ILC Beam Delivery System and Interaction Region: Backgrounds, Radiation, Beam Halo, Collimation, Mac

1
ILC Beam Delivery System and Interaction Region
Backgrounds, Radiation, Beam Halo, Collimation,
Machine-Detector Interface, Machine and
Environment Protection
USPAS-2007
Houston, January 2007
Nikolai Mokhov Fermilab

• The US Particle Accelerator School
• Houston, Texas
• January 22-26, 2007

2
OUTLINE

• Beam-Beam and Machine-Related Backgrounds.
• Detector and Radiation Tolerable Limits.
• Synchrotron Radiation.
• Electromagnetic Showers, Muon/Hadron Production.
• Collimation in Beam Delivery System.
• Dealing with Muon Spray.
• Particle Flux, Hit Rate and Occupancy in
  Detector.
• 4. Radiation Loads in BDS, IR and Extraction
  Line.
• Machine and Environment Protection.
• 5. Simulation tools.

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BACKGROUNDS, RADIATION AND IR/DETECTOR DESIGN

• The high physics potential of the ILC is reached
  only if a high luminosity of ee- collisions in
  the TeV range is achieved (say, 2x1034 cm-2
  s-1). The overall detector performance in this
  domain is strongly dependent on the background
  particle rates in various sub-detectors. The
  deleterious effects of the background and
  radiation environment produced by the accelerator
  and experiments have become one of the key issues
  in the Beam Delivery System (BDS), Interaction
  Region (IR) and detector design and development.

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14/14 mrad BDS and IR
muon wall tunnel widening
polarimeter laser borehole
9m shaft for BDS access
IP2
10m
IP1
beam dump service hall
alcoves
1km
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SiD AND MACHINE-DETECTOR INTERFACE

ILC compact detector SiD with 5-Tesla
solenoidal field
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BACKGROUNDS AND DETECTOR PERFORMANCE

• Two sources
• IP backgrounds Particles originated from the
  interaction point (IP) beam-beam interaction
  products and collision remnants.
• Machine backgrounds Unavoidable bilateral
  irradiation by particle fluxes from the beamline
  components and accelerator tunnel.
• Backgrounds affect ILC detector performance in
  three major ways
• Detector component radiation aging and damage.
• Reconstruction of background objects (e.g.,
  tracks) not related to products of ee-
  collisions !!!
• Deterioration of detector resolution (e.g., jets
  energy resolution due to extra energy from
  background hits).

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IP BACKGROUNDS

• Source
• Beam-beam interactions (disrupted primary beam,
  beamstrahlung photons, ee- and mm- pairs and
  hadrons from beamstrahlung and gg interactions,
  and extraction line losses) and radiative Bhabhas
  (ee- ee- g).
• From the standpoint of integrated background,
  ee- linear colliders are relatively clean
  machines. Average integrated hadronic fluxes
  produced at the IP are about six orders of
  magnitude lower compared to LHC.
• However, the instantaneous rates are not so
  drastically different. Say, for the gg option, a
  peak radiation field is about 10 of that at LHC.
  The ee- option is 10 times better.
• In general, this source is well understood and
  under control it scales with luminosity, one
  should transport interaction products away from
  IP and shield/mask sensitive detectors, and
  exploit detector timing.

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THREE DETECTOR CONCEPTS
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MACHINE-RELATED BACKGROUNDS

• Synchrotron radiation, spray from the dumps and
  extraction lines, beam-gas and beam halo
  interactions with collimators and other
  components in BDS create fluxes of muons and
  other secondaries which can substantially exceed
  the tolerable levels at a detector
  keep these sources from IP as far as possible.
• With appropriate IR/IP design no strong
  magnetic field / no intense synchrotron radiation
  generation with masks in the detector vicinity,
  with a multi-stage collimation set and a system
  of magnetic iron spoilers, one can meet the
  design goal of allowing a continuous 0.1 beam
  scraping rate, resulting in a tolerable particle
  fluxes at the detector.

