Laser-Driven Ion Acceleration from Plasma Micro-Channel Targets

Abstract

Efficient energy boost of the laser-accelerated ions is critical for their applications in biomedical and hadron research. Achiev-able energies continue to rise, with currently highest energies, allowing access to medical therapy energy windows. Here, a new regime of simultaneous acceleration of ~100 MeV protons and multi-100 MeV carbon-ions from plasma micro-channel targets is proposed by using a ~1020 W/cm2 modest intensity laser pulse. It is found that two trains of overdense electron bunches are dragged out from the micro-channel and effectively accelerated by the longitudinal electric-field excited in the plasma channel. With the optimized channel size, these “superponderomotive” energetic electrons can be focused on the front surface of the attached plastic substrate. The much intense sheath electric-field is formed on the rear side, leading to up to ~10-fold ionic energy increase compared to the simple planar geometry. The analytical prediction of the optimal channel size and ion maximum energies is derived, which shows good agreement with the particle-in-cell simulations.

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

“…For given r 0 and σ 0 , η is determined by a 0 . Both the radial electron momentum p r and the longitudinal electron momentum p x from the high-ordermode electric field E x are proportional to a 0 [5]. For the contribution of the laser ponderomotive force to p x , the superluminous phase velocity of the wave in the plasma waveguide must be taken into account if a 0 >a cr , where = -…”

“…c v c 2 cr ph 1 2 is the critical amplitude and v ph is the light phase velocity [5]. In fact, it changes from as a 0 is further increased.In addition, we found that the density of the pulled-out wall electrons scales as c a 0 , where χ is related to the ionization degree of the wall material [5]. Therefore a 0 is closely related to η and therefore can affect the energy conversion efficiency from the laser to the TM modes.…”

“…With higher laser intensity, a large amount of high-energy gamma photons can be generated via Compton backscattering.If collided with a counter-propagating laser pulse, the accelerated electrons may lead to pair production via the Breit-Wheeler process [38]. Furthermore, focused energetic electrons, useful for target normal sheath acceleration, can be achieved by using a proper channel size [5,39]. It is also of interest to note that there is no change of the central frequency of the incident laser as it is converted into the lowest-order waveguide mode.…”

“…Such laser-driven accelerators can generate MeV, or even GeV, energetic charged particles within a centimeter or less [2,3] and have thereby opened the door for exploring high energy density physics and astrophysics in the laboratory. Recently, it was shown that intense short wavelength optical modes with inherent longitudinal electric fields are particularly effective for electron acceleration [4][5][6][7]. The resulting electrons have typically superponderomotive temperature [4] and structures that are suitable for generating bright x-rays [4], energetic ions [5], etc.…”

“…Recently, it was shown that intense short wavelength optical modes with inherent longitudinal electric fields are particularly effective for electron acceleration [4][5][6][7]. The resulting electrons have typically superponderomotive temperature [4] and structures that are suitable for generating bright x-rays [4], energetic ions [5], etc. However, realizing such high-order short wavelength light in the laboratory is still challenging, mainly because of radiation damage of the optical modulators.…”