Liquid Nitrogen Autofill

Figure 9: Control GUI for the LN2 Autofill Sequencer.

Liquid nitrogen is provided to the LN2 heat shield from the Hall C cryogenics through a vacuum insulated hose. The hose splits at the cryostat end, leading to two cryogenic-rated solenoid valves. The first SV91110, or ``CoolDown Valve'', vents the incoming nitrogen to atmosphere, while the second, SV91111, supplies nitrogen to the cryostat.

When the sequencer is ENABLED, the operation is as follows. When the LN2 level falls below MIN, the CoolDown Valve opens, permitting nitrogen to flow through the hose. This precools the hose, as came be seen by monitoring a silicon diode thermometer, TD91110, installed near the junction between the two valves. When the Set pt. temperature is achieved, the CoolDown valve closes and the Fill Valve opens. When the MAX LN2 level is reached, the Fill Valve closes. The current status of the LN2 sequencer is displayed at the top of the control screen.

The LN2 jacket can be filled at any time by operating the CoolDown and Fill solenoids manually.