Target-normal sheath acceleration (TNSA) of ions by >100-fs relativistic laser pulses irradiating a multichannel target consisting of a row of parallel long wires and a plane back foil is studied. Two-dimensional particle-in-cell simulations show that the laser light pulls out from the wires a large number of dense hot attosecond electron bunches, which are synergetically accelerated forward by the relativistic ponderomotive force of the laser as well as the longitudinal electric field of a transverse magnetic mode that is excited in the vacuum channels between the wires. These electrons are characterized by a distinct two-temperature energy spectrum, with the temperature of the more energetic electrons close to twice the ponderomotive potential energy. After penetrating through the foil, they induce behind its rear surface a sheath electric field that is both stronger and frontally more extended than that without the channels. As a result, the TNSA ions have much higher maximum energy and the laser-to-ion energy conversion efficiency is also much higher. It is found that a laser of intensity 1.37 × 1020 W/cm2, duration 165 fs, and energy 25.6 J can produce 85 MeV protons and 31 MeV/u carbon ions, at 30% laser-to-ion energy conversion efficiency. The effects of the channel size and laser polarization on the TNSA ions are also investigated.
Enhancement of target normal sheath acceleration in laser multi-channel target interaction
D. B. Zou, D. Y. Yu, X. R. Jiang, M. Y. Yu, Z. Y. Chen, Z. G. Deng, T. P. Yu, Y. Yin, F. Q. Shao, H. B. Zhuo, C. T. Zhou, S. C. Ruan; Enhancement of target normal sheath acceleration in laser multi-channel target interaction. Phys. Plasmas 1 December 2019; 26 (12): 123105. https://doi.org/10.1063/1.5096902
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