Akihiko Mizuno

Stable top-up operation at SPring-8

Top-up operation allows SPring-8 to provide highly stable X-ray beams with arbitrary filling patterns. The implementation of top-up operation is described, with a focus on the simultaneous achievement of stability of stored current, beam orbit, purity of an isolated single bunch, and beam injection efficiency. Stored-current fluctuations have been routinely reduced to a level of 10(-3). Stored-beam oscillation on frequent beam injection, which was originally regarded as the most serious problem, has been successfully suppressed to a sufficiently low level that it never perturbs imaging experiments. Current impurities in nominally empty buckets have been reduced to a level of 10(-9) over more than one week of operation, making possible the measurement of time-resolved spectra using high-current bunches. Finally, excellent injection efficiency, higher than 80%, is routinely obtained, even for small undulator gaps, which is critical for preventing radiation damage to insertion-device magnets and to reduce leakage radiation. The process of achieving highly stabilized top-up operation at SPring-8 and its utility for user experiments are described.

Stabilization of the rf system at the SPring-8 linac

Abstract Beam energy variation of the SPring-8 linac was 1% or more at the start of beam commissioning. Depending on fluctuation, beam transmission efficiency from the linac to the booster synchrotron was significantly affected, and beam intensity in the booster synchrotron changed 20–30%. This caused delay of optimization of the various parameters in the booster synchrotron. More problematic, the beam intensities stored in each rf (radio frequency) bucket of the storage ring at SPring-8 were all different from each other. The users utilizing synchrotron radiation requested that the beam intensity in each rf bucket be as uniform as possible. It was thus a pressing necessity to stabilize the beam energy in the linac. Investigation of the cause has clarified that the various apparatuses installed in the linac periodically changed depending on circumstances and utilities such as the air conditioner, cooling water and electric power. After various improvements, beam energy stability in the linac of

Review of Recent Development of Photoinjectors in Japan

Systematic developments of the photoinjectors for ultrashort and high quality electron beam works are under way in Japan. Sumitomo succeeded in transformation of the Gaussian shape to the trapezoidal one in the temporal and transverse profiles of the drive laser and achieved 0.9 πmm.mrad with 1 nC/bunch. It is the best data in the transverse aspect. Himeji Inst. Tech. is operating very unique needle‐shaped photocathode RF gun with the original Nd/Glass laser for IR‐FEL and Compton scattering X‐rays. U.Tokyo/JASRI(SPring8)/KEK/NIRS/BNL/etc. are developing and operating the S‐band photoinjectors with Cu, Mg and Cs2Te cathodes, and transmission‐type one in near future. Further, U.Tokyo/KEK/NIRS are designing and constructing a new X‐band RF‐gun/linac/laser system to generate inverse Compton scattering hard X‐rays(33–50keV) for intraveneous angiography.

Overview of the SPring-8 linac future plan

We carry out incidence operation in proportion to the commissioning to the storage ring at present, after SPring-8 linac started beam commissioning from August, 1996, and after it confirmed the beam performance early. In the future, the improvement in beam performance and equipment performance is tried, while we advise the improvement of the beam monitor. We develop the new applied research with it. We consider the application using various beams as part of the effective utilization of SPring-8 linac. In this paper, we introduce the plan of the free electron laser with the aim of the lasing at 4nm wavelength as one of the inside. And, we also introduce simulation result of the RF photocathode electron gun for it.

Bunch compression and beam transport for SPring-8 linac SASE

For SASE, a bunch compression and a beam transport system which follow the layout of the present SPring-8 linac are designed. This is the first order evaluation trying to preserve the emittances at an RF photocathode gun. There are two bunch compressors in the injector section. There are one energy compressor, 90° bending system and two bunch compressors in the final compression section. The RF gun generates electron beam which has the normalized transverse emittances of 1.5πmm⋅mrad, and the longitudinal emittance of 0.16πps⋅MeV. The final emittances before a undulator become 3.5πmm⋅mrad for x direction and 0.38πps⋅MeV respectively.

Beam tracking simulation for an rf gun apparatus in the SPring-8

A photo cathode rf gun has been studied in the SPring-8 Linac to obtain a lower emittance beam. In order to perform a comparison with the beam characteristics, a beam tracking simulation code for an rf gun test apparatus has also been developed. In this code, the electric and magnetic forces between all particles are calculated. Accordingly, a lot of time is required, but a high accuracy can be expected in the calculations in comparison with other codes like PIC. In this paper, we describe the above rf gun test apparatus in the SPring-8, the simulation code, and present some calculation results such as the emittance of the emitted beam compared with MAFIA’s data.

New method of Helmholtz coil alignment

A new alignment method for Helmholtz coils is proposed. This method is based on a probe, whose axis is the same as the alignment axis. This probe includes one magnetic sensor, whose position is slightly shifted from the probe axis, and which is set perpendicular to the axis. Using this probe, the tilt and shift of the magnetic centre of Helmholtz coils can be aligned to within an order of 0.1 mrad and 0.1 mm, respectively. Moreover, by this method, effects of terrestrial magnetism and tilt of the magnetic sensor can be removed from the measurement. This alignment method is presented along with an estimate of the alignment accuracy of the SPring-8 linac injector.