Pre-commissioning of Critical Beam Instrumentation Systems

1. Pre-commissioning of Critical Beam Instrumentation Systems E.B. Holzer, O.R. Jones CERN AB/BDI Second LHC Project Workshop - Chamonix XIV January 18, 2005 CERN

2. Outline • Beam Position Monitor (BPM) System • Polarity errors • Testing of electronics • BPM Database issues • Timing issues • Beam Loss Monitor (BLM) System • Hardware set-up and testing • Calibration • Threshold determination • Emittance and Current Measurement Systems • Sector Test • Summary – Critical Issues for Commissioning

3. Beam Position Monitors Polarity errors Testing of electronics BPM database issues Timing issues

4. Polarity – Cryostat Cabling Errors • Each SSS contains 2 BPMs (beam 1 and beam 2). • Each BPM measures both planes. The 4 pick-up electrodes are connected to 4 semi-rigid coaxial cables. • Mounting of the cables is performed in SMI2. • Since the cables are preformed, no mix-up is possible on the BPM side. • Exit flanges for beam1 and beam2 pick-ups are separated. Crossing beam1 and beam2 cables should not be possible. • The connections to the outer cryostat flange, however, allow the possibility of an error. In order to minimise this risk the following procedure is adhered to: • Installation of each cable in a predefined sequence. • Test of the complete installation.

5. Polarity – Cryostat Cabling, SSS BPM

6. Connect 600 MHz generator to one electrode via flange outside cryostat (one horizontal and one vertical tested) Verify amplitude and phase response on 2 neighbouring electrodes If amplitude is out of range this will signal one of the following Unconnected or broken cable Broken button Incorrectly cabled pick-up (H and V mixed up) Beam 1 / Beam 2 cables mixed up Phase out of range will indicate in addition Bad cable connection Incorrectly mounted button Expert is called in either case Cabling errors which will not be detected: Swap H1 with H2 Swap V1 with V2 Rotation of all contacts by arbitrary number of positions Polarity – Test Procedure of complete Installation

7. 2 coax cables before electronics 2 fibre patch cords after Racks not directly under cryostat output ports 3 coax cables before electronics 2 fibre patch cords after F I P Power Supply BLM BPM only Polarity – Cabling Errors before Front-end Electronics • Would result in incorrect polarity or in measuring adjacent electrodes • Possible sources: • Arc Case • 2 cable connections before electronics • Cryostat cables (verified during installation) • Short coax cables • DSS and Warm BPMs • 3 cable connections before electronics • Cryostat cables (verified during installation) • Long coax cables of up to 200m • Small coax cables • Errors before electronics impossible to verify remotely after installation – will be seen with beam and can be visually inspected.

8. Polarity – Cabling Errors after Front-end Electronics • Would result in mixed up BPMs • Possible Sources: • 2 fibre patch links per plane after front-end • Errors after electronics are easier to track down and should be spotted during hardware commissioning as each station is turned on individually. Single-Mode Fibre-Optic Link VME based Digital Acquisition Board TRIUMF (Canada) Very Front-End WBTN Card WBTN Mezzanine Card (10bit digitisation at 40MHz)

9. Tests of Electronics without beam • All front-end cards: • Adjusted and calibrated individually in the lab (data stored in MTF). • Individual linearization will reduce errors from 6% to 1%. • Calibrator sits at the very input (only one resistor before) of the electronic circuitry and enables the testing of the complete acquisition chain. • Front-end cards will be tested in calibration mode locally during installation. • All digital conversion cards (on the surface): • Adjusted and calibrated individually in the lab (data stored in MTF). • Once installed their correct functioning can be verified by setting the front-end to calibration mode. • Same electronics and procedure had been used in TI8: • 3 planes of 51 gave problems (5%) • 2 wrongly cabled special BPMs (measure CNGS and LHC beam). Only detected with beam! • 1 malfunctioning plane (electronics was replaced) • 5% for LHC would imply 50 incorrect or broken planes per beam.

10. BPM Database Management • Important during and after installation • During installation have to take into account • Beam 1 and beam 2 position (internal or external) in each sector. • Rotated cryostats where beam 1 and beam 2 BPM output ports change places within the same sector. • Directional coupler BPMs where upstream and downstream ports on the same BPM provide the 2 beam signals (one of them rotated by 45°). • After installation • Complete database of components for the whole acquisition chain will be required to calculated the beam positions: • BPM Type - Linearization for BPM geometry will depend on type of BPM. • Electronics - Calibration will require knowledge of which card is installed where. Currently trying to implement automatic identification of all cards.

11. Timing Issues • All setting-up and calibration is performed in asynchronous mode • Data throughput is driven by the auto-triggered front-end. No external timing is used or required. • In calibration mode the signals are generated by a 40 MHz crystal oscillator. • Setting–up with beam • Single Pilot over few turns (RF synchronization ?) • FIFO stores all valid auto-triggers. • Single Pilot over many turns • Can use asynchronous mode as for calibration. • Single or multiple pilots over many turns with RF synchronized • Use BST to give 40 MHz bunch synchronous clock. • Requires individual timing adjustments for all BPMs to compensate for different cable lengths. • Phase margin quite large (auto-triggered input is stable during 20 ns out of 25 ns). • Currently looking into ways of automatically adjusting phase if errors are detected. • Allows bunch tagging and turn counting. • Once BST is in use real-time data is available for orbit feedback.

