Seeding magnetic fields for laser-driven flux compression in high-energy-density plasmas

Gotchev, O. V.; Knauer, J. P.; Chang, Po-Yu; Jang, N. W.; Shoup, M. J.; Meyerhofer, D. D.; Betti, R.

doi:10.1063/1.3115983

Cited by 56 publications

(32 citation statements)

References 36 publications

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“…at the Laboratory for Laser Energetics [27,28,29] (Rochester, NY, USA) and at the Institute of Laser Engineering [30] (Osaka, Japan). However, the B-fields they develop have short spatial (mm) and temporal (10-100 ns) scales.…”

Section: Historical Contextmentioning

confidence: 99%

Detailed characterization of laser-produced astrophysically-relevant jets formed via a poloidal magnetic nozzle

Higginson

Revet

Khiar

et al. 2017

High Energy Density Physics

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This manuscript is distributed under a Creative Commons Attribution-NonCommercial-NoDerivs License (https://creativecommons.org/licenses/by-nc-nd/4.0/), which permits distribution and reproduction for non-commercial purposes, provided the author and source are cited. General rightsCopyright for the publications made accessible via the Queen's University Belfast Research Portal is retained by the author(s) and / or other copyright owners and it is a condition of accessing these publications that users recognise and abide by the legal requirements associated with these rights. AbstractThe collimation of astrophysically-relevant plasma ejecta in the form of narrow jets via a poloidal magnetic field is studied experimentally by irradiating a target situated in a 20 T axial magnetic field with a 40 J, 0.6 ns, 0.7 mm diameter, high-power laser. The dynamics of the plasma shaping by the magnetic field are studied over 70 ns and up to 20 mm from the source by diagnosing the electron density, temperature and optical self-emission. These show that the initial expansion of the plasma is highly magnetized, which leads to the formation of a cavity structure when the kinetic plasma pressure compresses the magnetic field resulting in an oblique shock [A. Ciardi et al., Phys. Rev. Lett. 110, 025002 (2013)]. The resulting poloidal magnetic nozzle generates a standing conical shock that collimates the plasma into a narrow jet [B. Albertazzi et al., Science 346, 325 (2014).]. At distances far from the target, the jet is only marginally magnetized and maintains a high aspect ratio due to its high Mach-number (M ∼ 20) and not due to external magnetic pressure. The formation of the jet is evaluated over a range of laser intensities (10 12 -10 13 W/cm 2 ), target materials and orientations of the magnetic field. Plasma cavity formation is observed in all cases and the viability of long-range jet formation is found to be dependent on the orientation of the magnetic field.

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Section: Historical Contextmentioning

confidence: 99%

Detailed characterization of laser-produced astrophysically-relevant jets formed via a poloidal magnetic nozzle

Higginson

Revet

Khiar

et al. 2017

High Energy Density Physics

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“…[19][20][21][22] The Laboratory for Laser Energetics performed radiation-driven implosions of spherical capsules, and diagnosed higher hot-spot temperatures, magnetic flux compression, and enhanced fusion yields when the target was pre-magnetized. [23][24][25] A team at the Lawrence Livermore National Laboratory computationally investigated pre-magnetization of indirect-drive ignition targets for the National Ignition Facility and found the imposed field may improve capsule stability and hot-spot formation, while relaxing the conditions needed for ignition. 26 Ultimately, each proposed fusion approach seeks to harness magnetic fields in order to reduce electron thermal conduction losses from the heated plasma, enhance particle and energy confinement, and lower the stagnation pressures required to reach fusion conditions, and therefore enable the use of drivers with lower energy and power.…”

Section: Introductionmentioning

confidence: 99%

Design of magnetized liner inertial fusion experiments using the Z facility

et al. 2014

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The magnetized liner inertial fusion concept has been presented as a path toward obtaining substantial thermonuclear fusion yields using the Z accelerator [S. A. Slutz et al., Phys. Plasmas 17, 056303 (2010)]. We present the first integrated magnetohydrodynamic simulations of the inertial fusion targets, which self-consistently include laser preheating of the fuel, the presence of electrodes, and end loss effects. These numerical simulations provided the design for the first thermonuclear fusion neutron-producing experiments on Z using capabilities that presently exist: peak currents of Imax = 18–20 MA, pre-seeded axial magnetic fields of Bz0=10 T, laser preheat energies of about Elas = 2 kJ delivered in 2 ns, DD fuel, and an aspect ratio 6 solid Be liner imploded to 70 km/s. Specific design details and observables for both near-term and future experiments are discussed, including sensitivity to laser timing and absorbed preheat energy. The initial experiments measured stagnation radii rstag<75 μm, temperatures around 3 keV, and isotropic neutron yields up to YnDD=2×1012, with inferred alpha-particle magnetization parameters around rstag/rLα=1.7 [M. R. Gomez et al., Phys. Rev. Lett. (submitted)].

