lhc emittance measurement preparation during lhc commissioning lboc meeting february 17, 2015 maria...
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LHC
Emittance Measurement Preparation
during LHC Commissioning
LBOC Meeting February 17, 2015
Maria Kuhn – February 17, 2015
LHC
M. Kuhn - 17/02/2015
MotivationGoal for LHC commissioning: operational emittance measurement tools at end of first two months with beam
− Measure optics
− Obtain optimum wire scanner working point
− Operational BSRT
− Quantify emittance growth through the LHC cycle
Motivation:
o Status quo after LS1:
− No fully trustable emittance measurements for LHC Run 1
o Problems:
− Instruments could not be fully commissioned at the start of Run 1
• Parasitic commissioning not possible, MDs not sufficient
− Instruments partially not working
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First 2 Months of LHC Commissioning
Instrument
Task Injection energy
Flattop energy
Squeezed optics
Wire scanner
Confirm BLM thresholds: find wire scan limits
~ 30 min ~ 30 min
Orbit bump calibration: validate calibration of all eight wire scanners
~ 80 min ~ 80 min
Qualify photo-multiplier saturation: find optimum wire scanner working points
~ 180 min
~ 180 min
Optics measure-
ments
K-modulation in IR4: measure b in the vicinity of the transverse profile monitors
~ 60 min ~ 60 min ~ 60 min
K-modulation in the IPs: measure b*
~ 240 min
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Need low intensity beams – very few bunchesExtra time needed to set up beams and the
machine
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Wire Scanners
o Orbit bump calibration
o Photomultiplier saturation measurements
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o Orbit bumps at injection and flattop energy
− For all 8 wire scanners
• Operational and spare LHC wire scanners
o Going from +3 mm to -3 mm in 1 mm steps
− Usually takes ~ 10 min per wire scanner and energy
~ 80 min in total per energy plateau
Wire Scanner Orbit Bump Calibration
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• Single bunches • ~ 5 - 10 bunches • Low bunch
intensity• Before: upper
wire scanner intensity limit to be checked
• BSRT in parallel if possible
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Wire Scanner Photomultiplier Saturation
o Find optimum wire scanner working point!
o Change filter and voltage of wire scanner photomultipliers
− All 8 wire scanners in parallel
− ~ 3 hour in total per energy plateau
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• Single bunches • ~ 5 - 10 bunches • Low bunch
intensity
Example photomultiplier saturation curve of a wire scanner in the Booster. Courtesy G. Sterbini
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M. Kuhn - 16/02/2015
New LHC Wire Scanner Application
Layout of the new operational wire scanner application for the LHC:
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• Wire scan limits with sublimation limits and BLM thresholds will be implemented in front end (like in 2012).
• New photomultipliers installed!
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M. Kuhn - 17/02/2015
K-Modulation
o Beta function measurements in IR4
− Turn-by-turn phase advance measurents absolutely necessary
• including optics measurements through the ramp (not possible with k-modulation)
o b* measurements!
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IP4
o Measure b at quadrupoles in IR4 at injection, flattop and with squeezed optics
o One quadrupole at a time (~ 5 – 10 min per quadrupole)
− Step or sine modulation possible
− ~ 1 hour required per beam mode
o Required beam conditions:
− Transverse damper off
− Injection tunes (less coupling)
− Only one nominal bunch or pilot beam
K-Modulation in IR4
Beam 1
MQY.5L4.B1 MQY.5R4.B1 MQY.6R4.B1 MQM.7R4.B1
Beam 2
MQY.5L4.B2 MQY.5R4.B2 MQY.6L4.B2
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o Measure b* at triplets in IP1/2/5/8 with squeezed optics
o One quadrupole at a time (~ 60 min per IP)
− Step or sine modulation possible
− ~ 4 hours in total
o Required beam conditions:
− Transverse damper off
− Only one nominal bunch or pilot beam
− Small amplitudes: with collision tunes
• Therefore, if possible, use injection tunes
− Without IR bumps in
− At 80 cm b*
K-Modulation in the IPs
Left MQXA1.L1 MQXA1.L2 MQXA1.L5 MQXA1.L8
Right MQXA1.R1 MQXA1.R2 MQXA1.R5 MQXA1.R8
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New K-Modulation Tool for the CCC
o K-modulation application
− Tune acquisition + filtering
− Enter modulation amplitude in or
− Automatic measurement – pre-defined modulation functions
− Integrated into LHC control system – pre-calculated modulation limits
− Online analysis
o Additional measurement mode: SINUSOIDAL EXCITATION − Smaller amplitude and higher
frequency than for step function
− In principle sinusoidal excitation transparent for Quench Protection System (QPS)
o Tested sinusoidal k-modulation in the SPS in November 2014
− Low energy (26 GeV)
− Tune chirp on 11
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SPS K-Modulation 12.November 2014
Screenshot of the application:
− Note: very good tune signal and response in the vertical plane!
