The Target Control Room

Temperature measurement below about 10 K is based on carbon and RuO resistors, read by 4-wire AC resistance bridges. Two carbon resistors are dedicated to monitor the microwave power at the target; other resistors are partly shielded against the microwave field. Higher temperatures are measured using Si diodes. High-accuracy pressure measurements, like for the 3He vapour pressure during NMR signal calibration, are done using capacitive pressure gauges. The evaporator and still levels are monitored by capacitance bridges, whose unbalance signals are measured by lock-in amplifiers. User-friendly graphical interface, based on a commercial software package SL-GMS, and running in a Unix workstation and X terminals, has been implemented to control the dilution refrigerator. The control programs are running in VME processors. More than 100 cryogenic parameters are logged by the programs which also generate alarms. Most readout instruments are read via a GPIB bus, either directly or using a 32-channel data logger/plotter (see Fig. 3). The controlled parameters include the needle valve for evaporator filling, the separator and microwave cavity flow rates and the still heater. The latter is to be controlled by the microwave power to maximize the cooling power of the dilution refrigerator. A PLC-based interlock system, powered by a 48 V uninterruptible supply, protects the target against loss of polarization and loss of 3He.

The superconducting magnet is also controlled from the control room. Below is a panel for following the field rotation procedure