Broadband single-shot electron spectrometer for GeV-class laser-plasma-based accelerators.

Laser-plasma-based accelerators can provide electrons over a broad energy range and/or with large momentum spread. The electron beam energy distribution can be controlled via accurate control of laser and plasma properties, and beams with energies ranging from approximately 0.5 to 1000 MeV have been observed. Measuring these energy distributions in a single shot requires the use of a diagnostic with large momentum acceptance and, ideally, sufficient resolution to accurately measure narrow energy spread beams. Such a broadband single-shot electron magnetic spectrometer for GeV-class laser-plasma-based accelerators has been developed at Lawrence Berkeley National Laboratory. Detailed descriptions of the design concept and hardware are presented, as well as a performance evaluation of the spectrometer. The spectrometer covered electron beam energies raging from 0.01 to 1.1 GeV in a single shot, and enabled the simultaneous measurement of the laser properties at the exit of the accelerator through the use of a sufficiently large pole gap. Based on measured field maps and third-order transport analysis, a few percent-level resolution and determination of the absolute energy were achieved over the entire energy range. Laser-plasma-based accelerator experiments demonstrated the capability of the spectrometer as a diagnostic and its suitability for measuring broadband electron sources.