Stability improvement of the cryogenic system at NSRRC

Negative gauge pressure appears in the helium suction line during the period of compressor starting up. The negative pressure induces the risk of air leakage into the cryogenic system and the damage to the burst disk of cryostat. A buffer tank is connected to the suction line to avoid the negative gauge pressure. Variation of nitrogen pressure changes the thermal-shielding temperature of the cavity cryostat and thus changes the length and frequency of the cavity. A phase separator with pressure control is installed before the cryostat to isolate the fluctuation of nitrogen pressure at the source side and prevent the trip of electron beam due to the frequency change or the overpressure at the cavity side. The stability improvement after usage of the phase separator shows that variation of the nitrogen pressure to the cavity cryostat is reduced from +0.6/-0.4 bar to +/-0.08 bar and the drift of nitrogen pressure is eliminated. The stability after usage of the buffer tank shows that the negative gauge pressure is avoided in the suction line and the peak pressure was reduced from 1.4 bar to 1.2 bar.