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DEALING WITH SYNCHROTRON RADIATION AT IP

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COLLIMATION SYSTEM AND MAGNETIC SPOILERS IN BDS

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TEMPORAL ASPECTS

• Temporal considerations in the IP and machine
  background analysis are of a primary importance.
  Integrated levels determine radiation damage,
  aging and radio-activation of detector components
  as well as the radiation environment in the
  experimental hall, accelerator tunnel and their
  surroundings. High instantaneous particle fluxes
  complicate track reconstruction, cause increased
  trigger rates and affect detector occupancy.
• One can define the instantaneous or effective
  luminosity - which determines the detector
  performance for the amount of radiation in the
  detector active element over the
  drifting/integration time ?td (sensitivity
  window) or the bunch train length, whichever is
  smaller. For detector elements most susceptible
  to occupancy problem ?td is 40 - 300 ns.

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BEAM PARAMETERS

• 250-GeV
• 5 trains per second
• 2820 bunches in each train
• 300 ns between bunches
• 199 ms between trains
• Train length 868 µs
• 2x1010 positrons/electrons per bunch
• Luminosity 2x1034 cm-2 s-1

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DETECTOR TOLERANCES
1 generic occupancy limit (per train or per SW)
implying x10 safety factor
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Background tolerance levels
() As per R. Settles et. al., TESLA St Malo
workshop
Detector-specific data from T. Maruyama
detector response to MDI questions, Aug 05.
Limits are expressed in particles either per
sensitivity window SW (typically 50 ?s 150
bunches in VXD/TPC), or per bunch train tr

• Notes
• No generic answers depend strongly on
  subdetector technology
• Need to clarify impact of TPC occupancy on track
  reco efficiency space charge
• Only rough estimates so far. Real answer needs
  detailed simulations, pattern recognition
  studies, space charge, understanding of
  background distribution....
• 1 may sound overconservative...but we need x
  10 safety factor!

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BACKGROUND TOLERABLE LIMITS SUMMARY

Calorimeter, tracker and vertex detectors in
smallest element, occupancy 1. To avoid
pattern recognition problem in tracker, hit
density from charged particles should be 0.2
hit/cm2/bunch. To avoid pile-up problem (from
previous BX !) in tracker, hit density from
charged particles should be 0.2
hit/mm2/train. Muon system the RPCs (sensitive
media) need 1 ms to re-charge a 1 cm2 area around
the avalanche, therefore, the hit rate in excess
of 100 Hz/cm2 would result in an unmanageable
dead time. With typical 80 sensitive layers in a
Muon Endcap, it corresponds to a muon flux at its
entrance of about 1 m/cm2/s.
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RADIATION LIMITS AND DESIGN CONSTRAINTS

• Site/Lab/Country-specific. For Fermilab as an
  example
• Peak residual dose rate Pg mSv/hr at 1-ft in tunnel (30 days / 1 day)
  hands-on maintenance (1 W/m)
• Prompt dose equivalent in non-controlled areas is
  DE mrem/hr for the worst case due to accidents it
  is DE access areas
• Ground-water activation do not exceed
  radionuclide concentration limits of 20 pCi/ml
  for 3H and 0.4 pCi/ml for 22Na in any nearby
  drinking water supply
• Peak energy deposition and absorbed dose in
  beamline and detector components below
  temperature rise, material integrity and
  radiation damage limits
• Air activation do not exceed radionuclide
  concentration limits

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IP BACKGROUNDS ee- and mm- pairs and hadrons

At 500 GeV, backgrounds x-section is orders of
magnitude larger than the physics one
Production of system X a) by two equivalent
photons emitted by e and e- b) in ee-
annihilation
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BEAMSTRAHLUNG

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IP BACKGROUNDS IN SiD

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PAIR BACKGROUND STUDIES

• GUINEA-PIG GEANT3 Simulations of Pair
  Backgrounds in the Large Detector with realistic
  Solenoid and DID Fields by Karsten Büßer.
• A lot of different geometries have been
  studied, including different crossing angles,
  holes for incoming/outgoing beams and magnetic
  field configurations. Realistic magnetic fields
  for TESLA solenoid (by F. Kircher et al) and
  Detector Integrated Dipole (by B. Parker and A.
  Seryi) have been introduced.
• 
  

DID field combined with FD offset to zero both
angle and position at the IP
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PAIRS AS A DOMINANT SOURCE

500 GeV
1 TeV
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Hits in the TPC with SolenoidDID
Karsten Büßer
Comparing configurations
Origin of TPC photons pairs hit edge of LumiCal
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VXD HITS FROM BEAM-BEAM PAIRS
GEANT3 modeling for SiD By Takashi Maruyama
N nominal Q Low Q Y High Y P Low P H
High Lum.
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e/e- Flux in SiD Tracker

