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- 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

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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?