Investigation of using the crystalline target in channeling mode for beam collimation

in the LHC

Igor YazyninInstitute for High Energy Physics (Protvino, Russia)

Acknowledgements: AB-ABP Collimation working group, collaboration UA9.

Outline

• The use of crystal (channeling effect) with optimal collimator gaps.

• The estimation inefficiency of beam cleaning system from any factors was considered.

• The possible variants of application the crystalline targets for beam cleaning in LHC were investigated.

Principal sketch of beam cleaning system

Main collimation systems in LHC:• Betatron cleaning (IR7), (Momentum cleaning (IR3)).

• 6 main radiation sources at 4 systems ( R,Z, and 2 skew).In the Pic. of angular beam distribution we can see 6 sources.

With using crystalline target the distribution of scattering beam changes -> efficiency changes and defined how particles put on collimators.

For decreasing losses may optimize size of gaps. The channeling fraction must be put only one absorber(collimator).

• Beam sizes and traces protons from crystal for two energies.

Calculation inefficiency of system

R0,mm Z0,mm η0% η1% η2%

1.7 0.0 0.091 0.112 0.098

0 - absolutely secondary collimators1- carbon secondary collimators (phase 1)2 - secondary + tertiary (W) collimators (phase 2)

• First coefficient defined losses only from primary collimators • Losses from secondary collimators • Part losses catch by tertiary collimators • From table we can see that main losses at E=7T defined by particles

escaping from PC.

Collision energy E=7000 GeV, R0’=-0.023 mrad, Impact parameters dR=0.3 um

%091.00 pc%021.001 sc

%014.021 tc

Using channeling effect at LHCin case of phase 1

1 2Fig.1: Angular beam distribution with any orientation of crystal 1-3:

4-images of collimator edges (V=1m/turn, E= 7TeV, R=80m)Bend angle of crystal = 50 urad for case of phase 1 (sizes of collimator gaps).Crystal stand in place of primary collimator and deflect in radial plane.

Fig2.: Inefficiency versus alignment(orientation) of crystal. (E=7 TeV) • Increase efficiency of system in ~10 times• Range of good efficiency -20.5:-23.5 urad.

rad 18,26,220

Using channeling effect at LHCin case of some changing gaps

• Beam distribution on the collimator TCSGb5 and orientation curve for channeling fraction.

• Bend angle of crystal (Si110) = 30 urad, gap of collimator=2mm• Beam size at crystal Rb=1.64mm, Zb=1.23mm

Choice of curve radius

1 2 • 1 - Channeling fraction from curve radius.• 2 – Losses on the crystal, Bend angle of crystal = 30 urad.• Optimum curve radius R~ 70-90 m, length = 2.1-2.7 mm• For energy 7TeV critical radius Rcrit =11.7m, critical ang.

=2.47urad

Phase plane of beam on the collimator TSCb5

1 2 • 1 – Optimal orientation (Angle = -22 urad) (R~ 70m, length = 2.1mm).• 2 – Bad orientation (Angle = 0 urad).• Density of beam on the edge of collimator decrease in ~1000 times• Losses on the crystal = 0.25% (losses on primary collim. ~50%)• Efficiency of collimation system increase in 50-100 times

Global inefficiency of system P=7TeV

• Orientation curve of full proton losses in accelerator for some curve radiuses of crystal. Bend angle = 30 urad.

• Minimum losses is in case R=70m, Ig=0.002%,That in ~ 50 times smaller than usual collimation.

Efficiency of system P=450GeV

1 2• 1 - Orientation curves for channeling fraction I_ch an for losses on

collimator TSGb5 (R = 10m, length = 1.4 mm). • 2 - Orientation curves of global losses and losses on the crystal.• Minimum losses is in case Angle=-95urad, Ig=0.0004%,That in 100 times smaller than usual collimation.

Investigation influence of crystal none perfection on the efficiency of system.

• Thickness of amorphous layer,• Skew parameter (torsion)• Miscut parameter,• Twist parameter(for strip crystal),• Surface parameter,• Offset and optimal position of elements.

• Efficiency of ideal crystal system• Collimat. Iscr,% I1mm,% Icr% Ia_glob% Ich%• Real 99.1615 0.1510 0.2580 0.00225 98.71• Absol. 99.3768 0.0868 0.2553 0.00100 98.92• Extraction efficiency defined Iout = Isc –I1mm will consist 99%. • At collimation system with crystal• Losses defined 2 sources: crystal and collimators.

• At optimal orientation, losses from crystal consist > 40% !• All losses definedby nuclear process: elastic and diffraction.•  ------------------------------------------------• E=7TeV, without crystal, gaps of primary collimator = 6 sigma.

Iscr,% I1mm,% Icr% Ia% I_global% 9.9533 0.4233 0.0000 0.28667 0.13000• At collimation system with crystal losses decreased in 50

times.

