Observation of channeling for 6500 GeV/c protons in the crystal assisted collimation setup for LHC

Contents lists available atScienceDirect

Physics

Letters

B

www.elsevier.com/locate/physletb

Observation

of

channeling

for

6500 GeV/c protons

in

the

crystal

assisted

collimation

setup

for

LHC

W. Scandale

a

,

b

,

e

,

G. Arduini

a

,

M. Butcher

a

,

F. Cerutti

a

,

M. Garattini

a

,

S. Gilardoni

a

,

A. Lechner

a

,

R. Losito

a

,

A. Masi

a

,

D. Mirarchi

a

,

S. Montesano

a

,

S. Redaelli

a

,

R. Rossi

a

,

e

,

P. Schoofs

a

,

G. Smirnov

a

,

e

,

G. Valentino

a

,

D. Breton

b

,

L. Burmistrov

b

,

V. Chaumat

b

,

S. Dubos

b

,

J. Maalmi

b

,

V. Puill

b

,

A. Stocchi

b

,

E. Bagli

c

,

L. Bandiera

c

,

G. Germogli

c

,

V. Guidi

c

,

A. Mazzolari

c

,

S. Dabagov

d

,

F. Murtas

d

,

F. Addesa

e

,

G. Cavoto

e

,

F. Iacoangeli

e

,

L. Ludovici

e

,

R. Santacesaria

e

,

P. Valente

e

,

F. Galluccio

f

,

A.G. Afonin

g

,

Yu.A. Chesnokov

g

,

A.A. Durum

g

,

V.A. Maisheev

g

,

Yu.E. Sandomirskiy

g

,

A.A. Yanovich

g

,

A.D. Kovalenko

h

,

A.M. Taratin

h

,

∗

,

A.S. Denisov

i

,

Yu.A. Gavrikov

i

,

Yu.M. Ivanov

i

,

L.P. Lapina

i

,

L.G. Malyarenko

i

,

V.V. Skorobogatov

i

,

T. James

j

,

G. Hall

j

,

M. Pesaresi

j

,

M. Raymond

j

a_{CERN, European Organization for Nuclear Research, CH-1211 Geneva 23, Switzerland} b_{Laboratoire de l’Accelerateur Lineaire (LAL), Universite Paris Sud Orsay, Orsay, France}

c_{INFN Sezione di Ferrara and Dipartimento di Fisica e Scienze della Terra, Università di Ferrara, Via Saragat 1 Blocco C, 44121 Ferrara, Italy} d_{INFN LNF, Via E. Fermi, 40 00044 Frascati (Roma), Italy}

e_{INFN Sezione di Roma, Piazzale Aldo Moro 2, 00185 Rome, Italy} f_{INFN Sezione di Napoli, Italy}

g_{Institute for High Energy Physics in National Research Centre “Kurchatov Institute”, 142281, Protvino, Russia} h_{Joint Institute for Nuclear Research, Joliot-Curie 6, 141980, Dubna, Russia}

i_{Petersburg Nuclear Physics Institute in National Research Centre “Kurchatov Institute”, 188300, Gatchina, Russia} j_{Imperial College, London, United Kingdom}

a

r

t

i

c

l

e

i

n

f

o

a

b

s

t

r

a

c

t

Article history: Received29March2016

Receivedinrevisedform29April2016 Accepted2May2016

Availableonline6May2016 Editor:L.Rolandi Keywords: Accelerator Beamcollimation Crystal Channeling

Twohigh-accuracygoniometersequippedwithtwobentsiliconcrystalswereinstalledinthebetatron cleaninginsertionoftheCERNLargeHadronCollider(LHC)duringitslongshutdown.Firstbeamtests wererecentlyperformedattheLHCwith450 GeV/c and6500 GeV/c storedprotonbeamstoinvestigate the feasibility of beam halo collimation assisted by bent crystals. For the first time channeling of 6500 GeV/c protonswas observed inaparticleaccelerator.Astrong reductionofbeamlosses dueto nuclearinelastic interactionsinthealignedcrystalincomparisonwithitsamorphous orientationwas detected.Thelossreductionvaluewasabout24.Thus,theresultsshowthatdeflectionofparticlesbya bentcrystalduetochannelingiseffectiveforthisrecordparticleenergy.