Forward Tracker Layer 1 hits innermost region
is at the limit for pattern recognition
Pat Rec Tol ( 0.2 cm-2 BX-1)
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NETRONS IN DETECTOR

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SYNCHROTRON RADIATION (1)
See SR theory in A. Seryis lecture

• Concerns
• backscattering from downstream aperture
  limitations
• edge- tip- scattering from upstream SR masks
• impact of a partially-shared beam line on SR
  masking (2mr)
• compatibility of stay-clear apertures (spent
  beam, pairs, beamstrahlung g) with effective
  masking of incoming SR

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SYNCHROTRON RADIATION (2)

• Lessons from existing detectors
• BaBar design SR background dominated by
  tip-scattering
• BELLE fried their first VDET by a combination
  of
• improperly masked incoming-beam SR (very soft
  X-rays from XYCORs)
• hard SR backscattered from the first beam-pipe
  wall on outgoing side
• Zeus H1 SR much of it backscattered
  absorbs a large fraction of their background
  budget

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SYNCHROTRON RADIATION (3)

• Photon loss at PDUMP, MSK1, MSK2 and passed
  through the IP from beam halo for collimation at
  8 sx and 65sy and from beam core.

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Beam Core and Halo Synch Photons at IP

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SYNCH PHOTON ENERGY SPECTRA AT MASKS

From halo
From core
Passed through IP
From beam halo
From beam core
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Electromagnetic Shower Basics

Intense electromagnetic showers (EMS) are
generated when electrons hit material of
beam-line components. At high energies, the
dominant processes are bremsstrahlung for
electrons and ee- pair product for g. At high
energies, properties of EMS are conveniently
described using Radiation length X0 electron
loses all but 1/e of its energy by brems, and 7/9
of the mean free path for pair production by
photons. Critical energy Ec 800 MeV/(Z1.2)
(dE/dx)ion (dE/dx)brems. Scale energy Es mec2
(4p/a)1/2 21.2 MeV. Molier radius RM X0
Es/Ec. Multiple Coulomb scattering Es/p
(x/X0)1/2 (1 0.038 ln x/X0)
/v2 EMS length 20-30 X0. (X0 0.35, 1.43,
1.77 and 35cm for W, Cu, Fe and Be,
respectively). EMS radius 2-3 RM.
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Bethe-Heitler Muons, Hadrons etc.

About 10-4 muons are generated per 250-GeV
electron hitting material (limiting apertures,
residual gas) which being accompanied by other
particles can reach the IP and create
background levels well above the tolerable
limits. These are mainly energetic muons from
Bethe-Heitler process gZ mm-Z. Also, muon
pairs from ee- annihilation, hadrons from photo-
and electro-nuclear inelastic interactions, and
decay products of all unstable particles. Make
these limiting apertures (collimators) as far
from IP as possible. Suppress muon flux far from
IP by thick magnetic walls or doughnuts. Studied
in very complex realistic BDS modeling.
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BEAM HALO

From beam loss point of view, beam halo can be
defined as a number of particles of any origin
which lie in the low-density region of beam
distribution far away from the dense core. At
ILC, as at any other accelerator, the creation of
beam halo is unavoidable. This happens because
of numerous reasons (next page). As a result of
halo interactions with limiting apertures,
electromagnetic showers are induced in
accelerator and detector components causing
numerous deleterious effects ranging from minor
to severe. An accidental loss of a small
fraction of the beam can cause catastrophic
damage to the collider and detector equipment.
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BEAM HALO ORIGIN

Particle processes - Beam-gas scattering
(elastic, inelastic, bremsstrahlung) - Ion or
electron cloud effects - Intrabeam scattering
(including large-angle Touschek) - Synchrotron
radiation - Scattering off thermal
photons Optic related - Mismatch, coupling,
dispersion - Non-linearities Collective
Equipment related - Noise and vibration - Dark
currents - Space-charge effects close to
source - Wake-fields - Beam loading
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BEAM HALO COLLIMATION (1)
Even if final focus does not generate beam halo
itself, the halo may come from upstream and need
to be collimated

• Halo must be collimated upstream in such a way
  that SR g halo e- do not touch VX and FD
• VX aperture needs to be somewhat larger than
  FD aperture
• Exit aperture is larger than FD or VX aperture
• Beam convergence depends on parameters, the halo
  convergence is fixed for given geometry
  qhalo/qbeam (collimation depth) becomes tighter
  with larger L or smaller IP beam size
• Tighter collimation MPS issues, collimation
  wake-fields, higher muon flux from collimators,
  etc.

