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

Status Report onStatus Report onLHC Beam InstrumentationLHC Beam Instrumentation

LHC Machine Advisory Committee

6th December 2007

Rhodri Jones

on behalf of the

CERN Beam Instrumentation Group

Rhodri Jones – CERN Beam Instrumentation GroupRhodri Jones – CERN Beam Instrumentation Group LHC Beam Instrumentation – MAC2007 LHC Beam Instrumentation – MAC2007

OverviewOverview

● 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


The LHC Beam Loss SystemThe LHC Beam Loss SystemRole 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 useMaskable with safe beam flag

Time resolution

BLMQI Ionisation Chamber ~3100 Arcs yes 1 turn

BLMEIBLMES

Ionisation ChamberSEM

~150~150

Collimation regions

no 1 turn

BLMEIBLMES

Ionisation ChamberSEM

~400~150

Critical aperture limits or positions

no 1 turn

BLM__ ACEM (phase II) ~10Primary collimators

No thresholds

bunch-by-bunch


LHC Beam Loss DetectorsLHC Beam Loss Detectors

● Design criteria: Signal speed and reliability

● Dynamic range (> 109) limited by leakage current through insulator ceramics (lower) and space charge saturation (upper)

Secondary Emission Monitor(SEM):

● Length 10 cm● P < 10-7 bar● ~ 30000 times smaller gain

Ionization chamber:● N2 gas filling at 100 mbar over-

pressure● Length 50 cm● Sensitive volume 1.5 l● Ion collection time 85 s

Both monitors:● Parallel electrodes

● (Al or Ti) separated by 0.5cm● Low pass filter at the HV input● Voltage 1.5 kV


BLM System Status BLM System Status ● Production

● Ionisation chambers (IC)● 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

0 10 20 30 40 50-10

0

10

20

30

40

50

60

70

80

time [s]

blm-030.dat QSEM

/Qbeam

= 4.0806

cha

rge

[pC

]

QSEM

Qbeam

*Geant4

QSEM

corrected

0 1 2 3 4 5 6 70

1

2

3

4

5

6

7

8

9

10

SEM calibration in H4 20cm Cu target 300 GeV/c protons SEM/beam ratio Mean: 3.40 sigma: 0.92

QSEM

/Qbeam

Integrated charge of 4 SPS cycles

SEM Calibration

● Very good production quality achieved for both● Only 16 from 4000 ionisation chambers & 2 from 250 SEMs failed the tests


● Installation● Follows LHC schedule

● 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 1013 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

BLM System Status BLM System Status


Status of Software Elements for the Status of Software Elements for the BLM SystemBLM System

● Tested:● Data

Concentrator● Change of

thresholds● Change of beam

energy● Transmission to

logging system● Triggered data

generation -40ms, 2ms data

● Post mortem ● XPOC● Collimation


Threshold Setting AccuracyThreshold Setting AccuracyHERA DUMP: M. Stockner (thesis)

Geant4

Geant4

Threshold setting accuracydepends 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%


Quench Level Simulations & Measurements Quench Level Simulations & Measurements

MQM magnets at 4.5 K

3700

3800

3900

4000

4100

4200

4300

4400

4500

4600

4700

25.00 30.00 35.00 40.00 45.00 50.00 55.00

P [mW/cm2]

I m

agn

et [

A]

MQM 627

MQM 677

MQMC 677

Ultimate current 4650 A

Nominal current 4310 A

-8

-6

-4

-2

0

2

4

6

8

30 35 40 45 50 55 60 65

P [mW/cm2]

DI m

agn

et [

%]

MQM 627

MQM 677

MQMC 677

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

% error between

measurement & simulation


LHC Beam Position Monitors – All InstalledLHC Beam Position Monitors – All Installed

Injection Lines: 100 Warm, Button BPMs(Buttons Recuperated from LEP)



912 Button Electrode BPMs (24mm)for the

Main Arcs & Dispersion Suppressors



24 Directional Couplers52 Enlarged Button& 8 Trigger BPMsInteraction Regions



36 WarmBPMs -

34mm ButtonElectrodes



54 Special BPMs for Tune & Chromaticity,Transverse Damper & RF, Beam Dump



All 1182 BPMs for the LHCand its Transfer Lines are now installed

(Sector 7-8 BPMs have survived firstthermal cycle without incident)


Status of BPM Acquisition SystemStatus 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


Status of BPM Acquisition SystemStatus of BPM Acquisition System

● Installation● 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

● 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● this attenuation is reached in the standard Ge-doped fibre after only 500 Gy


Aperture Restriction Localisation using the RF Mole Aperture Restriction Localisation using the RF Mole (Ping-Pong Ball) and the LHC BPM System(Ping-Pong Ball) and the LHC BPM System

AB/BI, TS/IC, AT/VACAB/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)


RF RF emitteremitter

● 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


Air FilterAnemometer

First Test (13/09)First Test (13/09)V2 line from Q11.L8 to Q26.L8V2 line from Q11.L8 to Q26.L8

Q11.L8Pump at Q26.L8Switched on once the cap was in place


BPM Ball TrackingBPM Ball TrackingBPM position

Beam aperture

Time stamp (in second)

Final BPM acquisition system

Interleaved BPMs (odd/even in arc) on separate front-end CPUs

Missing BPM trigger in Q13 ?

Last BPM trigger in Q22

Ball stopped between Q22 and Q23


Localisation by BPM Reflectometry (AB/RF)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


Damaged PIM in 23L8Damaged 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


8-7 Complete Sector Test (V2 line)8-7 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 & 8-1so far all OK

● Test of BPM system in final configuration


Measuring Beam SizeMeasuring 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


Rest Gas Ionisation Monitors (BGI)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 350C 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


Rest Gas Ionisation Monitors (BGI)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


Wire ScannersWire ScannersOpen 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

Energy per interacting proton Energy per interacting proton

Mariusz SapinskiMariusz Sapinski


Wire Scanners – When does the wire break?Wire Scanners – When does the wire break?● Simulations corroborated by SPS measurements show that a 30m 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)

● 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.

Mariusz Sapinski


Wire Scanners – Do we quench during a Scan?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 1012 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

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

Mariusz Sapinski


US-LARP ContributionsUS-LARP ContributionsCollision Rate Monitoring (LBNL)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


LHC TAN Collision Rate Monitor (LBNL)LHC TAN Collision Rate Monitor (LBNL)Results from 2007 Tests at RHICResults from 2007 Tests at RHIC

RHIC ZDC

LBL Lumi


US-LARP ContributionsUS-LARP ContributionsSchottky Monitoring (FNAL)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


US-LARP ContributionsUS-LARP ContributionsSchottky Monitoring (FNAL)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 LOResults

New System - first LOResults


● Test of all instruments with beam in TI2 successful● Screens● BPMs & BLMs● BCT● Software

Advances on Other SystemsAdvances on Other Systems


● Beam current transformers installed & baked-out in the LHC ring and the Dump Lines



● 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)

Vertical

Horizontal

Raw Data Corrected Data



● Continuous chromaticity measurement via RF modulation using LHC PLL system tested in SPS● Dp/p ~2x10-5 DQ ~1x10-4 for Q=6● Radial change of only 40m in SPS● Easily tracked by PLL at modulation frequency of 0.5Hz

● Resolution of better than 1x10-5 obtained for the tune measurement



● 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



SummarySummary● 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

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

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