©2016TheAuthors.PublishedbyElsevierB.V.ThisisanopenaccessarticleundertheCCBYlicense (http://creativecommons.org/licenses/by/4.0/).FundedbySCOAP3_.

1. Introduction

In the Large Hadron Collider (LHC), a multi-stage collimation systemisusedto absorbagrowing haloofthe circulatingbeams and to ensure a reliable operation below quench limits of su-perconducting magnets [1]. LHC primary collimators made from Carbon FibreComposites(CFC) deflect halo particles by Coulomb

*

Correspondingauthor.

E-mail address:alexander.taratin@cern.ch(A.M. Taratin).

scattering,thusincreasingtheirimpactparameterswithsecondary collimators.Proton interactions withthe collimator material gen-eratediffractiveprotons thatmayleakout ofthecollimatorsand be lostincoldmagnets,limitingthecleaning performance ofthe presentcollimationsystem.Abentcrystalusedinsteadofprimary amorphouscollimatorsdeflectsmostparticles by meansof chan-neling,directing themfarfromthesecondary collimatoredge.As a result the leakage of diffractive protons from both collimators shouldbestronglyreduced,thusthecollimationefficiencyshould beincreased.

http://dx.doi.org/10.1016/j.physletb.2016.05.004

0370-2693/©2016TheAuthors.PublishedbyElsevierB.V.ThisisanopenaccessarticleundertheCCBYlicense(http://creativecommons.org/licenses/by/4.0/).Fundedby SCOAP3_.

Experiments on the beam halo collimation with short bent crystals have been performed at the IHEP synchrotron [2], RHIC

[3]andTevatron

[4]

.In thelast case, thebackground intheCDF experimentwasreducedbyafactoroftwobyusingacrystalasa primary collimator.Acrystalassisted collimationschemeforLHC wasunderstudyin

[5,6]

.

TheexperimentUA9studyingcrystalassistedcollimationatthe

CERN Super Proton Synchrotron (SPS) [7–11] showed strong

re-ductionofthecollimationleakagewhenthecrystaldeflectorisin channelingconditions

[11]

.Perfectalignmentofthecrystaltohave deflectionofhaloparticlesduetochannelingwasalwaysobtained quicklyby usinginformationfromthebeamloss monitors(BLM) installeddownstreamofthecrystal.Channeledparticleswithsmall oscillationamplitudes inthe crystalplanar channelsdonot have closecollisions withthe nuclei inthe crystal, and, consequently, donotexperiencenuclearinteractions.Therefore,thebeamlosses inthe aligned crystalare strongly decreased incomparison with thecaseofitsamorphousorientation.

The SPS experiments were performed with stored beams of

protons andPb ions with120 GeV/c and 270 GeV/c momentum

per charge. The collimation leakage was measured by the beam

lossmonitorinstalledinthefirsthighdispersion(HD)area down-streamofthecollimator–absorber,whereoff-momentumparticles havethefirstpossibilitytohitthebeampipeafterinteractingwith thecrystalandtheabsorber.Withthecrystalperfectlyaligned,the rateofthebeamlossmonitorswasreducedbyatleastanorderof magnitude

[11]

.

Twopiezoelectricgoniometersequippedwithbentsilicon crys-talswererecentlyinstalledintheRing1oftheLHCinitsbetatron cleaning insertion,IR7. Inthisletter theresultsof thefirst beam testswithbentcrystalsattheLHCarepresented.Channelingwas observed with proton beams at injection and collision energies.

This observation opensnew roads for high-energy beam

manip-ulationinhadroncolliders. 2. Theexperimentdescription

Aparticlecanbecapturedintothechannelingregimeifthe an-glebetweenitsmomentump (velocityv)andthecrystalplanesis smallerthanthecriticalangle

θ

c

= (

2Uo

/

pv

)

1/2,whereUo isthe

welldepthofthecrystalpotentialaveragedalongtheplanes

[12]

. Forthe(110)planar channelsofa siliconcrystalata room tem-perature,Uo

=

22.7 eV andfor6500 GeV/c protons

θ

c

=

2.6 μrad.

