the PFL kicker magnet

SI-thyristor is expected as a solid-state high power switching semi-conducting device for the kicker magnet in the circular accelerator. Current rise has reached to 100 kA//spl mu/s. We noticed this characteristic and tried the use it for the pulse forming line (PFL). Preliminary results of the proto-type power supply of 20 kV-120 ns, with various impedance, although the intention is 75 kV-100 ns, are presented.

A Compact Hadron Driver for Cancer Therapies with Continuous Energy Sweep Scanning

The compact hadron driver for future cancer therapies based on the induction synchrotron concept, which has been proposed recently, is discussed. This is a fast cycling synchrotron that allows the energy sweep beam scanning. Assuming a 1.5 T bending magnet, the ring can deliver heavy ions of 200 MeV/au at 10 Hz. A beam fraction is dropped from the barrier bucket at the desired timing and the increasing negative momentum deviation of this beam fraction becomes enough large for the fraction to fall in the electrostatic septum extraction gap, which is placed at the large D(s) region. The programmed energy sweeping extraction makes spot scanning beam irradiation on a cancer area in depth possible.

Super-Bunch Induction Acceleration Scheme in the KEK Digital Accelerator

KEK Digital Accelerator (KEK-DA) [1] is a fast cycling induction synchrotron with induction cells driven by switching power supplies (SPS). The rectangular pulse voltages are precisely controlled by a field-programmable gate array (FPGA). One of our next missions for the KEKDA is to demonstrate super-bunch (very long beam) acceleration technique in which the beam occupies over half of the ring at injection [2]. For that, power supplies for the SPS have to be upgraded from fixed voltage to timevarying voltage to provide beam-required acceleration. This is effective to suppress the blow-up of the longitudinal emittance and ensures the super-bunch acceleration stably.

Solid-state high-voltage switching unit for accelerator applications

Solid-state high-voltage switching units are being developed for applications to power supplies of high-energy accelerators. The ultimate goal is to replace most of the traditional thyratron-based switching units for both present and future accelerators. Solid-state semiconductor power devices are advantageous in many respects such as lifetime, stability, maintenance, and cost. In this study, static-induction thyristor (SIThy) is selected as the switching device for the reason that it is faster than IGBT and is more powerful than MOSFET. A prototype SIThy-based switching unit has been made and tested for operation at 20 kV and 400 A. It consists of 10 SIThys connected in series. Detailed studies have been carried out on voltage balance and timing control, before this switching unit is put on a real accelerator for experimental evaluation. The KEK digital accelerator (KEK-DA), which is an induction synchrotron, requires a 20 kV pulser for its electrostatic injection kicker. This originally thyratrondriven pulse supply has been selected as the platform for the initial experimental demonstration of our SIThy switching unit. The results have proved that the solid-state switching unit is not only capable of replacing the traditional thyratronbased unit but also improves the performance of the pulsed high-voltage supply.

Space charge effects in the KEK-Booster synchrotron

Space charge effects have been observed in the KEK-PS Booster synchrotron. Beam-profile measurements by the BEAMSCOPE method show that a beam blow-up in the vertical plane occurred during the RF capture process. The intensity dependence of beam blow-up and deformation of beam profile were observed.

How to decrease the rise time of a current from a thyratron housing

Abstract Means of decreasing the rise time of the output current from a thyratron housing are discussed. An equivalent circuit, from which calculated results are in good agreement with measurements, is introduced. The simulation shows that the main cause of an increased rise time is not the inductance but the capacitance of the floating housing associated with the cathode heaters and grid supplies. By inserting a large inductance in series with the floating capacitance, the rise time achieved can be very close to that calculated from an ideal circuit which has no floating capacitance or inductance.

Transverse Bunched Beam Instability in KEK Booster

A transverse bunched beam instability has been observed over the past few years in the KEK booster synchrotron, and the kicker magnet for the fast beam extraction has been thought to be responsible for this instability. To check this supposition, the instability was observed quantitatively using a spectrum analyzer and its growth rate was compared with calculations assuming various termination conditions at the feeding end of the coaxial cable of the kicker. The variation of the growth rate with time for a realistic case is well explained by the reflection of the current induced in the kicker at the feeding end of the cable.