Bid document

Proceedings of EPAC 2004, Lucerne, Switzerland

HIGH-TEMPERATURE KICKER ELECTRODES FOR

HIGH-BEAM-CURRENT OPERATION OF PEP-II 

U. Wienands† , R. Akre, D. Anderson, S. DeBarger, K. Fant, D. Kharakh, R.E. Kirby, A. Krasnykh, A. Kulikov, J. Langton; SLAC, Stanford, CA, USA
Abstract

INTRODUCTION

The kickers of the transverse bunch-by-bunch feedback
systems at PEP are of stripline design, driven push-pull by one power amplifier for each electrode[1]. At the nondriven end the electrodes are terminated into 50 1 loads. Active cooling by LCW of these electrodes is difficult due to the isolation and impedance-match requirements, therefore, the electrodes are blackened on the outside and cooled primarily by radiation to the kicker housing. The blackening is CuO, applied using a sputtering process to achieve high emissivity of nominally ¡ 0 8. The electrodes themselves are made of an aluminum alloy and specified to operate at up-to 100 ÆC (212Æ F). This limit is set both by material properties and to limit the thermal expansion of the electrodes, which puts stress onto the electrode mounts. Temperature of the electrodes is monitored by optical pyrometers operating in the 8. . . 15µm band, looking through a fused-silica window.

1200
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t (°F)

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The strip line electrodes of the kickers used in the
transverse bunch-by-bunch feedback systems see significant power deposition by beam and HOM-induced currents. This leads to elevated temperatures of the aluminum electrodes and will ultimately become a limit for the beam current in the Low Energy Ring. Heat is transported to
the environment primarily by radiation from the blackened surface of the electrodes. In order to extend the beamcurrent range of these kickers, new electrodes have been fabricated from molybdenum which are able to run at significantly higher temperature, thus greatly increasing the efficiency of the radiative cooling of the electrodes. Blackening of the electrodes is achieved by oxidation in air at 530Æ C (1000 ÆF) using a recipe first applied in aviation research for supersonic aircraft. Emissivity was measured on coupons and a whole electrode to be about 0.6. In addition, the match at the terminations of the electrodes is improved following field calculations and measurements on a model of the kicker.

Month in 2004

Figure 1: History of pyrometer reading.
appeared unreasonably high, the pyrometers were recalibrated using a spare pyrometer and a prototype of the longitudinal feedback kicker. This prototype had a geometry similar to the kickers considered here and an identical