TheMoliereapproachfortheatomicpotentialisusedhereandin our simulations of the crystal assisted collimation presented be-low.Thisimposeschallengingrequirementstotheangularcontrol ofthecrystalsthathastobeinthesub-microradianangular reso-lutionrange.

Thepresentsetupforstudyingcrystalassistedcollimationwas designedwithaminimumimpactontheLHCcollimationsystem. Layout and the crystal parameters were chosen such that exist-ingsecondary collimatorscanbe usedtointerceptthechanneled beams

[13]

.Twopiezo-goniometers withbent siliconcrystals for horizontalandverticalcollimationoftheLHCbeamhavebeen in-stalled according to the recommendations [13] in Ring 1 of the betatroncleaninginsertionoftheLHCduringitslongshutdownin 2014. Goniometerswhich satisfiedthehighrequirements of sub-microradianangularresolutionweredeveloped

[14]

.Somerelevant goniometerparametersarepresentedin

Table 1

.Animportant fea-tureofthegoniometerdesignisitscompletetransparencyforthe normalLHCoperations. Thisisensured by amovablesegment of the beampipe that masks the crystaland the goniometer itself. It is remotely retracted only during the special collimationtests, toallow thecrystalinsertion. Thegoniometerswere mountedon

Table 1

Relevantgoniometerparameters. Angularrange (mrad) Angularresolution (μrad) Linearrange (mm) Linearresolution (μm) 10 0.1 40 5 Table 2

ParametersoftheSTcrystalafteritsproduction. Length (mm) Bendangleα (μrad) Torsion (μrad/mm) Miscutangleθm (μrad) 4.1 52 <1 6

standardcollimationsupportsusingthesamefastplug-in technol-ogy,whichensuresfasthandlingoftheobjectinthetunnel.

The value of the crystal bend angle was chosen for reasons

of obtaining the maximal impact parameters of deflected halo

particles with the collimator–absorbers while ensuring that the

deflected halo should remain at a safe distance from the beam

pipe [13]. The bend angle of the crystal for the LHC beam col-limation was selected to be

α

=

50 μrad from these considera-tions.Thisbendanglevalue

α

canberealizedwithdifferent crys-tal length L and consequently with different bend radius R

,

L

=

α

R.However, thebendradiusshould beconsiderablylarger than the critical one [15] Rc

=

pv

/

e Emax, where Emax is the maximal

strength oftheplanar electricfield. Forprotonswith6500 GeV/c

momentum, Rc

=

11 m in the (110)silicon channels. The

chan-neling efficiency of protons for the crystal with a given bend

angle

α

, considering the possibility of their multiple passages through thecrystal, ismaximal when itsbendradius R is inthe interval

(3

÷

10)Rc.The length ofthe LHC crystalswas chosen to

be L

=

4 mm,thatistheirbendradius R

=

80 m

≈

7Rc.

Twodifferentmethodsforthecrystalbendingwereused.A sil-iconstrip(ST)crystalbentalongthe(110)planesduetoanticlastic deformation

[16,17]

wasinstalledfortheLHCbeamcollimationin thehorizontaldirection.AQMcrystalbentalongthe(111)planes dueto thequasi-mosaiceffect

[18]

was installedforthe collima-tionintheverticalplane.Thebendingdevicesofboththecrystals

were made from titanium to reduce possible electron emission

from them when the LHC proton bunches pass the azimuths of

theirlocation.

Table 2

reportsthemainparametersfortheST crys-tal atthemanufacturingstage. Thestudiesdescribed belowshow thatthebendangleoftheSTcrystalincreasedto65 μrad in com-parison withits designvalue.Thisissue,now understood,willbe discussedinaseparatepublication.

