Non-intercepting beam position measurement
Optimal for single-pass short bunches
Beam charge range > 50 dB | Repetition frequency ≤ 500 MHz |
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.
Signal processing
Signals from the pickups are stretched to produce bursts. This is essential to measure the single pass of a bunch.
Four parallel logarithmic amplifiers detect the burst envelopes.
Amplifiers’ response is log of amplitude.
Logs of opposite pickups are subtracted.
If pickups are rotated, axes are translated to obtain X and Y positions.
The process is all-analog, wideband.
The Log-Ratio Beam Position Monitor (LR-BPM) is an electronics module for fast analog processing of beam pickups signals.
Input signals parallel processing allows single-pass position measurement.
Bunches at any repetition rate up to 500MHz. Individual bunches can be distinguished from one another up to 5 MHz repetition.
±2V X and Y outputs are held until the next bunch when Sample & Hold mode (optional) is activated.
Provides log signal from each pickup electrode for computer analysis, with 5MHz bandwidth.
Cables length matching not critical: pickup signals don’t need to be in phase
Beam intensity range | >50dB |
Bunch/group train | Fmax = 500MHz |
Output frequency | <5MHz rep rate: individual position is measured |
Outputs | X and Y: -2V…0...+2V, 40mA max |
X and Y gain | 1.5V = ½ of aperture radius for orthogonal pickups |
