Abstract
The dynamics of electron acceleration driven by laser wakefield inside a 30.5 mm long dielectric capillary tube is analyzed using radiation emitted in the x-ray range. 3D particle-in-cell simulations, performed with parameters close to the experimental ones, show that in long plasmas, the accelerated electrons catch up and finally overrun the driving laser owing to a higher velocity of the electrons in the plasma. The electrons are then transversely scattered by the laser pulse, and penetrate the capillary wall where they generate bremsstrahlung radiation, modeled using geant4 simulations. The signature of bremsstrahlung radiation is detected using an x-ray camera, together with the betatron radiation emitted during electron acceleration in the plasma bubble. The reflection of betatron radiation from the inner capillary surface also accounts for a fraction of the observed signal on the x-ray camera. The simulation results are in agreement with the experimental ones and provide a detailed description of the electron and radiation properties, useful for the design of laser wakefield accelerators or radiation sources using long plasma media.
Highlights
Charged particle accelerators play an important role in the development of modern science and technology, as the produced high energy particle beams are essential for several domains of fundamental and applied research
We analyzed the dynamics of electrons acceleration by laser wakefield inside a long plasma medium when the laser is guided by a dielectric capillary tube
This phenomenon is undesired for the generation of collimated beams of high energy electrons, and can be avoided by making the laser pump depletion length shorter than the dephasing length, so the laser becomes greatly damped before the electrons catch up with it
Summary
Charged particle accelerators play an important role in the development of modern science and technology, as the produced high energy particle beams are essential for several domains of fundamental and applied research. In order to achieve GeV-class electron beams [13] or betatron radiation with photon energy of ∼100 keV or above [14], a few centimeter long plasma channels have been employed. We report on the analysis of the radiation emitted during the acceleration of an electron bunch by LWFA in a plasma long enough for the electron bunch to catch up with the laser pulse. It is found that the trapped electrons are first accelerated and wiggled in the plasma bubble, producing betatron radiation, and the accelerated electrons catch up and overrun the driving laser pulse, a process during which electrons are scattered transversely by the laser ponderomotive force. Numerical simulations of the electron acceleration process and radiation generation are performed to support the analysis of experimental observations
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