Fig. 1showsthehorizontalprojectionofthetrajectoryofahalo particledeflectedbythestripcrystalduetochannelingatthebend angle

α

=

65 μrad (solid line): (a) for the beam injection with

450 GeV/c,(b)forthemaximummomentum6500 GeV/c.Adashed

lineshowsthebeamenvelopeat5.4

σ

x.Thisvalue correspondsto

the operational positionof thecrystals in themeasurements de-scribedbelow.CollimatorsoftheLHCmulti-stagecleaningsystem have horizontal, vertical and skew (45◦) orientations. The verti-cal lines show the longitudinal positions of primary collimators (TCP)andsecondarycollimatorsmadefromCFC(TCSG)aswellas theshower-absorbercollimatorsmadefromatungstenheavyalloy (TCLA). All horizontal and skew collimators are shown in Fig. 1. However, informationis presented below only forthe horizontal collimators behind the crystal, whichare relevantfor our exper-iment. Few collimators instead of a larger one are used because

the beam energy absorption should be allocated between them

to reduce their heating. TCSG andTCLA collimators were placed at about7

σ

x and 10

σ

x,respectively, in theinjection caseandat

about8

σ

x and14

σ

x,respectively,inthetopmomentumcase.The

mea-Fig. 1. (Coloronline.) Thehorizontalprojectionofthetrajectoryofahaloparticle deflectedbythecrystalduetochannelingatthebendangleα=65 μrad (solidline uptothefirsthorizontalTCSG1andthenbydot-dashedlinetoshowthetrajectory propagationinthecasewithoutthecollimators):(a)forthebeaminjectionwith 450 GeV/c,(b)forthe maximummomentumof6500 GeV/c. Dashedlinesshow thebeamenvelopeforthecrystaldistancefromtheorbit.Verticallinesshowthe positionsofthecollimatorsTCSGandTCLAandtheprimarycollimatorsTCP(they arenotvisiblefortheinjectioncasebecausetheywereshiftedfarfromtheorbit forthemeasurements).ThepositionsofBLM1andBLM2formeasuringthelosses inthecrystalandinthefirsthorizontalTCSG1behindthecrystal,respectively,are shownschematically.

Table 3

Relevantacceleratorparameters.

Parameter BC TCSG1 TCSG2 TCLA1 TCLA2 TCLA3 βx(m) 342.98 141.22 338.96 161.71 66.20 64.12

σx(mm) 0.416 0.267 0.414 0.286 0.183 0.180

xim(mm) 3.2 16 8 2.5 −0.2

μxfrom BC (2π) 0 0.0443 0.3166 0.3425 0.3979 0.4456

suringthe lossesin thecrystal andin thefirst horizontalTCSG1

downstreamthecrystal,respectively,arealsoshown.Therelevant acceleratorparametersattheazimuthsofthecrystalandthe hor-izontalcollimatorsbehindthecrystalare listedin

Table 3

,where

β

x isthehorizontalbeta-function,

σx

istheRMSvalueofthe

hor-izontalbeamsize (forthe beamof6500 GeV/c protons withthe RMSnormalizedemittance

ε

∗

=

3.5 μm rad),ximistheimpact

pa-rameterwiththecollimatorsforaparticledeflectedbythecrystal with65 μrad, and



μ

x is thehorizontalphase advance between

thecrystal andcollimators,TCSG1 andTCSG2 are two horizontal

collimatorsbehindthecrystal.

Table 4

CollimatorpositionsinunitsofRMSbeamsize.

Nominal Crystal MD

Injection (σx) Flat top (σx) Injection (σx) Flat top (σx)

TCP 5.7 5.5 out 8.0

TCSG 6.7 8.0 6.7* _8.0

TCLA 10 14 10 14

CRY out out 5.4 5.4

* _{TCSGsupstreamofthecrystalareinoutpositions.}

Fig. 2. (Coloronline.) ThedependenceofthebeamlossesobservedwiththeBLM1 downstreamofthecrystal(curve1)fortheinjectioncasewith450GeV/c protons. Curve2showsthedependenceofthenumberofinelasticnuclearinteractionsof protonsinthecrystalonitsorientationangleobtainedbysimulation.

3. Experimentalresults

Asinglebunchwith1011_{protonswas injectedinourfirstrun}

on the LHC collimation studies withbent crystals. At the begin-ningallcollimatorsofIR7wereplacedattheir standardinjection settings: the primary collimators (TCPs) at 5.7

σ

x, the secondary

collimators (TCSGs) at 6.7

σ

x and the absorbers (TCLAs) at 10

σ

x.

