11.5T VF Magnet with Dilution Refrigerator (Top Loading)

With a base temperature of 20mK and maximum field of 11.5T this is currently our lowest temperature and highest field piece of equipment all in one. Achieving these two respective points, however, adds a degree of difficulty not found in the other superconducting magnet systems. Close coordination with the Sample Environment Team is essential before, during and after the use of this system. Below you will find useful information regarding this system.

New! The temperature range has been extended from 4K up to 30K. This was made possilble by the addition of a higher powered heater on the mixing chamber stage. However; this heater is not intended for precise temperature control. It is controlled through an external power supply that has no feedback from a temperature sensor.

11T SCMag and Dilution Refrigerator Drawing


Magnet Properties
Max Field at 4.2K 9.5 T
Max Field at 2.2K 11.5 T
Current at 9.5 T 93.359 A
Current at 11.5 T 113.014 A
Field Calibration 9.827 A/T
Max Ramp Rate 0-6T 0.5 T/min
Max Ramp Rate 6-9T 0.3 T/min
Max Ramp Rate 9-11.5T 0.1 T/min
Persistence Switch Current 64 mA

Cryostat Properties
LN 2 Capacity 52 L
LHe Capacity 38 L
Static LHe Boil-off 0.6 L/hr
Sample Temp. Range 0.02 - 30 K
*Click Here for Sample Mounting Info*
Cool Down Info
LN 2 Pre-Cool Time 24 hrs.
LHe Cool Time 3 Hrs.
LHe Consumption ~150 L
Field Limits at Instruments
BT-7 11.5 T
BT-9 8.5 T
DCS 11.5 T
SPINS 11.5 T 
These are the instruments where
max fields are known, to use 
the magnet elsewhere contact 
Dan Dender.

Time Considerations

As mentioned above this is a very complicated system to run and seemingly simple tasks can take much longer than might be expected by an inexperienced user. This is certainly the case for sample loading, unloading and changing. Although this is a top loading system the loading process takes at least five hours from mounting the sample to sample temp. less than 4 K. For these reasons at least one full day is scheduled between consecutive experiments for the unloading and loading of samples. Experimenters should plan on having their samples here and ready to mount one full day before their beam time begins.

Additional Sample Mounting Information

The maximum diameter of 25mm as stated on the sample mounting page is a crucial dimension that does not allow for any error on the high side. In addition to this, however, it is suggested that sample holders have some solid bottom piece with a much smaller diameter and a gradual slope up to the point of maximum diameter. The bottom of the sample holder is what leads the way down through the restriction in the body of the cryostat and this sloped leading edge can prevent a slightly off center sample holder from hanging up. Since the entire loading process is done blind it is best to take the precautions up front that give the highest probability of a clean load.


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Last modified 13-April-2006