Masanori Satoh

Propagation and stability characteristics of a 500-m-long laser-based fiducial line for high-precision alignment of long-distance linear accelerators

A laser-based alignment system with a He-Ne laser has been newly developed in order to precisely align accelerator units at the KEKB injector linac. The laser beam was first implemented as a 500-m-long fiducial straight line for alignment measurements. We experimentally investigated the propagation and stability characteristics of the laser beam passing through laser pipes in vacuum. The pointing stability at the last fiducial point was successfully obtained with the transverse displacements of ±40 μm level in one standard deviation by applying a feedback control. This pointing stability corresponds to an angle of ±0.08 μrad. This report contains a detailed description of the experimental investigation for the propagation and stability characteristics of the laser beam in the laser-based alignment system for long-distance linear accelerators.

The effects of the insertion devices at the Super SOR light source

The Super SOR ring is a third generation light source constructed at Kashiwa Campus of the University of Tokyo. In this paper, we present the formalization of the circularly polarizing undulator and beam optics correction.

New beam-charge interlock system for radiation safety at the KEKB injector linac.

A new beam-charge interlock system is under development for radiation safety and machine protection at the KEKB injector linac. A hardware-based interlock system is required instead of the present software-based interlock system in order to boost its reliability. This system restricts the integrated amount of beam charges delivered to four different storage rings. The beam charges are measured using wall-current monitors and detection electronics at six locations along the linac. The detection electronics independently transmits a beam-abort request through a twisted hardwire cable directly to the safety control system of the linac, when the integrated amount of beam charges exceeds a certain threshold level prescribed for each location. We describe the characteristics and performance of the new beam-charge interlock system along with the details of the experimental tests.

Experimental investigation on focusing characteristics of a He-Ne laser using circular Fresnel zone plate for high-precision alignment of linear accelerators

We experimentally investigate the focusing characteristics of a He-Ne laser at the focal region for the high-precision alignment of long-distance linear accelerators using a circular Fresnel zone plate. The laser wave passing through the Fresnel zone plate having a focal length of 66.7 m propagates for a 268-m-long distance at atmospheric pressure. A new laser-based alignment system using Fresnel zone plates as the alignment targets is discussed. The transverse displacement of the focused spot of the laser is measured as a function of the displacement of the target by a detector installed at the focal point. Systematic studies on the focusing characteristics and alignment precision have been successfully conducted in this experiment. The experimental results are in good agreement with theoretical calculations, and the alignment precision of the target is determined to be less than ±30 μm. In this study, we perform a detailed experimental investigation on the laser propagation and focusing characteristics using the circular Fresnel zone plate at the focal region along with theoretical calculations.

Progress of 7-GeV SuperKEKB Injector Linac Upgrade and Commissioning

KEK injector linac is being upgraded for the SuperKEKB project, which aims at a 40-fold increase in luminosity over the previous project KEKB. SuperKEKB asymmetric electron and positron collider with its extremely high luminosity requires a high current, low emittance and low energy spread injection beam from the injector. Electron beams will be generated by a new type of RF gun, that will inject a much higher beam current to correspond to a large stored beam current and a short lifetime in the storage ring. The positron source is another major challenge that enhances the positron bunch intensity from 1 to 4 nC by increasing the positron capture efficiency, and the positron beam emittance is reduced by introducing a damping ring, followed by the bunch compressor and energy compressor. The recent status of the upgrade and beam commissioning is reported.

Emittance Growth by Misalignments and Jitters in SuperKEKB Injector Linac

SuperKEKB injector linac have to transport high-charged beam with low emittance to SuperKEKB ring for high luminosity, 8 × 1035. For the low emittance, photocathode RF gun was adopted as electron source. One of the main reason of the beam emittance blow-up electron linac is generally induced by wakefield in acceleration cavities. A charged beam with a offset from a center of a cavity is affected by the wakefield depending on the offset size in the acceleration cavity and the beam emittance is increased. This emittance blow-up can be eliminated by appropriate steering magnet control so as to cancel the wake effect in the acceleration cavity. We perform particle tracking simulation with some misalignments and beam jitter. Emittance growth by the misalignments and the beam jitter is evaluated in this report.

Design of an injector of Super SOR ring

We present a design of the injector part for the Super‐SOR ring of the University of Tokyo, which is a 3rd generation type vuv light source and is aimed to operate with top‐up operation scheme. In order to realize top‐up operation, this injector consists of a pre‐injector and a synchrotron. The pre‐injector is a 200MeV linac and injects the electron beam into the synchrotron. In the synchrotron, the electron beam is accelerated from 200MeV up to 1.8GeV and its emittance and energy spread are reduced. In order to realize this low emittance beam, modified FODO lattice is applied. The details are presented in this section.

Two-bunch orbit correction using the Wakefield kick

In the KEKB injector linac, a two-bunch acceleration scheme has been used for doubling the positron injection rate to the KEKB low-energy-ring (LER). In this operation mode, the multi-bunch transverse wake field caused by the first bunch affects the beam orbit of the second bunch. In the KEKB linac, an orbit correction method based on the average minimum of two-bunch orbits has been adopted, and has worked stably. However, a new two-bunch orbit correction method is strongly required to make the loss of charge less. We propose a new two-bunch orbit correction method based on a local bump method. In this scheme, some local bumps are intentionally constructed in a low-energy area. Adjusting the local bump height can control the wake field strength affecting the second bunch. In this paper, we report on the results of a preliminary beam test to confirm that this new method is useful