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.
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
Fmax = 500MHz
<5MHz rep rate: individual position is measured >5MHz rep rate: average position is measured with 5MHz bandwidth
X and Y: -2V…0...+2V, 40mA max Sum of logs: 0...+2V, 40mA max
X and Y gain
1.5V = ½ of aperture radius for orthogonal pickups 1.0V = ½ of aperture radius for rotated pickups