Helium is available for purchase in 50, 60, 80, 100, and 120 L dewars from the Oxford Cryomagnetics Group, which is under administrative control by the Physics department. CAESR users should create their own recharge accounts for the helium by filling out the new user account form. Please ask the CAESR manager for a brief safety introduction to familiarize yourself with the ICL liquid helium procedures. Helium purchases are made directly from the cryomagnetics group, and orders should be placed
at least 5 weekdays prior to intended delivery date. To guarantee an early start, it is recommended to request delivery of your helium dewar on the day prior to EPR reservation. Dewars are delivered and collected from the ICL building basement return line. Unused portions of liquid helium are deducted from the total cost. Rates are set by periodic efficiency audits of the ICL gaseous helium return manifold by the cryomagnetics group staff.
He Log 001, 20 May 2019 ; He Log 002, 04 Jun 2019 ;
Helium procedure summary:
1. Assuming your order is placed in the booking system
at least 5 weekdays prior to intended delivery date (one day before measurements), in days prior to delivery day you may check schedule to see that you are not one of more than 4-5 orders for the day. If so, you might negotiate delivery on a day prior or subsequent to your original intention, to help ensure delivery. Do not order a tank to arrive on a Bank Holiday!
2. Check for tank on delivery day --- e-mail, call, and/or seek out Cryomagnetics staff if the tank is not delivered in due course. If your tank is delivered as heavily frosted near top and frozen to ICL return line, please promptly notify the CAESR Scientific Applications Manager and Cryomagnetics staff and wait until the tank and hose thaws before attempting disconnection.
3. Take tank up elevator to lab and don't ride the elevator with it!
4. Dip-test (Always check tank pressure before opening valves) tank, record volume delivered and tank ID code for your own records.
5. Connect tank to return line in lab, first open the return valve and then open the tank valve, release pressure at a slow bleed if more than ca. 75 mBar, e.g. at the 0.5 Bar safety valve limit.
6. Attach 0.26 Bar over pressure valve and brass helium dewar connector for transfer arm for use with EPR cryostats.
7. Double check both tank return hose and cryostat flow meter exhaust hose are connected to the return line, with their respective valves open.
8. When measurements are concluded, release any tank pressure (0.26 Bar) via slow bleed into the return line and then remove transfer arm with tank at low pressure.
9. Dip test tank and record the remaining volume with dry erase marker on tank and in your own records. This will be useful for checking during billing.
10. After disconnecting the tank in the lab, make sure that all helium return valves are closed, and return the tank to ICL basement return line via elevator.
11. Double check that the tank is placed on the ICL basement raised dock and connected to the basement return line under minimal pressure. First open the return valve and then open the tank valve. If your tank is under pressure and requires a slow bleed into return line, please return later to fully-open the tank valve. Check other tanks, that they are on the dock with both tank and line valves open.
12. Please promptly e-mail Cryomagnetics staff to notify them that your tank has been returned to the ICL basement liquid helium tank dock, providing the tank ID, tank capacity, and the amount of helium remaining in the e-mail.
Nitrogen is available at no cost from 200L dewars in the hallway adjoining the CAESR facility or directly above them on the 2nd floor. These dewars are filled daily by the ICL facilities staff. Small liquid N2 sample dewars are available for CAESR users, as demarcated in the wet lab. Please check that the cryostat flow meter exhaust is not connected to the helium return line.