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Light Sources in 2018

1. Status of UVSOR Accelerators

  In the fiscal year 2018, 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 July we had a trouble in the linac and we could not operate the machine in the top-up mode almost for one week, in adding to 12 hour loss. In cases of other minor troubles, we extended the operation time for compensation. We had a scheduled shutdown period in April and May for about 6 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. In addition, we had 4 weeks for machine conditionings and studies, in October, November, January and March. 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 multi-bunch 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 FY2017.

 

  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 9am to 9pm, the machine is operated for users. From Thursday 9am to Friday 9pm, 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 trouble in the high voltage power supplies and the cooling water system for the linac in July. The former case, it took about several days to completely repair the power supply. In the latter, the chilling water unit was malfunctioned. We gave up to use it and alternatively we started supplying the chilling water to the linac from the cooling water system for other part of accelerator system. It has been working well without any trouble. In February 2018, a cooling water leakage was found at a sextupole coil wound on a pole face of a multipole (quadrupole/sextupole) magnet. After about one year, we have found similar leakage on nine of same coils. The hollow conductor used for these coils has relatively thin wall. It is supposed that, after the installation in 2003, the walls have been eroded by the water flow. In the spring shutdown 2019, we are applying liquid sealant for all the coils for life prolonging. In parallel, we have started constructing coils for replacement.

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

  In the UVSOR accelerator system, there are still some components which have been used since the construction of the facility early in 1980’s. This year, after more than 35 year operation, the pulse transformer for the klystron modulator of the linac was replaced (Fig. 3). The cooling water system for the RF cavity in the booster synchrotron was also replaced with the one which has a good temporal stability of 0.1 degree C. The control system of the undulator U6 was replaced after 15 year operation. The signal generator as the master oscillator of the accelerator complex was also replaced this year. The chilling water system for the linac had troubles several times in the past, which were mainly due to the unstable cooling water supply from the facility. This system provided 20 degree chilling water to the temperature control system of the linac. We tried to use about 25 degree water from the facility instead of he 20 degree chilling water and found that the linac could be operated stably without any problem. We stopped using the chilling water system.

         

storage ring

Fig. 3. New power supplies for the extraction septum at the booster synchrotron (left) and those for the beam transport line magnets (right).

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 beam from undulators in collaboration with Hiroshima U., Nagoya U. and other institutes. Since the UVSOR electron beam is diffraction-limited in the UV range, we could precisely investigate the optical properties of the vortex beams from undulators using conventional optical components. Moreover, we succeeded in producing optical vector beam which has a tailored distribution of the polarization in the transverse plane.
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. We started new experiments on positron lifetime spectroscopy experiments in collaboration with Yamagata U., Nagoya U. and AIST.

Masahiro Katoh (UVSOR Synchrotron Facility)

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