Facility for measuring microwave properties of radiation - damaged ceramics for RF windows and other fusion applications

The objective of this work was to apply state-of-the-art hardware to measuring, both within waveguide and in free space, the dielectric constants and loss tangents at millimeter-wave frequencies of ceramics and other materials, especially those with low loss before and after fast-neutron irradiation. In response to materials needs connected with electron cyclotron resonance heating (ECRH) in magnetic fusion reactors, the facility at Los Alamos for electrical and dielectric properties measurements on materials is being upgraded to include a capability in the millimeter-wave region. Three chief-candidate hardware systems accordingly have been identified for measuring dielectric constants and loss tangents over at least a 10 GHz portion of the W-band (75-110 GHz). All three can process microwaves transmitted through materials, with loss tangents in the range of 0.001 to 0.0001. This includes the least accurate of the three systems, as confirmed by preliminary data on an unirradiated BeO matchstick specimen inserted within a WR-10 waveguide section in that system. Specimens of both alumina and beryllia have been irradiated in the EBR-II reactor to a fluence of 1 x 1026 n/m2 (E > 0.1 MeV) at 3850C and are now available for testing