Application of M-type cathodes to high-power cw klystrons

• Published in: Applied surface science Vol. 146; no. 1; pp. 89 - 96
• Main Authors: Isagawa, S, Higuchi, T, Kobayashi, K, Miyake, S, Ohya, K, Yoshida, M
• Format: Journal Article Conference Proceeding
• Language: English
• Published: Amsterdam Elsevier B.V 01.05.1999; Elsevier Science
• Subjects: Applied sciences; Barium evaporation; Condensed matter: electronic structure, electrical, magnetic, and optical properties; e +e − Collider; Electron and ion emission by liquids and solids; impact phenomena; Electronic tubes, masers; Electronics; Exact sciences and technology; High-power klystrons; Impact phenomena (including electron spectra and sputtering); Lifetime; M-type cathodes; Microwave tubes (eg, klystrons, magnetrons, traveling-wave, backward-wave tubes, etc.); Physics; Thermionic cathode; Thermionic emission; 79.20.Nc; 85.10.Ka; CJH; BC; 79.40.+z; IN; e +e − Collider; Thermionic cathode; M-type cathodes; Lifetime; Barium evaporation; High-power klystrons; 85.10.Dt; Barium; High power; M type; Klystrons; KEK linac; Evaporation; Colliding beam accelerators; Experimental study; Thermionic cathodes
• ISSN: 0169-4332; 1873-5584
• DOI: 10.1016/S0169-4332(99)00044-6

Two types of high-power cw klystrons have been widely used at KEK in both TRISTAN and KEKB e +e − collider projects: one is a 0.8 MW/1.0 MW tube, called YK1302/YK1303 (Philips); the other is a 1.2 MW tube, called E3786/E3732 (Toshiba). Normally, the dispenser cathodes of the `B-type' and the `S-type' have been used, respectively, but for improved versions they have been replaced by low-temperature cathodes, called the `M-type'. An Os/Ru coating was applied to the former, whereas an Ir one was applied to the latter. Until now, all upgraded tubes installing M-type cathodes, 9 and 8 in number, respectively, have worked successfully without any dropout. A positive experience concerning the lifetime under real operation conditions has been obtained. M-type cathodes are, however, more easily poisoned. One tube installing an Os/Ru-coated cathode showed a gradual, and then sudden decrease in emission during an underheating test, although the emission could fortunately be recovered by aging at the KEK test field. Once sufficiently aged, the emission of an Ir-coated cathode proved to be very high and stable, and its lifetime is expected to be very long. One disadvantage of this cathode is, however, susceptibility to gas poisoning and the necessity of long-term initial aging. New techniques, like ion milling and fine-grained tungsten top layers, were not as successful as expected from their smaller scale applications to shorten the initial aging period. A burn-in process at higher cathode loading was efficient to make the poisoned cathode active and to decrease unwanted Wehnelt emission. On top of that, the emission cooling, and thus thermal conductivity near the emitting layer could play an important role in such large-current cathodes as ours.