Status Report on LHC Beam Instrumentation

Transcription

1 Status Report on LHC Beam Instrumentation LHC Machine Advisory Committee 6 th December 2007 Rhodri Jones on behalf of the CERN Beam Instrumentation Group

2 Overview Status of BI Systems Beam loss measurement Installation Status Beam Test Results Orbit & trajectory measurement Installation Status Use of the system for aperture checks with the RF ball Transverse Beam Size Measurement Rest Gas Ionisation Monitors Wire Scanners US-LARP Contributions Collision Rate Monitors (LBNL) Schottky Monitors (FNAL) Advances on Other Systems

3 The LHC Beam Loss System Role of the BLM system: 1. Protect the LHC from damage 2. Dump the beam to avoid magnet quenches 3. Diagnostic tool to improve performance of LHC Name Type Number Area of use Maskable with safe beam flag Time resolution BLMQI Ionisation Chamber ~3100 Arcs yes 1 turn BLMEI BLMES BLMEI BLMES BLM Ionisation Chamber SEM Ionisation Chamber SEM ACEM (phase II) ~150 ~150 ~400 ~150 ~10 Collimation regions Critical aperture limits or positions Primary collimators no no No thresholds 1 turn 1 turn bunch-bybunch

4 LHC Beam Loss Detectors Design criteria: Signal speed and reliability Dynamic range (> 10 9 ) limited by leakage current through insulator ceramics (lower) and space charge saturation (upper) Secondary Emission Monitor (SEM): Length 10 cm P < 10-7 bar ~ times smaller gain Ionization chamber: N 2 gas filling at 100 mbar over-pressure Length 50 cm Sensitive volume 1.5 l Ion collection time 85 μs Both monitors: Parallel electrodes (Al or Ti) separated by 0.5cm Low pass filter at the HV input Voltage 1.5 kv

5 Production Ionisation chambers (IC) BLM System Status 4250 produced at IHEP & delivered to CERN Relative gas gain verified at CERN-GIF (gamma irradiation facility) for 4000 Secondary Emission Monitors (SEM) 350 produced at IHEP & 250 tested so-far in proton beam at CERN Vacuum verified (< 5x10-5 bar) If too high ionisation chamber & gives ~2300 times more gain charge [pc] blm-030.dat Q SEM /Q beam = Integrated charge of 4 SPS cycles 10 Q SEM 0 Q beam *Geant4 Q SEM corrected time [s] SEM calibration in H4 20cm Cu target 300 GeV/c protons SEM/beam ratio Mean: 3.40 sigma: 0.92 SEM Calibration Q /Q SEM beam Very good production quality achieved for both Only 16 from 4000 ionisation chambers & 2 from 250 SEMs failed the tests

6 Installation Follows LHC schedule BLM System Status 66% of ionisation chambers installed 29% of SEMs installed (collimation areas missing) Electronics installed in Sector 8 1 BLM Testing Complete BLM system tests in SPS shots of protons on collimator High intensity & short duration simulated LHC transient beam impact Tested the complete LHC BLM system: hardware & software Results Cross talk observed in multi-conductor cables carrying both ionisation & SEM signals Re-cabling required in all LSS to separate IC & SEM signals (done except 5L) Cross talk observed between different ionisation chamber channels Low pass filter to reduce signal slope for straight section ICs (to be done) Next Tests EMC with injection kicker magnets & availability of installed BLMs

7 Tested: Status of Software Elements for the Data Concentrator Change of thresholds Change of beam energy Transmission to logging system Triggered data generation - 40ms, 2ms data Post mortem XPOC Collimation BLM System

8 Threshold Setting Accuracy Threshold setting accuracy depends mainly on Secondary shower simulation Quench level knowledge Secondary Shower Simulation Difficult to simulate far transverse tails Compared with HERA measurements Geant4 and FLUKA agree with each other within errors bars at 39 GeV and 920 GeV Discrepancy of factor ~2 between measurements and simulation Not unexpected from simulation uncertainties for far transverse tails Consequences for LHC: Geant4 (QGSP-BERT-HP) & FLUKA qualified for threshold simulation Can expect systematic error for the LHC simulation of 50% HERA DUMP: M. Stockner (thesis) Geant4 Geant4

9 Quench Level Simulations & Measurements Quench Level Knowledge Network model (PSpice) used to simulate thermodynamic behavior of LHC superconducting magnets in steady state Compared to measurements via quench heaters & inner coil heating Results obtained for MQM, MQY, MQ and MB magnets at 4.5K Measurements and simulation agree within 20% Qualified network model at 4.5K Quench limits simulated for beam induced energy deposition Power density deposition found to vary by up to a factor 2 compared to design value of 5 mwcm -3 I magnet [A] ΔImagnet [%] MQM 627 MQM 677 MQMC 677 MQM magnets at 4.5 K MQM 627 MQM 677 MQMC 677 P [mw/cm 2 ] Ultimate current 4650 A Nominal current 4310 A % error between measurement & simulation P [mw/cm 2 ]