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“…2(a), coil diameter and separation are both 4 mm], coaxial with the cylindrical target [14]. A portable capacitive discharge system [14] delivers up to 80-kA current to the coils. The on-axis seed field was 50 to 90 kG at the target and 120 to 160 kG in the coil planes because of the coil separation chosen to avoid obscuring laser beams.…”

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confidence: 99%

“…The seed field was provided by a Helmholtz-like double coil [ Fig. 2(a), coil diameter and separation are both 4 mm], coaxial with the cylindrical target [14]. A portable capacitive discharge system [14] delivers up to 80-kA current to the coils.…”

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confidence: 99%

Laser-Driven Magnetic-Flux Compression in High-Energy-Density Plasmas

et al. 2009

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The demonstration of magnetic field compression to many tens of megagauss in cylindrical implosions of inertial confinement fusion targets is reported for the first time. The OMEGA laser [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)] was used to implode cylindrical CH targets filled with deuterium gas and seeded with a strong external field (>50 kG) from a specially developed magnetic pulse generator. This seed field was trapped (frozen) in the shock-heated gas fill and compressed by the imploding shell at a high implosion velocity, minimizing the effect of resistive flux diffusion. The magnetic fields in the compressed core were probed via proton deflectrometry using the fusion products from an imploding D 3 He target. Line-averaged magnetic fields between 30 and 40 MG were observed. In the magnetic fusion energy (MFE) concept, a strong magnetic field confines the plasma and reduces the electron thermal conduction to the vessel wall [1]. The magnetic pressure of typical $0:1-MG fields is higher than the total energy density of the plasma (with ¼ 2 0 p=B 2 < 1). MFE plasmas are fully magnetized and characterized by a Hall parameter ! ce > 1 since the modest gyrofrequency ! ce is matched by long collision times . In contrast, typical inertial confinement fusion (ICF) plasmas have collision frequencies higher by 10 to 12 orders of magnitude because of their extreme density. In such systems, thermal conduction losses are a major factor in the energy balance of an implosion. While it can be more difficult, magnetizing the hot spot in ICF implosions can lead to improved gains and to a reduction of the energy required for ignition. A similar approach is used in the magnetized target fusion concept [2], where the fusion burn requires relatively low-implosion velocities, provided there is an adequate magnetic thermal insulation. In ICF implosions, lower implosion velocities lead to higher gains [3]. However, tens of MG are needed to achieve ! ce $ 1 in the hot spot of a typical, direct drive DT ignition target [4] with hot-spot density of $30 g=cc and a temperature of $7 keV. Such a field is higher than both the self-generated magnetic fields (see Ref. [5]) and the external fields that can be generated by coils. Magnetic-flux compression [6] is a viable path to generating tens of MG magnetic fields with adequate size compression of a metal liner driven by high explosives [7,8] or by pulsed power. The latter approach has been pursued by the Z-pinch [9] communities. The results from the first experiments on a new approach that provides very effective flux compression are reported here. The field is compressed by the ablative pressure exerted on an imploding ICF capsule by the driving laser [10]. This approach was proposed in the 1980s [11] as a way to achieve record compressed fields with possible applications for fusion [12] but no laser experiments were performed. There are numerous advantages to this approach as the implosion velocity is high (a few 10 7 cm=s) and the hot plasma is an effective conductor that tra...

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Seeding magnetic fields for laser-driven flux compression in high-energy-density plasmas

Cited by 56 publications

References 36 publications

Detailed characterization of laser-produced astrophysically-relevant jets formed via a poloidal magnetic nozzle

Detailed characterization of laser-produced astrophysically-relevant jets formed via a poloidal magnetic nozzle

Design of magnetized liner inertial fusion experiments using the Z facility

Laser-Driven Magnetic-Flux Compression in High-Energy-Density Plasmas

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