Cryostats on CRISP
Two cryostats are available on CRISP to provide operating temperature down to 1.5K, both may be mounted within the Newport magnet in order to obtain fields of up to ~5 kOe. Higher fields may be achieved using the Orange cryostat and the Goudsmit magnet.
Oxford Flow Cryostat
Temperatures of 4K can be achieved rapidly (~1-2 hrs) by the use of the Oxford Instruments Continuous Flow Cryostat. The need to have a helium dewar attached to the cryostat at all times means that it is especially important that users liaise with their local contact if they wish to make use of this equipment.
Only one sample may be mounted at a time but rapid turn over may be achieved because of the fast cool down speed. The sample changing procedure is relatively simple but the correct procedures must be followed. Users should contact their local contact if they are unsure the method of correct operation.
Samples may be up to 2.5cm x 2.5cm and in preference should have a surface area of the order of 1cm2 . In order to prevent slipping from the sample holder it is necessary to apply a small amount of vacuum grease to the bottom the sample.
Control of temperature is best achieved by manual operation of the helium flow with automated heating. This method provides temperature stability to the order of <0.1K.
The CRISP Orange Cryostat
A specially adapted "Orange ILL" type Helium cryostat is available on CRISP to provide operating temperatures down to 1.4K. For temperatures below 4K a "Roots" vacuum pump set is provided. Cooling times are of the order of ~5-6 hrs so the CRISP center stick has been designed to allow four samples to be mounted in the Orange cryostat with computer control of the height and angle axes. The maximum sample dimensions are: 29 ´ 30 mm.
The RAL reports 93-006 and 92-041 describe the operation of the cryostat and we outline only the salient points here. At the beginning of the experimental run the prepared cryostat will be installed on the instrument by the user support group. Given the relative complexity of the cryostat it is essential that users should contact either their local contact or the cryogenics group within the Sample Environment Group if they are uncertain of any of the correct operational procedures for changing samples, cooling, warming etc.
The valves on the cryostat, in particular the cold valve, are very delicate and should only be closed finger-tight. Do not over-tighten these valves as serious damage may result.
Typical temperature ranges achievable by orange cryostat:
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