Part 1. The Almost Quench
Previously I have shared with you a story about how we moved our little baby 300 MHz Varian Gemini 300 across the room, while it was still at field. And just this weekend I mentioned in the #AcademicHalloween thread on Twitter a brief summary of the tale when the baby 300 nearly died for lack of helium due to an unfortunate incident involving a botched liquid helium delivery. So here is the story in full.
Back in the early 90’s we* were anticipating our regular delivery of liquid helium to fill our 300. It was down to a very low level of helium and was just short of going critical. Imagine our horror when the delivery van turned up and we discovered to our horror that the transport dewar was empty. It had fallen over and emptied during the 11 hour night road trip from Sydney. Panic ensued, and quick phone calls to the gas supplier in Sydney to send an emergency dewar our way. Now helium is a different beast entirely to say liquid nitrogen, and filling a transport dewar is a lot more involved than simply turning a big tap on. It takes time. At the time it took half a day to fill a new dewar, and of course another 11 hour road trip back Sydney-Brisbane before we could attemt to fill the magnet. By this time the magnet was so low, we didn’t dare “dip” it to measure how much helium was still there. We just very, very carefully started the fill. Thankfully it all worked out for the best and the the machine continued to give us more years of solid service, even after we added a new shiny 500 MHz Bruker system downstairs. The 300 remained the workhorse for the chemistry groups in the building
This incident did however cause a brief lapse in judgement and bad science poetry ensued:
|NIGHT OF THE BIG CHILL
the night was dark, the cold winds blew,
Martin J Stoermer, July 1991
Part 2: The floor polisher incident
In early 2000 during the night, the cleaners came in to polish the lab floors. Normally the NMR and Mass Spec lab was off limits for these regular cleanings but a special annual clean was organised with additional safety precautions to be adhered to. The cleaning staff were informed of the additional hazards associated with strong magnetic fields and that under no circumstances was the automated floor polisher to be allowed beyond the 5 Gauss line (typically marked with coloured tape on the floor). The remainder of the floor up to the base of the magnet was to be done by hand. The critical nature of this piece of equipment was emphasised several times. Our warnings must have been understood, because when the evening came, the cleaning manager decided not to delegate the floor polishing part of the job to any of the normal cleaning staff, but rather to do it himself. This unfortunately did not go to plan. The pictures below (each one should open a slideshow) show the aftermath the next morning. Essentially, yes the magnet sucked in the floor pusher and it stuck to the base of the magnet, causing the magnet to quench. There are no photos of the quench itself, because the cleaners did exactly what they were told to do in such an event, which was to run away and call security. By the time everyone had got in the next morning the clouds of helium had dissipated and it was safe to enter the room, taking photos of the poor wee beast. The pictures of people clowning around trying to pull the polisher off the magnet are only half staged. The magnet was no longer an actual magnet, but the force of the impact had jammed the polisher between the legs of the magnet. Photos credit: Robert Dancer.
Fortunately there was minimal damage to the probe itself, just a few bent tuning rods. The magnet had to be brought back up to field by the Varian technicians, and once again the machine kept soldiering on. It’s next minor trauma was when the IMB moved in 2003 into our purpose built facilities a short way across campus. This time the Varian service technician did a controlled quench, and the little R2D2 was trundled across campus on a trolley to it’s new location, and brought back up to field. It now also shared a room with a new 600 MHz Bruker magnet, until a second 600 arrived in 2005. This necessitated the 300 being moved “live” across the room to sit midway between the two 600s. And there it sat for a number of years until it started to get a bit long in the tooth and it was eventually to be replaced by a new walk-up workhorse 400. So we simply stopped filling it with helium and just topped up the nitrogen every week and waited for it to eventually die. But it didn’t. The helium boil-off actually slowed down. So as the delivery date for the new 400 drew near, we stopped feeding it liquid nitrogen as well. It continued to boil off slowly, to the point where neither the nitrogen or helium levels could be measured. And it still kept going, and we kept measuring spectra. Finally we just took off all the caps to the nitrogen and helium ports and left it overnight. Still nothing. In this photo you can see what we did next. After disconnecting all the electronics, Bob Reid and I connected a compressed air line and stuck it down the helium port and turned it on. And with a sad little final flourish of helium, the brave little magnet finally quenched.
In the pictures, you can’t see the compressed air line as it was blown out by the rush of helium. After we vacated the room, and allowed the system to settle, we blew all the remaining nitrogen from the outer dewar out as well. It then got picked up and put on a trolley for disposal, but not before stopping by my fumehood for cheesy photos. It was all a rather sad end really for a lovely little machine that had done such sterling work for so long. But the march of progress and especially the need for better offline processing capabilities meant that it’s time was up. Unhappily it did sit for sometime alone at the end of the level 1 corridor by the workshops, until I believed it was eventually sent off for scrap metal recovery.
* In this sense, we refers the the Centre for Drug Design and Development (or 3D Centre) at the University of Queensland. It was in 2000 that the 3D Centre and the Centre for Molecular and Cellular Biology (CMCB) merged to become the Institute for Molecular Bioscience