HIGH-POWER 170 GHZ TEST OF CVD DIAMOND FOR ECH WINDOW

In order to check the usability of large-size CVD (Chemical Vapor Depo sition) diamond disks for high power millimeter wave vacuum barrier wi ndows at room temperature (T = 293 K) a first series of experiments, u sing a 170 GHz, 0.4 MW, 0.2 s JAERI/Toshiba gyrotron (1)), have been p erformed. The dielectric loss tangent at a frequency of 170 GHz has be en determined to be tan delta = 1.3.10(-4). By comparing the experimen tal results to numerical simulations the thermal conductivity was esti mated to be about k approximate to 1800 W/mK. This preliminary results indicate that a single-disk CVD diamond window assembly using a water -edge cooling could fulfill the requirements for a continuous wave (CW ) transmission of millimeter wave power in the megawatt range. This is needed for the Electron Cyclotron Heating (ECH) on the International Thermonuclear Experimental Reactor (ITER).