Improvement of the noise figure of the CEBAF switched electrode electronics BPM system

The Continuous Electron Beam Accelerator Facility (CEBAF) is a high-intensity continuous wave electron accelerator for nuclear physics located at Thomas Jefferson National Accelerator Facility. A beam energy of 4 GeV is achieved by recirculating the electron beam five times through two anti-parallel 400 MeV linacs. In the linacs, where there is recirculated beam, the BPM specifications must be met for beam intensities between 1 and 1,000 microA. To avoid a complete redesign of existing electronics, they investigated ways to improve the noise figure of the linac BPM switched electrode electronics (SEE) so that they could be used in the transport lines. This paper will focus on the source of the excessive out-of-band noise and how it was reduced. The development, commissioning and operational results of this low-noise variant of the linac style SEE BPMs as well as techniques for determining the noise figure of the RF chain will also be presented