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Experimental and simulated heating in nanocrystalline diamond charge exchange injection films using an electron beam to mimic...

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Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment
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Nanocrystalline diamond (NCD) foils have been in use at the Spallation Neutron Source as primary stripper foils for charge exchange injection since the machine’s inception. NCD’s low atomic number leads to reduced beam scattering while still being easy to handle, as opposed to even lighter elements. NCD foils also have the benefit of being free-standing, and rigid when grown under the right conditions to minimize residual stresses. This study overviews a method to mimic the Spallation Neutron Source (SNS) beam and characterize thermally driven failure of NCD foils. To do this, a foil test stand was developed with in situ diagnostics that tracks signs of foil sublimation and thinning. The foil test stand’s electron beam is equated to the SNS beamline by comparing peak deposited energy densities for both beams. Post-mortem testing is also conducted to help elucidate changes the NCD foils undergo during exposure to the beam. A COMSOL simulation was also developed as a method to assess potential future changes to the NCD film and predict how changes to beam conditions will effect foil temperatures. This method allows for examination of the NCD foil’s thermal limits and can be used to assess future changes to SNS stripper foils.