A method to achieve rapid localised deep heating in a laser irradiated solid density target

H Schmitz,A P L Robinson

doi:10.1063/1.4961958

Abstract

Rapid heating of small buried regions by laser generated fast electrons may be useful for applications such as extreme ultraviolet (XUV) radiation sources or as drivers for shock experiments. In non-structured targets, the heating profile possesses a global maximum near the front surface. This paper presents a new target design that uses resistive guiding to concentrate the fast electron current density at a finite depth inside the target. The choice of geometry uses principles of non-imaging optics. A global temperature maximum at depths up to 50 μm into the target is achieved. Although theoretical calculations suggest that small source sizes should perform better than large ones, simulations show that a large angular spread at high intensities results in significant losses of the fast electrons to the sides. A systematic parameter scan suggests an optimal laser intensity. A ratio of 1.6 is demonstrated between the maximum ion temperature and the ion temperature at the front surface.

Highlights

When a high intensity laser impinges on a solid density target, a large part of the electromagnetic energy of the laser is converted into kinetic energy of fast moving electrons
Rapid heating of small buried regions by laser generated fast electrons may be useful for applications such as extreme ultraviolet (XUV) radiation sources or as drivers for shock experiments
Note that no magnetic field is observed at the circular tip of the concentrator. This is to be expected since the fast electron current here is perpendicular to the surface, and only the parallel component of the fast electron current generates a magnetic field

Summary

Introduction

When a high intensity laser impinges on a solid density target, a large part of the electromagnetic energy of the laser is converted into kinetic energy of fast moving electrons. The ponderomotive force of the laser accelerates electrons to relativistic energies, and typically around 15%–30% of the laser energy is converted while conversion rates up to 90% have been shown.2 These electrons can be useful for a number of different applications, such as the Fast Ignition scheme for inertial confinement fusion, ion acceleration, or as a means to heat localised regions within the target.. A radiation source located at a finite depth inside the target will be tamped by the surrounding material preventing a rapid expansion Another application might be the use of the heated region as drivers in shock experiments, for example, for laboratory astrophysics.. A proposal has been made to produce astrophysically relevant jets using locally heated targets.7 This scheme relies on the heated region to be located not too far from the rear surface of the target A proposal has been made to produce astrophysically relevant jets using locally heated targets. This scheme relies on the heated region to be located not too far from the rear surface of the target

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Conclusion