The crystalwasalignedprecisely tothe circulating beamandset attheTCPopening.Thenthecrystalwasmovedby0.5mm(about 0.3

σ

x) towards the beam orbit to become the primary

collima-tor.Inthispositionangularscanswiththecrystalwereperformed withthecollimatorssettingslistedinTable 4.Asmentionedabove, well-channeled particles do not experience nuclear interactions, therefore thechanneling orientation ofthe crystalmaybe found through the beam loss reduction in the crystal. This loss

reduc-tion was indeedobserved with the BLM downstream the crystal

– BLM1. Three angular scanswere made andin all ofthem the

crystal orientation for channelingwas aboutthe same. Twofirst scanswere made withagoniometer rotation speed of0.5 μrad/s when all collimatorsupstream the crystalwere intheir standard injectionpositions.Onescanwasperformedwith1 μrad/s rotation speedwhenallcollimatorsupstreamofthecrystalwereretracted. Forthelast case,curve 1inFig. 2showstheobserved depen-denceoftheBLM1count ontheangularpositionofthecrystalat

450 GeV/c.Thedot-dashed lineshowsthelosslevelforthe crys-tal orientations far from alignment with the (110) planes,when

it works as an amorphous substance (“amorphous” orientation).

Thelossesarenormalizedtothebeamfluxandthelossvaluefor theamorphousorientation.Curve2showsthenumberofinelastic nuclear interactionsofprotons inthe crystalasa functionofthe crystalorientation angleobtainedbysimulations.Theyweredone withthetoolsdescribedin

[19]

byaddingalsotheinteractionwith

Fig. 3. (Coloronline.) ThedependenceoftheBLM2signalonthehorizontalposition ofthefirstTCSG1behindthecrystalduringitsscanfromthebeamperiphery to-wardstheorbit( X=0)isshownbydot-dashedline.Thecrystalangularposition wasfixedtobeintheoptimalconditionsforchanneling.Theerrorfunctionfitis shownbythesolidline.

other collimatorsrelevantfor theexperimental setup,takinginto accountionizationlosses,multipleCoulombscatteringandnuclear interactions.

The deep minimum on the right corresponds to the optimal

orientation for channeling. There is a wide area of a beam loss

reduction on the left of the minimum, which is due to volume

reflections(VR)ofhaloparticlesinthecrystal. Thisreduction oc-cursbecause theparticles perform asmaller numberofpassages throughthecrystaltoreachtheTCSGaperturethanforamorphous orientationsofthe crystal. Agreementofthe simulationwiththe experimentissufficientlygood.Somediscrepanciesneartheedges

of the beam loss dependence are not yet well understood and

will be investigatedin newmeasurements. The lossreduction in channelingis47.3 and 50.7fromtheexperimentandsimulation, respectively. The loss reduction values in the VR region are also veryclose.

The first horizontal collimator TCSG1 behind the crystal was

usedtoscanhorizontalpositionsacrossthebeamdeflectedbythe crystalwhenitsangularpositionwasfixedclosetothebeamloss

minimumdetectedintheangularscan. TheBLM2 downstream of

thecollimator registered secondaryparticles generatedby inelas-ticnuclear interactions ofprotons inthe collimator.Fig. 3 shows thedependenceofthe BLM2 signalon thecollimator positionby

adot-dashedline.TheBLM2 signalincreaseswhenthecollimator,

moving from X1

=

9 mm up to X2

=

7 mm,interceptsthe beam

halo deflected in channeling states by the crystal. The observed profileisconsistentwiththepresenceofawell-definedchanneled haloseparatedfromthebeamcorebyadistancethatcanbe deter-minedwithoptical transportbetweenthetwolocationsafterthe angularkickofthecrystalbendanglevalue.The lossdependence givestheintegralofthedeflectedbeamdistribution.Thesolidline in

Fig. 3

showsafitofthedependencewithanerrorfunction.The fitcenter isat xm

=

7.9 mm.An error functionis the integral of

a Gaussian therefore xm is the center ofthe Gaussian which fits

thedeflectedbeamdistribution.Thedetected displacement xm of

thedeflectedbeamhalofromthebeamenvelopeatthecollimator location determines the angularkick produced by the crystalfor channeledparticles,

θ

m

=

65 μrad. Thisdeflectionshouldbeequal

tothebendcrystalangleifthecrystalplanesatitsentrancewere reallyparalleltothebeamenvelopeforthecollimatorscan.

