Enhancement of betatron x-rays in a laser plasma accelerator

Summary form only given. Betatron radiation is a highly collimated laser-driven hard x-ray source with fs duration which generated by electron transversely oscillation during acceleration in underdense plasmas. We will present our recent progress in enhancing acceleration to optimize the x-ray photon yield/energy. 1) A new method is demonstrated for generating intense betatron x-rays using a clustering gas target [ 1]. The yield of the Ar x-ray betatron emission has been measured to be 2x108 photons/pulse. Simulations point to the existence of clustering as a contributor to the DLA mechanism, leading to higher accelerated electron charge (x40) and much larger electron wiggling (-8 μm) amplitudes in the plasma channel, thereby finally enhancing the betatron x-ray photons. 2) Another concept of generation of bright betatron radiation during electron acceleration was newly invented [2]. Two electron bunches were injected sequentially into the wakefield. The first one is a mono-energetic electron bunch with energy of GeV level, and the second one is injected continuously with large charge and performs resonantly transverse oscillation with large amplitude during the subsequent acceleration, which results in the enhancement of betatron x-ray emission. After optimize interaction conditions, Gamma-rays with yield reaches to 10 11 can be obtained by using 200TW laser [3]. 3) In order to control the stability of betatron x-ray generation as well as enhance its yield and energy, ionization injection with N2 gas is studied. In experiment, we obtained stably accelerated monoenergetic electron beams with energy spread 5% only for the first time [4]. 109 photons in hard xrays and 108 photons in gamma-rays are stimulated, results in a peak brightness 1023 phs/s/mm2/mrad2/(0. 1%BW). Quick injection, acceleration and oscillation in the wake of the ionization injected electron leads to the effective resonant betatron oscillation, which result in gamma -ray photon energy and peak brilliance beyond that of 3rd generation synchrotron facilities [5].