Topic: Cryogenic Systems.

Chairperson: Simon Mitchinson, Oxford Instruments, and Superconductivity.

The question was asked "what are the your requirements from cryogenic refrigerator systems and what would you like to see available in the future"

The following points were made:

• PTR or GM coolers should have separate grounding for compressors. Electrical noise is an issue with the current detector application.
• Reduced vibration. With the most sensitive operations, such as the use of SQUIDs, low vibration is essential.
• PTR and GM system compressors are noisy. A reduction in noise would be useful.
• Electrical protection against interferance, such as a Faraday cage for the cryostat and cabinet for the system compressor.
• Electrical interference from control electronics should be reduced or eliminated.
• Temperature stability is of great importance for applications such as voltage standard measurements.
• For use in ground and air based radio telescopes it would be desirable to tilt the cryostat over angles of +/-15°.
• Functionality of system at altitudes in excess of 5,000m would be desirable.
• Institutes with very high He4 cryogen consumption would appreciate a general purpose system based on PTR or GM cooler for cryogen-free operation.
• Safety is very important. Cryogen-free operation promotes safety of operation.

Summary:

The general consensus was that cryogen free systems were highly desirable due to the ease of operation and greater level of safety than that of a "wet" system. Temperature stability was a great benefit for some applications. Improvements to current systems would be to reduce vibration, reduce electrical noise from electronics and compressors and specify maximum altitude and angle of tilt for operation.