Proton acceleration enhanced by a plasma jet in expanding foils undergoing relativistic transparency

Powell, H W and King, M and Gray, R J and MacLellan, D A and Izquierdo, Bruno and Stockhausen, L C and Hicks, G and Dover, N P and Rusby, D R and Carroll, D C and Padda, H and Torres, R and Kar, S and Clarke, R J and Musgrave, I O and Najmudin, Z. and Borghesi, M and Neely, D and McKenna, P (2015) Proton acceleration enhanced by a plasma jet in expanding foils undergoing relativistic transparency. New Journal of Physics, 17. 103033. ISSN 1367-2630 (

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Ion acceleration driven by the interaction of an ultraintense (2x10^20 Wcm^-2) laser pulse with an ultrathin (40nm) foil target is experimentally and numerically investigated. Protons accelerated by sheath fields and via laser radiation pressure are angularly separated and identified based on their directionality and signature features (e.g. transverse instabilities) in the measured spatial-intensity distribution. A low divergence, high energy proton component is also detected when the heated target electrons expand and the target becomes relativistically transparent during the interaction. 2D and 3D particle-in-cell (PIC) simulations indicate that under these conditions a plasma jet is formed at the target rear, supported by a self-generated azimuthal magnetic field, which extends into the expanded layer of sheath-accelerated protons. Electrons trapped within this jet are directly accelerated to super-thermal energies by the portion of the laser pulse transmitted through the target. The resulting streaming of the electrons into the ion layers enhances the energy of protons in the vicinity of the jet. Through the addition of a controlled prepulse, the maximum energy of these protons is demonstrated experimentally and numerically to be sensitive to the picosecond rising edge prole of the laser pulse.


Powell, H W, King, M ORCID logoORCID:, Gray, R J ORCID logoORCID:, MacLellan, D A, Izquierdo, Bruno, Stockhausen, L C, Hicks, G, Dover, N P, Rusby, D R ORCID logoORCID:, Carroll, D C, Padda, H ORCID logoORCID:, Torres, R, Kar, S, Clarke, R J, Musgrave, I O, Najmudin, Z., Borghesi, M, Neely, D and McKenna, P ORCID logoORCID:;