LHe Batch Fill

Figure 10: Control GUI for the LHe Batchfill Sequencer.

Liquid helium is automatically supplied to the magnet dewar from the 500 l buffer dewar through a 2 m long, vacuum insulated transfer hose. There is a small, stepper-motor actuated needle valve, EV91102, located on the buffer dewar end of the hose to control the flow of liquid. This valve is controlled by PID software, although it is normally left in manual mode.

When the batchfill sequencer is enabled, the automatic fill procedure operates as follows. The LHe level in the magnet is continuously monitored, and when it falls below the MIN value, the fill sequence begins. First it checks that the buffer dewar pressure exceeds the magnet dewar pressure. If so, the needle valve opens partially to a value specified by Init Valve Pos. It stays at this position for a time given by Cool Down Time in order to precool the line. Then the valve opens fully, to Full Valve Pos. It stays open until the LHe level exceeds the MAX value. At this point the valve closes to Close Valve Pos.

At times it can be advantageous to open solenoid valve SV91115 which vents the magnet boil off to atmosphere. This reduces the pressure in the magnet and makes it easier to fill. This option is usually not necessary, but can be chosen with the No/Yes buttons in the lower righthand corner of the control GUI. The vent solenoid will close at the end of the fill sequence, after a time given by Warm Up Time. This delay is intended to allow the excess pressure in the magnet to bleed down before closing the vent solenoid and returning the boil off gas to ESR.