Ijaz Ahmed Ijaz Ahmed Helmut Burkhardt Andrea Latina Beam-Halo Generation Study in CLIC CLIC Beam Dynamics Meeting, CERN: 13/02/08

Collimation System: (1) Reduce the background by removing particles at large betatron amplitudes (Halo) or energy Offsets. (2) The choice of the collimator apertures should guarantee good cleaning efficiency of Halo. (3) to avoid wakefields that might degrade the orbit stability. Final Focus System (1)Need to provide a very strong focusing. (2)Reduces the transverse sizes of the beam at the IP sufficiently to provide the required luminosity (3)The correction of chromatic and geometric aberrations. Beam Delivery System BDS Purpose: Reduce the beam sizes to nanometer sizes to produce the luminosity

βxβx m αxαx βyβy m αyαy entrance β*xβ*x 7 mm α*xα*x 0. β*yβ*y 90 μm α*yα*y 0. IP E1.5 TeV γε x 680 nm γε y 10 nm IP CLIC BDS Optics

Halo and tail sources Particle processes: beam-gas scattering (elastic, inelastic) Synchrotron radiation (coherent/incoherent) Scattering off thermal photons Ion/electron cloud effects Intrabeam scattering Touschek scattering Optics related: Halo modeling – Mismatch – Coupling – Dispersion – Non-linearities Various (equipment related, collective) – Noise and vibration – Dark currents – Space charge effects close to source – Wake fields – Beam loading – Spoiler scattering

Beam-halo collimation Beam halo : damping ring, linac, final focus aberrations etc Beam halo : damping ring, linac, final focus aberrations etc The beam halo can result in electromagnetic showers and SR reaching the detector (+ muon background). The beam halo can result in electromagnetic showers and SR reaching the detector (+ muon background). Halo removed by physically intercepting the particles using mechanical spoilers + thick absorbers to remove the debris. Halo removed by physically intercepting the particles using mechanical spoilers + thick absorbers to remove the debris. Thick absorbers then become a source of muons – should be within tolerable levels at the detector. Thick absorbers then become a source of muons – should be within tolerable levels at the detector. IR layout and mainly final doublet dominate. IR layout and mainly final doublet dominate.

Beam Halo/tail and Background at IP Major source of detector background:Major source of detector background: particles in the beam tail which hit FD and/or emit photons that hit vertex detectorparticles in the beam tail which hit FD and/or emit photons that hit vertex detector Tails can comeTails can come From FF, due to aberrationsFrom FF, due to aberrations From damping ring, linac, etc.From damping ring, linac, etc. Tails must be collimated, amount of collimation usually determined byTails must be collimated, amount of collimation usually determined by Ratio : FD bore / beam size at FD ????????Ratio : FD bore / beam size at FD ???????? This criterion defines a maximum allowed amplitude of particles at the entrance to the FD. Secondary muons produced by halo interaction with collimators or with other aperture restriction beamline elementsSecondary muons produced by halo interaction with collimators or with other aperture restriction beamline elements

Beam-gas scattering phenomena Beam-gas scattering parameters # of particles = # initial energy = 1496 GeV # of slices = 31 # of macro particles = 1000 N2 gas at room temperature (300K) Gas pressure = 10 nTorr  Angular cut-off for mott scattering cross-section Where,  Angular distribution of scattered electrons Beam divergence: ee

Beam profile at the entrance Horizontal Vertical Horizontal Horizontal angle Vertical angle Vertical

Beam profile in the final quadrupole Horizontal Vertical Horizontal Horizontal angle Vertical angle Vertical

Halo: Phase space plots in final quadrupole  rad Horizontal Vertical Vertical

Placet-htgen simulation FullTracking Temperature 300 K Pressure 10 ntorr Scattering angle 10 nrad Residual Gas (N 2 ) Lattice with no collimators: PLACET-Development for tracking HTGEN for halo generation Total no. of elements 637Total no. of elements 637 No. of slices 31No. of slices 31 No. of macroparticles 100No. of macroparticles 100 Linac injection energy 1496 GeVLinac injection energy 1496 GeV Charge 4 nCCharge 4 nC Emitt. along x-axis 680 nradEmitt. along x-axis 680 nrad Emitt. Along y-axis 10 nradEmitt. Along y-axis 10 nrad

Beam core Beam-Halo Collimations regionFinal Focus Halo—particles with large betatron amplitudes or with large energy off-sets Longitudinal coordinate Beam Delivery System Beam squeezing leads the vertical dispersion

Beam-Halo (Residual Gas pressure dependence) 8.4% >1mm 1.7% > 10mm 5.3% >1mm 0.5% > 10mm 8.2% >1mm 0.4% > 10mm No significant change in vertical halo (above 1mm) as we go from 1-10 ntorr

