NARROW BANDWIDTH ION SPECTRA FROM RADIATION PRESSURE ACCELERATION
S. Kar1, K.F. Kakolee1, D. Doria1, B. Ramakrishna1, G. Sarri1, K. Quinn1, M. Borghesi1, M. Zepf1,
X. Yuan2, P. McKenna2, M. Cerchez3, J. Osterlholz3, O. Willi3, A. Macchi4, T. Liseykina4
1 Department of Physics, Queen’s University of Belfast, UK
2 Department of Physics, University of Strathclyde, Glasgow, UK
3 Institut für Laser-und Plasmaphysik, Heinrich-Heine-Universität,
Düsseldorf, Germany
4 Dipartimento di Energetica, Università di Roma 1 ‘La Sapienza’, Roma, Italy
Abstract. Ion acceleration from solid targets irradiated by high-intensity pulses has been one of the most attractive areas of research in the last decade due to its widespread potential applications in science, technology and healthcare [1]. The field emerged with the discovery of MeV ions accelerated by the so-called Target Normal Sheath acceleration (TNSA) mechanism, where the ions are driven by sheath fields established by relativistic electrons produced during the laser interaction. Radiation pressure acceleration (RPA) mechanism is currently attracting a substantial amount of experimental [2,3] and theoretical [4,5] attention worldwide, due to its superior scaling in terms of ion energy and laser-ion conversion efficiency. RPA, particularly in its so-called light sail (LS) implementation employing ultrathin foils [4], is predicted to produce ion beams of GeV/nucleon energy with next generation lasers. Employing the Petawatt lasers of the Rutherford Appleton Laboratory, UK, both the Hole-boring (HB) and LS regimes of RPA have been extensively explored. The striking features in the results are narrow band (few MeV/nucleon) proton and carbon spectra, centred at energies in a range 5-15 MeV/nucleon depending on the laser (intensity, polarisation) and target (thickness) parameters. The role of laser radiation pressure in such intense interaction conditions, producing narrow band spectral feature, is studied by 2D particle-in-simulations. The conditions (range of laser and target parameters) required for a sustained snow-plough acceleration mechanism are characterised from the parametric scans carried out in the experiments. The aftermath of RPA is observed in the late time (0.1 - 1 ns) evolution of collimated plasma jets ejected from the target rear surface [3], obtained from a complementary time resolved transverse interferometer.
References:
[1] M. Borghesi et al, Fusion Science and Technology, 49, 412 (2006)
[2] A. Henig, et al, 2009 PRL 103 245003 (2009)
[3] S. Kar et al, Phys. Rev. Lett., 100, 225004 (2008)
[4] A P L Robinson et al, New J. Phys. 10 013021 (2008)
[5] A. Macchi et. al, New J Phys., 12, 045013 (2010)
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