ISSN:
1089-7623
Source:
AIP Digital Archive
Topics:
Physics
,
Electrical Engineering, Measurement and Control Technology
Notes:
A bellows assembly with a radio frequency (rf) shield has been designed and developed for the KEK B factory (KEKB). The rf shield is the usual finger type but has a special spring finger to press contact fingers onto the beam tube. A test of the mechanical performance using a trial model shows good results. Further experimental studies are focused on the two key points of the finger-type rf shield, that is, the contact force of fingers and the length of slits between adjacent fingers. First, to reduce the excess abrasion at contact points, the necessary contact force is studied experimentally utilizing microwaves. Abnormal heating is checked by transmitting a 508 MHz cw microwave through a trial model in a coaxial line. Arcing at the contact point in vacuum is observed by transmitting a 2856 MHz pulse microwave in a rectangular waveguide equipped with a model piece of the rf shield. A contact force of 50 g/finger is found to be necessary. Second, the optimum slit length is studied with a strategy to minimize the higher order mode (HOM) power leaked from the beam tube into the inside of the bellows while keeping a sufficient sliding stroke. The coupling coefficient, β, of the rf shield is measured experimentally from the Q value of a TE mode resonance in a cylindrical cavity connected to the bellows assembly. Using the measured dependence of β on the slit length, a rough estimation of leaked HOM power is tried for the KEKB. The expected leaked power is about 6–18 W for a slit length of 20 mm, which is in the allowable range. The results obtained through these experiments are reflected to the design for the KEKB: the contact force of 80–100 g/finger will be adopted finally considering the manufacturing error of typically ±10 g/finger in our test and leaving a margin for higher frequencies. The nominal slit length will be set to be 20 mm, keeping the expansion/contraction of ±10 mm. © 1996 American Institute of Physics.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1063/1.1147110
Permalink
