Light Sources in 2020
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.
[画像: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 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)
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