DRY ICE 1.5K 100mm
Large Sample Space Cryostat, 12 Tesla Magnet
System Type: DRY 1.5K
Customer: University of Cambridge
Sample Space: 100mm
Magnet: Solenoid, 12T
Temperature Stability: +/- 50mK across whole range
The University of Cambrdige required a dry system with a large sample space inside a 12T magnet in order to test HTS samples at high currents. Therefore it was essential to not only increase the size of the top loading VTI but also ensure that there was sufficient cooling power to test the high heat load samples. We successfully achieved all of these requirements and the system now forms the basis of a very important user facility at The University of Cambridge.
The cryostat is fully insulated and has an Aluminium radiation shield which is thermally linked to the 1st stage of the cold head that sits at approximately 50K. The cryostat vacuum, super insulation and radiation shield all minimise the conduction and radiation heat load on to the sample space. The variable temperature insert (VTI) forms an integral part of the cryostat and uses the same outer vacuum space that is used for the cryostat. The variable temperature insert is a continuous flow, dynamic sample space type with access for a top loading probe.
After cool-down the system can be changed to a static sample space. This eliminates any direct contact between the flow of 4He used to regulate the temperature and the sample region. The 4He exhaust gas from the heat exchange of the VTI is pumped along the outside of the sample space tube and not directly over the sample. The sample is cooled by introducing a controlled amount of exchange gas into the sample space.
The top loading probe option allows the end user access to the sample space without the need to warm up the cryostat leading to fast turnaround sample times.
The VTI can be operated in two distinct modes:
- Continuous flow operation: In this mode the temperature of the VTI / Sample region can be controlled at a given temperature indefinitely. The He4 is circulated continuously around the system by use of the 4He gas handling manifold, circulation pump and the needle valve of the VTI which regulates the gas flow.
- Single Shot operation: In order to get the lowest temperature possible a reservoir of liquid helium can be allowed to collect in the Heat exchanger of the VTI. Once liquid helium has collected the feed needle valve of the VTI can be closed and the sample space allowed to reach the lowest pressure, lowest temperature.
- The sample space requires less than 50 mbar of Helium exchange at Room Temperature to perform over the entire temperature range.
'You have asked if I could set down my assessment of this system now that it has been in service for six months. I should add that this is my personal professional opinion as a researcher and does not in any way constitute a formal endorsement of ICEoxford, or its products, by the University.
I very pleased to be able to say that I am very satisfied with this system. In particular, the dual cooler configuration provides plenty of cooling power, which was my primary concern going to a conduction cooled system for such a large volume. As an example of this we have found that a very high heat leak probe with copper 100A leads will cool to below 20K overnight just in static mode.
The magnet appears to be very well behaved and after a couple of quenches reliably achieves to within 0.003T of the rated field. We have not conducted extensive checks of homogeneity, but it would appear that the system easily meets the tender specification.
I have also been impressed with the supplied ancillaries, which are from high quality manufacturers and it is clear that corners have not been cut in fitting this system out.
The inevitable minor snags in such a custom system were cleared up promptly and professionally by your excellent team and the system is starting to be used heavily by users both within and without the University.
Many thanks again for all your assistance with this project.
John Durrell (2018)'