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