High power long pulse tests of the IFP-CNR dummy load for the European ITER gyrotron

The development of high power gyrotrons needs matched loads with good performance capable of absorbing and measuring powers as high as 1 MW in ITER and higher (up to two times) in future devices like DEMO. At IFP-CNR (Milano), several spherical loads were developed with identical absorbing geometry but different heat removal systems for operation with pulse lengths from a few ms to CW. A dummy load designed for 170 GHz/2 MW has been constructed in the frame of the development programme of European gyrotron for ITER. The first prototype hemisphere of this load, joined with an uncoated one, has been successfully tested with long pulses and under vacuum using the JAEA gyrotron for ITER in Naka. The symmetry of the system is such that the equivalent power load of the absorbing (coated) hemisphere is doubled when the second one is reflective (uncoated), with almost unchanged distribution with respect to a fully coated load. The tests demonstrate the capability of the IFP-CNR load to withstand and measure radiation at an equivalent power in excess of 1.5 MW. Gyrotron pulses with increasing power and pulse length have been performed in the load and are reported. The maximum equivalent power load reached in the tests was ~ 1.8 MW for 15 s while the longest pulse was 300 s, at ~ 1 MW. During the experiments, the temperatures of either the load or the preload were monitored using thermocouples and multiple infrared cameras. The results of the tests are described in the paper.