Berkeley Lab

MeV Photon Sources and Nuclear Security Applications

Compact LPAs produce GeV electrons in centimeter accelerating structure lengths, enabling transportable quasi-monoenergetic photon sources

Conceptual diagram of a gamma-ray interrogation system based on a Thomson-scattering source.

Conceptual diagram of a gamma-ray interrogation system based on a Thomson-scattering source.

BELLA Center researchers are developing laser-plasma accelerators (LPAs) to enable compact, collimated, monoenergetic photon sources for special nuclear material (SNM) detection, as well as for nuclear physics studies, via Thomson scattering of laser light off the electron beam. Such sources offer the promise of improved sensitivity at greatly reduced dose for active interrogation, and new capabilities in treaty verification, NDA of spent nuclear fuel and emergency response. Compact, efficient accelerators with low energy spread and emittance in the 0.2-1 GeV energy range are required to drive the photon source.

Monoenergetic photon sources allow SNM signatures to be obtained with greatly reduced radiation doses to the target compared to broadband bremsstrahlung sources. In addition, the narrow energy spread reduces background, improving detection in nuclear resonance fluorescence (NRF) screening, where a very narrow linewidth signal must be detected. The same properties are important for basic nuclear physics studies, including scattering. Small beam divergence offers the potential for high resolution scans or for interrogating targets tens of meters away.

Thomson scattering is a demonstrated source of monoenergetic, low divergence MeV gammas, and requires a ~0.2-0.8 GeV accelerator, scattering laser beamline, and beam stop. To accomplish this with traditional approaches, the rf linac must be tens of meters long to reach the required electron energies, and the scattering lines are themselves several meters long, especially for high-repetition-rate systems; plainly these are large fixed facilities.

BELLA researchers are pursuing experiments and theory to develop LPAs that will greatly reduce photon source size. LPAs have produced e-beams at the required 0.2-0.8 GeV in one to three cm. Project experiments have developed and demonstrated accelerator injector and structure control to reduce energy spread and increase efficiency. Photon source designs integrating these components are being developed. Thomson sources (regardless of accelerator) and many other active interrogation sources produce pulsed gamma beams, and detectors capable of handling many gammas per shot are being developed. This will develop the required techniques for an LPA based compact gamma source to take advantage of compact and rapidly developing lasers.