Choice of alumina ceramics for 5MW pulsed power klystron

Abstract

<span style="font-size: 16.0pt;mso-bidi-font-size:9.0pt;font-family:" times="" new="" roman","serif""="">This paper describes different applications of alumina ceramics in the form of metal-alumina vacuum tight seals for development of 5 MW klystron. The klystron is a high power microwave amplifier operated at 2856 MHz with 5 MW rf output power. The klystron tubes with ceramic-metal seals are more rigid and are capable of handling relatively large power and allowing higher degassing temperature during processing than their glass-metal equivalent. The vacuum tight seals

<span style="font-size: 16.0pt;mso-bidi-font-size:9.0pt;font-family:" times="" new="" roman","serif""="">fabricated with different compositions of 94-99.9% purity alumina have been used for the construction of HV feedthrough of electron gun, RF window, collector isolating seal and heater isolation seal of the klystron tube. The HV feed through for electron gun has been constructed using 94% alumina which makes vacuum tight seal with kovar and stands for 150 kV pulse voltage without any failure. The rf window has been fabricated from 99.9% pure alumina to transmit 5 MW rf power from vacuum to high pressure wave guide line. The choice of high purity alumina reduces the heat losses at high operating frequencies. The physical properties of different alumina parts such as thermal expansion, surface volume resistivity and dielectric constant permitivity, which are highly significant for tube application, have been analyzed. Joining of different size and type of alumina parts with different metals to make vacuum tight seals and their characterization is also discussed.

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