Lhc beam instrumentation future developments
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LHC Beam Instrumentation & Future Developments. Workshop on Optics Measurements, Corrections and Modeling for High-Performance Storage Rings 21 st June 2011, CERN Rhodri Jones (CERN Beam Instrumentation Group). Outline. Limited to main systems for optics related measurements

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Lhc beam instrumentation future developments

LHC Beam Instrumentation&Future Developments

Workshop on Optics Measurements, Corrections and Modeling for High-Performance Storage Rings

21stJune 2011, CERN

Rhodri Jones

(CERN Beam Instrumentation Group)


Outline

Outline

Limited to main systems for optics related measurements

  • Existing Systems

    • LHC BPM system

    • LHC Tune system

  • Possible Future systems

    • Continuous LHC b-beat measurement system

    • LHC Injection Matching

OMCM Workshop, CERN, June 2011 Rhodri Jones (CERN BE/BI)


Lhc beam position monitors

24 Directional Couplers

52 Enlarged Button

& 8 Trigger BPMs

Interaction Regions

54 Special BPMs for Tune & Chromaticity,

Transverse Damper & RF, Beam Dump

912 Button Electrode BPMs (24mm)

for the

Main Arcs & Dispersion Suppressors

Injection Lines: 100 Warm, Button BPMs

(Buttons Recuperated from LEP)

36 Warm

BPMs -

34mm Button

Electrodes

LHC Beam Position Monitors

A total of 1182BPMs

for the LHC and its Transfer Lines)

OMCM Workshop, CERN, June 2011 Rhodri Jones (CERN BE/BI)


Lhc bpm system performance i

LHC BPM System Performance I

  • On line analysis of BPM Data

    • Powerful on-line tools developed by the CERN Operations crew

    • Polarity errors easily identified with 45 BPM sampling

    • Quick indication of phase advance errors

  • Some statistics

    • 2009:

      • 4 polarity errors : 2 H to V inversions : 7 BPM mapping errors (LSS8L)

      • 1 B1 to B2 inversion

    • 2011:

      • 18 out of 2152 channels with acquisition problems

      • 50 channels deselected for feedback with physics beams (mainly cross-talk on directional pick-ups)

OMCM Workshop, CERN, June 2011 Rhodri Jones (CERN BE/BI)


Lhc bpm system performance ii

LHC BPM System Performance II

  • Orbit & BPM Stability

    • Short term stability (15 minutes) better than 10mm

    • Alternating high/low peaks follow the beta function indicating that:

      • large fraction of this noise results from beam itself

      • resolution & stability of BPM system orbit mode with single pilot bunch ~5mm

    • BUT - surface electronics sensitive to temperature (~50mm per °C)

      • Currently mitigated by temperature calibration of each channel

      • Active rack temperature stabilisation being looked into

OMCM Workshop, CERN, June 2011 Rhodri Jones (CERN BE/BI)


Lhc bpm system performance iii

LHC BPM System Performance III

  • Resolution of LHC BPM system in closed-orbit mode is <5mm rms

  • Long term stability better than ~100mm

    • Mainly given by remaining temperature dependence of surface electronics

Courtesy E. Calvo

OMCM Workshop, CERN, June 2011 Rhodri Jones (CERN BE/BI)


Lhc bpm system performance iv

LHC BPM System Performance IV

  • Bunch-by-Bunch / Turn-by-Turn Mode

    • Main mode used for optics measurements in LHC

    • Allows up to 128000 samples (bunch × turns) from all BPMs

      • Read-out limited to few thousand turns due to data transfer & concentration issues

    • Requires synchronisation to bunch clock for tagging

      • Automatic phase-in now possible & performed before all optics measurements

    • Resolution

      • From ~200mm rms (single pilot bunch) to ~50mm rms (single nominal bunch)

High sensitivity

OMCM Workshop, CERN, June 2011 Rhodri Jones (CERN BE/BI)


Controlling tune chromaticity using the base band q measurement bbq system

Controlling Tune & Chromaticity using theBase Band Q Measurement (BBQ) System

Direct Diode Detection (3D)

  • Base band operation

    • Excellent 24 bit audio ADCs available

    • Signal conditioning / processing is easy

Courtesy M. Gasior

OMCM Workshop, CERN, June 2011 Rhodri Jones (CERN BE/BI)


Lhc tune system performance

LHC Tune System Performance

  • Base Band Tune (BBQ) Measurement System

    • Extremely high sensitivity

    • Coherent micron level tune oscillations nearly always observed

      • most measurements possible with residual beam oscillations

      • Typical tune measurement resolution in the range 10-4 … 10-6

  • Issues

    • Cohabitation with transverse damper (ADT)