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Planning
o Wire scanner calibration and k-modulation into LHC commissioning plan
o LHC commissioning planning: slides from Jorg‘s LMC talk (December 10, 2014)
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LHC Commissioning - Requests1. Injection – probe bunch
− 60 min dedicated k-modulation in IR4 at 450 GeV
− Optional: 30 min parasitic wire scans to confirm BLM thresholds
2. Ramp – probe bunch
− 60 min dedicated k-modulation in IR4 at 6.5 TeV
− Optional: 30 min parasitic wire scans to confirm BLM thresholds
3. Squeeze - probe bunch
− 60 min dedicated k-modulation in IR4 with squeezed optics
− 240 min dedicated k-modulation to measure b*
4. Injection – nominal bunch
− 80 min dedicated wire scanner orbit bump calibration
− 180 min (parasitic) wire scanner photomultiplier saturation studies
5. Ramp, squeeze, collide – nominal bunch
− 80 min dedicated wire scanner orbit bump calibration
− 180 min (parasitic) wire scanner photomultiplier saturation studies14
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Injection – probe bunch
Injection
Squeeze
Ramp
Collide
First turn.Capture and closed orbit.
o No bumps (Xing & separation) at this stage.
Tune, chromaticity & optics - measure & correct.RF loops, correct buckets.Basic instrumentation checks (calibrations, signal
swaps,…).Settings up of orbit and tune feedbacks.
o Systematic check of tune, chromaticity and orbit corrector circuit polarities.
flat
probe
1 hour dedicated k-modulation in IR4 needed
0.5 hours parasitic wire scans needed to confirm BLM thresholds
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Ramp – probe bunch
Injection
Squeeze
Ramp
Collide
First ramps with probe bunches, orbit and tune feedbacks ON. o Flat orbit, coarse collimators (TCP, TCDQ).
Optics measurement and correction on flat top.o On the fly optics measurements in the ramp.
Coarse collimator setup / check on flat top.o Preparation for squeeze – TCP and TCDQ.
Dump checks at different energies along ramp.
flat
probecoarse
1 hour dedicated k-modulation in IR4 at flattop energy needed
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0.5 hours parasitic wire scans needed to confirm BLM thresholds at flattop energy
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Squeeze – probe bunch
Injection
Squeeze
Ramp
Collide
Squeeze in steps to 40 cm, optics measurements, orbit & tune & Q’ corrections.
o Flat orbit, coarse collimators (TCP, TCDQ).
Repeat with optics corrections in place, measure corrected optics.
o Iterate corrections (or cycles) if required.
Local triplet apertures to asses b* reach.o Confirm measurements at injection.o At b* of 40 or 80 cm – tbd.
40 cm
flatprobe
coarse
1 hour dedicated k-modulation in IR4 with squeezed optics needed
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4 hours k-modulation to measure b*
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Injection – nominal bunch
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Injection
Squeeze
Ramp
Collide
Establish flat reference orbit for cycle.Switch on bumps (Xing and separation) and experiments magnets. Injection and transfer line fine setup.Alignment of collimators and protection devices (dump, injection).Aperture measurements (global, local: triplets, injection, dump).Beam instrumentation checkout.RF and ADT set up. FIDEL measurements and corrections.And much more.
bumps
nominaltight
80 min dedicated wire scanner orbit bump calibration + 3 hours (parasitic) wire scanner photomultiplier saturation studies
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RSC – nominal bunch
Injection
Squeeze
Ramp
Collide
Ramp nominal bunch with longitudinal blowup.
