In 3D simulations, PIC codes cannot resolve the radiation of short wavelength compared to the grid spacing,
which raises challenges in multi-dimensional simulations because of memory constraints. However, in many
plasma physics scenarios (e.g. laser wakefield acceleration) the radiation mechanisms can cover several orders of
magnitude in energy/frequency (from the THz range, associated with transition radiation of relativistic electron
beams, to gamma-rays, associated with the betatron radiation of self-injected electrons in the bubble or blow-out
regime). We describe a massivelly parallel post-processing radiation diagnostic that takes the track information
from 3D/2D particle-in-cell simulations and determines the full radiation spectrum of the corresponding particle(
s). Benchmark examples with cyclotron/synchrotron radiation as well as betatron radiation are presented
and compared with the analytical predictions. Special emphasis is given to the numerical properties of the
diagnostic, in particular the resolution of the particle tracks, the diagnostic spectral and spatial resolutions, as
well as the different aproximations on the numerical calculation of the radiation integral over the trajectory of
the particles. We then use this diagnostic to probe different scenarios, taking advantage of the spatial, temporal
and frequency resolved characteristics of the diagnostic.
C. Clayton, S. Martins, J. Martins, D. K. Johnson, S. Wang, K. Marsh, P. Muggli, M. J. Hogan, D. Walz, R. Fonseca, E. Oz, C. D. Barnes, C. L. O'Connell, I. Blumenfeld, N. Kirby, R. Ischebeck, C. Huang, M. Zhou, W. Lu, S. Deng, T. Katsouleas, W. Mori, R. H. Siemann, L. Silva, C. Joshi
When a highly relativistic electron is injected off-axis into an ion channel, the restoring force of the radial field of the
ions will cause the electron to accelerate towards the axis, overshoot, and begin to undergo oscillations about the ioncolumn
axis at a characteristic frequency; the betatron frequency. This so-called betatron motion will cause the electron
to radiate hard x-rays in the forward direction. In two recent experiments at the Stanford Linear Accelerator Center
(SLAC), betatron x-rays in the 1-20kV range and in the 1-50MV range were produced with an electron beam with an
energy of 28.5 GeV for ion densities of about 1 x 1014 cm-3 and 1 x 1017cm-3, respectively. To make such an x-ray source
more compact, the 3km long SLAC linac would be replaced by a source of electrons from a Laser Wakefield accelerator
(LWFA). To increase the efficiency of converting laser into photons at high photon energies, we propose adding a
second stage where the LWFA electrons radiate via a second ion channel, independent of the accelerating process. This
two stage concept allows one to control the critical frequency of the emitted radiation as well as the efficiency of the
process.
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