LHC BPM Talk to LARP

1
LHC BPM Talk to LARP

• Bob Webber August 2, 2005

2
OUTLINE

• I will show slides from
• Rhodri Jones
• Tune Feedback Workshop
  BNL - 9th-11th March 2005
• http//www.agsrhichome.bnl.gov/LARP/050309_TF_work
  shop/index.html
• Eva Barbara Holzer and Hermann Schmickler
• Workshop Chamonix XIV, Second LHC Project
  Workshop, January 2005 at CERN
• http//indico.cern.ch/conferenceDisplay.py?confId
  044
• See also D. Coqc et al. on BPM electronics
• D. Cocq, The wide band normaliser a new
  circuit to measure transverse bunch position in
  accelerators and colliders, Nuclear Instruments
  and Methods in Physics Research A 416 (1998)
  p.1-8.
• http//www.esrf.fr/conferences/DIPAC/Proceedings/s
  tampedpdfs/PM-17.pdf
• DIPAC01
• http//bel.gsi.de/dipac2003/papers/PT08.pdf
• DIPAC03

3
LHC Beam InstrumentationCommissioning
Tune Feedback Workshop BNL - 9th-11th March
2005 Rhodri Jones (CERN AB/BDI)
4
Outline

• LHC Beam Instrumentation
• The BPM system
• The BLM system
• Luminosity monitors
• Emittance measurement
• Tune, chromaticity coupling measurement this
  workshop
• LHC Commissioning
• General commissioning strategy
• Commissioning the beam instrumentation

5
LHC BPM System - General Layout
922 Button Electrode BPMs (24mm) for the Main
Arcs Dispersion Suppressors
Total of 1158 BPMs for the LHC and its Transfer
Lines
6
The Arc BPM - SSS Layout
7
Arc BPM - Detailed Layout
Beam Pipes
BPMs
Cryogenic Coaxial Cables
8
Arc BPM - Button Feedthrough
Button Feedthrough
Beam Screen
Liquid Helium Cooling Capillary
9
Insertion Region Directional Couplers
10
The Front-End Electronics
11
The Wide Band Time Normaliser
A
B
12
The Wide Band Time Normaliser
A (B 1.5ns)
A
B
13
The Wide Band Time Normaliser
A
B
A(B1.5ns)
B(A1.5ns)10ns
Interval 10 ? 1.5ns
System output
14
Sensitivity Observation

• WideBand Time Normalizer
• Full range of 1.5nsec for 24.5mm radius arc
  pickup
• 61ps/mm
• Tevatron AM/PM system
• 6 degrees at 53MHz (300ps) per dB difference
• Pickup sensitivity of 1.5 mm/dB
• 200ps/mm

15
The Wide Band Time Normaliser
16
The LHC BPM Acquisition System
Tunnel
Surface
17
WBTN - Linearity v Intensity
For LHC Arc BPMs 1 130mm
18
WBTN - Linearity v Position
For LHC Arc BPMs 1 130mm
19
Bunch-by-bunch Results in the CERN-SPS
System extensively used in SPS for electron cloud
instability studies.
20
Orbit feedback results from the CERN-SPS
feedback off
BPM Reading (?m)
450 GeV
Time (ms)
feedback on
ramp
injection at 26 GeV
Position distribution _at_ 100 Hz s 8.5 mm
measurement noise !!
21
The LHC Beam Loss System

• Role of the BLM system
• Protect the LHC from damage
• Dump the beam to avoid magnet quenches
• Diagnostic tool to improve the performance of the
  LHC

• Acquisition requirements
• Calculation of quench level equivalent chamber
  signal
• Electric currents from 600 pA to 300 ?A
• A dump should be requested at 50 of the quench
  level
• i.e. from 300 pA to 150 ?A
• Extend dynamic range for sufficient sensitivity
  at low losses
• Measuring current from 60 pA to 300 ?A
• Arc BLM acquisition rate not faster than one turn
  (89 ?s)
• Fastest total loss is 6 turns will be
  detected by special BLMs.

22
Structure of the BLM Readout Chain

• transforms particle losses into an electric
  current
• 6 per quadrupole (3 for each LHC ring) ? 3000
  monitors
• Analogue Front-End
• measures current and transmits data from Tunnel
  ? Surface
• Dump Controller
• processes data and interfaces to the beam
  interlock system

• Ionisation Chamber

23
Quench Level EquivalentChamber Current
300 ?A
600 pA
One turn
60 pA
24
Charge-Balanced Converter
iin(t)
iin(t) Iref
25
Current-Frequency Characteristics
26
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

27
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

28
Beam Position Monitors

• Polarity errors
• Testing of electronics
• BPM database issues
• Timing issues

29
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.

30
Polarity Cryostat Cabling, SSS BPM
31
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

32
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.

33
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)
34
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.

35
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.

36
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.
• Settingup 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.

37
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.

