Based on the pioneering work of Robert E. Shafer at Los Alamos Laboratory, the Log-Ratio BPM derives beam position from logarithm of the ratio of opposite pickup signals: Log(A/B). Position measured by this method is more linear, over a wider range, than difference-over-sum.
Front-end Filter and Amplifier BB-BPM-FEFA
Four BB-BPM-FEFA are required for each BB-BPM plug-in module, one per pickup. BB-BPM-FEFA has been specifically developed to measure low intensity ion beams. It is best to install it very close to the stripline or shoebox pickups to minimize capacitive loading. Control of BB-BPM-FEFA gain is done by FO fiber optics, one per front-end amplifier. FO high level switch the gain from 0dB to nominal value. A single control FO can be daisy-chained to all front-end amplifiers. The FO signal is under user's control.
The BaseBand BPM is a log amplifier-based beam position monitor. It operates up to 25MHz.
Output signals are analog voltages:
X&Y narrowband outputs for close orbit measurement
X&Y wideband outputs for machine study, to see orbit changes or instabilities during the ramp
Cable length matching not required: pickup signals don’t need to be in phase
To prevent noise pickup by way of ground loops:
The front-end amplifiers and filters are powered via their RF output coaxial cables
The front-end amplifiers gain is controlled by fiber optic signals