Performance analysis for 2K heat exchanger for superfluid cryogenic system at KEK

The niobium superconducting radio frequency cavities (1.3 GHz) operate at temperatures of 2.0 K or below, cooled with superfluid helium. A 2K heat exchanger increases the production rate of superfluid helium by reducing the inlet liquid helium temperature from 4.4 K to 2.2 K or above, recovering sensible heat of evaporated gaseous helium from the helium tanks of the cavities at 2.0 K. Effectiveness of a heat exchanger is the ratio of actual heat transfer to maximum possible heat transfer between the fluids. The required minimum effectiveness is 85% to cool liquid helium down to 2.2 K. At KEK, we have laminated-fin type 2K heat exchangers for thermal loads up to 100W. The effectiveness of the heat exchanger has been determined by computational flow dynamics, and the results are being verified experimentally using a heat exchanger test stand, specifically designed to test performance of 2K heat exchangers.