Dynamics of charge-displacement channeling in intense laser–plasma interactions

S Kar,T V Liseykina,R Jung,L A Gizzi,M Galimberti,O Willi,C A Cecchetti,M Borghesi,L Romagnani,J Osterholz,A Macchi,F Ceccherini,A Schiavi,R Heathcote

doi:10.1088/1367-2630/9/11/402

Abstract

The dynamics of transient electric fields generated by the interaction of high intensity laser pulses with underdense plasmas has been studied experimentally with the proton projection imaging technique. The formation of a charged channel, the propagation of its front edge and the late electric field evolution have been characterized with high temporal and spatial resolution. Particle-in-cell simulations and an electrostatic, ponderomotive model reproduce the experimental features and trace them back to the ponderomotive expulsion of electrons and the subsequent ion acceleration.

Highlights

The study of the propagation of intense laser pulses in underdense plasmas is relevant to several highly advanced applications, including electron [1] and ion acceleration [2, 3], development of X- and γ-ray sources [4], and fusion neutron production [5]
Strong space charge electric fields are generated during the early stage of the propagation of a superintense laser pulse through an underdense plasma as the ponderomotive force acts on electrons, pushing them away from the axis
The development of the the proton projection imaging (PPI) technique [15] has provided a very powerful tool to explore the fast dynamics of plasma phenomena via the detection of the associated transient electric field structures

Summary

Introduction

The study of the propagation of intense laser pulses in underdense plasmas is relevant to several highly advanced applications, including electron [1] and ion acceleration [2, 3], development of X- and γ-ray sources [4], and fusion neutron production [5]. We report on an experiment using the PPI technique to study of the formation and subsequent evolution of a charge-displacement channel in an underdense plasma These investigations have led to the first direct experimental detection of the transient electric fields in the channel, providing an insight of the fundamental physical processes involved. Due to the Bragg peak energy deposition properties of the protons, the use of multilayered stacks of Radiochromic film (RCF) detector permits energy-resolved monitoring of the proton probe profile, as each layer will primarily detect protons within a given energy range This allows to obtain single-shot, multi-frame temporal scans of the interaction in a time-of-flight arrangement [15]. The reconstructed electron density profile along the propagation axis before the high-intensity interaction [see Fig. 1(b)], broadly consistent with the neutral density profile of the gas jet [25] suggests complete ionisation of the gas by the ASE prepulse

Experimental Results

Data analysis by numerical simulations

Conclusion