Relativistic laser driven electron accelerator using micro-channel plasma targets

Abstract

We present an experimental demonstration of the efficient acceleration of electrons beyond 60 MeV using micro-channel plasma targets. We employed a high-contrast, 2.5 J, 32 fs short pulse laser interacting with a 5 m inner diameter, 300 m long microchannel plasma target. The micro-channel was aligned to be collinear with the incident laser pulse, confining the majority of the laser energy within the channel. The measured electron spectrum showed a large increase of the cut-off energy and slope temperature when compared to that from a 2 m flat Copper target, with the cutoff energy enhanced by over 2.6 times and the total energy in electrons >5 MeV enhanced by over 10 times. Three-dimensional particle-in-cell simulations confirm efficient direct laser acceleration enabled by the novel structure as the dominant acceleration mechanism for the high energy electrons. The simulations further reveal the guiding effect of the channel that successfully explains preferential acceleration on the laser/channel axis observed in experiments. Finally, systematic simulations provide scalings for the energy and charge of the electron pulses. Our results show that the micro-channel plasma target is a promising electron source for applications such as ion acceleration, Bremsstrahlung X-ray radiation, and THZ generation.

Intense proton acceleration in ultrarelativistic interaction with nanochannels

“…By considering the continuity relation of E y at the vacuum-wall interface, the transverse electric field E y into the overdense plasma is expected to be lower than into the gap by a factor of ≈(1 − n e,+ /γ n c )/(1 − n e,− /γ n c ) ≈ 50, where n e,+ and n e,− are the electron densities in the wall and in the gap, respectively. The spatial distribution of the e.m. field is here significantly different from that obtained with microchannel targets [10], where the larger size allows the laser light to freely propagate into the channels. Nevertheless, the fields obtained by Zou et al [20] at the edge of the channels, including e.m. and electrostatic surface waves, is similar to our results.…”

“…Depending on the target geometry, the improved laser-target coupling can result in a volumetric heating of the plasma up to extreme temperatures [5], in a more efficient x-ray emission [6] or in an efficient production of HE [7][8][9]. It was shown that for aligned arrays of micropillars or microchannels, the interaction can lead to mega-Ampere currents of relativistic electrons propagating into the target [10], resulting in the self-generation of a mega-Gauss magnetic field on its rear surface [11]. Kinetic particle-in-cell (PIC) simulations suggest that the larger HE generation is related to the enhancement of electrostatic fields [8] or to the generation of propagating electromagnetic (e.m.) waves [12] in the proximity of the nanostructures.…”

Generation of relativistic high-order-mode laser pulse using plasma waveguide

“…Such and other novel methods can be useful for fabricating the hollow waveguides needed in our scheme. In fact, the use of a micro-channel target of diameter 5μm has been successfully used in an electron acceleration experiment [37]. On the other hand, the ubiquitous laser-spot quivering in real situations may post a problem for the target aiming since the waveguide aperture here is comparable with the laser spot size.…”

Copious positron production by femto-second laser via absorption enhancement in a microstructured surface target

“…1. A MST is a solid planar target with fabricated fine structures, such as layers 22 , wires [23][24][25][26][27][28] , slots 29 or holes 30 on its surface. By the surface modulation, the interaction between laser and target can be changed from "surface heating" to "volume heating", thus increasing laser absorption and electron heating 25 .…”

“…By the surface modulation, the interaction between laser and target can be changed from "surface heating" to "volume heating", thus increasing laser absorption and electron heating 25 . MSTs have been widely used in the Kα-rays production 23,24 , electron acceleration 22,25,26,30 , ion acceleration 27,29 and neutron generation 28 . Here, we firstly propose to use a MST to enhance positron production.…”