《《pop》》.pdf

PHYSICS OF PLASMAS 17, 056708 2010 Scalings for radiation from plasma bubblesa… A. G. R. Thomasb Department of Nuclear Engineering and Radiological Sciences, University of Michigan, Ann Arbor, Michigan 48109, USA Received 27 December 2009; accepted 2 March 2010; published online 14 April 2010 In this paper, electron trajectories are studied analytically in the rest frame of a plasma bubble using nonevolving, linear, radial electric and azimuthal magnetic fields in a spherical structure. The electron motion is broken into two distinct periods; one where it orbits around the periphery to the rear of the bubble, and one where it performs oscillations within the bubble interior. By using the first period as an initial condition for the second, general scalings are developed for the x-ray radiation produced by the electron oscillations. The equations are also analyzed to give self- trapping conditions for the electron and to examine the sensitivity of the transverse momentum to small variations from an orbit that is a circular arc. The scalings are in reasonable agreement with recent experiments on x-ray generation and predict a peak spectral brightness of 27 photons / s mrad mm 0.1%BW of radiation with a critical energy of 300 MeV using a S 6 10 single stage accelerator driven by a 120 PW laser. © 2010 American Institute of Physics. doi: 10.1063/1.3368678 I. INTRODUCTION wavelength, b . The spectrum of radiation produced by a