21 kkII colcryglob , 008.0,004.0 21 kk

• Influence of amorphous layer• S_amor(um) Iscr,% I1mm,% Icr% Ia_glob% Ich% • 0 99.1615 0.1510 0.2580 0.00225 98.71• 2 98.8984 0.1539 0.4671 0.003 98.41• 10 97.5932 0.1554 1.5750 0.00625 96.91• Losses at Sam=10um increase in ~3 times, and channeling

efficiency decrease on ~2%.• By orientation curve -> may only estimate collimation efficiency.

• Influence of torsion (skew) parameter• Torsion Iscr,% I1mm,% Icr% Ia_glob% Ich% • 0 98.7845 0.2278 0.4208 0.00375 98.17• 0.02 95.1690 0.5708 2.9247 0.01475 92.34• Losses at torsion=0.02mrad/mm increase in 4 times, and

channeling efficiency decrease on 6%.• orientation (Angle= - 21 urad)

Influence of miscut parameter

miscut(mrad) Iscr,% I1mm,% Icr% Ia_glob% Ich%• 0 99.1615 0.1510 0.2580 0.00225 98.71• 1 95.1298 2.0448 0.5186 0.02088 91.89• -1 99.1456 0.1510 0.2489 0.002 98.68

•Negative miscut angle practically don’t change efficiency of system,•Positive miscut angle = 1mrad in 9 times increase losses. !!!•That explained increasing proton density at edge of collimator•Channeling efficiency will decrease only on 7 % at badly situation of positive miscut,•At negative miscut channeling efficiency don’t change. !!!•We will use such orientation of crystal.

Influence of crystal thickness

• S(mm) Iscr,% I1mm,% Icr% Ia_glob% Ich% • 1 99.1615 0.1510 0.2580 0.00225 98.71• 0.1 99.1525 0.1958 0.2446 0.00263 98.63

• For such big energy how in LHC may use very thin crystals 0.2-0.5 mm.

• Then more energy, then smaller scattering particles on crystal.

Influence of collimator’s offset (from gap of collimator TCSGb5)

• Gap(mm) Iscr,% I1mm,% Icr% Ia_glob% Ich% • 2.0 99.1615 0.1510 0.2580 0.00225 98.71• 1.8 97.5829 1.9366 0.4025 0.01312 92.59

• Decreasing gap of collimator to 6.35 sigma -> in 6 times increase losses. !!!

• It defined by particles scattering and put with small impact parameter on the collimator.

Influence of PC gap size on the efficiency

• Gap_PC Iscr,% I1mm,% Icr% Ia_glob% Ich% • 6.12 96.8994 0.1371 0.2114 0.00350 96.56• 6.3 98.0480 0.1340 0.2170 0.00263 97.8• 6.6 98.3978 0.1365 0.2176 0.00200 98.1• 7.2 98.7761 0.1346 0.2241 0.00200 98.41• 9.0 99.1615 0.1510 0.2580 0.00225 98.71

• When size of gap PC > 6.4 then losses don’t change and for stable work system size of gap stand at level 6.3 – 6.5 sigma.

• Such if crystal destroy the usual collimation system will work.

Using crystal with decreasing curvature

• Optimal orientation (Angle= - 22 urad)• C Iscr,% I1mm,% Icr% Ia_glob% Ich% • 0 99.1615 0.1510 0.2580 0.00225 98.71• 1 99.4557 0.0035 0.2787 0.00075 97.7

• Losses decrease in 3 time, channeling efficiency decrease at 1%.

Source of losses only crystal !• Collimat. Iscr,% I1mm,% Icr% Ia_glob% Ich% • carbon 99.4557 0.0035 0.2787 0.00075 97.7• absol. 99.6804 0.0015 0.2585 0.00090 97.7• carbon* 99.5100 0.0020 0.2679 0.00000 97.7

• All losses defined by protons go out from crystal !• That protons created in nuclear process; elastic and

diffraction.• Carbon* - case when processes nuclear elastic and

diffraction in crystal off, I_glob = 0 !!!• When will use added cold collimators losses = 0.

Influence of amorphous layer• S_amor(um) Iscr,% I1mm,% Icr% Ia_glob% Ich% • 0 99.4557 0.0035 0.2787 0.00075 97.7• 2 99.2055 0.0061 0.4844 0.00125 97.0• 10 97.8460 0.0151 1.6140 0.00487 95.7

• Losses at Sam=10um increase in ~5 times, and channeling efficiency decrease on ~2%.

• Amorphous layer must be <= 2um

Conclusion and proposals:• Using crystals in channeling mode has

advantages for beam cleaning system LHC:1.Efficiency increase in ~100-50 times at

E = 450-7000GeV.2.All none ideality of crystal treatment (amorphous

layer <=2um, torsion <=0.01,miscut, twist) may increase losses in two time.

3.Using crystal with decreasing curvature increase collimation efficiency in 3 time.

4. In collimation system may use only two crystals in horizontal and vertical planes.