Chihiro Tsukishima

Design of a compact storage ring for industrial research

An 800‐MeV compact storage ring is under construction for development of the technology of a compact ring and for research of x‐ray lithography and material analysis. Synchrotron radiation with a critical wavelength of 0.65 nm is emitted from a pair of superconducting bending magnets. A straight section of the ring has only one quadrupole magnet to make the smaller ring. An injection efficiency with a single kicker magnet is optimized by computer simulation. The kicker field strength and an injection angle are determined. A beam tracking with a numerical integration method shows this ring has a sufficiently wide dynamic aperture of ‖x‖≂30 mm and ‖y‖≂50 mm at the center of the bending magnet, which has βxmin and βymax. A 1‐GeV synchrotron is used as an injector, which has accelerated a beam up to 1 GeV.

Construction and beam experiment of a compact storage ring at MELCO

A compact storage ring has been developed for industrial research such as x‐ray lithography and material analysis. This machine is of a racetrack type with two superconducting bending magnets and only two normal conducting quadrupole magnets. The circumference is as short as 9.2 m. One quadrupole magnet per cell contributes to making the smaller machine. The injector is a synchrotron, and a full energy injection of 600 MeV is performed. The bending magnets excite a field of 3.5 T, and are operated in a persistent current mode. A decrease in a coil current is ΔI/I<3×10−3/year. The helium consumption is as low as 2 l/h for two magnets. An iron shield of the magnet decreases a leakage flux to a terrestrial level at a point 3 m from the magnet. A beam current of 380 mA has been stored with no beam instability in spite of there being no correction of the chromaticities. Beam emittances were obtained from measured beam sizes and were in good agreement with calculated values. The coupling coefficient ey/ex is ca...

A high energy electron beam facility for industrial research

A high-energy electron beam facility is under commission. This facility consists of a 20-MeV linac and a 1-GeV synchrotron. The synchrotron is designed to act as a storage ring as well as an injector to a compact storage ring.<<ETX>>

Injection system of a superconducting compact storage ring

Abstract An injection system for a superconducting compact storage ring is designed and fabricated. The system consists of a septum magnet and a kicker magnet. The injection septum magnet has a very thin septum width (2.5 mm) and generates a 1.8 T magnetic field. The septum coil and the beam duct are held with high heat-conductivity mold material, and a coolant tube is placed at the return coil. The kicker magnet generates a pulsed magnetic field of 1300 G maximum and the pulse width is 400 ns. The ceramic duct coating is very thin (10 nm) due to the short pulse width of the magnetic field. The injection tests are performed and the system successfully injects the electron beam into the storage ring.

Margin estimation and disturbances of irradiation field in layer-stacking carbon-ion beams for respiratory moving targets

Abstract Carbon-ion therapy by layer-stacking irradiation for static targets has been practised in clinical treatments. In order to apply this technique to a moving target, disturbances of carbon-ion dose distributions due to respiratory motion have been studied based on the measurement using a respiratory motion phantom, and the margin estimation given by the square root of the summation Internal margin2+Setup margin2 has been assessed. We assessed the volume in which the variation in the ratio of the dose for a target moving due to respiration relative to the dose for a static target was within 5%. The margins were insufficient for use with layer-stacking irradiation of a moving target, and an additional margin was required. The lateral movement of a target converts to the range variation, as the thickness of the range compensator changes with the movement of the target. Although the additional margin changes according to the shape of the ridge filter, dose uniformity of 5% can be achieved for a spherical target 93 mm in diameter when the upward range variation is limited to 5 mm and the additional margin of 2.5 mm is applied in case of our ridge filter. Dose uniformity in a clinical target largely depends on the shape of the mini-peak as well as on the bolus shape. We have shown the relationship between range variation and dose uniformity. In actual therapy, the upper limit of target movement should be considered by assessing the bolus shape.

Design and Power Tests of 500 MHz RF Cavity of CW Microtron for Industrial Applications

The 500 MHz RF cavity of a high intensity CW microtron for industrial applications was designed, and power tests of this cavity have been carried out. The cavity is composed of two cells with nose cones and coupling slots, having a total gap voltage of about 1 MV. The calculated Q-value was 37400 and the measured value was about 93% of the calculated one. An input power of 40 kW was successfully obtained in 65 h conditioning.

A fast extraction instrument of a 1‐GeV electron synchrotron

A kicker magnet and a modulator were developed as a fast extraction instrument of a 1‐GeV electron synchrotron. A 1‐kG pulsed magnetic field was generated by the kicker magnet with the rise time of 40 ns. The ripple of the flattop of the current wave form was less than ±1%, and the shot‐to‐shot fluctuation of the peak current was no more than 0.1%. The modulator consists of two Blumleins in series which operate at a quarter of the charging voltage as compared to a pulse forming network (PFN) type modulator. The damped oscillating wave form of the current could decrease the residual field to be less than 0.5 G. The effect of the residual field of the kicker magnet on the dynamic aperture of the low‐energy electron beam was estimated by the tracking calculation. The result shows the dynamic aperture decreases as the residual field increases. To obtain enough accelerated current, the residual field must be less than 1 G. This restriction could be satisfied by the developed kicker magnet and the modulator. Su...

Design and experiment of a far-infrared FEL

Abstract To design a FEL system, we have developed a three-dimensional simulation code including nonlinear effects such as interaction of electrons with laser fields. The code can calculate the motion of electrons and the variation of laser fields in a wiggler. It can simulate processes of bunching of electrons, and amplification and saturation of laser fields. This code, however, cannot include the effects of inhomogeneity of the wiggler field and beam misalignment. To estimate the gain reduction due to the above effects, we have also developed a linear simulation code based on Madeys theorem including the following effects: actual wiggler field, beam envelope, energy spread, and electron beam misalignment to the wiggler axis. The FEL system we have designed consists of a 20 MeV, 100 mA rf linac and a wiggler with 6 cm pitch, 28 periods and 2.5 kG peak field. The simulation results show that the FEL system has about 30% gain and several MW output power at 37 μm laser wavelength. Our FEL system has been completed and experiments have been started.