TOPOS: A new Tool for Beam Position Measurements at SIS18

The new Tune, Orbit and Position Measurement System for the SIS18, called TOPOS, is a replacement for the present POSI BPM System. Currently TOPOS is installed in parallel and uses the same analogue amplification chain as POSI. TOPOS consists of 12 Libera Hadron units [1] for front-end processing. The Libera stations sample the four analog plate signals of a BPM pick-up with four 14 Bit ADCs at 125 MHz. One of the main improvements of the TOPOS is the capability of Bunch-By-Bunch measurement and recording. To achieve a proper position calculation at bunch rates from 850 KHz up to 6 MHz, several processing steps like bunch detection [2] and baseline restitution [3] have to be performed online. Implementation of these algorithms is done inside Libera’s FPGA which uses the sampled ADC values to perform the signal correction and calculation of the beam position values. For validation of consistency of the measured positions and timing purposes, the Liberas receive in addition four digital signals. Two signals are used as Startand StopTrigger. Three timestamps are calculated for time measurement and consistency checking. These timestamps are derived from the rf signal of the accelerating cavity. To minimize measurement divergences due to skew, jitter and clock inaccuracy, all Liberas are clocked synchronously with an 125 MHz timing signal. All these signals are generated externally and distributed by a low skew fan-out. Because of the high signal dynamics over the different acceleration cycles, information about the signal in form of SNR and overand under-load (including ADCclipping) is retained. The complete set of measurement data and parameters are collected in a 96 Bit data package per bunch and produces a maximum data rate of about 580 MBit/s per BPM. The data stream of all 12 Libera stations is handled by a dedicated 10 GbE LAN and two so called Concentrator and Control Computers (CCCPs). TOPOS is also the pilot project for DAQ software integration in FESA at GSI, which was realized on the CCCPs [4, 5]. In the design and implementation phase of TOPOS great care was taken to realize a scalable and modularized data acquisition system for BPMs which serves also as a prototype for the future SIS100.