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BEAM HALO COLLIMATION (2)

• Collimators have to be placed far from IP, to
  minimize background
• Ratio of beam/halo size at FD and collimator
  (placed in FD phase) remains
• Collimation depth (esp. in x) can be only 10 or
  even less
• It is not unlikely that not only halo (1e-3
  1e-6 of the beam) but full errant bunch(s) would
  hit the collimator

38
BEAM COLLIMATION

Only with a very efficient beam collimation
system can one reduce uncontrolled beam losses to
an allowable level.
Beam collimation is mandatory at any high-power
beam accelerator, superconducting hadron
(Tevatron, LHC) and ee- (ILC) colliders. The
purpose is to reduce backgrounds in the
experiments to acceptable levels, protect
components against excessive irradiation,
maintain operational reliability over the life of
the machine, provide acceptable hands-on
maintenance conditions, and reduce the impact of
radiation on environment, both at normal
operation and accidental conditions.
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BEAM-INDUCED COLLIMATOR DAMAGE

All collimators must withstand a predefined
fraction of the beam hitting their jaws and - at
normal operation - survive for a time long enough
to avoid very costly replacements.
0.5-MW, 2-mm diam e-beam, grazing on 60-cm Cu it
took 1.5 s to melt in
All beam collimation systems nowadays are based
on a two-stage approach.
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TWO-STAGE BEAM COLLIMATION (1)

The system consists of a primary collimator
(spoiler, thin scattering target), followed by a
few secondary collimators at the appropriate
phase advance (locations) in the lattice. The
purpose of a spoiler is to increase the amplitude
of the betatron oscillations of the halo
particles (give them an angular kick) via
scattering/interaction in a thin object and thus
to increase their impact parameter on secondary
collimators. For ILC it simply means to start
the electromagnetic shower earlier and let
particles diverge on the way to a downstream
massive absorber. One can make the impact
parameter on secondary collimators a factor of up
to 1000 larger than on primary ones.

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TWO-STAGE BEAM COLLIMATION (2)

This results in a significant increase of the
collimation efficiency substantially lower
backgrounds on detectors, beam loss in the
lattice, and jaw overheating as well as easier
collimator alignment. With such a system, there
are only several significant but totally
controllable restrictions of the machine
aperture, with appropriate radiation shielding in
these regions.

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MACHINE PROTECTION COLLIMATOR DESIGN

• The beam is very small single bunch can punch
  a hole the need for MPS (machine protection
  system)
• Damage may be due to
• electromagnetic shower damage (need several
  radiation lengths to develop)
• direct ionization loss (1.5MeV/g/cm2 for most
  materials)
• Mitigation of collimator damage
• using spoiler-absorber pairs
• thin (0.5-1 X0) spoiler followed by thick
  (20-30 X0) absorber
• increase of beam size at spoilers
• MPS diverts the beam to emergency extraction as
  soon as possible

Picture from beam damage experiment at FFTB. The
beam was 30GeV, 3-20x109 e-, 1mm bunch length,
s45-200um2. Test sample is Cu, 1.4mm thick.
Damage was observed for densities 7x1014e-/cm2.
Picture is for 6x1015e-/cm2
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SPOILER-ABSORBER SPOLIER DESIGN
Thin spoiler increases beam divergence and size
at the thick absorber already sufficiently large.
Absorber is away from the beam and contributes
much less to wakefields.
Need the spoiler thickness increase rapidly, but
need that surface to increase gradually, to
minimize wakefields. The radiation length for Cu
X01.43cm and for Be is X035cm. So, Be is
invisible to beam in terms of losses. Thin one
micron coating over Be provides smooth surface
for wakes.
44
a
r1/2 gap
As per last set in Sector 2, commissioning
Extend last set, smaller r, resistive WF in Cu
7mm
cf. same r, tapered
45
BDS COLLIMATION SYSTEM
The system is designed to shave 0.1 of the beam
intensity, and capable to withstand up to two
full errant bunches.
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BDS COLLIMATION SYSTEM PARAMETERS