      • Raises noise floor by 30dB

      • Aggressive damping leads to very broad tune peak

OMCM Workshop, CERN, June 2011 Rhodri Jones (CERN BE/BI)


Tune feedback in the lhc

Tune Feedback in the LHC

Hor. spectrum with Tune-FB OFF

Hor spectrum with Tune-FB ON

  • With full pre-cycling the fill-to-fill stability is typically 2-3·10-3

  • Variations frequently increase up to 0.02

    • Due to partial or different magnet pre-cycles after e.g. access or sector trips

  • Tune-FB routinely used for all ramps to compensate these effects

    • Using peak fit on FFT with 0.1..0.3 Hz Bandwidth

The

'hump'

OMCM Workshop, CERN, June 2011 Rhodri Jones (CERN BE/BI)


Chromaticity measurement in the lhc

Chromaticity Measurement in the LHC

  • Q'-Tracker demodulates sinusoidal frequency trims

    • Increased original modulation of Δp/p from 10-5 @2.5 Hz to 10-4 @2Hz

      • Mitigates tune stability effects at injection (ΔQres ~ 3-4·10-4)

    • Achieved nominal Q' resolution (±1 unit)

      • Used as feed-forward (combined with magnetic model predictions)

Q (dotted) and Q' (solid) during snap-back

Courtesy R. Steinhagen

horizontal

vertical

OMCM Workshop, CERN, June 2011 Rhodri Jones (CERN BE/BI)


Using the lhc tune system

Using the LHC Tune System

  • Recent Measurement of Q’’ with and without octupoles at injection

Octupolesoff

Octupoles on

OMCM Workshop, CERN, June 2011 Rhodri Jones (CERN BE/BI)


Future systems being developed

Future Systems being Developed

OMCM Workshop, CERN, June 2011 Rhodri Jones (CERN BE/BI)


Continuous beta beat measurements

Continuous Beta Beat Measurements

  • Makes use of very high sensitivity of BBQ system

    • Test system acquired using audio acquisition module & proliant machine

    • ONLY provides PHASE information

      • No meaningful turn by turn data

  • Advantages

    • >100 times sensitivity than phase from standard turn by turn BPM data

    • Minimal excitation required (mm level at any frequency)

  • Under test in SPS & the betatron collimation region of LHC

    • Uses 3 dual plane BPMs

      • Phase-advance between consecutive BPMs of Δμ≈ 45°

      • In parallel to standard BPM system

OMCM Workshop, CERN, June 2011 Rhodri Jones (CERN BE/BI)


Continuous beta beat measurements1

Continuous Beta Beat Measurements

  • Example from the SPS

    • Quadrupole trim : 0A → +50A → -50A → 0A

    • Hysteresis observed

Courtesy R. Steinhagen

Measured oscillation data

(~10-50mm excitation)

Measured change in b

OMCM Workshop, CERN, June 2011 Rhodri Jones (CERN BE/BI)


Continuous b beat measurements lhc results

Continuous b-Beat MeasurementsLHC Results

  • Pre-cycled machine, off-resonance < 1 μm excitation

    • Excellent phase resolution

      • Reduces with energy due to constant kick strength

  • Excellent fill-to-fill reproducibility

    • about 1% provided that the machine was fully pre-cycled

Courtesy R. Steinhagen

OMCM Workshop, CERN, June 2011 Rhodri Jones (CERN BE/BI)


Lhc injection matching monitor

LHC Injection Matching Monitor

  • Turn by turn OTR monitor

    • Permanent 2D profile installation as initially hoped not feasible

      • high cost & low radiation tolerance of fast cameras

    • Developing fast 1D array readout for turn by turn profile measurements

Courtesy S. Burger

OMCM Workshop, CERN, June 2011 Rhodri Jones (CERN BE/BI)


Summary

Summary

  • LHC BPM system performing well

    • Combined with AC dipole excitation provides a very good tool for optics measurements

  • LHC Tune system

    • Excellent sensitivity allows measurement without excitation provided transverse damper is not required

    • Combined with RF frequency modulation allows measurement of both first & second order chromaticity

  • The Future

    • Continuous b-beta measurement demonstrated

      • Could be deployed in critical locations if required BUT

        • LHC fill-to-fill stability remarkable under full pre-cycle conditions

    • New LHC matching monitor being developed for injection optimisation

OMCM Workshop, CERN, June 2011 Rhodri Jones (CERN BE/BI)


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