Electromagnetic pulses at short-pulse laser facilities

Abstract

Electromagnetic Pulse (EMP) is a known issue for short-pulse laser facilities, and will also be an issue for experiments using the advanced radiographic capability (ARC) at the National Ignition Facility (NIF). The ARC diagnostic uses four NIF beams that are compressed to picosecond durations for backlighting ignition capsules and other applications. Consequently, we are working to understand the EMP due to high-energy (MeV) electrons escaping from targets heated by short-pulse lasers. Our approach is to measure EMP in the Titan short-pulse laser at Lawrence Livermore National Laboratory (LLNL) and to employ that data to establish analysis and simulation capabilities. We have installed a wide variety of probes inside and outside the Titan laser chamber. We have high-frequency B-dots and D-dots, a photodiode, and fast current-viewing and integrating current transformers. The probe outputs are digitized by 10 and 20 Gsample/s oscilloscopes. The cables and oscilloscopes are well shielded to reduce noise. Our initial measurement campaign has yielded data useful mainly from hundreds of MHz to several GHz. We currently are supplementing our high-frequency probes with lower-frequency ones to obtain better low-frequency data. In order to establish analysis and simulation capabilities we are modeling the Titan facility using various commercial and LLNL numerical electromagnetic codes. We have simulated EMP generation by having a specified number of electrons leave the target and strike the chamber wall and other components in the chamber. This short impulse of electrons has a corresponding broad spectrum, exciting high-frequency structure in the resulting EMP. In this paper, we present results of our initial measurement campaign and comparisons between the measurements and simulations.

Analysis of electromagnetic pulse (EMP) measurements in the National Ignition Facility's target bay and chamber

“…An advanced diagnostic system planned for NIF, the Advanced Radiographic Capability (ARC), requires shorter pulse durations in the 1 to 10 ps range. Based on results presented here and data from our work at the short-pulse Titan laser facility [5,6], we expect the EMP on NIF to increase significantly during ARC operation. We fielded similar EMP sensors in NIF's target bay and chamber that we used earlier on Titan.…”

“…However, it is not possible to completely shield any diagnostic and still obtain the needed data. In addition, our work on the Titan short-pulse laser showed that the EMP can extend out to higher frequencies (5 GHz and above) [5,6], which is higher than NIF's original design specification for shielding. This provided motivation to measure EMP on NIF prior to full energy operation to measure energy scaling and to also determine if some targets produced larger EMP.…”

“…See [1][2][3][4][5][6] for previous work on EMP in laser facilities. The National Ignition Facility (NIF) is the world's largest laser with up to 1.8 MJ of 3 laser energy.…”

Investigation into the electromagnetic impulses from long-pulse laser illuminating solid targets inside a laser facility

“…During this process, the ps and ns laser pulses generated quite different ion emission current densities, leading to up to 100 MeV by sub-picosecond laser plasma [6]. On the other hand, Brown et al [7] also reported that the EMP signals collected at Lawrence Livermore National Laboratory mainly covered the frequency domains from several hundreds of MHz to several GHz. Chen et al [8] reported the microwave emission generated by a laser pulse incident on a metallic disc surface had a frequency ranges from 0.5 GHz to 4 GHz.…”

Strong electromagnetic pulses generated in high-intensity short-pulse laser interactions with thin foil targets

“…With the advent of petawatt lasers and MJ laser facilities the issue of EMP became of considerable practical interest, because such pulses strongly interfere with the electronics used to collect data and manipulate targets and hence pose a serious threat to safe and reliable execution of experiments. Therefore a dedicated effort was made to study the EMP effect at facilities such as Vulcan, Titan, Omega, NIF, LMJ and other (Mead et al, 2004;Raimbourg, 2004;Stoeckl et al, 2006;Remo et al, 2007;Brown et al, 2008; Bourgade et al, 2008; Eder et al., 2009; Brown et al, 2010; Eder et al, 2010;Chen et al, 2011;Bateman & Mead, 2012;Brown et al, 2012;Brown et al, 2013;). Pulses of 100's ns duration and electric fields of 100's kV/m strength were recorded.…”