High power 170 GHz gyrotron with synthetic diamond window

A large sized synthetic diamond window assembly was installed on a 170 GHz gyrotron. An aperture and a thickness of the window are 83 and 2.23 mm, respectively, whose edge was directly cooled by water. Gyrotron performances of 520 kW at 6.2 s and 450 kW at 8 s were attained. A temperature increase of the window stabilized after similar to 5 s, whereas the power had been limited to below 170 kW with conventional windows. This drastic improvement of a deliverable power was obtained from the outstanding properties of the diamond, that is, an extremely high thermal conductivity (similar to 1800 W/mK) and a low value of loss tangent (tan delta<1.3 x 10(-4)). The gyrotron was inspected after the similar to 1300 times operation at 520 kW (>1 s), but no damage nor trouble was found both on the gyrotron and the diamond window. These results give a prospect for a multimegawatt power output from the gyrotron, i.e., the diamond window gives a solution for the window problem which has been regarded as the most serious issue on the development of high power long pulse gyrotron. (C) 1999 American Institute of Physics. [S0034-6748(99)01201-0].