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Collimation MDs R. Bruce

on behalf of collimation team, aperture team. R. Bruce, . 2016.06.28. R. Bruce, . 2016.06.28. 1. R. Bruce, . 2016.06.28. 2. MD . 1673: Detailed IR aperture measurement for . β. *-reach (1). Motivation: aperture measurements in commissioning showed some features that are not well understood.

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Collimation MDs R. Bruce






Presentation on theme: "Collimation MDs R. Bruce"— Presentation transcript:

Slide1

Collimation MDsR. Bruce on behalf of collimation team, aperture team

R. Bruce, 2016.06.28

R. Bruce, 2016.06.28

1

Slide2

R. Bruce, 2016.06.282MD 1673: Detailed IR aperture measurement for β*-reach (1)Motivation: aperture measurements in commissioning showed some features that are not well understoodWhy large asymmetry between the aperture with two signs of the crossing angle in IR1, B1V? Why significantly better aperture in IR5 than IR1? Was the bottleneck really on Q3, or on D1 (no BLMs on D1)? Why was bottleneck found on Q3/D1, although MADX predicts Q2?Proposal: measure in detail the aperture in IR1/5, B1/2, with special bump that displaces bottleneck to Q2, with both signs of crossing. Check also separation plane aperture. Would be good to have movable BLMs on D1Goal: assess the aperture of Q2/Q3 in both IRs to understand whether anything can be done to gain apertureNote on scheduling: would be good if movable BLMs available (i.e. after TS3), but still useful withoutParticipants: R. Bruce, R. de Maria, M. Giovannozzi, S. Redaelli, collimation, BLM & aperture teams. Many are away in August – better to have it in July block

Slide3

R. Bruce, 2016.06.283MD 1673: Detailed IR aperture measurement for β*-reach (2)MD procedure:Go to 40cm with 2 nominals and train of pilots. Stay separated. Blow out nominals and save pilot orbitWould be better if we had movable BLMs installed on D1 (with BLM team - only possible with access. Wait for TS3 or longer involuntary stop)For IR1/5, B1/2, both signs of crossing:Perform standard aperture measurements, as done in commissioning, using ADT blowup + beam-based alignment of collimatorsIncrease Q3 bump in steps, with aperture measurement on each step. See whether we gain aperture and at what bump amplitude the bottleneck moves to Q2Measure also separation planes: set crossing to zero and do global measurement. Possibly introduce crossing angle bump in separation plane to probe aperture for possible future flat-beam operationRequested time: 10h

Slide4

R. Bruce, 2016.06.284MD 1690: Control of losses during off-momentum loss maps (1)Main goals and possible gains for the machine:Reduce at least by a factor two the number of fills needed for off-momentum LM at 6.5 TeV State of the art:

Feedback to stop the RF frequency trim was implemented in java last year. The feedback was too slow to stop on time the frequency trim. This year: New FESA class is being developed to improve the feedback reaction time.Parameters to stop the feedback need to be tuned (maximum BLM losses allowed, ratios of losses between DS and Collimation, etc. )Consistent results obtained w.r.t. std. method using javaη(B2)=5.5e-4η(B1)=

1.5e-3

η

(B2)

=5.1e-4

η

(B1)

=1.7e-3

Standard

Gentle

Slide5

R. Bruce, 2016.06.285MD 1690: Control of losses during off-momentum loss maps (2) Time required: 8hSpecies: ProtonsCategory: Normal MDBeam: BothBeam energies:

Flat topOptics: Top energySqueezedProcedure:The goal: tune the feedback parameters at top energy, in particular squeeze where losses at TCTs are higher (and cause dumps during the loss maps)Try several frequency trims and monitor BCT change and BLM fast data. Bunch length: 1Bunch intensity (1011 ppb): 1.1Number of bunches: 3Transverse emittance (μm): 3.75

Beam Parameters:

Gentle

Participants

:

S

. Jackson, D.

Mirarchi

, M.

Pojer

,

S

.

Redaelli

,

B

.

