Abstract
Fast ignition inertial confinement fusion requires the production of a low-density channel in plasma with density scale-lengths of several hundred microns. The channel assists in the propagation of an ultra-intense laser pulse used to generate fast electrons which form a hot spot on the side of pre-compressed fusion fuel. We present a systematic characterization of an expanding laser-produced plasma using optical interferometry, benchmarked against three-dimensional hydrodynamic simulations. Magnetic fields associated with channel formation are probed using proton radiography, and compared to magnetic field structures generated in full-scale particle-in-cell simulations. We present observations of long-lived, straight channels produced by the Habara–Kodama–Tanaka whole-beam self-focusing mechanism, overcoming a critical barrier on the path to realizing fast ignition.This article is part of a discussion meeting issue ‘Prospects for high gain inertial fusion energy (part 2)’.
Highlights
The propagation of intense laser pulses into plasma, and the properties of the plasma structures these pulses leave behind, is an area of active research with a wide range of potential applications
In the near-critical density regime, and in plasma close to a quarter of critical density, channelling by laser pulses is subject to strong hosing and filamentation instabilities which can quickly disrupt the forward progression of the channelling pulse
Even if a pulse does survive to propagate beyond the quarter-critical surface, its progress will be slowed once it reaches the critical density surface
Summary
The propagation of intense laser pulses into plasma, and the properties of the plasma structures these pulses leave behind, is an area of active research with a wide range of potential applications. A sufficiently intense pulse, with dimensionless amplitude/normalized vector potential a ≥ 1 will induce a relativistic increase in electron inertia by a factor γ = 1 + |a|2 /2 (assuming linear polarization) and increase the effective critical density for the pulse by the same factor This allows such a pulse to propagate further up a density gradient than a lower-intensity pulse of the same wavelength before reaching relativistically critical plasma and entering the hole-boring regime. Work carried out at Osaka University’s Institute for Laser Engineering (ILE) by Tanaka et al [17], Kodama et al [18] and Habara et al [19] suggests combining the two relativistic effects—relativistic self-focusing and relativistically induced transparency—described above to increase the penetration depth of ultra-intense laser pulses into fast ignition-relevant plasmas These plasmas typically contain density gradients ranging from significantly underdense to relativistically critical.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
