Abstract
Sudden decreases in the beam lifetime, which are attributed to the dust trappings, sometimes occur at the electron storage ring Photon Factory Advanced Ring (PF-AR). Since these dust events cause difficulties in user operations, we have been carefully observing this phenomenon for many years. Our observations indicated that the dust trappings could be caused by electric discharges in vacuum ducts. In order to demonstrate this hypothesis experimentally, we designed a new vacuum device that intentionally generates electric discharges and installed it in PF-AR. Using this device, we could repeatedly induce sudden decreases in the beam lifetime because of the generated electric discharge. We also detected decreases in the beam lifetime caused by mechanical movement of the electrodes in the device. Moreover, we could visually observe the dust trapping phenomenon; the trapped dust particle was observed by two video cameras and appeared as a luminous body that resembled a shooting star. This was the first direct observation of a luminous dust particle trapped by the electron beam.
Highlights
The phenomenon of the decrease in the beam lifetime during accelerator operations has been observed in many electron storage rings [1,2,3,4,5,6,7,8,9]
After reducing the gap to 1 mm, a DC high voltage (HV) was applied to the lower electrode A-2, and the gap was repeatedly reduced in 0.2-mm steps until electric discharge occurred
Sparks produced at the electric discharge events were detected by video camera A, and increases in the vacuum pressure were observed by the Bayard-Alpert gauge (BAG)
Summary
The phenomenon of the decrease in the beam lifetime during accelerator operations has been observed in many electron storage rings [1,2,3,4,5,6,7,8,9]. The decreases in the beam lifetime were still observed Continuous observations of these events in PF-AR suggested that harmful dust particles were produced by the DIPs and by electric discharges in the vacuum chambers. The latter hypothesis was supported by the fact that, when the decrease in the beam lifetime occurred, a momentary increase in vacuum pressure in the in-vacuum undulators (vertical gap: 10 mm) or the radio frequency (rf) kicker with stripline electrodes for the fast feedback system was observed. We expect our experimental results to be useful in investigating the characteristics of the dust trapping phenomenon
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