A.  INTRODUCTION :

A.1      Calibration data for:

Calibration constants:

FIELD CONTROL COILS:

Sense region trim coils:

These coils are helmholtz pairs of 15 turns each coil of 0.016 inch insulated copper wire wrapped directly on the 21 inch OD dewar vacuum jacket.

The Axial trim coil:  1 milliamp = 60 gamma

The SQUID direction trim coil:  1 milliamp = 70 gamma

TEMPERATURE SENSORS:

The equilibrium diode voltages at temperatures shown are:

(N/A = not applicable.) 

FLOW GAUGE CALIBRATION:

The floating ball flow gauge was calibrated against an absolute displacement gauge at three points as given below:

Flow gauge reading      boil off

20 cc/m                      0.07 liter per day

30 cc/m                      0.10 liter per day

40 cc/m                      0.15 liter per day

A.2. SUMMARY TRANSFER PROCEDURE - SRM DEWAR

1. Preparation : Collect all equipment near the SRM dewar (SRM).

• Supply dewar (SUPPLY).   

• Helium gas supply 

• Heat Gun

• Transfer line (LINE).  

• Transfer adapter (ADAPTER) with stoppers and clamps.

• Record all health parameters (2-1-c). Numbers in (--) refer to detailed procedures. 4 temperatures, SQUID bias levels, safety pressure, cryocooler pressure

2. Bleed the pressure in the SUPPLY to atmospheric pressure (2-1-f) and measure liquid level.

3. Bleed the SRM to 2 psig (2-1-g). Close the needle valve at popoff valve from vent damper (2-1-h).

4. Attach the ADAPTER to the SRM side of the transfer LINE. Adjust clamps to snug fit on LINE

§    (2-1-i).

5. Thoroughly flush LINE with helium gas (about 1 minute) , holding as an inverted "U", and make certain that the closed end extension is attached to SUPPLY side of line. Slowly insert the LINE into the SUPPLY (2-2-c), keep SUPPLY vent open and at one atmosphere.

6. Apply about 1/4 psig helium gas pressure to SUPPLY to get a small flow of gas out of the LINE. Open flip valve on ADAPTER. While exit gas is still warm  quickly insert the LINE with ADAPTER into fill port. Tighten the hose clamp around the fill port  and gently push LINE into fill port until it bottoms, then pull out 1/2 inch.(2-2-c).

7. Increase the transfer (SUPPLY) pressure to 2 psig (2-2-c).

8. When this exhaust gas get cold and ADAPTER is beginning to frost, close the flip  valve (2-2-c) NOTE: the gauge on ADAPTER will oscillate by about +/- 1 psig when LINE is precooled. Push LINE  to seat in fill port. Tighten hose clamp, ADAPTER to LINE, so no gas leaks.

9. Slowly increase the transfer pressure to 3 psig, monitoring the SRM safety pressure. When the SAFETY pressure reaches about 2 psig FULLY open the SRM vent valve (2-2-d). Turn vent valve back and forth when opened until it is cold, to help prevent valve stem seal from freezing.

10. THIS IS THE MOST CRITICAL TIME OF THE TRANSFER- EXTREME CAUTION MUST BE USED TO PREVENT BACK DRAFTING OF AIR INTO THE SRM  VENT PORT (10-2-e).

11. If the safety pressure falls below 1 psig the VENT valve must be closed. Seal vent with red stopper & heat VALVE if necessary to close. Continue the transfer without changing transfer pressure, with the VENT valve closed. Hold the transfer pressure constant until safety pressure rises to 2 psig , open the vent valve (2-2-f).

12. Maintain the transfer pressure at 3 psig CONTINUOUSLY MONITORING THE SAFETY PRESSURE. If the safety pressure falls again to below 1 psig the vent valve must be closed again , then repeat step 11, (2-2-e).

13. Hold the transfer pressure constant and read the helium level gauge every minute - the level should increase at about 5 percent per minute (2-2-g).

14. When the SRM is full or the SUPPLY is empty the SAFETY pressure will abruptly rise about one psig. Also, the level gauge readings will stop increasing. At this time stop the transfer by opening the vent valve on the SUPPLY and start venting to one atmosphere (2-2-i). Leave the SRM VENT valve open at this time.

15. As soon as the SAFETY pressure falls to 2 psig close the VENT valve on the SRM (2-2-j).

16 The transfer may be continued from a second SUPPLY or it may be stopped.

17 To continue from a second SUPPLY, remove the transfer line and adapter from the SRM fill port and immediately plug the fill port (2-3-b). Now remove the LINE  from the depressurized SUPPLY and warm the inside of the line to room temperature by flowing helium gas thru the line. Do not try to conserve helium by starting the next transfer with the cold line, the probability of getting air and/or moisture into the fill port is much too great.

18 Follow steps 5 thru 14 above.

19 Additional SUPPLY dewars may be used as necessary.

20 Termination of the transfer from step 15 above, with the SUPPLY at one atmosphere, the safety pressure at 2 psig , and the LINE still in the SUPPLY and SRM

21 Loosen the hose clamp on the ADAPTER to FILL port and quickly remove the LINE  and  ADAPTER from the fill port. Plug the port immediately with the black  rubber stopper (2-3-b).

22 Warm the FILL and VENT ports with a heat gun then remove the stopper from the FILL port and fit the brass cap with its pop off.

23 Check to make certain that  the SRM vent  valve is warm and closed. Open the valve at the flow gauge Pop-off valve. All vent  gas will now flow through this pop-off valve and the flow gauge (2-5-b).

24 Remove the transfer line from the SUPPLY and close its transfer port  (2-4-a). Measure the helium left in the SUPPLY and the final level in the SRM and record.

A.2. Suggested data recording for 755 and 760 2G magnetometers

DAILY:

1. Gas flow gauge. Should be between 0 and 40 divisions.

2. Pressure on safety gauge. Should be about 2.0 psig.(2/15 bar).

3. Atmospheric pressure, if convenient.

4. Measure and record standard sample. Dipole moment to be about

• 1 X E-5 emu on each axis.

5. Wipe sample handler bars with clean cloth and use light spray of dry silicone or teflon lubricant.

WEEKLY:

1. SQUID signals with scope. Record peak to peak AC voltage, and value of I BIAS potentiometer.

2. Liquid helium level gauges, #1 and #2.

• Should decrease about 2 % on one gauge per week. Each gaugemeasures 50% of the total liquid volume, unless the system has a single level gauge sensor.

3. Temperatures T1 and T2 using boxes #2 and #3. DO NOT USE BOX #1 except for heating the shield, SQUIDS or pickup coils.

4. Cryocooler compressor pressure. This should be about 270/280, and should fluctuate by about 5 psig each cycle..

EACH YEAR:

Change the cryocooler adsorber. This takes about 30 minutes and is done with the magnetometer cold. New adsorbers are available through directly from CTI new adsorbers cost about US$550. Please refer to the CTI manual for addresses.

SYSTEM EVACUATION AND COOL DOWN:

The system is normally pumped out and cooled to liquid helium temperatures prior to delivery and whenever possible we deliver systems filled with liquid helium. This section of the manual is provided in the event that the system needs to be warmed to room temperature for any reason and then the customer needs to check the vacuum and conduct the complete cool down. In the following discussion, we assume that the SRM (Superconducting Rock Magnetometer) is at room temperature and under vacuum.