Collimator setup (IR7+3) on flat top.Ramp and squeeze to 80 cm with bumps
(Xing & separation).o Align TCTs: FT, end of squeeze.
Collide - find collisions (if not already done).
o Align TCTs and TCLs, possibly also roman pots.
80 cm
bumps
bumps bumps
nominaltight
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80 min dedicated wire scanner orbit bump calibration + 3 hours (parasitic) wire scanner photomultiplier saturation studies at flattop energy
Measure cycles with wire scanner and BSRT (parasitic)
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Emittance Measurements
o Injection
o Ramp
o Flattop
o Squeeze
o Collisions
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After LHC Cycle Setupo Requirement: BSRT has to be commissioned early on as well!
o Measurements with few bunches during many ramps
− Mainly with wire scanners and BSRT
o Measurements with few bunches during the entire cycle including collisions
− Mainly with wire scanners and BSRT
− (BGI not possible for protons, BGV only later in 2015)
− Comparison with emittance from luminosity if applicable
o Comparison of transverse profile measurements during Van der Meer scans at the end of LHC commissioning phase
− With wire scanners, BRST and LHCb SMOG
− Comparison with emittance from luminosity
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Not possible! Beam intensity
too high.
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2015 Q2o From Mike‘s LMC talk (Jan 28, 215)
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Use the first week of collisions to compare emittances from wire scans and BSRT to emittances from luminosity and LHCb SMOG data during stable beams!
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Stable beams
M. Kuhn - 17/02/2015
Injection
Squeeze
Ramp
Collide
First stable beams with few bunches.
80 cm
bumps
bumps bumps
bumps
STABLE BEAMS
nominaltight
Squeeze + collide part to be repeated for medium b* (20-40 m).
Measure parasitically with wire scanners and BSRT. Close LHCb Velo and measure with SMOG in parallel!
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Planning First Week of Collisions
o Tentative dates: week 21 (May 18 – 22, 2015)
o Wire scan limit at 6.5 TeV: ~ 10 bunches per beam!
o ATLAS/CMS luminosity not calibrated before Van der Meer scans, but could be analysed later
− Need colliding bunches
o For LHCb SMOG the Velo needs to be closed
− Need stable beams declared
− Minimum 1 colliding bunch per beam
− At least 6 non colliding bunches for meaningful measurement
• Could collide in ATLAS/CMS to obtain emittance from lumi in parallel
− Minimum stable beams time ~ 1 hour
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Emittance Measurements Run 2o During LHC Run 1 it was possible
to measure bunch-by-bunch emittances of the first 144 bunch batch at injection of physics fills
− Can be compared to emittanc from peak luminosity
− Important for evolution of growth through the year
o Considerations for emittance measurements during LHC Run 2
− Injection scans
• Problem: wire scans not possible with 288 bunches!
− Question: start of filling scheme with 144 bunches possible?
• To be able to measure emittances at injection of physics fills
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SummaryDuring LHC commissioning we want to:
1. Measure beta functions
2. Fully calibrate wire scanners and BSRTs
3. Quantify transverse emittance growth during the LHC cycle
− Including injection, ramp, squeeze, and collisions
Due to time constraints and high beam current we will not have the possibility to complete these measurements during the run!
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Thanks for your attention!
Questions? Comments?