1. Betatron spoilers SP1,SP2 SP4 in high-beta
region at 1582, 1483 and 1286 m from IP,
respectively, 0.6 X0 thick (0.6cm Cu), positioned
at 8sx and 65sy. 2. Momentum spoiler SPEX in
high-dispersion region at 990 m from IP, 1 X0
thick (3.56cm Ti), at 8sx and 65sy. 3. Absorbers
(secondary collimators) AB1-AB5, at 1500 to 1200
m, 30 X0 thick (43cm Cu), and ABE, AB7, AB9
AB10, at 826 to 450 m, 30 X0 (10.5cm W). 4.
Protection collimators PC1-PC11, at 1420 to 785
m, 15 X0 thick (21.45cm Cu) (it seems they need
to be increased to 25-30 X0). 5. Synchrotron
radiation masks MSK1, MSK2, at 50 and 13 m, 30 X0
thick (10.5cm W). Last three types are
positioned far from the beam at 16sx and
150sy.
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COLLIMATION DEPTH (?halo/?beam)
It is primarily determined by clearance of final
doublet sync radiation through the IR. All
collimation tracking simulations are done for
beam halo falling off as 1/R2 in phase space.
20 mrad
2 mrad

• Limiting aperture r 12 mm (20 mrad), 15 mm (2
  mrad)
• Spoiler gaps ax 1mm, ay 0.5 mm
• Tighter collimation for 2 mrad

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BEAM HALO AND SR DISTRIBUTIONS ENVELOPE

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COLLIMATION EFFICIENCY AND BEAM LOSS

IP
Collimation efficiency defined here as a
fractional loss of halo charged particles,
integrated back starting the IP and normalized to
the nominal bunch charge
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BDIR MARS MODEL 1700 m BDS, SiD (GEANT4) at IP,
followed by 200-m extraction line
Model includes all magnets, tunnel, concrete
walls, dirt, multi-stage collimation system
(spoilers, absorbers, protection collimators, and
photon masks), muon tunnel spoilers, SiD
detector, and extraction line (for high-lum
250-GeV beams).
51
BDS MODEL X-SECTIONS IN MARS15
52
MARS Magnet and PC Geometries

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MUON SPOILER
Thick steel 1.5-T magnetic wall sealing tunnel
x-section, to spray the muons out of the tunnel
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Five 4-m Thick Doughnut Scheme
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Magnetic Doughnuts
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Ultimate Doughnut Scheme
57
HALO ON SPOILERS
and dose isocontours with 5-m steel magnetic wall
mSv/hr
58
Muon Flux Isocontours
1/100
1/20
cm-2 s-1
59
Muon Fluxes from Hottest PCs
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Energy Spectra at Detector
Red lines no spoilers, blue 5 donuts
Red lines no spoilers, blue 5m wall
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Radial Distributions of Backgrounds at Detector
Red lines no spoilers, blue 5 donuts
Red lines no spoilers, blue 5m wall
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SiD SUB-DETECTORS (one quadrant)

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Hit Rates in Detector Subsystems

• Machine-related background with and without
  spoilers STRUCTMARS15 SLIC.
• Here only from e beam.
• 2. IP-related background radiative Bhabas from
  beam-beam interaction and synchrotron radiation
  from beam. Guineapig GEANT3
• 3. ee- events at 500 GeV- PYTHIA SLIC

Per ee- event
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BDS Induced Detector Backgrounds
65
Tracker

• Tolerable limits
• pattern recognition
• 0.2 hits/cm2/bunch
• pile-up problems
• 0.2 hits/mm2/train
• Machine bckgrs in Tracker Endcap
• 7 10-4 hits/cm2/bunch
• 0.02 hits/mm2/train
• Machine bckgrs in Tracker Barrel
• 4 10-5 hits/cm2/bunch 0.001 hits/mm2/train

Tracker Endcap No spoilers
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BDS Background Occupancy
Assuming cell size of 1 cm2
Should be bunch) SW (VTX, TPC)
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Hits in Muon Endcap

• RPCs need 1ms to recharge 1 cm2 area around the
  avalanche.
• Background rate should be
• Otherwise, an unmanageable
• dead time.
• There are 14100 bunches per second
• Tunnel background is about
• 400 Hz/cm2 without spoilers

