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Calculation of radiation produced by dark current
in the Cornell ERLLisa Nash, University of North
Carolina at Chapel HillAdvisor: Val Kostroun
Motivation
• Radiation fields from dark current in unknown
• Measurements will be taken later this month– Goal of project was to simulate possible
results
Motivation Cont. : JLab measurements
• Cryomodules at JLab are similar to those for Cornell ERL– Cavities are 20 MV/m at Jlab, 16 MV/m at
Cornell ERL– Neutron and gamma spectra will be
measured at entrance and exit of a cryomodule
Radiation generated by electrons
• Electrons in ERL accelerated to energies as high as 5 GeV– Bremsstrahlung radiation – Electromagnetic shower created can
cause emission of neutrons
Monte-Carlo
• Probability distributions randomly sampled to determine the outcome of each step– Reliability of models is important
e-g
e+
Monte-Carlo Method and MCNP
• 1930s :Fermi used method to solve problems in neutron physics, but never published results.
• WWII: Statistical sampling to solve problems discussed at LANL by several scientists. Method named for Monte-Carlo casino.
• 1963: First general-purpose particle transport code developed at LANL
• 1977: MCNP developed as Monte-Carlo Neutron Photon (now Monte-Carlo N-Particle, MCNPX=Monte-Carlo N-Particle eXtension)
Old Monte-Carlo code card
Using MCNPXc Created on: Friday, July 15, 2011 at 15:19 1 1 -8.57 -9 3 13 -15 2 1 -8.57 -10 5 14 -16 3 1 -8.57 -6 1 15 11 4 1 -8.57 -6 1 -11 16 5 1 -8.57 -2 7 -13 -18 6 1 -8.57 -4 8 -14 -18 7 0 -3 -5 -13 -14…
1 tz 0 0 0 6.731 4.135 3.557 2 tz 0 0 5.765 5.712 1.235 2.114 3 kz 5.72789 19.713405481652 -1 4 tz 0 0 -5.765 5.712 1.235 2.114 5 kz -5.72789 19.713405481652 1 6 tz 0 0 0 6.731 4.435 3.857…
mode n p e m1 41093.24c 1 $MAT1c --Physicsphys:p 330 0 0 1 1phys:e 330 0 0 0 0 1 1 1 1phys:n 330 2j 0 -1 0 0phys:h 330 j 0…
Simple niobium runs• 0.3 cm thick piece of niobium
simulated for varying angles and energies
• Energy deposition by electrons and gamma/electron currents tallied from surfaces
Electrons incident
θ
e-
Angles and energies varied
MCNPX tallies
Number of gammas per source particle exiting opposite face of niobium at 40 degrees, 40 MeV
Spatial distribution of radiation
Gamma fluence at 0 degrees Gamma fluence at 80 degrees
Secondary electrons
Fraction of electrons scattered backwards (per source electron)
Average energy of electrons in MeV
Energy Deposited
Energy deposited per incident particle in niobium
Cavity and Cryomodule Geometry
• Needed geometry components (tori and cones) solved for in Mathematica
• MCNPX visualization of single 7-cell cavity
• View down the MCNPX cryomodule
Cryomodule approximation
Coaxial cylinders of cryomodule materials
Linear source of electrons incident on niobium cylinder
Stainless Steel
Aluminum
Titanium
Niobium
e-
Gammas through steel end-cap
Average energy of gamma exiting the cryomodule through an end-cap
Number of gammas through end-cap per square centimeter (per source particle)
Summary
• Varying degrees of detail have been added to problem geometry and are ready for simulation with Christie’s data
• Val is preparing for measurement at the end of August
Acknowledgements
• I would like to thank Val for teaching me about nuclear physics and simulations in MCNPX and everyone involved in setting up the REU program
• This work was supported by the NFS
Questions?