10 LHC Beam Position Monitors All Installed Injection Lines: 100 Warm, Button BPMs (Buttons Recuperated from LEP)

11 LHC Beam Position Monitors All Installed 912 Button Electrode BPMs (24mm) for the Main Arcs & Dispersion Suppressors

12 LHC Beam Position Monitors All Installed 24 Directional Couplers 52 Enlarged Button & 8 Trigger BPMs Interaction Regions

13 LHC Beam Position Monitors All Installed 36 Warm BPMs - 34mm Button Electrodes

14 LHC Beam Position Monitors All Installed 54 Special BPMs for Tune & Chromaticity, Transverse Damper & RF, Beam Dump

15 LHC Beam Position Monitors All Installed All 1182 BPMs for the LHC and its Transfer Lines are now installed (Sector 7-8 BPMs have survived first thermal cycle without incident)

16 Status of BPM Acquisition System Series Production of all components nearing completion Wide Band Time Normaliser (40MHz position measurement) All 2282 front-end cards required received All 2288 front-end cards required received Delivery of all spares to be completed by end 2007 Digital Acquisition Board (DAB64x - TRIUMF) Standard for BPM, BLM, Fast BCT, Wire Scanners, Luminosity & Q measurement All 1300 BPM type modules received All 500 BLM type modules received Reception Testing 2 automated test benches constructed and manned by external personnel Used for adjustment and calibration of all Wide Band Time Normaliser Cards Beam simulator allows position & intensity linearity measurement for all cards All data stored in MTF & linked to serial number chip located on each card Over 70% of the cards have been tested so far

17 Status of BPM Acquisition System Infrastructure Nearly all fibre-optic, coaxial cable and WorldFIP control links in place LSS7 & LSS3 are equipped with radiation hard fibres (Fujikura, Japan) Tests have shown that radiation induced attenuation in this fibre for light at 1310 nm is 5 db/km after 1 MGy Installation this attenuation is reached in the standard Ge-doped fibre after only 500 Gy Tunnel installation and hardware commissioning has been completed in arcs of Sector 4L Sector 4-5 Sector 5-6 Sector 6-7 (underway) Sector 7-8 Sector 8-1

18 Aperture Restriction Localisation using the RF Mole (Ping-Pong Pong Ball) and the LHC BPM System AB/BI, TS/IC, AT/VAC Aim To find a method to quickly check for obstacles in the beam pipe at warm Principle Air flow to move a lightweight ball that contains an emitter able to trigger the LHC Beam Position Monitor (BPM) system Test location The whole continuous cryostat in each sector (~2.6km)

19 RF emitter Polycarbonate shell Diameter 34mm exterior 30mm interior Total weight ~15 g (ball 8g) RF characteristics 40MHz resonant circuit Generates 20V between copper electrodes Battery powered Over 2hr lifetime Capacitive coupling to BPM electrodes 1V ~5mV -45db Coupling BPM trigger threshold at ~3mV

20 First Test (13/09) V2 line from Q11.L8 to Q26.L8 Anemometer Air Filter Q11.L8 Pump at Q26.L8 Switched on once the cap was in place

21 BPM position Beam aperture BPM Ball Tracking Time stamp (in second) Final BPM acquisition system Missing BPM trigger in Q13? Interleaved BPMs (odd/even in arc) on separate frontend CPUs Last BPM trigger in Q22 Ball stopped between Q22 and Q23

22 Localisation by BPM Reflectometry (AB/RF) 4-8GHz signal coupled into the beampipe using BPM & associated cables Reflected signals analysed for several polarisations No clear signal of the ball location when stopped was obtained by BPM reflectometry comparing the V1 and V2 lines Test performed from Q22.L8 and Q24.L8 (ball expected to be at Q23.L8) However once the ball was sucked back away from the obstruction a very clear signal of the original ball location was observed

23 Damaged PIM in 23L8 Nothing expected at this location Re-check of the X-rays showed that 2 fingers were indeed bent into the vacuum chamber

24 8-77 Complete Sector Test (V2 line) RF Mole Results: Allows aperture check in the arc Localisation to 50m possible using BPMs Now systematically carried out on all sectors before cooldown: 5-6, 7-8 & 8-1 so far all OK Test of BPM system in final configuration

25 Measuring Beam Size Beam Profile Measurements in the LHC Workhorses Synchrotron light monitor Wire scanners for cross calibration For injection & matching OTR screens For ions Rest Gas Ionisation Monitor (BGI) Also used as back-up for SR monitor

26 Rest Gas Ionisation Monitors (BGI) Beam 1 and Beam 2 monitors were installed in early 2007 Wrong programming of the bake-out led to both horizontal and vertical beam 2 monitors being cooked at 350 C instead of baked-out at 200 C All parts of these monitors suffered The brazing material of the window (Pb/Ag alloy) completely melted The ensuing vacuum leak sucked the melted material into the vacuum chamber, polluting the chamber and detector The anti-reflective coating of the quartz widow and one prism were destroyed The Multi Channel Plate (detector) and Electron Generator Array (calibration source) were severely damaged Aluminium pieces were plasticised

