Coaxial wire impedance measurements of BPM buttons for the PEP-II B- factory
The coaxial wire impedance measurement uses a conducting rod placed along the beam axis in the vacuum chamber, forming the center conductor in a coaxial line system. Tapers at either end of this section allow for smooth impedance transformation from the 50{Omega} lines used in common microwave measurement equipment, to the characteristic impedance of the vacuum chamber and center conductor, typically around 200{Omega}. RF and microwave absorptive material placed in the ends of the vacuum chamber and in the impedance matching tapers minimizes reflections which cause trapped modes within the apparatus, allowing measurements to be made above the traveling-wave cut-off frequency of the vacuum vessel (typically 2.5 - 3.0 GHz for PEP-II). A smooth vessel of the same cross-section as that containing the device under test is used in a reference measurement Resonances within the apparatus are difficult to avoid completely and require careful placing of absorptive material, manufacture of test and reference chambers, and assembly of apparatus.
- Research Organization:
- Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
- Sponsoring Organization:
- USDOE, Washington, DC (United States)
- DOE Contract Number:
- AC03-76SF00098
- OSTI ID:
- 200662
- Report Number(s):
- LBL-37782; CBP-Note-157; CONF-9506279-6; ON: DE96004322; TRN: 96:008257
- Resource Relation:
- Conference: CEIBA95: international workshop on collective effects and impedance for B-factories, Tsukuba (Japan), 12-17 Jun 1995; Other Information: PBD: Sep 1995
- Country of Publication:
- United States
- Language:
- English
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