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Spare Slides
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K-Modulation Overview
Set Up60 min
Injection10
min
K-mod
IR460
min
Prepare + ram
p30
min
K-mod
IR460 min
Squeeze 30
min
K-mod
IR4 + IPs300 min
450 GeV injection energy
6.5 TeV collision energy
• Single bunches • One or two nominal
bunches• Transverse damper off• Injection tunes
In total ~ 10 hours measurememt time
Optional dump + re-inject
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M. Kuhn - 17/02/2015
Wire Scanner Calibration Overview
Set Up30 min
Injection10 min
Orbit bumps
80 min
PM saturation60 min
Prepare + ramp30 min
Orbit bumps
80 min
PM saturation60 min
Squeeze + collide60 min
450 GeV injection energy
6.5 TeV collision energy
optional
• Single bunches • ~ 5 - 10 bunches • Low bunch intensity• Upper wire scanner
intensity limit to be checked
In total ~ 6 – 8 hours measurememt time
Optional dump + re-inject
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LHC
M. Kuhn - 03/12/2014
First Measurements in the SPSo Requirements
− Relatively long magnetic plateau (10 s or more)
− Low energy (26 GeV)
− Good tune signal (turn on chirp)
o Note: SPS magnets are conventional (room-temperature) electromagnets
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o Testing sinusoidal k-modulation:
− Modulation to quadrupole directly at power converter
− Power converter parameters: number of periods, amplitude, frequency
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SPS Tune Signalo Easily detectable tune peak in the vertical plane
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K-Modulation Analysis (1)o Unfortunately power converter data was not saved correctly
o Repeated measurement on 13 November 2014
− Caveat: tune acquisition not during entire cycle
o Reminder:
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𝜷𝒙 ,𝒚 ≈𝟒𝝅∆𝑸 𝒙 ,𝒚
𝒍 ∙∆𝒌
Window for fitting: discard half cosine at start and end of modulation.
Fit both curves with sine to get amplitude :
with offset and phase
Example:
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o and obtained from fit to sinusoidal modulation
o from transfer function
− For now neglecting absolute transfer fct error and transfer fct error fromhysteresis effects
K-Modulation Analysis (2)
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Vertical beta function:
0.4 % uncertainty from fit
Nominal:
First tests of sinusoidal k-modulation were successful - proof of principle.
To do: implement analysis in the application! Work in progress: further tests in the SPS and the LHC will follow.
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M. Kuhn - 03/12/2014
Measurement Precision Comparison
o Comparison of b function measurement accuracy:
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Accelerator b uncertainty Method Year
Tevatron 10 % BPM phase advance
1995
LEP ~ 1% K-modulation 2001
SPS ~ 5 - 10 % BPM phase advance
2012
LHC IP1/5 3 – 5 % K-modulation 2011
LHC wire scanner
1.3 – 10.9 % K-modulation 2012
LHC wire scanner
0.7 – 9.4 % BPM phase advance
2012
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LHC Inner Triplet – b* Measurement
MQXA3MQXB2
MQXB2MQXA1
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IP1/5
Q3 Q1Q2
𝑰𝑸𝟏= 𝑰𝑹𝑸𝑿+𝑰 𝑹𝑻𝑸𝑿 𝟏
𝑰𝑸𝟐= 𝑰𝑹𝑸𝑿+𝑰 𝑹𝑻𝑸𝑿 𝟐
𝑰𝑸𝟑= 𝑰𝑹𝑸𝑿
Modulation of quadrupole Q1 with power converter RTQX1
Nested circuits!
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First Step Modulation in the LHCo Power converter in simulation, no beam
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First Sinusoidal Modulation in the LHC
o Power converter in simulation, no beam
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First Sinusoidal Modulation of the LHC Triplets
o Power converter in simulation, no beam
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Quench Protection System (QPS)
o Quench detector output while the power converter of the corresponding circuit performs a sinusoidal current modulation:
− sinusoidal current of 15 A amplitude and a frequency of 0.25 Hz resulting in a maximum dI/dt of about 24 A/s
− maximum inductance of 21 mH per coil 250 mV sinusoidal voltage
o The common mode caused by sinusoidal excitation is well suppressed: For QPS the sinusoidal excitation will be transparent!
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J. Steckert
The green line is the voltage difference between the compared coils in the magnet which are used to detect a quench.