Stripline beam position monitor for the MIT-Bates South Hall Ring

The MIT-Bates South Hall Ring (SHR) is an electron storage ring currently being commissioned. It is designed to operate at an rf frequency of 2856MHz with all the 1812 buckets filled and a circulating current of 80mA or greater. This leads to a small charge per bunch and the requirement for sensitive Beam Position Monitors (BPM). Since there will be 31 BPMs in the vacuum system, it is important to suppress trapped modes which may excite coupled bunch instabilities. The stripline BPM built for the SHR is a stainless steel structure, designed to be manufactured using standard machining techniques and commercial feedthroughs. With proper 50 Ohm matching and a geometry derived by insight from MAFIA calculations the BPM was constructed having a nearly flat rf response up through 10 GHz over the range of measurement. The stripline electronics allows the measurements within 0.1mm resolution, maintains orbital harmonics information past the 10th harmonic, and operates over a dynamic range of 1 ma to greater than 80 ma of beam current