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Light Sources in 2019

1. Status of UVSOR Accelerators

  IIn the fiscal year 2019, we had scheduled to operate UVSOR-III from May to March, for 36 weeks for users. We had several machine troubles as described later. In June we had a trouble in the vacuum chamber of the booster synchrotron. Since we had another trouble on the beam-line vacuum in the same week, we canceled users operation for one week, which was compensated with a machine study week which had been scheduled in the latter half of the year. In cases of other minor troubles, we extended the operation time for compensation. We had a scheduled shutdown period in April for 4 weeks. This was mainly for the scheduled maintenance works. We had one week shut down period in August and October, two week one around the New Years day and one week one at the end of March. We had 2 weeks for machine and beamline conditioning in May after the spring shut down. We had 4 weeks for machine conditionings and studies, in the latter half of the year, although one week was replaced with users run as described above. The machine study week in November was mainly for the machine conditioning after the annual planned power outage.
  We operated the machine for 34 weeks in the multibunch top-up mode at 300 mA, and 2 weeks in the single-bunch top-up mode at approximately 40 mA. The monthly statistics of the operation time and the integrated beam current are shown in Fig. 1.

Fig. 1. Monthly statistics in FY2018.


  The weekly operation schedule is as follows. On Monday, from 9 am to 9 pm, the machine is operated for machine conditionings and studies. On Tuesday and Wednesday, from 9 am to 9 pm, the machine is operated for users. From Thursday 9 am to Friday 9 pm, the machine is operated for 36 hours continuously for users. Therefore, the beam time for users in a week is 60 hours. In the single bunch operation weeks, the machine is operated for 12 hours per day from Tuesday to Friday.
  We had a vacuum leakage trouble at the booster synchrotron. We quickly localized the leaking position, which was on the vacuum chamber at a bending magnet. Fortunately, we could stop the leakage by using a liquid vacuum seal.
  The cooling water leakage from the sextupole coils wound on the pole faces of the multipole (quadrupole/ sextupole) magnets have been getting more serious. As cutting the hollow conductor which was removed, from the magnet, it was confirmed that the walls of the hollow conductor have been eroded by the water flow during the fifteen year operation. In the spring shutdown 2019, we applied liquid sealant for all the coils for life prolonging. However, even after this, some coils started leaking. In parallel with repairing the leaking coils, we have constructed new coils for a half of the 32 multipole magnets in FY2019. We have started the replacement in March, 2020. The coils for the half of the magnets will be replaced by the end of April 2020. Those of another half will be replaced by the end of April 2021.

Beam Current

Fig. 2.The beam duct at a quadrupole in the booster synchrotron. A vacuum leakage was found in the middle of the duct.


2. Improvements and Developments

  The pulse magnet power supplies for the injection kickers of the booster-synchrotron malfunction a few times in a year. It has been recognized that the IGBT in the power supply caused the trouble. We have started replacing them one after another with more robust ones for high voltage.
  The vacuum data acquisition system was replaced after nearly 15 year operation, which has been collecting the vacuum pressure for all part of the accelerator system and beam-line front ends. The PLCs were replaced and the data display ability was improved.
  The timing system of the linear accelerator was improved. Now the trigger of the electron gun and that of the klystron can be adjusted independently from the control room.
  The access bridge to the inside of the storage ring was replaced to create a space for a new beam-line. The pulse motor of an undulator U6, which was constructed in 2002, has been replaced to be compatible with the new control system.

Light Source Developments and Beam Physics Studies

  We continue the efforts to develop novel light sources technologies and their applications such as free electron lasers, coherent harmonic generation, coherent synchrotron radiation, laser Compton scattering gamma-rays, intense polarized and vortex UV radiation at the source development station BL1U, which was constructed under the support of Quantum Beam Technology Program by MEXT/JST.
  In these years, we continued studying the generations of structured light beams, such as optical vortex beams and optical vector beams, from undulators in collaboration with Hiroshima U., Nagoya U. and other institutes. Moreover, we have demonstrated a novel method to utilize temporal structure of undulator radiation for coherent control of atoms. BL1U is a unique beam-line, which enables us to use the direct beam from a tandem undulator system for coherent control experiments, which are described in these reports.
  The laser Compton scattering gamma-rays are powerful tools for nuclear science and technologies. By using various external lasers, we have demonstrated generating quasi-monochromatic gamma-rays in the energy range from 1MeV to around 10MeV. We continue the experiments in collaboration with Kyoto U., AIST and QST towards imaging applications. At BL1U, we have a special port for the laser injection for 90 degree Thomson scattering, which enable us to generate short gamma-ray pulses of sub-picosecond order. With this novel light source, we have started new experiments on positron lifetime spectroscopy in collaboration with Yamagata U., Nagoya U. and AIST.

Masahiro Katoh (UVSOR Synchrotron Facility)