38
Summary Critical Issues for Commissioning

• BPM system
• Cabling errors (lt 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)

39
Beam Commissioning of LHC instrumentation

• Chamonix XIV, January 2005
• H.Schmickler on behalf of the AB-BDI group

40
Prerequisites (same slide as last year)

• Working and exploitable instruments need-
  sensors and electronics AB-BDIdetails see
  AB-LHC review recurrent problem Design
  support- controls infracstructure AB-CO, in
  progress- RT software and expert tools
  AB-BDI-SW will be based on FESAII framework
• Operational application programs AB-CO
  AB-OPwork needs to be organized soon (that is
  the text of last year)work needs to be
  organized now (see following slides)

41
Design effort still needed

• There are still major BDI components, for which
  the mechanical design is not done / finished.
• The situation was similar at Chamonix 2004.
• After the workshop a significant improvement in
  design office support was notable.
• With the QRL problem higher priorities defined,
  present support insufficient
• Without the requested support - some special
  BPMs ( special BPMs of the normal orbit system
  and special BPMs for tune measurements)- the
  synchrotron light telescope- the wire
  scannerswill not be ready

42
Prerequisites Software effort

• Example Time resolved chromaticity
  measurementsat day 0 We should not count on PLL
  tune tracking and momentum modulation ? use
  head-tail method (despite emittance growth)
• SPS application program- needs visual
  inspection of result- gives chromaticty as
  number onthe screen- needsautomation,
  integration into a measurement system

Solution Define for the key system System
commissionersand start definition, design and
coding of the application programs
43
Lessons learnt from LEP (1/2)

• Provide reduced functionality of instruments
  without beam synchronous timing (BST)-
  BPM-system works without BST, but no
  bunch/turn identification, reduced noise
  immunity- BLM system most of the system
  acquires data in an asynchronous 1ms rhythm-
  BCT DC no timing- BCT BB needs beam
  synchronous timing, was a problem for the
  downstream BCT in TI8, people are working on a
  input filter to stretch the signal for single
  bunch operation- tune measurement
  systems tune kicker needs rough timing, tune
  meter will have one front-end not depending on
  timing? basic functionality without BST- all
  TV based monitors will work without BST,
  obviously no bunch gating (sync-light
  telescope, ionisation profile monitor, screens)-
  wire scanners and luminosity monitors will
  have an acquisition mode without BST- AGM and
  LDM need the BST in order to work.

44
Lessons learnt from LEP (2/2)

• Hardware can not be tested because software not
  ready,Software can not be developed because
  hardware not available- The FESA framework
  provides the possibility to have device emulation
  of missing hardware, such that the software can
  be developed and tested at a time when the
  hardware is still partially missing
• This feature will help having software/hardware
  ready in time

45
Commissioning with Beam BPM system
Day 0 performance without adjustments No BST adjusted, 1 pilot bunch can measure orbit, turn by turn data possible with BST turn clock Immediate!
Systematic check for inverted cables/planes/rings Per ring and per plane non closed bumps with two correctors at 900 phase advance. If well automated, one shift for detection of problems.Requirement for scripting tool. If 5 error rate, one week to fix problems.
Adjustment of BST One circulating bunch Scan of timing setting for all front ends. Two shifts interleaved by a few days check for stability of settings
Systematic confirmation of system performance Resolution as function of beam intensity, linearity over aperture, dependence on long. beam structure, crosstalk between beams Long process. Several months. Demands LDM to be operational.
46
BPM system

• Application softwareThis should be in good
  shapeSystem commissioner at work since
  years. Application programs very similar to
  those of LEP and SPS.Attention The turn by
  turn analysis program as provided for the SPS
  needs more work.

47
Commissioning with Beam BLM system
Day 0 performance All slow ( 1ms) monitors will deliver loss rates Calibration of loss rates from simulation.Tolerated error factor 5 Initial working condition. Channel assignment tested with radioactive source.
Adjustment of BST for fast loss monitors (collimation region) One circulating bunch. Automated scan. A few hours. Repeated after some time to check stability. Parasitic.
Verification of calibration. Delicate machine experiment. Calibrated loss rates have to be produced into the cryo-magnets Dedicated experiment. A couple of shifts. Necessary step in order to establish dump thresholds.
Crosstalk between channels, in particular between the two beams, longitudinal coverage Dedicated machine experiments Crosstalk between beams simulated to be below 10. Only a problem if beam currents very different.
Determination of dump thresholds Many dedicated machine experiments and operational experience See next slide
48
Beam Commissioning BLM dump thresholds

• There will be more than 3000 beam loss monitors.
  Each of them can be enabled to dump the beam.
• The dependence of the dump level as function of
  the duration of the loss (3 orders of magnitude)
  is realized with 11 different integrators with
  exponential staggering of integration times
  (about factor 2)
• The dependence on beam energy represents another
  2 orders of magnitude (multiplication factor)

Clear need for a system- commissioner
49
Conclusions

• The BDI group makes an attempt to have integrated
  into all instruments basic modes of operation,
  which will give acceptable measurements in the
  conditions of bootstrap.
• The essential systems for commissioning have an
  acquisition mode independent of beam synchronous
  timing.
• The BLM system for machine protection will need a
  considerable commissioning effort.
• All systems need a large investment into the
  corresponding application programs.
• The recently proposed concept of system
  commissioners should be implemented soon with the
  right people selected for the key beam
  instruments. This is for me the most urgent line
  of action.

50
My Impressions

• What must be done is known
• Critical aspects that will lead to success have
  been identified (many in common with those faced
  here, e.g. in implementing new Recycler,
  Tevatron and MI BPM systems)
• Resource limitations that also feel familiar are
  being experienced
• Its a long road to commissioning and then on to
  operations