EMP control and characterization on high-power laser systems

P Bradford,Y Zhang,P J R Jones,Z Zhang,Y Li,F Consoli,S Astbury,C Spindloe,I East,P Brummitt,D Neely,P Mckenna,N C Woolsey,P G Huggard ,David D Haddock ,Hao Liu ,Ian Musgrave ,C M Brenner ,Egle Zemaityte ,Pedro Guedes De Oliveira ,R J Gray ,Chris Armstrong ,Eric Montgomery ,Dean Rusby ,Graeme Scott ,Baojun Zhu ,Guoqian Liao ,Brianna Summers

doi:10.1017/hpl.2018.21

Abstract

Giant electromagnetic pulses (EMP) generated during the interaction of high-power lasers with solid targets can seriously degrade electrical measurements and equipment. EMP emission is caused by the acceleration of hot electrons inside the target, which produce radiation across a wide band from DC to terahertz frequencies. Improved understanding and control of EMP is vital as we enter a new era of high repetition rate, high intensity lasers (e.g. the Extreme Light Infrastructure). We present recent data from the VULCAN laser facility that demonstrates how EMP can be readily and effectively reduced. Characterization of the EMP was achieved using B-dot and D-dot probes that took measurements for a range of different target and laser parameters. We demonstrate that target stalk geometry, material composition, geodesic path length and foil surface area can all play a significant role in the reduction of EMP. A combination of electromagnetic wave and 3D particle-in-cell simulations is used to inform our conclusions about the effects of stalk geometry on EMP, providing an opportunity for comparison with existing charge separation models.

Highlights

Ongoing advances in high-power laser technology[1] have led to renewed interest in the processes that drive electromagnetic pulse (EMP) generation
We demonstrate that target stalk geometry, material composition, geodesic path length and foil surface area can all play a significant role in the reduction of electromagnetic pulses (EMP)
No advantage was found for using the sinusoidal stalk over the dielectric cylinder and only a modest additional reduction was found for the spiral stalk (26% at P1 and 12% at P2). These results show striking EMP attenuation when switching from conducting to insulating stalks, they do not explain the lower attenuation of the cylindrical dielectric stalk compared with the sinusoidal and spiral designs

Summary

Introduction

Ongoing advances in high-power laser technology[1] have led to renewed interest in the processes that drive electromagnetic pulse (EMP) generation. A number of different mechanisms have been proposed to explain the broad spectral profile of laser-driven EMP and they all rely upon the acceleration of hot electrons within the target. When a sufficiently intense laser pulse (I λ2 1015 W · cm−2 · μm2) interacts with a material, a portion of its energy is resonantly and parametrically absorbed, leading to the production of hot electrons with energies exceeding 10 keV[5]. It is thought that these electrons contribute towards the EMP in three key stages, starting with the emission of THz radiation as they propagate across the target surface[7]. Significant currents may be associated with this THz emission, the frequency is generally too high to pose

Methods

Results

Conclusion