Beam Background Simulations for HL-LHC at IR1

Regina Kwee-Hinzmann, R.Bruce, A.Lechner, N.V.Shetty, L.S.Esposito,F.Cerutti, G.Bregliozzi, R.Kersevan,

L.Nevay, S.Gibson, S.Boogert

3rd Joint HiLumi LHC-LARP Annual Meeting, 11-15 November 2013, Daresbury Laboratory

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Outline

• Beam background sources in IR1 and IR5• HL LHC cases for beam background

simulations• Simulation setup– beam-halo– local beam-gas

• Results: background spectra at the detector interface

• Summary and outlook

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Beam Background Sources to Experiments

Main sources of BB in IR1 and IR5:• beam-halo leakage

from tertiary collimators (TCTs)

• beam-gas – local BG: sample beam-

gas interactions close to IP (140 m upstream)

– global BG: sample through entire LHC

• other sources: cross-talk these interactions generate showers entering the detector region

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Geometry Layout at IR1

separation dipole (D1)

TCTs

inner tripletQ1 Q2 Q3

inte

rface

pla

ne a

t 22.6

m

detector side machine side

incoming/outgoing beam

x [c

m]

z [cm]

IP

as used in Fluka(same geometry as used for energy deposition studies –

WP10)

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TCTHTCTV

x[cm]

z [cm]

example of vertical halo distribution

Simulation Setup for Beam-Halo

• Halo simulation in 2 steps: 1. beam tracking through

machine using SixTrack• ATS optics• new aperture model• use 2 types of halo input

distribution to SixTrack– vertical + horizontal

distribution

2. shower generation at detector interface with Fluka• force inel. interaction at

position given by SixTrack

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Simulation Setup for local Beam-Gas

• Use Fluka only• Force interaction based on

simulated pressure profile• Consider 2 cases for gas

pressures:– start-up conditions– after conditioning

• per case 2 levels:– high and low due to

uncertainties in layout, effective dimensions, pumping speed

all pressure profiles are highly preliminary!

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Normalisation

local beam-gas (BG): use high pressure levels only (due to high uncertainties)

1. start-up 2. after conditioning

• Both data, BH and BG, especially the pressure profiles, are given for the nominal HL-LHC scenario, i.e.

2.2 x 1011 p/bunch, 2808 bunches, 25 ns, Ebeam = 7 TeV• Normalisation considers 2 scenarios for BH and BG

beam-halo (BH):1. beam lifetime of 12 min

– corresponds to design parameter of collimation system

2. beam lifetime of 100 h– according to operation

experience in 2012

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HL LHC Beam Background Simulation Cases

ATS optics with layout HLLHCv1.0 for β* = 15 cm➡new larger triplet with larger apertures➡larger half-crossing angle (295 μrad at IP)This talk: IR1 geometry only, present TCT layout as pessimistic assumption (not final for HL, additional TCT's further upstream are expected to help) round beam: σx = σy

nominal collimator settings as in the design report (WP5, Task 3), possibly optimistic for background

✗more relaxed collimator settings

✗flat beam: σx ≠ σy – different collimator settings (as above)

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Neutron fluence per primary beam-halo interactionhorizontal cut

TCTs

TANinterface plane at z = 22.6 m

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Neutron fluence per primary beam-halo interaction

vertical cut

TCTsTAN

interface plane at z = 22.6 m

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Energy Spectra of Proton Ratesat interface plane

distinctive differences:• clear single-

diffractive peak in halo distribution

• halo protons show double bump structure

• lowest background possibly from halo protons during normal operation

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Energy Spectra of Muon Ratesat interface plane

• many background muons to be expected for very short beam lifetimes and during start-up

• BG contribution after cond. similar to level at 3.5 TeV

• BH for normal beam lifetimes is about x10 higher than at 3.5 TeV 

3.5 TeV analysis published in NIMA, 729:21, 825–840 2013

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Energy Spectra of Neutron Ratesat interface plane

• triple bump structure in halo neutrons

• most of the background neutrons may be expected during machine start-up

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Energy Spectra of Photon Ratesat interface plane

• expect highest rates from photons

• at high energies, local BG contribution comparable to very short beam lifetimes

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Energy Spectra of Electron/Positron Ratesat interface plane

• high energy electrons expected mostly from beam-gas

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Transverse Radial Distributions for μ± and e±

at interface plane

• differences at very short radii more pronounced• “shoulder” from BG is more “washed out”

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Transv. Rad. Distrib. for Neutrons and Protons at interface plane

• expect more neutrons than protons (about x10)

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Summary & Outlook• Presented first beam background studies with updated HL

geometry for design case.– Comparison of 2011 machine to HL: expect similar level of high

energy muons from local BG after conditioning, but x10 increase from BH during normal operation.

– Results are available to experiments for further analysis.

• Preliminary results need to be updated, once– final decision on layout is made (e.g. no JSCAA shielding

included in geometry),– pressure profile simulations are updated.

• More HL cases in pipline – use flat optics, use more relaxed/HL collimator configurations, – extend studies to IR5, consider new HL TCT’s.

• More studies for future– global beam-gas, cross-talk.

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Additional slides

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Proton fluence per primary beam-halo interactionhorizontal cut

TCTs

TANinterface plane at z = 22.6 m

z [cm]

x [c

m]

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Proton fluence per primary beam-halo interaction

vertical cut

TCTs

TAN

interface plane at z = 22.6 m

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Energy Distribution for Particles within or outside of beampipe

many more pions arrive at the interface from halo interactions than from beam-gas.

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Particle distribution in x-y plane at interface

• geometric features visible at interface plane

• see similar distribution for other particles (e.g. kaons, pions, neutrons)

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JCSAA concrete shielding

• Halo spectra at interface plane can show specific features of the HL geometry (missing JSCAA, JSCAB and JSCAC shielding in HL layout)