Dear Charles G. Fry and BUM users,
To begin with thank you all very much to all for your interest and
your great aid and advise.
The problem was not a sudden change in lineshape but a continously
worsening lineshape over the period of two or three months. I don´t
know for sure if this time are the cryoshims or the room temperature
shims what are causing the problem, all I know is that the first time we
had the bad lineshape problem in this magnet it was caused by the
cryoshims. Last week
a Bruker technician came to the lab and after a first feeling around
with the magnet, he got the impression that this time is still the same
problem. They are scheduled to come and repair the magnet during the
present week.
About what could be the cause of the trouble, I am inclined to
discard the possibility that it is caused by improper helium refilling
since we have got two other magnets in the lab and we have being doing
He filling with all of them too since several years. We have not face a
similar problem with any of the other magnets (some of them are also
Bruker magnets too).
Yours sincerely
Manuel Martin-Pastor
Charles G. Fry wrote:
>Dear Manuel,
>
>It is a bit difficult to comment, as you give so little information about what has happened. In particular, is your problem one of a cryoshim quench--a sudden change in line shape from one day to the next morning, or during an afternoon when a small cryo-cloud was observed above the magnet, etc.--or is it one of continuously worsening line shape over the period of a year or more?
>
>Cryoshim quenches can occur from improper filling; Bruker should be able to correct these kinds of problems with better instruction as to how to properly fill the magnet. There are other possible causes of cryoshim quenches, but the magnet vendors are best consulted about those.
>
>Strong cryoshim drift is another problem completely, and one that may be difficult to impossible to correct. We have a couple magnets that had fairly strong cryoshim drifts; one was corrected by Oxford by performing a special cycling of the Z1 (the main contributor for that magnet) cryoshim to reduce the drift. The cycling did work, although the Z1 shim still does drift (will cause us to go into the magnet to correct the cryoshim in another couple years, at ~7 years). The other magnet simply needed more time than normal to calm after energization; after about 1 year the cryoshims (esp. Z3) slowed in their drift to very good values (essentially non-measurable in 72 h).
>
>If you have a cryoshim drift problem, it might be best for you to acquire a magnet power supply from Bruker, and learn how to re-energize the cryoshims yourself (presuming this is possible on an ultrashield magnet).
>
>Good luck with the problem,
>Charlie
>
>
>
>At 07:26 PM 5/21/2004, you wrote:
>
>
>>Dear Bruker users,
>> We are having some problems with the cryoshims in our four year old
>>BRUKER 11.7 T ultrashielded magnet
>>
>>This is the second time we expect the same problem with this magnet which is
>>connected to a AVANCE DRX-500 console. and as result the lineshape becames
>>so badly degraded that it is not possible anymore to obtain a good
>>lineshape with the normal shimming process.
>>
>>The solution for this problem is relative expensive, a technician have to
>>come to the lab to recharge the bad cryoshim/s and do a new re-shimming of
>>the magnet.
>>
>>I wonder if somebody has experienced the same problem with this type of
>>magnet or if there is any suggestion about what could be the origin of this
>>problem.
>>
>>
>>
>>Manuel Martín Pastor
>>Unidade de Resonancia Magnética
>>RIAIDT, edif. CACTUS
>>Tel.: 981 594488 16231
>>e-mail: mmartin@usc.es
>>
>>
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>>
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>>
>>
>
>
>~~~~~~~~~~~~~~~~~~~~~~~
>Charles G. Fry, Ph.D. Tel: (608)262-3182
>Director, MR Facility Fax: (608)262-0381
>Chem. Dept., 1101 University Ave, Univ. Wisconsin-Madison
>Madison, WI 53706 USA email: fry@chem.wisc.edu
>
>
>
>
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