A Dual Operational Refrigerator/Flow Cryostat with Wide Bore Medium Field Magnet for Application Demonstration

Since stand alone cryocooler systems have become more widely available, there has been increased commercial interest in superconductor applications in the temperature range intermediate to liquid helium and liquid nitrogen. There are however few facilities that have large in-field bore size with variable temperatures. A large bore system can reduce costs associated with full scale demonstration magnets by testing smaller coils and qualify medium length (up to meters) conductors. A 5 T, wide bore, (170mm) Nb3Sn Oxford Instrument magnet has been integrated into a custom built dual mode refrigerator/helium flow cryostat with 600A HTS current leads. In one mode the system can be used with zero field without cost of liquid helium relying for cooling on a Sumitomo GM cryocooler with 1.5W at 4.2K: (no He) this can be used either as the sole characterisation method, or as a preliminary check before more expensive and extensive measurements are taken. The first measurements using MgB2 wire from 10 to 20K were made using a transient current step of similar to 5s duration, as opposed to a DC measurement. This has the advantage of not requiring thermal equilibrium to be achieved at nominal current. The feasibility of this technique for determining critical transport properties is discussed. (C) 2012 Published by Elsevier B. V. Selection and/or peer-review under responsibility of the Guest Editors.