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Light Sources in 2017

1. Status of UVSOR Accelerators

  In the fiscal year 2017, we had scheduled to operate UVSOR-III from May to March, for 36 weeks for users. Although we had several machine troubles as described later, fortunately, we could operate the machine mostly as scheduled only with one day and a few hour losses. 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, in which the beam current was kept at 300 mA, and 2 weeks in the single-bunch mode, in which the machine was operated in single-bunch top-up mode with the beam current of 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.   The most serious trouble in this year was the vacuum leakage at the booster synchrotron, which happened in July. We observed an unusual pressure rise in a part of the synchrotron. After the careful check, we found a vacuum leakage at a beam duct (Fig. 2). Fortunately, a temporal expedient with vacuum sealant was effective, and the vacuum pressure recovered. We could restart the users operation after a shut down for one day. Another vacuum trouble was also in July. In this case, the leakage occurred at a beamline frontend. After a temporal expedient, we could restart the users time with 4 hour loss.   In February, a cooling water leakage was found at a sextupole coil wound on a pole face of a multipole (quadrupole/sextupole) magnet. Due to the space constraints, an expedient was difficult. Therefore, we decided to continue the operation for about one month as monitoring the leakage carefully. In the spring shut down, the coil will be repaired. Concerning the water leakage from the coils of quadrupole magnet in the booster synchrotron, which occurred twice in these years, the preventive treatment with sealant seems effective. No recurrence has been observed so far.   In this year, other than the troubles described above, we had a few less serious troubles on the power supplies of the injection/extraction magnets. Fortunately, in all cases the beam time for users was not lost. Due to the unusual low temperature in this winter, in the cooling tower of the cooling water system, the pipe was partly frozen and damaged. It should have been avoided by an interlock system but, unfortunately, the temperature detection system was malfunctioned. In order to prevent the recurrence, we are going to improve the routine inspection.

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 power supply for the extraction septum magnet in the booster synchrotron was replaced in spring 2017 (Fig. 3), following the replacement of the power supply for the injection septum magnet in the previous year. As the result, there was no pulse power supply which had been used since the beginning of the facility. The small power supplies for beam transport line were also replaced (Fig. 3), which had been used for more than 20 years.   The cooling water system of the main RF cavity in the storage ring was replaced with the one which has a good temporal stability of 0.1 degree C. We expected that this would improve the beam stability.

         

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 optical vortex beam from a helical undulator 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. In 2016, we installed a mirror and a monochromator at BL1U, which would be used for exploring the applications of novel light sources. We designed the beamline to be flexible as much as possible to various experimental configurations. By using this beam-line, we continued the experimental study on the interaction between optical vortex VUV light and atoms in collaboration with Saga LS and Niigata U.
  In March 2018, we tested the operation of the optical cavity for the resonator free electron laser at BL1U, in collaboration with Kyoto U. We have checked the alignment and the length of the cavity. In FY2018, we will try the FEL oscillation, which had been terminated for several years.
  The laser Compton scattering gamma-rays are powerful tools for nuclear science and technologies. By using various external lasers, we have demonstrated to generate 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 will start new experiments on positron lifetime spectroscopy experiments in collaboration with Yamagata U., Nagoya U. and AIST.
  Some studies on the beam dynamics have been carried out in collaboration with Nagoya U. We continue studying longitudinal coupled bunch instabilities and its suppression mechanism with the harmonic cavity. We are also studying the single bunch instability which limits the single bunch beam current around 40-50mA.

Masahiro Katoh (UVSOR Synchrotron Facility)

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