Short-pulse calorimetric load for high power millimeter-wave beams

A spherical compact matched load, for high vacuum operation suited for short pulses (2 MW, 0.1 s) precise measurement has been designed to test high power gyrotrons. In order to enhance the power handling capability of the load and to reduce the operation problems that may arise from an excessive reflection from the load, a ray tracing code has been written to model the power distribution on the inner surface and the pattern of the reflected radiation. The outcome of this code has been used to select a more convenient profile for the spreading mirror of the load and to optimize a pre-load specially conceived to minimize the power reflected fraction.