Speaker
Description
GeV ($\gamma_e$ > 2000) electron bunches from petawatt-laser-driven plasma accelerators can be converted to tunable, narrowband or to broadband continuum $\gamma$-ray ($h\nu$ > 10 MeV) pulses by Thomson backscattering (TBS) or bremsstrahlung, respectively. Inserting a plasma mirror (PM) near the accelerator exit converts electrons to $\gamma$-rays compactly and inexpensively [1], in a TBS/bremsstrahlung mixture determined by PM thickness, material and location. Characterizing the γ-ray spectra accurately is a challenge, usually addressed with bulky pair production/Compton spectrometers. Here, we spectrally characterize PM-generated TBS/bremsstrahlung $\gamma$-rays from 1-2 GeV Texas-Petawatt-Laser-accelerated electron bunches using a compact stack calorimeter, consisting of alternating absorbers and imaging plates, to record energy-dependent particle showers generated by incoming γ-rays. An iterative Bayesian algorithm, based on a calorimeter response matrix built from GEANT4 simulations, reconstructs TBS and bremsstrahlung contributions for each shot, as PM and electron parameters vary. The method should be widely applicable to plasma-accelerator-based radiation with MeV photon energies.
[1] H.E. Tsai et al., Phys. Plasmas 22, 023106 (2015); T. Phuoc et al., Nat. Phot. 6, 308–311 (2012); A. Döpp et al., Plasma Phys. Control. Fusion 58, 034005 (2016); C. Yu et al., Sci. Rpts. 6, 29518 (2016)
