BaseBand BPM - Bergoz Instrumentation - #1

Text version of the page

BaseBand Beam Position Monitor Designed for cancer therapy synchrotrons Ideal for heavy ion synchrotrons Tracks the beam during the energy ramp Handles >70 dB beam intensity range The BaseBand BPM is a log amplifier-based beam position monitor. It operates from 1 to 11 MHz. Output signals are analog voltages: X&Y narrowband outputs for close orbit measurement: ±2V X&Y wideband outputs for machine study, to see orbit changes or instabilities during the ramp: ±2V Cable length matching not required: pickup signals don’t need to be in phase. BB-BPM may be custom-built on daughter card for installation on user’s FPGA/DSP mother boards. Operating principle 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). Y [mm] Y [V] = ky log A/B = ky (log A - log B) ! ! ky r +-r log log A B Position measured by this method is more linear, over a wider range, than difference-over-sum. The position of the beam from rotated pickups is obtained by axes translation to the vertical resp. horizontal plane by wideband analog circuits. Input sensitivity BB-BPM requires -70 dBm minimum signal at its 50-ohm inputs. Typical ion accelerator beam position stripline or shoe box pickups must be measured in a high-impedance load. An amplifier with highimpedance input is therefore required for each pickup. It is preferable to install the preamplifiers near the pickups, to minimize RF interference effects on the coaxial cables. GSI in Darmstadt use 40dB preamps from German company Femto. Kyoto cancer facility use preamps from Japanese maker NF. v.2.0 BB-BPM Y X B A C D