Magnet Cooldown Scheme 17 th February 2012 Roy Preece (STFC RAL)

Leak Checking –Wang leak checking Helium chamber envelope. Helium chamber has been checked for leaks before welding cooler tubes In last week, we have pumped the MICE#2 LHe system to 3 to 5 micron vacuum with booster pump, then we fully open the VEECO MS-50 leak detector while we throttle booster pump to 40-50%. The sensitivity scale is 10E-09. There is no detectable leak. We then bag each possible leak port and find no leak. We have pump down 3 times & leak check. The last one was made after Mr. Lo made soldering additional superconductor to each of 2 pair of four feedthrus.Instrumentation – New sensors, harness and feedthroughs. External cabling and hardware. After welding of the cooler tubes to the Helium chamber stub tubes, the weld and brazing were checked for leaks. Same leak rate level a above. –Wang Leak Checking Vacuum envelope After closing the vacuum chamber envelope the volume will be pumped. Comprehensive leak checking will be carried out. The pumping of the volume may take 2 – 3 days to attain a good vacuum for the leak checking.

Vacuum Purging with warm N2 –As soon as the leak checking is complete. –Using a LN2 dewer for the gas delivery –Fermi Lab gas heater will be used, 120F gas temp –Purge for as long as possible. Installation –Fermi Lab team to install the system –Test running of the system Pump and Purge –Using the same heater system. –Cycle pumping and purging may take up to 2 weeks –Vacuum Vessel and Radiation shield Outgassing / Leak rate –Isolate pumping system and record the rate of rise of the vacuum.

Pre Cool Stage Liquid Nitrogen delivery system –Installation and initial operated by Fermi Lab personnel –Control the temperature of delivery. –Approximately 2 days for this stage Personnel –24 Hour operation to ensure uniform cool down. –Must have minimum of 2 people per shift –Minimum of 2 shifts per day, preferably 3 shifts LN2 –Enough supply onsite to pre cool to 80k Preperation for LHe –Use the fill line heaters to remove residual LN2.

Cool Down to 4K Preperation –Purge Helium chamber with Helium gas to remove residual Nitrogen gas. –Pump on Helium chamber –Repeat Purge and pump 5 – 7 times. Cryo Coolers –Once no Nitrogen gas is in the Helium chamber volume the cryo cooler can be turned on. –Monitor operation and temperatures at the first and second stages. Liquid Helium fill –After confirmation of the cooler operation –Slow fill of Liquid Helium can proceed –Monitoring of level gauges –When level is nearing the top of the volume move the stinger to the top input within the vent tube. Personnel –24 Hour operation to ensure uniform cool down. –Must have minimum of 2 people per shift –Minimum of 2 shifts per day, preferably 3 shifts

Operation Characterisation (Thanks to Alan Bross) –Instrumentation check – do all sensor measurements give meaningful information? –Investigation of heater control circuit (if running sub-atmospheric – we hope!). –Measurement of loads on all cryocoolers (1 st & 2 nd stage on two stage) as fn. of heater power. –Calculate heat load to shield and cold-mass (at desired heater power). –Possibly repeat the above at a few LHe levels. –Vacuum rate-of-rise measurement (check for cold He leaks). –Stable operation at set point (T, P and LHe level) for min of 24 hr.