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Off-momentum tail scraping for passive abort gap cleaning
(MD 444)
D. Mirarchi, R. Bruce, S. Redaelli
On behalf of the LHC Collimation Team
LHC Study Working Group , 14th July 2015
MotivationMain goals and possible gains for the machine: Study the possibility to establish a passive AG cleaning (throughout the whole cycle)
Sharing of losses between IR3 and IR7
Main experimental steps
II. Once steady conditions are achieved, the jaws is opened in one step
Lifetime of warm magnets in the two insertions
Tests were performed as End of Fill MD the 16th December 2012, at 4 TeV and 25 ns spacing: Demonstrated that similar level of AG
population obtained with active method can be achieved
Loss sharing between the two IRs can be obtained with predicted collimator settings
Measured off-momentum tail population
Measured AG re-population rate
I. IR3-TCP jaws on the negative off-momentum side closed in steps while keeping IR7-TCP still the bottleneck for particles in the bucket
Main goal of this MD: reproduce with present machine parameters such results to possibly deploy new IR3 settings
(CERN-ACC-NOTE-2014-0061, 6th LBOC in 2013)
14/07/15 LSWG, Daniele Mirarchi 2
LSWG, Daniele Mirarchi
MD request
14/07/15
• Time required: 8h (2x4h)
• Species: Protons
• Category: End of Fill MD
• Beam: Both
• Beam energies: Flat top
• Optics: Nominal
• Only changes of IR3-TCPs settings are required
• Parallel studies are not possible
• Detailed procedures and collimator settings ready
Bunch length: 1
Bunch intensity (1011 ppb): 1.1 Number of bunches: up to several trains Transverse emittance (μm): 3.75
• Beam Parameters:
Example of active/passive AG cleaning
Example of loss sharing between IR3-IR7
Improved off-momentum loss maps(MD 275)
D. Mirarchi, S. Redaelli, B. Salvachua, G. ValentinoP. Baudrenghien, M. Jaussi, H. Timko
On behalf of the LHC Collimation Teamand RF Team
LHC Study Working Group , 14th July 2015
MotivationMain goals and possible gains for the machine: Reduce at least by a factor two the number of fill needed for off-momentum LM at 6.5 TeV
Main experimental stepsI. Longitudinal blow-up induced through RF noise
II. Frequency shift adequate to evaluate beam lossin IR3-DS, but without losing the beam
III. Back to nominal frequency,and then shift on the opposite sign
Good results achieved during the commissioningusing manual method (requires presence of experts)
Smaller RF freq. shift needed than used now
Transversally wider bunches in IR3 (high dispersion)
Consistent results obtained w.r.t. std. method Java application in preparation to automatically
use gentle method in operation, without presence of experts
Main goal of the MD: final test of software developed to use gentle method in operation
η(B2)=5.5e-4 η(B1)=1.5e-3
η(B2)=5.1e-4η(B1)=1.7e-3
Standard
Gentle
LSWG, Daniele Mirarchi
MD request
14/07/15
• Time required: 12h
• Species: Protons
• Category: Normal MD
• Beam: Both
• Beam energies: Flat top
• Optics: Top energy Squeezed
• Only cavities HV and RF frequency change is required
• Parallel studies are not possible
• Detailed procedures and collimator settings ready
Bunch length: 1
Bunch intensity (1011 ppb): 1.1 Number of bunches: 3 Transverse emittance (μm): 3.75
• Beam Parameters:
Standard
Gentle
Crystal Collimation(MD 333)
D. Mirarchi, S. Redaelli, W. Scandale
On behalf of the LHC Collimation Teamand UA9 Collaboration
LHC Study Working Group , 14th July 2015
LSWG, Daniele Mirarchi 8
Motivation
14/07/15
Future LHC upgrades may demand for improved cleaning performance
Different advanced collimation concepts are under study:
• Crystal collimation represents a promising option to improve cleaning performance (factor ~10 better a top energy) and reduce impedance (less IR7 collimators in place)
Promising results have been obtained in the SPS:
Feasibility studies in the LHC itself are mandatory before relying on this approach for future upgrades
Main goals of first tests in the LHC:
2) Perform angular scan to find crystal channeling at 450 GeV. (also at 6.5 TeV if enough time)
Two crystals (H&V planes) have been installed during LS1 in the IR7 (Beam 1)
1) Verify with LHC beam if the installed hardware (crystals and goniometers) are adequate and fulfil the required specs (critical check to decide on potential upgrades at the end of 2015)
• Strong reduction of off-momentum leakage observed when in channeling w.r.t. amorphous orientation
• Piezo goniometer (LHC style) successfully tested during last MD in the SPS
3) Perform betatron loss maps with ADT for direct comparison with present system.
LSWG, Daniele Mirarchi
MD request
14/07/15 9
• Time required: 16h (or 2x8h)
• Species: Protons
• Category: Normal MD
• Beam: Beam 1
• Beam energies: Injection Flat top (if tests at inj. fast enough)
• Optics: Nominal
• Only changes of collimator settings are required
• Parallel studies could be performed in Beam 2. (Crystals installed only in Beam 1)
• Detailed procedures and collimator settings ready
Bunch length: 1
Bunch intensity (1011 ppb): 0.5 Number of bunches: several Transverse emittance (μm): 3.75
• Beam Parameters:
Standard
Crystal
Expe
cted
per
form
ance
at 6
.5 T
eV
Backup
14/07/15 LSWG, Daniele Mirarchi 10
Backup MD 333
Simulation tools fully benchmarked, and SPS data successfully reproduced:
Off-momentum leakage on 1st dispersive peak Off-momentum leakage on 2nd dispersive peak
Reductions:Measurement = 8.3 ± 2.0 Simulation = 9.1 ± 0.1
Reductions:Measurement = 18.1 ± 2.8 Simulation = 20.1 ± 1.5
14/07/15 LSWG, Daniele Mirarchi 11
14/07/15 LSWG, Daniele Mirarchi 12
Backup MD 333
Expected performance during first tests in the LHC:
Standard Crystal
CH
AM
Backup MD 333Piezo goniometer successfully tested during last MD in the SPS (7th July 2015)
Angular scan performed with angular speed of 0.5μrad/s
Average angular stability < 0.3μrad.Improvements expected after intervention
during next TS.
Beam instability
Active halo control(MD 312)
R. Bruce, S. RedaelliOn behalf of the LHC Collimation Team
LHC Study Working Group , 14th July 2015
15
MD 312: Active halo control
• Could possibly be done in parallel with crystal MD on other beam (with ADT).
• In Run 1: Seen loss spikes and beam dumps during orbit jitter, when beam is scraped on the primary collimators. Potential issue in Run II and HL-LHC. Possible mitigation: halo cleaning with hollow electron lens, under consideration for HL-LHC
• Alternatives using existing hardware: ADT excitation or tune ripple to excite the halo without perturbing the core( https://espace.cern.ch/lhc-machine-committee/
Presentations/1/lmc_197/HL_LHC_halo_RBruce.pptx )
• This MD: first investigation of feasibility at injection in “easy” conditions, increase tune spread with octupoles
• Procedure: Inject, measure halo, excite, re-measure
• To measure halo: use collimator scans (destructive) or wire scanner with high gain
– Setup time ideally needed beforehand. Working halo measurement could be very good also for other purposes / MDs
• Collimation team in collaboration with O. Bruning, B. Dehning, R. de Maria, M. Giovannozzi, M. Fitterer, W. Hofle, T. Pieloni, G. Stancari, H. Thiesen, D. Valuch