(Color online) Scaling of the photon efficiency with (a) target material Z for 0.5 cm thickness and (b) target thickness for an Al target. The upper line represents the efficiency for all photons and the lower line the efficiency for photons >1 MeV. Efficiency is independent of the electron energy, divergence and electron source-target distance.
(Color online) Scaling of the effective photon source size with (a) electron beam divergence for source-target distance of 5 cm and (b) electron source-target distance for an e-beam divergence of 1 mrad. Photon source size is independent of the electron energy, target material Z and thickness.
(Color online) Scaling of the photon divergence with (a) electron energy for a 0.5 mm thick Cu target placed 5 cm from the electron source, (b) target material Z for a 250 MeV electron beam, 0.5 cm thick target placed 5cm from the source and (c) target thickness placed 1 m from the source for a 250 MeV electron beam with a 1 mrad divergence. The photon source size is independent of the electron divergence and electron source-target distance.
(Color online) Scaling of the photon pulse duration with target thickness for aluminum (straight line) copper (upper curved line) and tungsten (lower curved line). The pulse duration dependence on the target thickness varies strongly with Z, which determines the net length and evolution of the electron path.
(Color online) (a) Experimental setup and (b) typical electron energy spectrum showing a central energy of 330 MeV, measured r.m.s. relative energy spread of 20% and charge 14 pC.
(Color online) (a) Imaging plate image (lower) and corresponding transverse profile (upper). The electron beam is the bright region on the left hand side and the gamma-ray beam produced by the electrons going through the Al and steel targets is the bright region on-axis. The experimental profile (red curve) is overlapped with the expected profile obtained with GEANT4 simulations (black squares) for a 220 MeV electron beam. (b) calculated energy spectrum of the bremsstrahlung radiation.
(Color online) Bremsstrahlung beam profile imaged inside the lead shadow. The high photon energy radiation is transmitted through 5 cm of lead and is recorded on the image plate.
(Color online) Example active area screen shot of the Timepix x-ray detector upon irradiation with bremsstrahlung photons. The number of detected counts for this shot is 768.
Electron and target parameters scanned in the simulation. The electrons parameters are typical values of LWFA electron beams.
Summary of the effects of increasing the parameters listed in the first column on the bremsstrahlung based gamma-ray source properties given in the first row. The symbols ⇑, ⇓ and = indicate increasing, decreasing and no effect, respectively.
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