Tests in helium to verify cryostability and replenishment

The cryostability analysis performed by General Dynamics Convair Division, of its pool-boiling conductor pack design for the Large Coil Program (LCP) required knowledge of the helium heat transfer and replenishment characteristics. This data was not available for the long vertical channels with complex helium flow passages. A test specimen was designed to simulate the flow and heat transfer characteristics of a conductor pack for use in the LCP superconducting magnet being designed by General Dynamics. The test program was conducted in a 200-liter liquid helium dewar. The test package simulated the flow in a single row, five layers high, and was tested in both vertical and horizontal orientations. The results showed that in the vertical position, steady-state heat transfer was nonhysteretic, with breakaway flux of 0.40 watt/cm². In the horizontal position, steady-state heat transfer was hysteretic, with breakaway flux of 0.40 watt/cm²and recovery flux of 0.27 watt/cm². In both horizontal and vertical tests, helium replenishment was sufficient to avoid dryout at steady-state fluxes up to 0.8 watt/cm². This testing technique, to verify the stability analysis for a large pool boiling magnet, was inexpensive compared to the cost of the magnet.