68
Red machine background (no spoilers)Green
machine background (with 9 18-m walls)Blue
ee- eventst0 is bunch crossing.
Hit Time Distribution in Muon Endcap
BDS background from e tunnel only
69

Hit Time Distribution in Tracker Endcap
Red machine background (no spoilers)Green
machine background (with 918-m walls)Blue ee-
eventst0 is bunch crossing
BDS background from e tunnel only
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Collimator Material Damage

• All the possible heat deposition sources guide to
  instant temperature rise which can be solved by
  integration of the specific heat equation.
• Heat transfer equation can be solved separately
  then to get real time dependant temperature
  distribution between bunches.
• For metals we need to use all the parameters with
  real dependency of temperature.
• The results of analytical models need to be
  compared with simulations. ANSYS simulation can
  be really useful here as it can include phase
  transformations or melting and possible cracks of
  material.

71
Thin Spoiler Material Damage

• Ionization (approximations used for analytical
  study)
• Main source of heating ionization with possible
  correction factor due to electromagnetic shower
  (1.4 - 2.5)
• Additional information needed for thick
  structures but not critical for Lapply 2D models
• One can assume instant temperature rise due to a
  short bunch length in comparison with the heat
  diffusion
• Then one can get the temperature rise per bunch
  by integration

72
Thin Spoiler Material Damage heat transfer and
limits

• Heat transfer should be solved using
• Temperature rise limits
• Temperature should be far enough from melting
• Induced thermal stress should be far enough from
  leading to cracks and damage. The stress limit is
  based on tensile strength, modulus of elasticity
  and coefficient of thermal expansion. Sudden T
  rise create local stresses. When DT exceeds
  stress limit, micro-fractures can develop.

Use as an upper limit minTmelt, Tstrees (see
next page).
73
Thin Spoiler Damage simple example
Simple case thin, no EMS buildup, specific heat
is const
DT 1/(psxsy) (dE/dx)/Cp 1.610-13 21010
Nb
Old example
74
Direct Hits on Titanium-Alloy Spoilers
Maximum ?T/ 2x1010 bunch at the Hit Location,
ºC/bunch

• Ti6Al4V alloy fracture 770 ºC, melt 1800 ºC
• Copper melt 1080 ºC

Notes
75
Collimator Jaw Heating Simple Case
Block of Copper
Meshed with SOLID90 elements
Temperature on this back face is set to 0C
1 GW m-3 heat is deposited in this front volume
76
Temperature distribution Simple Case
Linear heat distribution in the non heated volume.
Quadratic fall in heat through the heated volume
77
Analytical Solution Lets Skip This!

• Thermal conductivity equation

QJ x LA and then rearranged to give
Where J is 1 W mm-1
This can then be integrated with respect to L to
give DT. This will give the temperature
distribution in the heated volume.
DT can be worked out using the original equation
and by considering the non heated volume. This
can then be used to find C and then temperature
on the front face
DT 105.882C
The analytical solution agrees with the answer
from ANSYS.
78
Survivable and Consumable Spoilers

• A critical parameter is number of bunches N that
  MPS will let through to the spoiler before
  sending the rest of the train to emergency
  extraction
• If it is practical to increase the beam size at
  spoilers so that spoilers survive N bunches,
  then they are survivable
• Otherwise, spoilers must be consumable or
  renewable

79
Renewable Spoilers
This design was essential for NLC.This concept
is now being applied to LHC collimation.
80
DYNAMIC HEAT AND RADIATION LOADS IN BDS
50 W/m on spoilers, 5-7 kW/m on protection
collimators, up to 80 W/m on quads (well above
the limit of 1 W/m local shielding). First
quad downstream of PC1 peak absorbed dose in
coils 300 MGy/yr (a few days of lifetime for
epoxy), residual dose on the upstream face is 7.7
mSv/hr (should be below 1 mSv/hr). Increasing PC1
length from 21 cm to 60 cm of copper, reduces
peak absorbed dose in the hottest coil by a
factor of 300, providing at least a few years of
lifetime. Temperature rise and stress are not a
problem except accidental conditions. Peak
heating per train 1.4 J/g and 2 K in SP2, and
4.7 J/g and 6.6 K in PC1.
81
MARS15 Energy Deposition and Radioactivation in
BDS

