E.B. HolzerChamonix XIV workshop, CERN January 18, 2005 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

E.B. HolzerChamonix XIV workshop, CERN January 18, 2005 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

E.B. HolzerChamonix XIV workshop, CERN January 18, 2005 3

Beam Position Monitors

Polarity errors Testing of electronics BPM database issues Timing issues

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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.

E.B. HolzerChamonix XIV workshop, CERN January 18, 2005 5

Polarity – Cryostat Cabling, SSS BPM

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Polarity – Test Procedure of complete Installation

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

0.00000 MhZ

RF ON

HP 8647A

0.000 dB 0.000 dB A BHP 8508 A

Générateur

Vecteur-Voltmetre

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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.

BLM

Pow

erS

upply

FIP

2 coax cables before electronics2 fibre patch cords after

BPM only

Racks not directlyunder cryostat output ports

3 coax cables before electronics2 fibre patch cords after

E.B. HolzerChamonix XIV workshop, CERN January 18, 2005 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.

WBTN Mezzanine Card(10bit digitisation at 40MHz)

VME basedDigital Acquisition BoardTRIUMF (Canada)

Single-Mode Fibre-Optic Link

Very Front-End WBTN Card

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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.

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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.

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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.

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Beam Loss Monitors

Hardware set-up and testing Calibration Threshold determination

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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)

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Beam Loss Monitor Installation

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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)

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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.

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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)

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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

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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.

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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)

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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.

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Emittance and Current Measurement Systems

Wires Scanners Synchrotron Light Monitor Ionization Profile Monitor Beam Current Transformers

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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.

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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.

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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.

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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)