Abstract
Ultrafast betatron x-ray emission from electron oscillations in laser wakefield acceleration (LWFA) has been widely investigated as a promising source. Betatron x-rays are usually produced via self-injected electron beams, which are not controllable and are not optimized for x-ray yields. Here, we present a new method for bright hard x-ray emission via ionization injection from the K-shell electrons of nitrogen into the accelerating bucket. A total photon yield of 8 × 108/shot and 108 photons with energy greater than 110 keV is obtained. The yield is 10 times higher than that achieved with self-injection mode in helium under similar laser parameters. The simulation suggests that ionization-injected electrons are quickly accelerated to the driving laser region and are subsequently driven into betatron resonance. The present scheme enables the single-stage betatron radiation from LWFA to be extended to bright γ-ray radiation, which is beyond the capability of 3rd generation synchrotrons.
Highlights
The betatron x-rays generated from electron oscillations in laser wakefield acceleration (LWFA) are a promising source owing to the high spatial coherence[12], high photon yield (>108/shot) and high photon energy[13]
We report the first study of bright, hard x-rays based on ionization-injected electron beams accelerated in LWFA via betatron oscillations
The laser pulses from a 100 TW laser system were focused by an off-axis-parabola mirror onto a 1.2 mm × 10 mm supersonic gas jet
Summary
The betatron x-rays generated from electron oscillations in laser wakefield acceleration (LWFA) are a promising source owing to the high spatial coherence[12], high photon yield (>108/shot) and high photon energy (up to MeV)[13]. Electrons trapped inside the laser wakefield are accelerated longitudinally[15] and undergo betatron oscillation owing to the presence of transverse electric and magnetic fields in the wakefield[14,16,17]. The oscillation period of the betatron motion in LWFA is thousands of times smaller than that of the conventional magnetic wiggler. In the case of LWFA, where αβ 1,the emitted x-ray beam has a synchrotron like broadband spectrum, which can be expressed as. The spectrum peaks at E~0.5Ec, beyond which the radiation tends to decay exponentially[12]
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