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Light Sources in 2016

1. Status of UVSOR Accelerators

  In the fiscal year 2016, we had scheduled to operate UVSOR-III from May to March, for 38 weeks for users as usual. However, due to a vacuum leakage trouble at the frontend of a beamline and the following recovery works, we canceled the user runs for four weeks and a half in November and December. We had a scheduled shutdown period in April and May for about 6 weeks. This was for the scheduled maintenance works and for replacing the RF power amplifier of the storage ring and the power supply for the injection septum of the booster-synchrotron.   We operated the machine for 31 weeks and a half in the multi-bunch top-up mode, in which the beam current was kept at 300 mA, and 1 week in the singlebunch 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. The deep dip around December was due to the vacuum trouble and the recovery work.

Fig. 1. Monthly statistics in FY2016.

 

  The weekly operation schedule is as follows. On Monday, from 9 am to 9 pm, the machine is operated for machine 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. We had 3 weeks dedicated for machine studies, in November, just after the New Year vacation and the last week in March. The machine study week in November is mainly dedicated for the accelerator conditioning after the annual planned power outage.   As described above, the most serious trouble in this year was the vacuum leakage that happened on 23th Nov. Just after the scheduled beam dump at 9 pm, the vacuum of the storage ring steeply rose. From the record of the vacuum pressure around the ring, it was suspected that a leakage took place around the frontend of a beam-line, BL3U. This was confirmed by opening the vacuum system on 25th Nov. We found that the cooling water of a mask in the frontend of the beamline was leaking out to the ultrahigh vacuum. We separated the beam-line from the storage ring by a gate valve and started the recovery work, which involved the baking of the entire ring. After the preparation works, we started the baking of a half of the ring on 5th Dec. and another half on 12th Dec., both of which we continued for one week. We started the machine operation for the vacuum conditioning by synchrotron radiation on 19th Dec. We restarted the user operation on 17th Jan. The beam lifetime recovery during the vacuum conditioning run is shown in Fig. 2.

Beam Current

Fig. 2. The lifetime recovery during the vacuum conditioning runs in Dec. 2016 and Jan. 2017. The horizontal axis is the integrated beam current and the vertical axis is the life time multiplied by the beam current ( Iτ ). The lifetime just before the vacuum accident is shown by a blue dotted line.

  In this year, other than the vacuum trouble described above, we had a few minor troubles on the power supplies of the injection/extraction magnets. However, fortunately, in all cases the beam time for users was not lost. The water leakages from a quadrupole magnet in the booster synchrotron happened but it was recovered by replacing the water cooling pipe during the shutdown period.

 

2. Improvements and Developments

  The solid state 90 MHz RF power amplifiers of the booster synchrotron and of the storage ring had been used for about 20 years. They had been working well without any serious problem. However it became difficult to maintain them because of the outage of electronic parts. We decided to replace the amplifiers with new ones which have basically same performances but much smaller sizes and are water cooled. We expect that the water cooling would be beneficial to stabilize the accelerator room temperature and also to reduce the sound noise in the experimental hall. In the spring shut down 2015, we replaced the amplifier for the booster synchrotron. It had been working well without any serious problem for one year. Then, in this year, we have replaced that of the storage ring. The new RF amplifier had an electric noise problem, however, it was soon improved by adding some filters.

         

storage ring

Fig. 3. An open space appeared in the storage ring after removing the old RF power amplifier.

Light Source Developments and Beam Physics Studies

  We continue the efforts to develop light sources technologies and their applications such as free electron lasers, coherent harmonic generation, coherent synchrotron radiation, laser Compton scattering gammarays, intense polarized and vortex UV radiation at the new source development station BL1U, which was constructed under the support of Quantum Beam Technology Program by MEXT/JST. This beam-line is dedicated to develop light source technologies and to explore their applications.
  This year, 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 in this wavelength range using conventional optical components such as a UV-CCD camera, bandpass filters and so on. In the spring shut down 2016, we collaborated with the beamline staffs, and installed a mirror and a monochromator at BL1U, which would be used for exploring the applications of novel light sources. 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. [1]. As a theoretical work, we have successfully shown that the origin of the vortex nature of the undulator radiation was in the radiation from an electron in circular motion [2].
  We are continuing the effort to reconstruct the optical cavity for the resonator free electron laser at BL1U, which has been investigated for many years at UVSOR. This time, the main objective is the high flux intra-cavity gamma-ray production for the nuclear resonance fluorescence imaging in cooperation with Kyoto University. Currently gamma-rays are produced by using conventional fiber laser for the proof-ofprinciple study [3]. The gamma-rays are also used for investigating the origin of the homo-chirality of biomolecules in nature in collaboration with Hiroshima U., Yokohama N. U. and others.
  Irradiation experiments using polarized ultraviolet light are being carried out in corporation with Tokyo U. Sci. and with Yokohama N. U and Hiroshima U. In the latter case, the circularly polarized UV-VUV light was used for the study on the origin of homo-chirality [4]
  A spin polarized electron gun is being developed in collaboration with Nagoya U. and KEK. This year, the temporal response of the photocathode was investigated by using femto-second laser system at BL1U [5].
  We continued designing a new harmonic cavity in collaboration with Nagoya U., to replace the present cavity which has a vacuum trouble. For this design study, we have started investigating present beam instabilities at UVSOR-III [6].

References
[1] T. Kaneyasu et al., in these reports
[2] M. Katoh et al., in these reports
[3] H. Zen et al., in these reports
[4] K. Matsuo et al., in these reports
[5] N. Yamamoto et al., in these reports
[6] A. Mochihashi et al., in these reports

Masahiro Katoh (UVSOR Facility)

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