PREIRRADIATION AND POSTIRRADIATION STUDIES ON MM-WAVE LOSSES IN REFERENCE WINDOW MATERIALS FOR ELECTRON-CYCLOTRON WAVE SYSTEMS

Dielectric materials for transmission windows in electron cyclotron (E C) wave systems are studied for the radiation effects on their dielect ric properties (permittivity, loss tangent). Based on comparative neut ron irradiation experiments performed at cryogenic and reactor pool te mperatures, it is shown here that fast neutron fluences up to at least 2-4 X 10(20) n/m(2) (E > 0.1 MeV) do not critically affect the mm-wav e losses in HEMEX grade sapphire, the reference : material for the cry ogenically cooled high power EC window. Fast neutron (10(20) n/m(2)) a nd electron (5 x 10(-6) dpa) irradiations on specially developed CVD d iamond grades for conventionally cooled windows demonstrate acceptable mm-wave loss levels, whereas loss at lower frequencies can be signifi cantly affected. In-beam measurements under X-ray irradiation show no additional loss terms in sapphire and CVD diamond, at least up to 0.45 Gy/s, Dielectric data obtained for synthetic quartz indicate that the observed changes due to neutron damage are not severe for fast neutro n fluences at least up to 10(22) n/m(2). (C) 1998 Elsevier Science B.V . All rights reserved.