Design of a low average power calorimeter for millimetre wave gyrotrons

The design of a low average power calorimeter for use with short pulse gyrotrons is presented. Taking advantage of the highly oversized waveguide a new simple construction of small volume is realized which gives quick response. The selection of appropriate liquid volume absorbers is discussed and a suitable combination of absorbing liquid and container gives little reflection for all waveguide modes over a broad millimetre wave band. To get the peak power of the gyrotron, the slope of the temperature rise is observed. The time response is explained by an equivalent circuit representation consisting of only four elements.