Beam-Halo (scattering angle dependence) 0.3% >1mm) 0.004% >10mm 6.2% >1mm 0.4 > 10mm 8.4% >1mm 1.7 > 10mm Small angle  less vertical expension Inverse of above

Halo- energy dependence Low energy beam Large energy spread (~1  Large energy spread (~1  Large vertical off-set Large vertical off-set

Halo > 102  m = 30% Halo > 1 mm = ~ 3% Halo > 10 mm = ~ 0.5% Beam and Halo Profile with aperture 10% 3.1% Lattice provided by Javier Resta-lopez, octupole collimator+ spoilers spoilers

Scatt. angle Gas pressure # of halo # of lost Lost probability File size q = ntorr ~ x MB q = ntorr ~ MB q = ntorr ~ MB q = ntorr ~ x MB q = ntorr ~ x GB Electron beam = (192 MB)lattice V # halo at angle = 0.01, P = 10nt, {ratio 10nt/5nt==1.28} # halo at angle = 0.01, P = 5nt, {ratio 5nt/1nt== 5} # halo at angle = 0.01, P = 1nt, (6.3 times 1---> 10 ntorr pressure) # halo at angle = 0.1, P = 10nt, # halo at angle = 0.05, P = 10nt, # halo at angle = 0.01, P = 10nt, (150 times, 0.1  rad--->  rad ) Halo Statistics (BDS)

Halo Distributions in LINAC FullTrackingFullTracking Temperature 300 KTemperature 300 K Pressure 10 ntorrPressure 10 ntorr Scattering angle 10nradScattering angle 10nrad Residual GasResidual Gas Standard PLACET latticeStandard PLACET lattice Total no. of elements 54068Total no. of elements No. of Quad. 1324No. of Quad No. of BPMs 1324No. of BPMs 1324 No. of slices 31No. of slices 31 No. of macroparticles 100No. of macroparticles 100 Linac injection energy 9.0 GeVLinac injection energy 9.0 GeV Charge 4 nCCharge 4 nC Emitt. along x-axis 680 nradEmitt. along x-axis 680 nrad Emitt. Along y-axis 10 nradEmitt. Along y-axis 10 nrad LINAC Beamline Energy of the halo particles is increasing almost linearly during passing through the acceleratoing structures of the LINAC PLACET-HTGEN Tracking: Several problems pointed out by me and then fixed immediately by Helmut

Halo spectrum in LINAC Horizontal Vertical

Found no loss of halo Beam-gas scattering + Bremsstraulung both processes are contributing here due to low energy beam at the time of injection

Halo in Post collision line Halo and beam looks same, so halo are not so important for extraction line, but beam distributions count PLACET-HTGEN Tracking: input from GUINEA-PIG (Beam-Beam effects at IP, soon will be presented) Lattice used contains only drifts With no collimators

PLACET vs DIMAD (Arnaud ferari) Horizontal phase space Vertical phase space # of entries Horizontal Vertical Horizontal

Summary : Halo estimates and simulations by H. Burkhardt, L. Neukermans 1, A. Latina, I. Ahmed ; CERN Done 2007 : htgen software package with installation instructions, interfaces to tracking codes and examples made available. htgen provides simulation and estimates of main halo production processes ; applied to ILC & CLIC Process available: Beam-gas elastic scattering (mott) Beam-gas in-elastic scattering (Bremsstrahlung)

SummarySummary Ongoing and future work : Online manual for the htgen software packageOnline manual for the htgen software package Improve the HTGEN packageImprove the HTGEN package Simplify HTGEN commands and provide control and diagnostics output implement further halo production mechanisms.Simplify HTGEN commands and provide control and diagnostics output implement further halo production mechanisms. Reduce dependence on external libs (CLHEP, GS in case of placet) cleaner interfaces -- less globals and copying of structuresReduce dependence on external libs (CLHEP, GS in case of placet) cleaner interfaces -- less globals and copying of structures Update to recent synchrotron radiation code work with HTGEN users, provide help and follow up on requests tests and benchmarking : measurements (ATF, CTF3) and with other codes -- Geant4, BDSIMUpdate to recent synchrotron radiation code work with HTGEN users, provide help and follow up on requests tests and benchmarking : measurements (ATF, CTF3) and with other codes -- Geant4, BDSIM

Objectives and upcoming  Halo estimation in Drive beam system (struggling but PETS--?)  Halo estimation in Beam Delivery System (Done)  Halo estimation in Post-collision line (Done, even not so important)  Halo estimation in Main LINAC (Done)

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