Dear Edward,
Now that your magnet is heading towards slow quench, the only
thing to put it back to operation fast is following.
1. Insert the charging stick in the magnet and connect back to back
connected doide with heatsink on the main Z0 connection and start the
heating (open the switch) of resistor to open the switch for main coil.
This will enhance the speed for slow quench. Monitor the field with a pin
tied to a string. At the end the pin will fall down indiating complete
quench without loss of much Helium.
2. Fill Liquid Helium.
3. Charge the Z0 again and feed the other supercon shims as well.
4. If required you may check with shim plot to get idea about linearity of
the magnetic field in the region of probe coil.
Good Luck.
L.S.Mombasawala.
NMR Laboratory
RSIC, IIT Bombay.
Phone: 0091-22-5767691/2/3
Fax:0091-22-572 3314
__________________________________________________________________________
On Thu, 14 Feb 2002, Edward T. Chainani wrote:
> We have a Magnex supercon (400/54 Year-hold circa 1996) used with a JEOL
> Lambda 400 NMR spectrometer.
>
> We have a problem that seems like field drift: lock was lost and the usual
> value of Z0 required to lock onto the sample has changed drastically.
>
> As of yesterday, boil-off of liquid helium was only slightly above normal
> (220 mL/min). This morning it was 280 mL/min and has slowly climbed to 350
> mL/min at noontime.
>
> I turned off then disconnected the RT shims, and tried to obtain the
> spectra of 10% H2O in D2O. I notice that the drift is very bad: using
> single-pulse acquisition and peak picking of the water peak, the peak
> position has changed -1486 Hz in the course of 6 minutes.
>
> JEOL Co. (Japan) has surmised that it could be a slow quench of Z0 or the
> main magnet field, although nothing unusual has happened to the magnet.
>
> Any advice is welcome!
>
> ------------------------------------------------------------------------------
> Edward T. Chainani Nuclear Magnetic Resonance Laboratory Manager
>
> National Chemistry Instrumentation Center (NCIC)
>
> Ateneo de Manila University phone: (632) 426-6001 loc. 5629
> Loyola Heights, Quezon City e-mail: etch_at_ginto.chem.admu.edu.ph
> Philippines FAX: (632) 426-1323
> ------------------------------------------------------------------------------
>
>
>
>
>
Received on Mon Feb 18 2002 - 10:16:56 MST