Photon Collimation For The ILC Positron Target

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Photon Collimation For The ILC Positron Target

• Lei Zang
• The University of Liverpool
• Cockcroft Institute
• 24th March 2007

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Contents

• Introduction of International Linear Collider
  (ILC)
• ILC positron source
• Photon Collimator
• Photon collimator design and Simulation tools
• FLUKA benchmarking test
• FLUKA simulation results
• Conclusion
• Plan for future work

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International Linear Collider (ILC)

• ILC is a proposed high-energy electron-positron
  linear collider with a baseline design of 500 GeV
  (CoM), supporting a later upgrade to 1 TeV and
  baseline luminosity of 21034 cm-2s-1. In order
  to achieve this luminosity we need order 1014
  positrons s-1.
• 60 polarised positron beam produced by the
  baseline source
• The ILC is important for future precision physics
  measurements.

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Positron Source

• 150 GeV Electrons Helical Undulator
  Photon Collimator Target Optical
  Matching Device (OMD) Capture RF NC
  Linac SC Booster Damping Ring

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Simulation Tools

• FLUKA is Monte Carlo code (written in the
  FORTRAN 77 programming language) for simulating
  and calculating the particle transport and
  interaction with matter with high accuracy. The
  code can model 60 different type of particles and
  handle complex geometries. For more applications,
  there are a number of user interface routine
  available for special requirements.
• SIMPLEGEO allows the user to build
  geometries interactively, in which we build
  up a logical tree to define the regions and
  bodies. After procedural modelling the
  geometries, it can be easily exported to FLUKA
  for simulation
• FLUKAGUI it is a graphical user interface
  for FLUKA. It is used to view standard FLUKA
  output and to inspect the implemented geometries
  following the traditional FLUKA 2D concept. This
  project is developed within the ROOT framework

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Design of Photon Collimator

• There are two purposes for photon collimator
• Scrape the photon beam to limit the
  extraneous halo
• Adjust the polarisation.

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FLUKA Simulations
1106 Events

• The plot is energy distributions of photons
  generated by electrons (150 GeV) passing through
  100 meters undulator (period of undulator of 1 cm
  and K1).
• A modified FLUKA user routine was used to
  generate the photon beam energies.
• The angular dependence was approximated by a
  Gaussian distribution of standard deviation 1/?.

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FLUKA Benchmarking Test

• Shape of Cascade shower
• where a0.5 for photon, E is the energy of
  incident particle and eis the critical energy of
  the material
• The shower depth for 95 of longitudinal
  containment is given approximately by
• And the transverse shower dimension with 95 of
  containment

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FLUKA Simulation-Energy Deposition
1106 Events
plot is energy deposition in 15 sections
of spoilers. Each of the horizontal line stands
for 15 spoilers with length from 1mm to 15mm (so
15 lines). The horizontal axis gives the
spoilers number (from the 1 located at the
entrance of collimator, to the 15 the last one).
Vertical axis gives the energy deposited in the
spoilers per machine pulse.
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FLUKA Simulation-Energy Deposition
1106 Events
Simulation of FLUKAGUI, Energy Deposition in
Photon Collimator.
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FLUKA Simulation-Peak Temperature Rise

• In order to approximate the temperature rise in
  the photon collimator, I use the specific heat
  capacity. The formula is
• ?T is instantaneous peak temperature change after
  absorbing energy Q in mass m, Cs is the specific
  heat capacity.

1106 Events
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FLUKA Simulation-Radiative cooling

• The total power radiated for a surface area is
  proportional to the 4th power of the Temperature,
  and is given by the Stefan Boltzmann law
• Assume the emissivity for Titanium is 0.5. The
  spoiler sections equilibrium temperature obtained
  for pure radiative cooling is

1106 Events
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FLUKA Simulation-Convective cooling

• We can calculate the convection heat transfer
  between a moving fluid and a solid in
  thermodynamics
• where Q is the power input or heat lost, h is
  overall heat transfer coefficient, A is the
  outside solid-fluid contact surface area, and ?T
  is the difference in temperature between the
  solid surface and surrounding fluid area. For now
  I will use the heat transfer coefficient equals
  to 100 W/K/m2 which is approximate value taken
  for forced convective cooling of the system.

1106 Events
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Conclusion

• An initial study of a previous design for the ILC
  positron source photon collimator have been
  carried out.
• With help of FLUKA, undulator photon energy
  spectrum is generated using an analytical
  expression for an ideal undulator.
• Benchmarking test show reasonable agreement with
  FLUKA.
• Instantaneous heating of the spoilers could be
  very large. Spoilers could be damaged from
  thermal shock. I will do a further investigation.
• Radiative cooling and convective cooling appear
  to be both possible. Further analysis will take
  place.

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Plan for future work

• Another version of DESY designed collimator with
  tilted spoiler sections need to investigate
• Simulate Cornell designed collimator
• Neutron production rate in the photon collimator
  need to be considered. Additional software would
  be needed to understand radiation damage.
• Remote handling system