B Roche Acknowledgments K Scheidt N Benoist F Taoutaou special thanks to A Nosych DEELS 2018 18 th April 2018 Outline BPM block characterization Button to button transmissions ID: 1001185
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1. Characterisation of ESRF-EBS BPM blocks B. RocheAcknowledgments: K. Scheidt, N. Benoist, F. Taoutaouspecial thanks to: A. NosychDEELS 201818th April 2018
2. OutlineBPM block characterizationButton to button transmissionsChambers reception and test procedureOutputProblems evidencedPerspectivesDEELS 2018 - B. ROCHEPage 2
3. Button to button transmissionsmeasurement of button to button transmission4 x 3 measurements → sensitivity (or gain) of each of the 4 buttonsPage 3DEELS 2018 - B. ROCHERF-in (352 MHz)-87 dB-88 dB-65 dBsparkSparkABCDRF352.2MHzlaptopABCDSw-APoERF-switch controlSw-BSw-CSw-DSw-P
4. button sensitivity calculationThe so-called Lambertson method gives a way to compute the button’s sensitivity from button-to-button transmissions:We get 3 values for the gi’s:Page 4DEELS 2018 - B. ROCHEVi is the voltage at the buttongi is the gain (or sensitivity) associated with the buttonGij is the capacity coupling coefficientCalibration of position electrodes using external measurementsGR Lambertson - LSAP Note-5, Lawrence Berkeley Laboratory, 1987Offset Calibration of the Beam Position Monitor Using External MeansY Chung, G Decker - AIP Conference Proceedings, 1992References:
5. Button to button transmissionsPage 5DEELS 2018 - B. ROCHEInterconnection plateAutonomous system:On a trolley to be able to move easily (along a girder, and in different buildings)No connection to ESRF network (for reliability)Give an immediate answer if BPM is OK or NOTRF generatorSwitch-boxassembly buildingOhm-meter
6. Chambers reception and test procedureEvery BPM blocks are measured 2 times:At reception, just after heater installationAfter assembly on a girder with magnets, cables from BPM to interconnection plate, etc.Between the two tests chambers experience bake-out, NEG-coating (not all of them)…Test procedure consists in:measuring DC resistanceperforming RF transmission measurementCurrent state (April 2018):127 BPM blocks received and measured over the 320 BPM84 assembled on a girder and ready for installationPage 6DEELS 2018 - B. ROCHE
7. Problem evidencedFinite resistance between button and chambera few cases found (8 chambers affected)resistances ranging from short-circuit to MOhmsworse case was a NEG coated chamber with all 4 buttons affected → solved by blowing gas on buttonsAlso had a freshly received chamber affected (pollution not only coming from NEG coating)We don’t know the origin of this pollution yet. So far we treated buttons by burning « impurities » under vacuum with a voltage source.→ all cases treated with successAn interconnection RF cable found groundedCable replaced, manufacturer informed Page 7DEELS 2018 - B. ROCHE
8. Problem evidencedRetracted buttons:A small number of buttons have been found retractedThese chambers will not be installed (kept as spares) Page 8DEELS 2018 - B. ROCHEperfectC-button strongly retracted-0.77 dB0.29 dB
9. Problem evidencedDiscrepancies between manufacturersChamber #1 and #14 are similar, with the difference that they are made by different manufacturersRF transmission measurements show different variability in buttons’ sensitivity Page 9DEELS 2018 - B. ROCHE
10. PerspectivesMore characterisations:A more suitable RF-switch box will be done (better switches, power calibration, …)BPM blocks will also be electrically measured after installation (check cabling, measure button to chamber resistivity).Minimize offset of a BPM block by compensating for:Mechanical offset → measured by alignment group (chamber deformation, misalignment with adjacent quadrupoles)Buttons’ sensitivityOffset due to electronics (Libera Spark) / RF-cablingAlso:Take non-linear effect of the BPM blocks into account→ work in collaboration with ALBA (A. Nosych)Compensating for BPM offsets will be essential for ESRF-EBS commissioning (first turns). Once we will have a stored beam, beam base alignment techniques will be used to measure BPM offsets more precisely.Page 10DEELS 2018 - B. ROCHE