The beamtestwith bentcrystalsfor 6500 GeV/c protonswas performedin the next run. In thiscase, 16bunches of 109

pro-Fig. 4. (Coloronline.) ThedependenceofthebeamlossesobservedwiththeBLM1 downstreamofthecrystal(curve1)fortheLHCcoastingbeamof6500 GeV/c pro-tons.Curves2(solidline)and3(dottedline)showsthedependenceofthenumber ofinelasticnuclearinteractionsofprotonsinthecrystalonitsorientationangle obtainedbysimulationaccordingto[19]and[13],respectively.

tons,evenlyspacedaroundthering,wereinjectedandaccelerated to 6500 GeV/c. The collimators were in their nominal positions for these conditions, as in Table 4, the primaries at 5.5

σ

x, the

secondary collimators at 8

σ

x and absorbers at 14

σ

x. The crystal

wasalignedwithrespecttotheprimarycollimatorsandthenwas

moved toward the orbitby about0.05 mm to interceptthe

pri-maryhalo.The angularscan wasperformedwiththegoniometer rotationspeedof0.2 μrad/s andwithcollimatorsettingsshownin

Table 4.Individualbuncheswereexcitedoneatatimetoincrease beamlossesduringthemeasurements.Curve1in

Fig. 4

showsthe dependenceoftheBLM1countontheangularpositionofthe

crys-tal.Channelingwasclearlyobserved.Itisclearlyseenthattheloss reduction“well”intheregionofchannelingandvolumereflection hassteeperwallsthanwhatwasobservedat450 GeV/c.Thismay be explainedby a strongreduction of multiple Coulomb scatter-ingathigherenergy;theresultsshowthataparticlecannotcome to thechannelingregionwhenits incidentanglewiththecrystal planesislargerthan10 μrad.

Thechannelingminimumontherightisnarrowerbecausethe criticalchannelingangleisabout4timessmallerthanatinjection energy. Theloss reduction inchannelingisabout24. Thesecond minimum on the left in the VR region is clearly seen here. This minimum was alsoobserved in ourstudies withbent crystalsat the SPS. The minimum is atan angulardistance from the chan-neling orientation about equal to the bendangle value, 65 μrad. In thiscase, thewhole VR regionis onthe sameside relative to thebeamenvelopedirection.Therefore,angularkicksduetoVR al-waysincreasetheoscillationamplitudesofparticlesandtheymore quicklyreachthesecondarycollimators.Curve2showsthe depen-denceofthenumberofinelasticnuclearinteractionsonthecrystal orientation obtained by simulation according to [19]. The agree-ment withthe experimentis goodenough. The wallsofthe loss reduction dependencecoincide well withthe experimental ones. Thismeansthatthecrystalbendanglemeasuredbythecollimator scanisright(theangularcrystalpositionforthisscanwaschosen closetotheperfectoneforchanneling).ThelossreductionforVR regionisthesameasintheexperiment.However,theloss reduc-tionvalueforchanneling, R

=

187,isconsiderablylargerthanthe experimental one.This differencemaybe explainedby the resid-ual angular instabilities of thegoniometer. Multi-turn simulation withaSixTrackcode,includingothercollimatorsinallring

inser-tions and a detailed beamaperture model [13], gives also good agreementwiththeangularscandata(curve3),althoughtheloss reductionvalue, R

=

140,isalsolargerthantheexperimentalone. Similarmeasurements performedwiththe QMcrystal forthe LHCproton beamcollimationin the vertical plane and measure-ments withthe stored beam ofPb ions for the injectionenergy alsoshowedastrongbeamlossreductioninthe alignedcrystals. Detailedresultswillbereportedinafuturepublication.

