High heat flux tests of a candidate design for MFTF-B neutral beam dumps

A test program on ASURF (100-kw, 18-keV e-beam facility) has provided engineering data on a design option for the neutral beam dumps for MFTF-B, a tandem mirror device. The option consists of an arrangement of 2.5-cm diameter copper tubes in which every other tube is shadowed by its nearest neighbors such that there are two levels of tubes. This beam dump intercepts the entire beam which heats only one side of the arrangement. The tubes have smooth internal walls which are 0.32 cm thick and for these tests were cooled with water flowing at 1.5 l/s (per tube) for a corresponding velocity of 5.4 m/s (18 ft/s). The water inlet pressure was 9.8 atm (145 psi). The tests were performed on a two-tube specimen provided by LLNL which was expected, based on previous tests to withstand absorbed heat fluxes of 3-4 kW/cm/sup 2/ for the above coolant conditions. Life tests for 20,000 cycles at a flux of 2 kW/cm/sup 2/ were required to qualify the design option