lhc beam instrumentation & future developments
DESCRIPTION
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 - PowerPoint PPT PresentationTRANSCRIPT
LHC Beam Instrumentation&
Future DevelopmentsWorkshop on Optics Measurements, Corrections and Modeling for High-
Performance Storage Rings
21st June 2011, CERN
Rhodri Jones(CERN Beam Instrumentation Group)
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
Outline
OMCM Workshop, CERN, June 2011 Rhodri Jones (CERN BE/BI)
LHC Beam Position Monitors
912 Button Electrode BPMs (24mm)for theMain Arcs & Dispersion Suppressors
24 Directional Couplers52 Enlarged Button& 8 Trigger BPMsInteraction Regions
54 Special BPMs for Tune & Chromaticity,Transverse Damper & RF, Beam DumpInjection Lines: 100 Warm, Button BPMs
(Buttons Recuperated from LEP)36 WarmBPMs -34mm ButtonElectrodes
A total of 1182 BPMsfor the LHC and its Transfer Lines)
OMCM Workshop, CERN, June 2011 Rhodri Jones (CERN BE/BI)
● 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)
LHC BPM System Performance I
OMCM Workshop, CERN, June 2011 Rhodri Jones (CERN BE/BI)
Horizontal kick
Vertical kick
Horizontal kick
Vertical kick
● 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
LHC BPM System Performance IITi
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Horizontal Vertical
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Horizontal Vertical
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OMCM Workshop, CERN, June 2011 Rhodri Jones (CERN BE/BI)
● 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
LHC BPM System Performance III
OMCM Workshop, CERN, June 2011 Rhodri Jones (CERN BE/BI)Courtesy E. Calvo
● 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)
LHC BPM System Performance IV
OMCM Workshop, CERN, June 2011 Rhodri Jones (CERN BE/BI)
-1000
-800
-600
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0
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1E+08 1E+09 1E+10 1E+11
Bunch Intensity (protons)
LHC
Arc
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M E
rror
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Linearity (Lab)Noise (Lab)Arc BPM Trigger Rate
PilotHigh sensitivity
Controlling Tune & Chromaticity using theBase Band Q Measurement (BBQ) System
OMCM Workshop, CERN, June 2011 Rhodri Jones (CERN BE/BI)
Direct Diode Detection (3D)
Base band operationExcellent 24 bit audio ADCs availableSignal conditioning / processing is easy
Courtesy M. Gasior
● 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
LHC Tune System Performance
OMCM Workshop, CERN, June 2011 Rhodri Jones (CERN BE/BI)
● Issues● Cohabitation with transverse damper (ADT)
● Raises noise floor by 30dB● Aggressive damping leads to very broad tune peak
● 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
Tune Feedback in the LHC
OMCM Workshop, CERN, June 2011 Rhodri Jones (CERN BE/BI)
Hor. spectrum with Tune-FB OFF Hor spectrum with Tune-FB ON
The'hump'
● 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)
Chromaticity Measurement in the LHC
OMCM Workshop, CERN, June 2011 Rhodri Jones (CERN BE/BI)
Q (dotted) and Q' (solid) during snap-back
horizontalvertical
Courtesy R. Steinhagen
● Recent Measurement of Q’’ with and without octupoles at injection
Using the LHC Tune System
OMCM Workshop, CERN, June 2011 Rhodri Jones (CERN BE/BI)
Octupoles on Octupoles off
Future Systems being Developed
OMCM Workshop, CERN, June 2011 Rhodri Jones (CERN BE/BI)
● 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
Continuous Beta Beat Measurements
OMCM Workshop, CERN, June 2011 Rhodri Jones (CERN BE/BI)
● Example from the SPS● Quadrupole trim : 0A → +50A → -50A → 0A● Hysteresis observed
Continuous Beta Beat Measurements
OMCM Workshop, CERN, June 2011 Rhodri Jones (CERN BE/BI)
Measured oscillation data(~10-50mm excitation)
Measured change in b
Courtesy R. Steinhagen
● 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
Continuous b-Beat MeasurementsLHC Results
OMCM Workshop, CERN, June 2011 Rhodri Jones (CERN BE/BI)Courtesy R. Steinhagen
● 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
LHC Injection Matching Monitor
OMCM Workshop, CERN, June 2011 Rhodri Jones (CERN BE/BI)Courtesy S. Burger
● 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
Summary
OMCM Workshop, CERN, June 2011 Rhodri Jones (CERN BE/BI)