27 Rest Gas Ionisation Monitors (BGI) Reconstruction began immediately salvaging as much as possible and using spare components Both tanks were chemically cleaned and could be re-used The quartz windows were re-polished All aluminium pieced were re-manufactured Two completely new detectors were built Installation of these new monitors was completed a few weeks ago The bake-out is now also complete Tests are underway to verify the correct functioning of the detector

28 Wire Scanners Open Issues from previous LHC MACs Where to place the PMT detectors? When does the wire break? Do downstream magnets quench during a scan? Where to place the PMT detectors Signal proportional to energy deposited - a lot of signal for nominal intensity Signal level at ~6m changes by less than 50% with energy Mariusz Sapinski Mariusz Sapinski Energy per interacting proton Energy per interacting proton

29 Wire Scanners When does the wire break? Simulations corroborated by SPS measurements show that a 30μm carbon wire scanned at 1ms -1 will survive ( T < 4000K ) with: 25% of nominal LHC beam at injection energy 7% of nominal LHC beam at top energy (a function of beam size not energy) Mariusz Sapinski Thermionic current plays crucial role as cooling process for temperatures above 3000 K RF-heating does not significantly affect wire temperature heat transfer plays minimal role as cooling mechanism eventual use of carbon nanotubes will not improve performance The carbon work function and wire emissivity are poorly known but are important parameters of the model.

30 Wire Scanners Do we quench during a Scan? Simulations show that: Number of events with large energy deposition is higher in Q5 than D4 The wire scanner can work to between 1 to 6 x protons at 7 TeV Less than one nominal 72 bunch PS batch Main uncertainty due to simulation of small number of interactions in small volume Mariusz Sapinski What can be done to increase this margin? Scan faster can gain up to factor 2 Reduce the wire diameter Reduces the number of interactions while reduction of signal strength no issue for PMT Add shielding Difficult as source of energy is from particles hitting the beam pipe close to & within Q5 inclusion of Schottky monitors (smaller aperture) in front of Q5 in the simulation had little effect

31 US-LARP Contributions Collision Rate Monitoring (LBNL) Detector Status 1 detector at CERN 2 detectors undergoing final testing at LBL (HV, Pressure...) 1 undergoing repair for leaky cable due at the end of December Installation Schedule Installation of dummy chamber successfully tested during 2007 Final installation of 3 detectors foreseen in Jan/Feb 2007 and one in March Electronics Status Final prototype of front-end electronics is working well & final package expected by January 2007

32 LHC TAN Collision Rate Monitor (LBNL) Results from 2007 Tests at RHIC RHIC ZDC LBL Lumi

33 US-LARP Contributions Schottky Monitoring (FNAL) Schottky Travelling Wave Structures All 4 tanks completed and installed in early 2007 Bake-out completed small Ar leak from internal cable on 1 module identified no VAC issue at this time Travelling wave structure response tested by FNAL team in May 2007 Electronics Status All Front-end electronics installed & tested by FNAL team in May 2007 Digital acquisition will be the same as for standard LHC tune measurement Front-end control currently being implemented by FNAL

34 US-LARP Contributions Schottky Monitoring (FNAL) Tevatron Tests Tevatron Schottky monitors fitted with LHC style front-end electronics Results very encouraging big improvement in S/N over current Tevatron system Triple down-mixing to baseband Reduction in instantaneous dynamic range with revolution line outside pass band of final 15kHz crystal filter Use of improved low phase noise local oscillators Old System - first LO Results New System - first LO Results

35 Advances on Other Systems Test of all instruments with beam in TI2 successful Screens BPMs & BLMs BCT Software

36 Advances on Other Systems Beam current transformers installed & baked-out in the LHC ring and the Dump Lines

37 Advances on Other Systems Fast camera for synchrotron light monitor (BSRT) successfully tested in the SPS used for SPS injection matching studies employed 4 times faster framing rate (& associated SW) Horizontal Vertical Raw Data Corrected Data

38 Advances on Other Systems Continuous chromaticity measurement via RF modulation using LHC PLL system tested in SPS Δp/p ~2x10-5 ΔQ ~1x10-4 for Q=6 Radial change of only 40μm in SPS Easily tracked by PLL at modulation frequency of 0.5Hz Resolution of better than 1x10-5 obtained for the tune measurement

39 Advances on Other Systems All 4 Cadmium Telluride collision rate monitors (for IP2 (Alice) & IP8 (LHCb) delivered by CEA-LETI Successfully tested with beam in the SPS North Area Full electronics acquisition chain developed & tested

40 Summary Over 60% of both large distributed systems (BPM/BLM) installed Complete slice of BLM system successfully tested in SPS Complete BPM system tested during aperture verifications with RF mole Issues resolved during the year Rest gas ionisation monitor accident during bake-out Huge effort by BI team responsible has enabled all monitors to be re-installed Outstanding wire-scanner issues are resolved Main limitation at top energy will be quench limit of Q5 magnet US-LARP Deliverables Use of RHIC as test bed for tune, coupling & chromaticity control very useful Despite problems delivery of LBNL luminosity monitors still on schedule Schottky collaboration with FNAL has been very effective Outlook for LHC commissioning All necessary instrumentation hardware for the start-up is now in place Most electronics is under test enabling the initial software to be written & tested The functionality will evolve through the commissioning phases