Post on 05-Jan-2016
transcript
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)