A. Kasugai et al., CHEMICAL-VAPOR-DEPOSITION DIAMOND WINDOW FOR HIGH-POWER AND LONG-PULSE MILLIMETER-WAVE TRANSMISSION, Review of scientific instruments, 69(5), 1998, pp. 2160-2165
To satisfy the electrical and thermomechanical requirements for a cont
inuous wave millimeter wave beam transmission, a window assembly using
a large size synthesized diamond disk has been developed. Such window
systems are needed as a vacuum barrier and tritium shielding in futur
e electron cyclotron heating systems for fusion plasma heating and non
inductive electron cyclotron current drive. The diamond used in this s
tudy was manufactured by chemical vapor deposition (CVD) and consists
of a polycrystalline diamond disk 96 mm in diameter and 2.23 mm thick.
The disk was built into an assembly in which two Inconel tubes were b
onded on both sides of the plate to provide vacuum shielding and water
cooling to the edge of the disk, leaving an effective window aperture
of 83 mm. It will be shown that, as a result of the high thermal cond
uctivity and low dielectric loss exhibited by this grade of CVD diamon
d, the temperature increase of the window due to the absorption of hig
h-power millimeter wave radiation could be minimized by simple water e
dge cooling at room temperature. During transmission of a focused Gaus
sian beam of 170 GHz, 110 kW, 10 s, the temperature increase at the ce
nter of the window reached a steady state condition at a value of appr
oximately 40 K, in good agreement with calculated values. Water-edge-c
ooled CVD diamond windows promise to provide a practical technical sol
ution for the transmission of continuous millimeter wave transmission
in excess of 1 MW. (C) 1998 American Institute of Physics.