Calculation of radiation
produced by dark current in the
Cornell ERL
Lisa Nash, University of North
Carolina at Chapel Hill
Advisor: 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+
e-
g
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 NParticle eXtension)
Old Monte-Carlo code card
Using MCNPX
c
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1
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Created
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0
on: Friday, July 15, 2011 at 15:19
-8.57 -9 3 13 -15
-8.57 -10 5 14 -16
-8.57 -6 1 15 11
-8.57 -6 1 -11 16
-8.57 -2 7 -13 -18
-8.57 -4 8 -14 -18
-3 -5 -13 -14…
tz
tz
kz
tz
kz
tz
0 0 0 6.731 4.135 3.557
0 0 5.765 5.712 1.235 2.114
5.72789 19.713405481652 -1
0 0 -5.765 5.712 1.235 2.114
-5.72789 19.713405481652 1
0 0 0 6.731 4.435 3.857…
mode n p e
m1
41093.24c
c --Physics
phys:p 330 0 0 1 1
phys:e 330 0 0 0 0 1 1 1 1
phys:n 330 2j 0 -1 0 0
phys:h 330 j 0…
1
$MAT1
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
Angles and
energies varied
θ
eElectrons
incident
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
• MCNPX visualization of single 7-cell cavity
• Needed geometry components
(tori and cones) solved for in
Mathematica
• View down the MCNPX
cryomodule
Cryomodule approximation
Coaxial cylinders of
cryomodule materials
Stainless Steel
Aluminum
Linear source of
electrons incident
on niobium cylinder
Niobium
eTitanium
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?