Inertial confinement fusion (ICF) is an approach to fusion that relies on the inertia of the fuel mass to provide confinement. To achieve conditions under which inertial confinement is sufficient for efficient thermonuclear burn, a capsule (generally a spherical shell) containing thermonuclear fuel is compressed in an implosion process to conditions of high density and temperature. ICF capsules rely on either electron conduction (direct drive) or x rays (indirect drive) for energy transport to drive an implosion. In direct drive, the laser beams (or charged particle beams) are aimed directly at a target. The laser energy is transferred to electrons by means of inverse bremsstrahlung or a variety of plasma collective processes. In indirect drive, the driver energy (from laser beams or ion beams) is first absorbed in a high‐Z enclosure (a hohlraum), which surrounds the capsule. The material heated by the driver emits x rays, which drive the capsule implosion. For optimally designed targets, 70%–80% of the d...

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Development of the indirect‐drive approach to inertial confinement fusion and the target physics basis for ignition and gain

560 TW peak power has been achieved experimentally using a Cr:forsterite master oscillator at 1250 nm, a stretcher, three optical parametrical amplifiers based on KD*P crystals providing 38 J energy in the chirped pulse at 910 nm central wavelength, and a vacuum compressor providing 43 fs pulse duration. To our knowledge, it is a world-record OPCPA system and one of the five most powerful laser systems currently available.

https://iopscience.iop.org/article/10.1002/lapl.200710008/pdf

Compact 0.56 Petawatt laser system based on optical parametric chirped pulse amplification in KD*P crystals

This review is concerned with the results of studies into the behavior of substances at ultimately high pressures and temperatures obtainable by way of kinetic or electromagnetic energy cumulation in laboratory conditions. Also considered are the diversified states of matter and the processes occurring under gravitational forces and thermonuclear energy release.

https://iopscience.iop.org/article/10.3367/UFNe.0179.200906h.0653/pdf

Extreme states of matter on Earth and in space

Laser driven fusion requires a high degree of uniformity in laser energy deposition in order to achieve the high density compressions required for sustaining a thermonuclear burn. The characteristic nonuniformities produced by laser irradiation, with multiple overlapping beams, are examined for a variety of laser-target configurations, Conditions are found for which the rms variation in uniformity is less than 1%. The analysis is facilitated by separating the contributions from (1) the geometrical effects related to the number and orientation of the laser beams and (2) the details of ray trajectories for the overlapping beams. Emphasis is placed on the wavelength of the nonuniformities in addition to their magnitudes, as the shorter wavelength nonuniformities are more easily smoothed by thermal conduction within the target. It is demonstrated how the geometrical symmetry of the laser system effectively eliminates the longer wavelengths, and how shorter wavelength nonuniformities can be “tuned out” by varying parameters such as the focal position and the radial intensity profile of the beam. The distance required for adequate thermal smoothing of the irradiation nonuniformities is found to be 2 to 3 times smaller than previously estimated due mainly to the relatively small spatial wavelength of the nonuniformities. This is a consequence of the geometrical symmetry of the laser system and is relatively insensitive to the details of overlapping beam profiles. The results are particularly important for irradiation with short wavelength laser light (e.g. 0.35 µm), as the small smoothing distances anticipated for moderate laser intensities are found to still produce adequate attenuation of the calculated nonuniformities. The effect of irradiation nonuniformity on target dynamics is illustrated by an implosion simulation using laser-target conditions anticipated for near-term high-density experiments.

Uniformity of Energy Deposition for Laser Driven Fusion

The 2018 Nobel Prize for Physics was shared by Gerard Mourou, Arthur Askin, and Donna Strickland. These papers are the text of the address given in conjunction with the award.

Nobel Lecture: Extreme light physics and application

A 24-beam phosphate-glass laser system has been built and tested. Major design features include Nd:phosphate glass, rod amplifiers up to 90 mm diameter, propagation of circularly polarized light, extensive image relaying and spatial filtering, utilization of large-aperture Pockels cells (PC's) hard-aperture (HA) input and polarizing beamsplitters for beam balance. The system has demonstrated focusable power in excess of 12 terawatts (TW) in 50 ps (FWHM) and over 1.75 kJ in 300 ps (FWHM). The pulse is near-diffraction limited with a peak-to-background energy contrast of 108. Shot rates have exceeded 2/h. A detailed description of the system design and performance is presented.

R. Hopkins

Papers

The omega high-power phosphate-glass system: Design and performance

Modular optical design