Dear colleagues that love enigmas: please read all before answer.
We found ice in the base of coldhead and the vacuum cap out in the plastic water collector over the magnet. It was "spit" from its position.
We retired and clean all as usual, nothing rare until now
A just installed coldhead in a GE LCC magnet doesn´t couple Recondenser_Ruo temp (4,51°K) and Coldhead_Ruo temp (3,042°K) after 48hours
others parameters are normal. Shield is in 46°K and descending slowly
He level 52%
We check & done:
Water temp and flow are ok, compressor replaced, no change
We change coldhead again, same results
Coldhead is full tight and aligned to meet 0,008 to 0,013mm slash separation. The screws are ok and full tight.
We noted that each time we took out the Coldhead to re install, the indium gasket of the top (no the ring) is just a little compressed and not full compressed as usual. we reinstalled 3 times the first replacement coldhead before attempt with another newone. same results with both coldheads.
Look like the coldheads were "shorter" than the hole in the magnet and do not reach the bottom to make good contact. 2nd stage indium gasket looks as flat as usual when the coldhead is desinstalled.
ANy clue?
I ran into this about a year ago, I ended up getting a thin indium disc and added it to the bottom of the cold head before installing the indium gasket as normal. The disc acted as a shim and allowed better compression of the indium at the base of the cold head and solved my issue. I believe this is a known issue from sumotomo. You can get the disc from sumotomo, or wherever you get your cold head supplies. Good luck!
May be the problem was a perforation in first cold head and with the 20 kg recondenser goes in. May be yo can put double indium at 90 degrees. Explain your results.
Dear Jose,
Recondenser 4K stage has loading springs under cooper thermal contact.
Seems that in the previous cold head replacemend screws was over tighten and springs deformed. The only solution is to over tight the new cold head to maintain 0,2K between C/H and Recondenser. Please tight the screws gradually (during the 1st hour after starting up) because indium is not soft at low temps.
Best Regards,
George
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Jose Morillo
GE COLDHEAD BAD COUPLING
December 10, 2021 09:46
Dear colleagues that love enigmas: please read all before answer.
We found ice in the base of coldhead and the vacuum cap out in the plastic water collector over the magnet. It was "spit" from its position.
We retired and clean all as usual, nothing rare until now
A just installed coldhead in a GE LCC magnet doesn´t couple Recondenser_Ruo temp (4,51°K) and Coldhead_Ruo temp (3,042°K) after 48hours
others parameters are normal. Shield is in 46°K and descending slowly
He level 52%
We check & done:
Water temp and flow are ok, compressor replaced, no change
We change coldhead again, same results
Coldhead is full tight and aligned to meet 0,008 to 0,013mm slash separation. The screws are ok and full tight.
We noted that each time we took out the Coldhead to re install, the indium gasket of the top (no the ring) is just a little compressed and not full compressed as usual. we reinstalled 3 times the first replacement coldhead before attempt with another newone. same results with both coldheads.
Look like the coldheads were "shorter" than the hole in the magnet and do not reach the bottom to make good contact. 2nd stage indium gasket looks as flat as usual when the coldhead is desinstalled.
ANy clue?
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Dean Kenney
re: GE COLDHEAD BAD COUPLING
December 13, 2021 10:30
Did you hear the sleeve properly ? If so your not inserting it far enough
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Doug Schwichtenberg
re: GE COLDHEAD BAD COUPLING
December 13, 2021 10:31
I ran into this about a year ago, I ended up getting a thin indium disc and added it to the bottom of the cold head before installing the indium gasket as normal. The disc acted as a shim and allowed better compression of the indium at the base of the cold head and solved my issue. I believe this is a known issue from sumotomo. You can get the disc from sumotomo, or wherever you get your cold head supplies. Good luck!
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toni alomar
re: GE COLDHEAD BAD COUPLING
December 13, 2021 10:31
May be the problem was a perforation in first cold head and with the 20 kg recondenser goes in. May be yo can put double indium at 90 degrees. Explain your results.
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George Georgalas
re: GE COLDHEAD BAD COUPLING
December 13, 2021 10:31
Dear Jose,
Recondenser 4K stage has loading springs under cooper thermal contact.
Seems that in the previous cold head replacemend screws was over tighten and springs deformed. The only solution is to over tight the new cold head to maintain 0,2K between C/H and Recondenser. Please tight the screws gradually (during the 1st hour after starting up) because indium is not soft at low temps.
Best Regards,
George
to rate and post a comment