4. Conclusions

First experiments on the study of the LHC beam halo colli-mation assisted by bent crystals were successfully performed in machinestudies duringthe LHCrun II,atthe injectionenergyof 450 GeVaswellasattherecordprotonbeamenergyof6500 GeV. Beam losses due to inelastic nuclear interactions of particles in thealignedcrystalwerestronglyreducedincomparisonwiththe amorphouscrystalorientations.Thisprovesthatdeflectionof par-ticlesduetochannelinginabentcrystaliseffectiveatthisrecord particleenergy.Itwillbevery importantto compareleakage val-uesforthecrystalassistedandstandardcollimationsinourfuture measurementsattheLHC.

Acknowledgements

Wewish toacknowledge thestrong supportofthe CERNLHC

CollimationProjectandoftheEUFP7“HiLumiLHC”Grant Agree-ment284404fortheconstructionofthehardwaresetup.TheCERN

BE-OP andthe Coordination Team of the LHC Machine

Develop-mentwereinchargeofsetting-uptheLHCparameters,duringthe data taking. The Imperial College group gratefully acknowledges support from the UK Science and Technology Facilities Council. ThePNPIandtheIHEPteamswishtoacknowledgesupportbythe

Russian Foundation for Basic Research Grants 05-02-17622 and

06-02-16912, the RF President Foundation Grant SS-1633.2014.2,

the “LHC Program of Presidium of Russian Academy of

Sci-ences”andthegrantRFBR-CERN12-02-91532.F.Addesa, E. Bagli, L. Bandiera, F. IacoangeliandG. Smirnov of theINFN team were partially supported by ERC Ideas Consolidator Grant No. 615089

“CRYSBEAM”.D. Mirarchi was partiallysupported by the EuCARD

programGA227579,withinthe“CollimatorsandMaterialsforhigh

powerbeams”workpackage(Colmat-WP).

References

[1] R.Assmann,etal.,RequirementsfortheLHCcollimationsystem, LHC-PROJECT-REPORT-599,in:8thEuropeanParticleAcceleratorConference:AEurophysics Conference,LaVilette,Paris,France,3–7Jun2002.

[2]A.G.Afonin,etal.,Phys.Rev.Lett.87(2001)094802. [3]R.P.Fliller,etal.,Nucl.Instrum.MethodsB234(2005)47.

[4]R.CarriganJr.,etal.,in:V.Lebedev,V.Shiltsev(Eds.),AcceleratorPhysicsat theTevatronCollider,Springer,2014,Chapter6.

[5]R.Assmann,S.Redaelli,W.Scandale,in:EPACProceedings,2006,p. 1526, Ed-inburgh.

[6]V.Previtali,Performanceevaluationofacrystal-enhancedcollimationsystem fortheLHC,PhDthesis,EPFLTheseN. 4794,CERN-THESIS-2010-133,2010. [7]W.Scandale,etal.,Phys.Lett.B692(2010)78.

[8]W.Scandale,etal.,Phys.Lett.B703(2011)547. [9]W.Scandale,etal.,Phys.Lett.B714(2012)231. [10]W.Scandale,etal.,Phys.Lett.B726(2013)182. [11]W.Scandale,etal.,Phys.Lett.B748(2015)451.

[12]J.Lindhard,K.Dan,Vidensk.Selsk.Mat.Fys.Medd.34 (14)(1965).

[13]D. Mirarchi,Crystal collimationforLHC,PhDthesis,CERN-THESIS-2015-099, 2015.

[14]M. Butcher, A.Giustiniani, R.Losito, A.Masi, in: IECONProceedings, 2015, p. 003887.

[15] E.N.Tsyganov,1976,preprintTM-682,TM-684,Fermilab,Batavia. [16]S.Baricordi,etal.,Appl.Phys.Lett.91(2007)061908.

[17]S.Baricordi,etal.,J.Phys.D,Appl.Phys.41(2008)245501.

[18]Yu.M.Ivanov,A.A.Petrunin,V.V.Skorobogatov,JETPLett.81(2005)99. [19]A.M.Taratin,W.Scandale,Nucl.Instrum.MethodsB313(2013)26.