Deal all,
I highly appreciate those who shared their experience and knowledge with me about my inquiry of magnet quench during charge up. I attached the almost original messages I got below without any identities. A few people asked me which brand of magnet we have because they are shopping for magnet, and I appologize that I could not reveal it. This could happen with any vendor's magnet and it does not necessarily mean it is not a good magnet anyway. By no means I want to even sound to promote/against any vendors here.
My original question: our replacement shielded 500M magnet queched four times in factory during charge up, and it quenched twice here before it finally reached field (today), does this behaviour have anything to do with what it is at field? Based on the response:
1. as long as each quench occurs at a higher current, it should be ok
2. there is no hard evidence to indicate any correlation between charge up behaviour and at-field behaviour
3. It might happen again when we need to relocate or reseal the magnet
4. Cost of liquid helium and engineer time is definitely a concern for future charge up
Our magnet queched at 85A and 107Amp, then went to field with frequently top-off liquid helium during charging process. Fortunately, the vendor is responsible for all the cost of this replacement except minor cost like nitrogen. We will observe the field closely in the next few months and hopefully this magnet will be ok.
Best regards
Wei Li
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We have an AAA magnet here at AAAA which likes to quench twice when
it is charged up. It did this upon installation and again when the seals
were replaced. I have not heard anything to indicate that how a magnet is
brought to field has any bearing on how it behaves once it is at field. I
would be concerned in case I ever had to replace the seals or had to
move the magnet in the future and was responsible for the He bill.
Does your purchase contract limit your how much He you are required to pay
for?
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I would worry about it. I have never had a magnet quench during installation without a known reason for it. Quenching 4 times in the factory sounds a bit unusual to me, but I don't have any hard data about that.
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Well, you're asking some good questions, and I'd be interested in seeing a anonymous (i.e., remove names of people that write back to you) summary from you, if you have time.
I would say that four quenches at the factory plus two during the installation is quite atypical these days, and I would be quite concerned if the magnet was mine. The number of quenches is likely reflecting some mechanical problem/instability in the main magnet windings. Main magnet drift, or line shape drift might be a problem, but you can test these now, and watch them closely over the next month(s). The bigger problem I would be concerned about is the ability to get the magnet back up to field if it has to go down for any reason in the future, e.g., for a move to a new room/building. We have one old 500 that had a lot of factory training quenches, and nearly didn't get it to field a couple years ago when we had to move it (quenched three times, then _finally_ came up to field). It also had a severe Z cryoshim drift, but the vendor was able to correct that with a 2nd visit about 2 month after the move.
I'm not certain, however, that there is much you can do about it if the magnet meets your acceptance criteria. The vendor most definitely will not replace the magnet unless you have a _lot_ of clout, presuming it looks ok over the next month. And it may be that this really isn't a problem; the vendors are the only people that do get to look at a _lot_ of magnets, other than companies like AAAA.
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Although I do not have any experience with magnet quenched (knock on wood
& hope not to have to experience it), I think the rate or the frequency of
the magnet quench of your shielded 500M magnet is too much. It is almost
for sure there are some problems with the magnet.
I have an AAAA 400M standard bore magnet (purchased through CCCC) for
over 12 years. It still runs well since the date of installation.
Nevertheless, during the installation we had so much problems to vacuum
the magnet. It ended up that the magnet had a hairline crack at the joint
between the LHe & LN2 dewers. Luckily the engineer was able to detect it
during installation and fixed it. Since then, our magnet was running very
well, very stable and still does.
I am not saying or suggesting that your magnet might have cracks, but I
would (if I were you) ask the engineer to find out the root cause of the
quench and fix the problem before accepting the magnet.
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Note carefully the gross current thru the main coil when quench occurs.
If it is less each time, then you have a magnet that is unreliable.
If it quenches but is going up in total current, it may be OK -- but your
vendor should be paying for the helium!
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Dont pay for it before you are satisified. Maybe withold part of payment. I have heard of the magnets quenching a few times when first energized. Six quenches would make me wonder about the long term stability. I doubt if anyone can predict when the magnet will do its last quench however there is history on magnet production and failure rate i would think. We have a Bruker narrow bore 500 mhz at field for 10 years now. I wuldnt install a magnet in place if it couldnt reach field at the factory. My $.02 .
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OUr experience with the installation of our 500 and our 600
magnets was that each quenched once on the way up. There
have been no spontaneous quenches in the total of 8 years
at field. Your case does not sound good....I would be
very worried about the future. I have never heard of such
a case of more than two quenches on the way ukp. I
hope they are paying for the helium!!!
The key point I think is whether the magnet quenches
at a lower or higher amperage than the previous quench.
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What brand of magnet is it that you are having all these problems with? We are going to be installing a new AAA AS500 BBB maganet this fall and I was curious if I needed to watch out for a particular vendor's magnet.
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I'm sure you will get a lot of answers. One thing to pay
attention to is the engineer bringing up your magnet. If they are
inexperienced or impatient then you will likely get more quenches. In over
20 years we have had very few quenches - maybe two that occurred for
unknown reasons - both were slow overnight quenches. We have five
instruments and our engineers take care of five more with field strengths
of 200-800 MHz. Our 200 MHz was stable for many years and had only
quenched once during a fill - then we moved it from one building to another
and it was quenched many times. during attempts to bring it up .. the
company sent a more experienced engineer and it went up the first time and
has stayed for several years now. If it is operator error then the magnet
is probably OK... if not, then you may need to worry. I'm sure you will
get more technical answers but in our experience it has never been the
magnet. Impatience to meet deadlines and get on with it is usually the
culprit.
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If it quenched when on-field sitting in the factory then I will be concerned
about it. If it quenched getting upto the field then it is not unushual for
magnets >400MHz..It is like airplanes, I guess, taking off and landing cause
more concern than on flight.
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In my experience it should not quench more frequently once at field. I would
suspect that the solenoid needs "training" to get to field. Once there, it
should be Ok. However, if you need to re-energize it from scratch, you might
see the same behavior, even if the magnet is kept at liquid He temperature.
Or you might not.
Who manufactured the magnet? Since we are about to decide which 500 to buy,
it would help to know what to look out for.
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We have an AAA 500 54 mm bore shielded magnet. It quenched twice while being brought up to field in June 1999. According to
the AAA technician who was at our site, the quenching was not unusual--but he said more than two quenches was a cause for concern. I have no information on the number of quenches in the factory during testing. The magnet has been at field for three
years.
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I would be curious to know what brand of magnet this is, as we are currently
shopping for a new 600 MHz system. Our 500 has been taken to field
twice (It had to be moved from one building to another) and did not quench
either time. I would be very suspicious about any magnet that quenched that many times,
but I have been told that as long as each quench is at higher current than the
previous one.
We have had three magnets (300, 360 WB and 500 - All BBB) and none have quenched.
Across town at the U of WWWW, a DDDD 200 (CCCC magnet) has quenched 5 times
in 9 years.
Received on Wed Aug 28 2002 - 12:07:28 MST