"Development of low loss dielectric CVD diamond window units for high power microwave transmission"
T.A. Scherer and D.
Strauss
IAM-AWP, Karlsruhe Institute of Technology, Assoc. KIT-EURATOM,
D-76021
Abstract
The development of artificial diamond disks, fabricated by special CVD processes, lead to a new generation of high power millimetre wave window units with extremely low absorption and scattering losses for high power transmission. A reduction of the loss tangent by CVD diamond surface engineering could qualify diamond for higher power applications in future fusion projects (e. g. DEMO) with more than 2 MW transmitted microwave power through a window unit. Up to now 1-2 MW is typically the power for the ITER fusion device. By means of physical analysis of artificially modified surfaces (e. g. electrical conductivity, contact angle measurement, polar and non-polar surface energy, Raman spectroscopy and surface microwave absorption measurements) the influence of the atomic surface finish to the microwave losses will be discussed on base of a H-, O- terminated diamond surface and as well of passivated diamond (SiO, AlN). To avoid a reaction of Tritium, which is necessary in the fusion device, with the diamond surface during fusion operation phase, a passivation layer for the diamond could be an important tool to protect the diamond disk against additionally absorbed heating power. The presented work shows also a first approach towards broadband windows aiming towards a frequency tuneable EC heating and current drive system for plasma reactors.