S. Shibuya

Advanced RF-KO slow-extraction method for the reduction of spill ripple

Two advanced RF-knockout (RF-KO) slow-extraction methods have been developed at HIMAC in order to reduce the spill ripple for accurate heavy-ion cancer therapy: the dual frequency modulation (FM) method and the separated function method. As a result of simulations and experiments, it was verified that the spill ripple could be considerably reduced using these advanced methods, compared with the ordinary RF-KO method. The dual FM method and the separated function method bring about a low spill ripple within standard deviations of around 25% and of 15% during beam extraction within around 2 s, respectively, which are in good agreement with the simulation results.

Source of spill ripple in the RF-KO slow-extraction method with FM and AM

The RF-knockout (RF-KO) slow-extraction method with frequency modulation (FM) and amplitude modulation (AM) has brought high-accuracy irradiation to the treatment ofa cancer tumor moving with respiration, because ofa quick response to beam start/stop. However, a beam spill extracted from a synchrotron ring through RF-KO slowextraction has a huge ripple with a frequency of around 1 kHz related to the FM. The spill ripple will disturb the lateral dose distribution in the beam scanning methods. Thus, the source ofthe spill ripple has been investigated through experiments and simulations. There are two tune regions for the extraction process through the RF-KO method: the extraction region and the diffusion region. The particles in the extraction region can be extracted due to amplitude growth through the transverse RF field, only when its frequency matches with the tune in the extraction region. For a large chromaticity, however, the particles in the extraction region can be extracted through the synchrotron oscillation, even when the frequency does not match with the tune in the extraction region. Thus, the spill structure during one period ofthe FM strongly depends on the horizontal chromaticity. They are repeated with the repetition f of the FM, which is the very source ofthe spill ripple in the RF-KO method. r 2002 Elsevier Science B.V. All rights reserved.

Laser Cooling for 3-D Crystalline State at S-LSR

At ICR, Kyoto University, an ion storage and cooler ring, S‐LSR has been constructed. Its mean radius and maximum magnetic rigidity are 3.6 m and 1.0 Tm, respectively. 24Mg+ ions with the kinetic energy of 35 keV are to be laser‐cooled by the frequency doubled ring dye laser with the wavelength of 280 nm. In order to avoid the shear heating, dispersion compensation is planned by the overlap of the electric field with the dipole magnetic field in all 6 deflection elements. Intermediate electrodes, which can be potential adjusted, are to be utilized so as to realize a uniform electric field radial direction within a rather limited vertical gap, 70 mm of the dipole magnet. Synchro‐betatron coupling needed for 3‐dimensional laser cooling is to be realized by placing the RF cavity at the siraight section with finite dispersion for the normal mode lattice, which is expected to realize 1 dimensional string. For the case of dispersion compensated lattice to suppress the shear heating, possibility of realizing “ta...

Design and measurement of the S-LSR quadrupole magnet considering the influence of a neighboring field clamp

The design and the magnetic field measurement of the quadrupole magnet for the compact ion ring, S-LSR, are presented. Because the S-LSR is a compact ring accelerator, whose components take up most of the space in the arc sections. Therefore, we have to optimize the integrated field gradient in the quadrupole magnetic field taking account of the effect of the neighboring field clamp. Under these conditions plus requirements from accelerator parameters, the design of the S-LSR quadrupole magnet was optimized by means of 2D and 3D modeling calculations. A magnet field measurement by a Hall probe is carried out together with the field clamp and S-LSR bending magnet. Both results of the calculation and the measurement present the almost same result as that for the effect of the field clamp.

S-LSR Cooler Ring Development at Kyoto University

A compact ion cooler ring, S‐LSR is under construction in Kyoto University. One of the subjects of S‐LSR is a realization of the crystalline beams using the electron beam and the laser cooling. The ring is designed to be satisfied several required conditions for the beam ordering, such as a small betatron phase advance, a small magnetic error and a precise magnet alignment. The design phase advance per a period is less than 127 degree. The calculated closed orbit distortion and the stopband is less than 1 mm and 0.001 without correction, respectively.

Experimental Study of Dispersion Control Utilizing both Magnetic and Electric Fields

An experiment to control dispersion of beams in one bending section has been carried out. This experiment is based on a theory that the dispersion of accumulated beams can be controlled, if they are bent by a cross field composed of magnetic and an electric fields. Suppression of the dispersion can ease a shear which affects the 3‐dimensionally ordered structure of the ultimate‐low‐temperature beams. In order to realize this scheme experimentally, we have manufactured a set of electrodes to create precise electric fields whose strength is 6.6 × 104 V/m for 24Mg+, 35keV beam. The electrodes have been inserted to the gap of dipole magnet. 3‐dimensional field calculation shows that the error of the electric fields is less than 0.1% within ± 5mm from the reference orbit. We also tested the effect of the electric field using a single set of bending elements. The result showed that the linear dispersion can be controlled or canceled by changing the ratio of magnetic and electric fields.