Properties of Thin Anti-Multipactor Coatings for Klystron Windows

摘要

Low secondary electron emission yield (1 to 1.3), low rf-loss films are of interest as coatings for alumina ceramic high power klystron windows. Air-oxidized Cr films offer an alternative to TiN. This work shows that they have the required resistivity for low rf-loss, combined with stability in the secondary electron emission (SEE) yield under backout and electron bombardment. SEE, AES, XPS, ELS, oxidation, bakeout and electron bombardment results are presented for Cr and TiN layers deposited by sputtering onto high density alumina substrates. The surface of TiN oxidized to a 9A thick TiO sub 2 layer which, under bakeout to 550 deg C in vacuum, thinned to 6A. This extreme layer-thinness resulted in a significant drop in the SEE yield which, unfortunately, was reversible upon re-oxidation. The oxidized layer on Cr was 17A of Cr sub 2 O sub 3 which thinned to 13A upon bakeout. This thicker oxide layer produced a stable SEE yield which, although not as low as oxidized TiN, is sufficient to prevent electron multipactor. Windows covered by air-oxidized Cr films are at least as good, under tube processing conditions, as the best TiN-coated windows. (ERA citation 11:013977)