VELA BPMs Alex Brynes
Position Measurement EM field of bunch induces travelling wave at four strips. Combination of signal from two H / V pickups yields bunch position. Signal is amplified, digitised and then passed into EPICS. Beam Trigger pickup Front-End Transmission cable T/4=13.83ns spacing Analog Processors ADCs & FIFOs
BPM Timing 2 stages: Pre-trigger (“AWAK”) - <1us before WCM signal Delays – ns level control Pre-trigger not fully understood – see wiki and shift #323 log. Timing of BA1 BPMs was an issue.
Attenuations + Delays Raw voltage at each pickup (inc. pedestal) should be ~0V. So attenuation needs to be set correctly for accurate measurement. Range of 20dB for 20 < q < 250 pC. Beam trigger pulses, synchronous with front-end BPM signals, trigger ADC clock pulses. Maximum BPM resolution and sensitivity is achieved when the timing of output pulses is maximised. Range of 512ns.
Hardware Controllers In order to make the interface to hardware more user-friendly, controllers for various VELA components were written. Currently have: scope, BPM, magnets, RF, screens, shutters, vac valves, cameras. See guide for more info: \\fed.cclrc.ac.uk\Org\NLab\ASTeC\Projects\\VELA\documentation\notes\VELA_Hardware_Controllers_Guide_v1.docx Type Function void monitorDataForNShots std::vector< double > getXVec / getYVec / getQVec std::vector<std::vector<double>> getBPMRawData getTimeStamps reCalAtt setSA1/2 / setSD1/2 long getRA1/2 / getRD1/2 double getXFromPV / getYFromPV getX / getY / getQ std::vector< std::string > getBPMNames
Calibration - Attenuation Set charge (at WCM) to 50 < q < 80 pC. Measure U1,2,3,4. Change ATT1,2 so that U1+U2 / U3+U4 ~2V These are ATTcal values for each BPM. Value for each BPM is incorporated into Hardware Controller. Now we can measure q at WCM and adjust attenuation accordingly using: And calculate q at each BPM using:
Calibration - Delay Prototype program implemented last year – results not very well understood. Lots of improvements could be made. Should only need calculating once to ensure optimal signal at each BPM.
Planned Improvements Improve DLY calibration program. Incorporate offset, jitter + resolution calculations into controller. Cross-calibration between BPMs and screens. Auto-centre program. Orbit monitoring / correction. Histogrammer – could be made generic to monitor any EPICS PV. Suggestions?