Local shielding is needed to meet
hands-on maintenance and ground-water activation
limits
Residual dose on contact (30day/1day)
Limit
82
MDI 2-mrad Extraction
Plan view
Polarimeter
Energy chicane
Side view
Compton detector
wigglers
SR detectors
83
MDI SiD Configuration
84
IP BDSIM MODEL 20-mrad SiD

84
85
2mrad Extraction LineLosses in SC QD0 from
Radiative Bhabhas
Pair Energy for 1TeV Nominal
QD0
T. Maruyama - BDS Meeting at SLAC 27/7/5

• Radiative Bhabhas created as a result of
  bremsstrahlung
• Can cause damaging heat loads in the
  Superconducting QD0
• Magnet designers have stipulated that this quad
  can only take 0.5mW/g before quenching

X
(QD0 Scored into 300000 volumes)
86
2mrad Losses - QD0 Power Density Maps for 250GeV
Nominal Case

• Power density maps for the first 5 rings (6th
  ring had no deposits)
• All density units in W/g

87
Integrated Extraction Line Design
Incoming Beam
Beamstrahlung
Outgoing Beam
(Picture from Walker)
88
BEAMSSTRAHLUNG TO EXTRACTION LINE

4 of the beam energy gets radiated into photons
due to beamsstrahlung
89
MDI Instrumentation for Luminosity, Luminosity
Spectra and Luminosity Tuning

90
MDI Functions of the Very Forward Detectors

91
MDI Extraction Line Diagnostics at 20 mrad

92
20-MRAD EXTRACTION LINE IN MARS15

Synchrotron photons generated by disrupted beams
elevation view (left) and plan view (right)
93
DYNAMIC HEAT LOADS IN EXTRACTION LINE

Up to 50 W/m without vertical displacement (left)
and up to 500 W/m with 120-nm vertical
displacement (right)
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RADIATION DOSES IN EXTRACTION LINES

Magnet at 60 m
2-mrad dose in mask at 153 m
20-mrad dose at 60 m
20-mrad x-ing Up to 40 MGy/yr with 120-nm
vertical displacement 1-month lifetime Up to 4
MGy/yr without VD (normal operation) 1-year
lifetime ? protection collimators (masks).
2-mrad x-ing 0.76 MW synch radiation loss ?
protection collimators with tens of kW on them
and up to 1 TGy/yr peak dose
Residual dose on the magnets is about 10 times
above the limits in the 25 to 70-m region from IP
(for 120nm)
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Beam Dump for 18MW Beam

• Water vortex
• Window, 1mm thin, 30cm diameter hemisphere
• Raster beam with dipole coils to avoid water
  boiling
• Deal with H, O, catalytic recombination etc.

20mr extraction optics
Undisrupted or disrupted beam size does not
destroy beam dump window without rastering.
Rastering to avoid boiling of water
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Collider Hall Shielding

• Shielding is designed to give adequate protection
  both in normal operation, when beam losses are
  low, and for maximum credible beam accident
  when full beam is lost in undesired location (but
  switched off quickly, so only one or several
  trains can be lost).
• Limits are different for normal and accident
  cases, e.g. what is discussed as guidance for IR
  shielding design
• Normal operation dose less than 0.05 mrem/hr
  (integrated less than 0.1 rem in a year with 2000
  hr/year)
• For radiation workers, typically ten times more
  is allowed
• Accidents dose less than 25 Rem/hr (SLAC number
  here) and integrated less than 0.1 Rem for 36MW
  of maximum credible incident (MCI).

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Radiation at IR Beam Accident
18MW loss on Cu target 9r.l \at s-8m. No
Pacman, no detector. Concrete wall at 10m. Dose
rate in mrem/hr.
For 36MW MCI, the concrete wall at 10m from
beamline should be 3.1m
10m
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Self-Shielding Detector
Detector itself is well shielded except for
incoming beamlines. A proper pacman can shield
the incoming beamlines and remove the need for
shielding wall.
18MW on Cu target 9r.l at s-8m Pacman 1.2m iron
and 2.5m concrete
18MW lost at s-8m. Pacman has Fe 1.2m,
Concrete 2.5m
Dose at pacman external wall dose at r7m
0.65rem/hr (r4.7m)
0.23rem/hr
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BACKGROUND AND RADIATION SIMULATION TOOLS

