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Title: Final Technical Report: Magnetic Reconnection in High-Energy Laser-Produced Plasmas

Abstract

This report describes the final results from the DOE Grant DE-SC0007168, “Fast Magnetic Reconnection in HED Laser-Produced Plasmas.” The recent generation of laboratory high-energy-density physics facilities has opened significant physics opportunities for experimentally modeling astrophysical plasmas. The goal of this proposal is to use these new tools to study fundamental problems in plasma physics and plasma astrophysics. Fundamental topics in this area involve study of the generation, amplification, and fate of magnetic fields, which are observed to pervade the plasma universe and govern its evolution. This project combined experiments at DOE laser facilities with kinetic plasma simulation to study these processes. The primary original goal of the project was to study magnetic reconnection using a new experimental platform, colliding magnetized laser-produced plasmas. However through a series of fortuitous discoveries, the work broadened out to allow significant advancement on multiple topics in laboratory astrophysics, including magnetic reconnection, Weibel instability, and collisionless shocks.

Authors:
 [1];  [2];  [2]
  1. Univ. of New Hampshire, Durham, NH (United States)
  2. Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
Publication Date:
Research Org.:
Univ. of New Hampshire, Durham, NH (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Fusion Energy Sciences (FES) (SC-24)
OSTI Identifier:
1349850
Report Number(s):
DOE-UNH-7168
DOE Contract Number:
SC0007168
Resource Type:
Technical Report
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY

Citation Formats

Germaschewski, Kai, Fox, William, and Bhattacharjee, Amitava. Final Technical Report: Magnetic Reconnection in High-Energy Laser-Produced Plasmas. United States: N. p., 2017. Web. doi:10.2172/1349850.
Germaschewski, Kai, Fox, William, & Bhattacharjee, Amitava. Final Technical Report: Magnetic Reconnection in High-Energy Laser-Produced Plasmas. United States. doi:10.2172/1349850.
Germaschewski, Kai, Fox, William, and Bhattacharjee, Amitava. Thu . "Final Technical Report: Magnetic Reconnection in High-Energy Laser-Produced Plasmas". United States. doi:10.2172/1349850. https://www.osti.gov/servlets/purl/1349850.
@article{osti_1349850,
title = {Final Technical Report: Magnetic Reconnection in High-Energy Laser-Produced Plasmas},
author = {Germaschewski, Kai and Fox, William and Bhattacharjee, Amitava},
abstractNote = {This report describes the final results from the DOE Grant DE-SC0007168, “Fast Magnetic Reconnection in HED Laser-Produced Plasmas.” The recent generation of laboratory high-energy-density physics facilities has opened significant physics opportunities for experimentally modeling astrophysical plasmas. The goal of this proposal is to use these new tools to study fundamental problems in plasma physics and plasma astrophysics. Fundamental topics in this area involve study of the generation, amplification, and fate of magnetic fields, which are observed to pervade the plasma universe and govern its evolution. This project combined experiments at DOE laser facilities with kinetic plasma simulation to study these processes. The primary original goal of the project was to study magnetic reconnection using a new experimental platform, colliding magnetized laser-produced plasmas. However through a series of fortuitous discoveries, the work broadened out to allow significant advancement on multiple topics in laboratory astrophysics, including magnetic reconnection, Weibel instability, and collisionless shocks.},
doi = {10.2172/1349850},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Thu Apr 06 00:00:00 EDT 2017},
month = {Thu Apr 06 00:00:00 EDT 2017}
}

Technical Report:

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  • Recently, novel experiments on magnetic reconnection have been conducted in laser-produced plasmas in a high-energy-density regime. Individual plasma bubbles self-generate toroidal, mega-gauss-scale magnetic fields through the Biermann battery effect. When multiple bubbles are created at small separation, they expand into one another, driving reconnection of this field. Reconnection in the experiments was reported to be much faster than allowed by both Sweet-Parker, and even Hall-MHD theories, when normalized to the nominal magnetic fields self-generated by single bubbles. Through particle-in-cell simulations (both with and without a binary collision operator), we model the bubble interaction at parameters and geometry relevant to themore » experiments. This paper discusses in detail the reconnection regime of the laser-driven experiments and reports the qualitative features of simulations. We find substantial flux-pileup effects, which boost the relevant magnetic field for reconnection in the current sheet. When this is accounted for, the normalized reconnection rates are much more in line with standard two-fluid theory of reconnection. At the largest system sizes, we additionally find that the current sheet is prone to breakup into plasmoids.« less
  • A table-top sub-picosecond terawatt laser was used to study experimentally the atomic and plasma physics of plasmas that are relevant to the recombination and photo-pumping x-ray laser schemes. Experimentally, x-ray spectroscopy with simultaneous temporal and spectral resolution was used to characterize the line and continuum emission of soft x-rays emitted from a solid density plasma. Numerically, we developed our non-LTE time-dependent collisional-radiative numerical code, which was used to interpret the experimental results. It was found that the results depended critically on the laser contrast conditions, and that the x-ray pulsewidth could be arbitrarily adjusted by simply adjusting a single parameter,more » the laser intensity, and thus the peak temperature of the plasma. This novel ultrafast broadband radiation source in the soft x-ray region of the spectrum can be used for time-resolved dynamical studies in ultrafast science and pumping x-ray lasers. It was measured to be six orders of magnitude brighter, and three orders of magnitude shorter in pulse duration (less than one picosecond), than any existing synchrotron source.« less
  • Magnetic fields in the megagauss range have been observed in the laser-produced plasma near the focus of a high power laser pulse. Faraday rotation measurements, using the light of a probing beam and the specularly reflected laser light, both show the presence of these large fields. (GRA)
  • The development of high average power pulsed solid-state lasers and the application of these lasers to the generation of laser-produced plasmas for soft-x-ray generation is described. A 44-W average power moving slab neodymium glass laser was demonstrated. In a separate experiment, injection seeding of this laser to produce 500-MW ll-ps pulses was attained. Soft-x-ray generation has been investigated with the moving slab laser, a fixed slab laser, and commercial rod-geometry lasers. The techniques that were demonstrated show the feasibility of scaling the operation of slab lasers to the kilowatt level. The rapid development of diode-laser pumping techniques suggests the potentialmore » for remarkable efficient, compact, and economical laser systems for short-wavelength lithography and microscopy applications.« less
  • The LITE fusion plasma research program at UTRC has been investigating the stabilization and confinement physics of a mirror plasma created by energetic neutral beam heating of a confined target plasma. During the period covered by this report work has been concentrated on the investigation of hot ion losses in a warm target plasma, development of a cryocondensation pump for the LITE beam line neutralizer, theoretical studies of ECRH modification of the ambipolar potential in mirror plasmas, and analysis of the effects of localized cold plasma on DCLC stabilization. The results of these investigations are summarized below and detailed inmore » four papers which comprise the body of this report. Measurements of the lifetime of hot ions in a mirror confined warm plasma have been carried out by observations of the hot ion buildup time obtained with energetic neutral beam injection. A cryocondensation pump of novel design has been constructed and incorporated in the neutralizer chamber of the LITE neutral beam line. Calculations have been carried out to evaluate the sizes and shapes of ambipolar potential modification produced by electron cyclotron resonance heated electrons and to determine the spatial distribution and densities of cold ions trapped in the potential wells. The effects of the spatial distribution of the cold ions on their effectiveness for stabilizing the drift cyclotron loss cone instability has been studied numerically using the formulation of Pearlstein in which the dispersion relation for the DCLC mode is solved for finite-size plasmas containing hot and cold components.« less