e.b. holzer chamonix xiv workshop, cern january 18, 2005 1 pre-commissioning of critical beam...
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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
E.B. HolzerChamonix XIV workshop, CERN January 18, 2005 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.
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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
E.B. HolzerChamonix XIV workshop, CERN January 18, 2005 7
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.
E.B. HolzerChamonix XIV workshop, CERN January 18, 2005 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.
E.B. HolzerChamonix XIV workshop, CERN January 18, 2005 12
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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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)
E.B. HolzerChamonix XIV workshop, CERN January 18, 2005 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.
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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)
0
0.2
0.4
0.6
0.8
1
1.2
Measu
red
/ T
hresh
old
Dete
cto
r 1
Dete
cto
r 2
Dete
cto
r 3
Dete
cto
r 4
Dete
cto
r 5
Dete
cto
r 6
. . .
Dete
cto
r
4000
R1
R2
R3
R4
R5
R6
Warn
ing
Du
mp
Inte
grati
on
Tim
e In
terva
ls
E.B. HolzerChamonix XIV workshop, CERN January 18, 2005 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
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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.
E.B. HolzerChamonix XIV workshop, CERN January 18, 2005 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)
E.B. HolzerChamonix XIV workshop, CERN January 18, 2005 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.
E.B. HolzerChamonix XIV workshop, CERN January 18, 2005 22
Emittance and Current Measurement Systems
Wires Scanners Synchrotron Light Monitor Ionization Profile Monitor Beam Current Transformers
E.B. HolzerChamonix XIV workshop, CERN January 18, 2005 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.
E.B. HolzerChamonix XIV workshop, CERN January 18, 2005 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.
E.B. HolzerChamonix XIV workshop, CERN January 18, 2005 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.
E.B. HolzerChamonix XIV workshop, CERN January 18, 2005 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)