• TURTLE MUCARLO (SLAC) many features are
  predicted and solutions proposed with this fast
  tool
• STRUCT MARS15 (FNAL)
• GEANT4 Toolkits BDSIM, MOKKA, SLIC, LCDD
• (2) (3) Realistic modeling, from halo to
  detector response and radiation loads use
  GuineaPig CAIN
• for beam-beam interactions

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MARS15 HIGHLIGHTS (1)

• The MARS code system is a set of Monte Carlo
  programs for detailed simulation of hadronic and
  electromagnetic cascades in an arbitrary 3-D
  geometry of shielding, accelerator, detector and
  spacecraft components with energy ranging from a
  fraction of an electronvolt up to 100 TeV. It has
  been developed since 1974 at IHEP, SSCL and
  Fermilab. The current MARS15 version combines the
  well established theoretical models for strong,
  weak and electromagnetic interactions of hadrons,
  heavy ions and leptons with a system which can
  contain up to 105 objects, ranging in dimensions
  from microns to hundreds kilometers in the same
  setup.
• http//www-ap.fnal.gov/MARS/

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MARS15 HIGHLIGHTS (2)

• A setup can be made of up to 100 composite
  materials, with arbitrary 3-D magnetic and
  electric fields. Powerful user-friendly GUI is
  used for visualization of geometry, materials,
  fields, particle trajectories and results of
  calculations. MARS15 has 5 geometry options and
  flexible histograming options, can use as an
  input MAD optics files through a powerful
  MAD-MARS Beam Line Builder, provides an MPI-based
  multiprocessing option, with various tagging,
  biasing and other variance reduction techniques,
  is linked to state-of-the art codes such as
  DPMJET, LAQGSM, ANSYS, STRUCT, GUINEA-PIG.

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MARS15 GUI Examples for ILC BDS
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SiD in GEANT4
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SiD in GEANT4
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SiD in GEANT4
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BDSIM overview

• Geant4 toolikit for beamline simulations
• Geometry construction framework
• Additional transportation processes
• Physics lists for various accelerator
  applications
• Extensive development/benchmarking underway and
  planned
• ttp//flc.pp.rhul.ac.uk/bdsim.html - docs, cvs,
  etc

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BDSIM geometry

• Accelerator description is in the GMAD language
  (EUROTeV-Memo-2006-003)
• parameters and commands relevant for Monte-Carlo
• Mokka (EUROTeV-Report-2006-XXX) and GDML support
• ILC decks are under cvs on http//cvs.pp.rhul.ac.
  uk/ILCdecks
• Integration into LCIO may be desirable in the
  future
• CAD tool will soon be ready (GDML)

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GMAD - accelerator description

• Extension of a MAD subset to support geometry
  features
• Commands for run control, process cuts etc.
• Provides drivers to other geometry formats, so
  arbitrarily complicated geometries are possible
• Can be used as a standalone parser library

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Mokka

• Several detector groups utilise the Mokka
  framework to interface Geometry into Geant4
• Built around a MySQL database containing the
  geometry descriptions
• BDSIM loads complex geometry from MySQL dump
  files
• Follows the same principle as the Mokka database
• Standardises the structure of the MySQL tables
• Allows for the detector regions to be included in
  the optics decks

2mrad Intertaction Region in BDSIM
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Mokka Geometry Description

• Constantly improving and adding functionality -
  currently allows for
• Field Maps - e.g. Solenoid Field (all fields use
  Runga-Kutta tracking methods)
• Basic solids (Box, Tube, Cone, etc)
• Complex Solids (Torus, Polycone, Trapezoid,
  Elliptical Cone, Boolean Solids, etc)
• Dipole, Quad, Sext, and Oct magnets
• Allows for one-off magnets to be modelled where
  realistic descriptions may be important
• Sensitive volumes

Complex geometry being used to build up
cryomodules in the linac for laserwire
signal/background studies (L. Deacon - PhD
Student _at_ RHUL)
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LCDD/GDML Interface

• SiD Group make use of Linear Collider Detector
  Descriptions format (LCDD)
• An extension of the Geometry Description Meta
  Language (GDML)
• Very portable and in a well defined XML format
• Work is currently underway to allow BDSIM to
  directly run an LCDD file (e..g the SiD detector)
  alongside beamlines

• One problem is that the description of the SiD
  (in particular) is that it is quite sophisticated
  (over 26,000 lines of XML!) and is more detailed
  than is required for BDSIM use

Screenshot of the SiD LCDD file loading in BDSIM
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