In Need of an Astral Choke Collar
My gremlin has been a bit overactive these past few days. We've been trying to bring one of our magnets back to field since having de-energized in June. The stability of magnet had suffered a problem in March and was pretty much unusable for most experiments 1. So, after an extended saga of chasing after liquid helium supplies (rather short of late 2) and getting an engineer here, we managed to get the field up to 80% of full and thus it set over the break. So, the engineer returns, but then gets an emergency call to go to Nashville to fill a magnet in danger of quenching 3. So, he's lining up a plane flight and juggling the next step in the increase in the magnet field when, our magnet quenches. We get to watch about 800 L of helium (at about $8.50/L) gracefully waft up into the air. Now, I need to arrange for another 1,000 or so L He as well as the inevitable time delay. Well, it's been this long, another week or so won't make that much difference.
Explanations in more detail for those that like the technicalities.
1 - One of the joint shields on the magnet coil quenched. The nominal drift of the 800 MHz magnet is about 1-3 Hz/hr. With a shield having quenched, the drift rate increased to about 700 Hz/hr. This made it impossible to run any experiments for longer than about 24 hrs as the control range of the frequency stabilization system (the "lock") reached the end of its range over that period.
2 - There was a worldwide He shortage that started in August. One of the liquifaction plants went offline for routine maintenance and this dropped capacity by about 15%. This wasn't a big deal in that everyone knew this was to happen so everyone planned accordingly. Then, another system went down unexpectedly, taking another 15% offline. This was followed by difficulties in the maintenance routine that kept the first plant down for at least 6 weeks rather than the normal 3. That's supposedly all back together now but there's a backlog to handle. During this period, we needed 4,000 L of liquid. That took a lot to get.
3 - "Quench", I've used that word a couple of times now and what it means is to take something that was superconducting and make it non-superconducting. In the case of the joint shields, these superconductors act to protect the solder joints that connect the various pieces of wire that make up the magnet from the strong magnetic field generated by the magnet when its operational. The solder joints are not as good as superconductors as the wires of the magnet. For the magnet itself, when it quenches, it takes all of the stored energy in the coil (120 amps in 480 Henrys, or 3.5 MJ, for this case) and dumps that into heat, which boils off the liquid helium. It is a spectacular, if depressing, sight. There are quite a few of these on youtube, but now this is new and improved with our magnet spewing forth.
Explanations in more detail for those that like the technicalities.
1 - One of the joint shields on the magnet coil quenched. The nominal drift of the 800 MHz magnet is about 1-3 Hz/hr. With a shield having quenched, the drift rate increased to about 700 Hz/hr. This made it impossible to run any experiments for longer than about 24 hrs as the control range of the frequency stabilization system (the "lock") reached the end of its range over that period.
2 - There was a worldwide He shortage that started in August. One of the liquifaction plants went offline for routine maintenance and this dropped capacity by about 15%. This wasn't a big deal in that everyone knew this was to happen so everyone planned accordingly. Then, another system went down unexpectedly, taking another 15% offline. This was followed by difficulties in the maintenance routine that kept the first plant down for at least 6 weeks rather than the normal 3. That's supposedly all back together now but there's a backlog to handle. During this period, we needed 4,000 L of liquid. That took a lot to get.
3 - "Quench", I've used that word a couple of times now and what it means is to take something that was superconducting and make it non-superconducting. In the case of the joint shields, these superconductors act to protect the solder joints that connect the various pieces of wire that make up the magnet from the strong magnetic field generated by the magnet when its operational. The solder joints are not as good as superconductors as the wires of the magnet. For the magnet itself, when it quenches, it takes all of the stored energy in the coil (120 amps in 480 Henrys, or 3.5 MJ, for this case) and dumps that into heat, which boils off the liquid helium. It is a spectacular, if depressing, sight. There are quite a few of these on youtube, but now this is new and improved with our magnet spewing forth.