LBNL PI: Cameron Geddes
Near-monoenergetic photon sources (MPSs) offer improved sensitivity at greatly reduced dose for active interrogation, as well as new capabilities in treaty verification, non-destructive assay (NDA) of spent nuclear fuel, and emergency response. The ability to select energy, energy spread, flux, and pulse structure to deliver only the photons needed can resolve many of the issues with current broad-band photon sources, including unnecessary dose that can interfere with the signatures to be detected and/or restrict operations. MPS applications have however been limited by the sizes of the required high-energy electron accelerator, scattering laser, and electron beam dump. The Venture addresses each of these issues. It will build a compact MPS, demonstrate techniques to make these systems transportable, and apply the source to initial application experiments. Thomson scattering (scattering of a laser from an electron beam) is a well-established, tunable photon source using conventional linacs, but these accelerators are long (>10m) for the energies required to generate MeV photons. Heavy shielding, which can dominate overall system size and weight as accelerators are made smaller, is conventionally required due to the high electron beam energy. This is compounded by the low photon production cross section, which has hitherto required either high electron current (and thus heavier shielding) or very large scattering lasers. Under this venture a high quality Thomson-scattering MPS (also referred to as a Compton-Scattering or Inverse Compton-Scattering source) driven by a compact LPA will be built using techniques developed over past project cycles and by the community. Using the LPA to decelerate the electron beam (demonstrated last cycle) can reduce undesired radiation, mitigating shielding needs. Deceleration will be implemented after photon production. Guiding and pulse shaping of the scattering laser will be implemented, to test techniques for high yield at realistic current and with lasers comparable to the LPA driver. Initial experiments will be conducted to validate the advantages of the LPA based MPS. Radiography is an attractive first application, and others will be explored by INL and LBNL. Suitable detectors for the pulsed source will be developed and deployed. Leading simulation programs at LBNL and LLNL support the venture. Advanced techniques will be developed to satisfy future application needs. Needs include high photon fluxes of 1010-1012 photons/sec. and repetition rates ≥ kHz, to support which new laser techniques will be developed in collaboration with U. Michigan. Narrow energy spreads ≤ 2% are also desired for use of Nuclear Resonance Fluorescence (NRF), which requires controlling electron divergence. The venture addresses the main limits on current application of MPSs, namely the sizes of the required: accelerator, radiation shielding, and scattering (photon generating) laser.