1. Status of UVSOR Accelerators

  In the fiscal year 2020, we had scheduled to operate UVSOR-III from May to March, for 36 weeks for users. Because of the COVID-19 pandemic, some of the users experiments were canceled. However, we operated the accelerators as scheduled. We had a few minor machine troubles, such as a discharge of the electron gun, malfunction of the cooling water system for the RF cavity, unstable operation of the klystron pulse modulator of the injection linac and unstable operation of the timing system. Fortunately, all of them could be solved quickly and we extended the operation time and compensated the scheduled users beam time.
  We had a scheduled shutdown period in April for 4 weeks. This was for the scheduled maintenance works as usual. In addition, this year, we replaced the coils of one third of the multipole magnets as described later. We had one week shut down period in August and October, two week one around the New Year’s 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. One of them 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.

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 cooling water leakage from the sextupole coils wound on the pole faces of the multipole (quadrupole/ sextupole) magnets had been getting more frequent. We confirmed that the hollow conductor walls have been eroded by the water flow during the fifteen-year operation. We decided replacing all the coils and, in March, 2020, we replaced the one-third of the coils. The remainder will be replaced in April, 2021.
  We started a design study for the future plan of UVSOR, UVSOR-IV. As its first step, we have analyzed the present magnetic lattice, seeking a possibility to reduce the emittance more [1]. Although, we did not find a drastically low emittance solution, we have found a few interesting solutions which may be useful for some machine studies which requires lower emittance as possible.
  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 are focusing on studying the temporal structure of undulator radiation and exploring its application. In collaboration with atomic physicists, we have successfully demonstrated ultrafast spectroscopy with undulator radiation [2] and polarization utilization of tandem undulator radiation [3]./br>   Laser Compton gamma-ray source is another research subject which we are focusing in these years. The applications are spreading to a range of research fields, quantum electrodynamics, imaging technologies, material sciences and so on [4,5]. The research activity at the gamma-ray source is now shifting from source development studies to users experiments.
  We have been collaborating with Nagoya University on the electron source development. In these years, we investigated utilizing graphene as a material for photocathode [6].
[1] E. Salehi and M. Katoh, presented at iPAC2021 (2021).
[2] T. Kaneyasu et al., Physical Review Letters 126(11) (2021) 1132202.
[3] T. Kaneyasu et al., New J. Phys. 22(8) (2020) 083062.
[4] K. Ali et al., IEEE Trans. Nucl. Sci. 67(8) (2020) 1976.
[5] K Fujimori et al., Appl. Phys. Express 13(8) (2020) 085505.
[6] L Guo et al., Appl. Phys. Lett. 116(25) (2020) 251903