Salvachua

, G. Valentino, M.

Wyszynski,

collimation team

Slide6

Resonance sidebandsTune footprintsIn Run 1: Seen loss spikes and beam dumps during orbit jitter, when beam is scraped on the primary collimators. Potential issue in Run IIPossible mitigation: clean halo actively in controlled wayIdea: using de-tuning with amplitude, one could resonantly excite the halo particles without perturbing the core, using sidebands in tune spectrum excited by quadrupole current ripplesnarrow bands excited by the ADT (first tries in 2015: CERN-ACC-Note-2016-0009 )This MD: first investigation of feasibility of tune ripple at injection in “easy” conditionsFor HL-LHC: Hollow e-lens could be deployed. Need to know if same functionality could be achieved with present hardware!Review of hollow e-lens foreseen for the autumn. This MD could provide important input

R. Bruce, 2016.06.286MD 1691: Active halo control with tune ripple (1)

Slide7

R. Bruce, 2016.06.287MD 1691: Active halo control with tune ripple (2)MD procedure: as similar as possible to previous ADT halo control MDStay at injection, inject 2 nominal bunches. One is blown up with ADT to induce tailsUse warm trim quadrupoles to induce tune ripple at given frequency and amplitudeStudy effect on tail and core by losses from diamond BLMs in IR7, both during active ripple and destructive scraping, wire scanner, BSRTNeed reference scraping without ripplePerform scan in frequency and amplitude, in particular around values indicated by simulationsRequested time: 8hParticipants: R. Bruce, H. Garcia, S. Redaelli, H. Thiessen, J. Wagner, collimation team

Slide8

R. Bruce, 2016.06.288MD 1415 – resonant excitation (1)hollow electron lens for halo control considered as part of HiLumi

upgradediffusion of halo particles can be increased by pulsing the e-lens. One possible operation mode: resonant excitation = skipping every kth turn with k=2,3,4,5,…

profile

imperfections can result in residual field in center

first estimate of residual field:

12

nrad

dipole

kick

due to profile imperfections the e-lens could induce noise on the proton beam in pulsed mode :

simulation results of effect on

core

due to resonant excitation: sensitivity

to pulsing every 7

th

and 10

th

turn (octupoles +

sextupoles

), small effect for every 3

rd

,4

th

,5

th

,6

th

and 9

th

turn, no effect for every 8

th

turn

=> MD Merit

:

dependence of the emittance growth on the pulsing

pattern

(try 7

th

, 10

th

, 8

th

turn pulsing)

scaling of emittance growth and beam losses with excitation amplitude (12nrad – 120

nrad

)

effect

of transverse

damper

Review of hollow e-lens scheduled for September – this MD could provide important input

note: decrease of emittance due to losses

Slide9

R. Bruce, 2016.06.289MD 1415 – resonant excitation (2)MD participants: R.

Bruce, M. Fitterer, W. Hoefle, S. Redaelli, G. Stancari, A. Valishev, D. Valuch, J. Wagner, collimation team. OP contact person: G. PapottiSetup:

mimic excitation with ADT

(n=7,8,10),

different amplitudes for different

bunches

only one beam

-> MD can be done in parallel with other MD requiring only one beam!

Injection

, injection tunes,

non-colliding, injection settings of

chroma

and

octupoles

only one excitation at the time possible -> three different

fills

48

single bunches with

N

b

=0.7e11,

ε

N

=2.5

mum (50 bunches max possible – restrictions from ADT excitation

window

- can

only fill half of the machine

)

I

nstrumentation: BSRT, wire scanners, BLMs and diamond detectors (optional)

Machine protection: all systems at nominal settings

MD readiness: ADT not ready (ready at time of MD)

requested MD time: 1.5 h (setup) + 3*1.5 h (3 fills) = 6h

witness bunch (

1-4)

h

ighest excitation amplitude (bunch 1,2)

smallest

excitation amplitude (bunch 19,20)

24 bunches without transverse damper + 24 bunches with transverse damper