12. Beam Loss Monitors Hardware set-up and testing Calibration Threshold determination

13. Hardware Set-up and Testing (1) • Normal beam operation does not allow checks for availability, channel mix-up or position errors. • Checks before commissioning • Regular dedicated checks during operation. • All components (electronics, chambers) and all functionalities individually tested before installation. • Barcode based installation (avoid mix-up of channels). • All electronics channels and chambers individually tested after installation • HV modulation on the ionization chambers (availability of all channels) • Source testing of each chamber (verify channel matching, chamber gain)

14. Beam Loss Monitor Installation

15. Hardware Set-up and Testing (2) • Regular testing during operation • Constant 10 pA baseline on each channel (availability of electronics) • HV modulation on the ionization chambers after each dump (availability of chamber and electronics)

16. Calibration • Test with radioactive sources • Before installation: production and reception tests of all ionization chambers (chamber gain). • After installation (and after maintenance) by posing a source on each chamber one by one: gain of chamber plus electronics channel. • During shut-down: plan to measure the gain every year. Only way to find problems with chamber gas composition. • Gain variations are expected to be small (few percent). No correction planned. • Bigger gain variations are a sign of a problem - replace chamber or electronics.

17. Threshold Determination • Based on simulations • Cross-checked by measurements when possible • Depending on the outcome of the cross-checks beam tests might be necessary “Artist’s View” of the Beam Loss Display (C. Zamantzas)

18. Threshold Determination – Simulations • Proton loss locations (ongoing efforts, talk in session 8: S. Redaelli.) • Hadronic showers through magnets (past and present GEANT simulations, AB/BDI/BL) • Magnet quench levels as function of proton energy and loss duration (future fellow, talk in session 8: A. Siemko) • Chamber response to the mixed radiation field in the tail of the hadronic shower (GARFIELD simulations, AB/BDI/BL) • Damage thresholds for collimators simulated (FLUKA team) • Simulations to determine the BLM signal per lost beam proton: E. Gschwendtner

19. Threshold Determination – Measurements • Measurement program at HERA/DESY • Hadronic shower through superconducting magnet combined with chamber response. Possible to lose 100 A protons at 40 GeV inside one magnet with a local bump without quench. • Quench level measurements without beam for different time constants • Program to be defined, workshop on quench levels in March, L. Rossi, R. Schmidt, A. Siemko • Sector test • Equip one magnet with several BLMs. Measure hadronic shower combined with the chamber response. • Some information on longitudinal loss pattern. • Partial test for quench levels: 450 GeV for instant losses (heat deposition combined with cable heat capacity). • Chamber response in various radiation fields measured (analysis ongoing). • Collimator material test measurements in TT40 in 2004.

20. Threshold Determination – Beam Tests • All losses (logging) and quenches (post mortem) can be analyzed and will allow to fine-tune the BLM system (long term effort). • Dedicated beam tests might be required to achieve the demanded absolute precision on the number of lost beam particles: A factor 5 initial and a factor 2 final absolute precision. • Controlled beam losses inside a cold magnet equipped with several BLMs (calibration and measurement of the shower topology). Sector test: short losses at 450 GeV, commissioning: all ranges. • Uncertainties in threshold levels are dominated by our knowledge of • Longitudinal loss distribution • Only possible experiment is the sector test (partial answers). • Quench levels • Safety factor of >300 between quench and damage for fast losses and a redundant system to catch dangerous long losses (quench protection system) • Issue of operation efficiency (avoid false dumps or magnet quenches)

21. Quench and Damage Levels • Pilot bunch: just below the quench level at 450 GeV, and just below the damage level at 7 TeV. Low intensity (during commissioning) will lead to few false dumps and a low probability for quenches. Probably no efficiency issue for low intensities.

22. Emittance and Current Measurement Systems Wires Scanners Synchrotron Light Monitor Ionization Profile Monitor Beam Current Transformers

23. Lab Tests and Installation • Lab Tests • All systems (hardware together with electronics) are tested in the lab. • Calibration is performed (where relevant). • Installation and installation tests • Generally planned between Jan 06 and Sept 06, if sufficient support of the design office is available. • Laser set-up for Synchrotron Light Monitor. • Undulators and final test of Synchrotron Light Monitor up to Dec 06. • Frequent access and vacuum interventions required.

24. Pre-commissioning Tests • System tests in the tunnel without beam special requirements • Current transformers • Normal operating conditions (ideally cycling machine), no beam: check for EM perturbations (1 week) • Timing system (BST), no beam: set-up of data acquisition (1 week) and calibration (1 day) • Ionization Profile Monitor • Bake-out finished: HV and detector tests (2 days) • Vacuum < 10-6 hPa, power, water cooling: magnets and power converter tests • All systems will require access - mainly to IP4. In case of problems with the equipment vacuum interventions will be needed.

25. Sector Test • BPM • Commissioning of BPMs in the sector (polarity checks, timing, database issues) and a part of the functionality of the BPM system. • Possibility to find problems and fix them before LHC start-up. • BLM • Commissioning of a part of the functionality of the BLM system (dump signal, setting of thresholds and beam flags, database issues, logging, post mortem, offline analysis). • Quench level calibration: Controlled beam loss in cold magnet equipped with several BLMs. • Longitudinal loss patterns (only way for measurements before LHC start-up). • Possibility to find problems and fix them before LHC start-up. • Could prove very useful considering the complexity of the system and the time needed to implement changes or fix problems.

26. Summary – Critical Issues for Commissioning • BPM system: • Cabling errors (< 5% in TI8) – access time during beam commissioning • Calibration / linearization database errors • wrong BPM type  wrong position readings • wrong linearization / calibration constants  reduced accuracy • BLM system: • Accuracy of quench level determination (factor 10 should be acceptable for initial commissioning) • Accuracy of the prediction of loss locations (accuracy of the aperture model) • Availability of application software (already for sector test)