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Buffer Dewar
A 500 l buffer dewar is used to store LHe for the target magnet and
refrigerator. The liquid helium in the buffer dewar is constantly
replenished by a PID loop operating the supply JT valve EV9180.
The liquid level inside the dewar is measured by LL91101.
A second PID loop sets the pressure inside the dewar by throttling
the flow of cold vapor back to ESR via EV9178.
The position of both valves, in percent open are determined by
LVDTs read back to the control computer via ADC channels.
Silicon diode thermometer TD9180 (TD9178) monitors
the temperature of the helium supplied to (returned from) the dewar.
The thermometers are read by an Oxford Instruments ITC-502 temperature
controller. The dewar pressure is measured by a 0-2000 mbar pressure
transducer, PI91105, mounted on the cryostat gas panel. The option of
using room temperature helium gas to pressurize the buffer dewar
exists via solenoid valve SV91108, also mounted
on the gas panel.
A LHe transfer line is used to provide LHe from the 500 l buffer dewar
to the magnet reservoir. A stepper-motor driven needle valve,
EV91102 is mounted at the buffer dewar
end of the line to control the flow of LHe to the magnet reservoir (see
Section 8). An optical encoder is mounted to the
valve stem to measure its exact position (in # of turns open).
The encoder is read by a US Digital ED2 display, connected to the IOC
over a serial interface.
Because the buffer is directly connected to the Hall C cryogenic
distribution system, improper operation of its control might
produce a serious disruption of cryogenic flow to the hall (or
even all three halls). Please refer to Section 10
at the end of this manual for further information.
Next: Magnet Reservoir
Up: Cryogenic Subsystems
Previous: Cryogenic Subsystems
Christopher D. Keith
2001-08-23