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Plasma Physics (Physics/ECE/NE 922) Seminar
The Plasma Physics of Fusion Indirectly Driven with a Laser
Date: Monday, April 7th
Time: 12:00 pm
Place: 2241 Chamberlin
Speaker: Bob Kirkwood, Lawrence Livermore National Laboratory
Abstract: Igniting fusion fuel that is driven indirectly with a laser presents significant challenges for plasma physics because the intense beams required can drive instabilities in the plasma formed in the target. The instabilities in turn, can scatter light significantly and affect power flow and deposition. The National Ignition Facility (NIF) was constructed to study the physics of inertial fusion and ignition with a laser [1] and has now been in operation for over four years [2]. The design of the facility was based on an understanding of plasma instabilities derived from a series of experiments carried out with smaller lasers and their modeling. That work made it clear that the large hot plasmas that would be created when NIFs multiple intersecting beams entered a hohlraum target would open a new realm of plasma interactions, where stimulated scattering would not only limit power coupling but also provide control of power deposition profiles in the target interior [3].

The initial experiments at NIF [4] were also designed based on this understanding which allowed optimization of laser intensity, wavelength and spot size, as well as target dimensions and materials, and further indicated the areas of greatest uncertainty where there was need for final empirical tuning. The recent studies at NIF have now confirmed for the first time that under ignition relevant conditions plasma instabilities produce self-generated optical scattering cells that are not only controllable but also useful. The experiments have further demonstrated that deleterious plasma scatter that depletes power from one set of beams can be compensated for by inducing a plasma scattering cell that redirects power from another set of beams. This has allowed induced plasma scattering to become the primary means to control the power deposition profile and the resulting implosion symmetry via adjustments to the laser wavelengths [5]. These techniques have allowed enhanced target performance that is essential to the present experimental campaigns that study precision implosions [6], and were also an essential ingredient in the recent demonstration that net energy can be extracted from fusion fuel [7]. This talk will review the plasma physics studied in the first few years of NIC experiments in the context of the earlier work and highlight its importance for fusion ignition with a laser.

[1] G. H. Miller, E. I. Moses, and C. R. Wuest, Nucl. Fusion 44, S228 (2004).
[2] J. D. Lindl et al Phys. Plasmas 11, 339 (2004).
[3] R. K. Kirkwood et al Plasma Phys. Controlled Fusion 55, 103001 (2013).
[4] S. H. Glenzer et al Phys. Rev. Lett. 106, 085004 (2011).
[5] P. Michel et al Phys. Plasmas 17, 056305 (2010).
[6] M. J. Edwards Phys. Plasmas 20, 070501 (2013).
[7] O. A. Hurricane et al Nature 506, 343 (2014).
Host: Cary Forest
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