In the next few years experiments will be performed first at the National Ignition Facility and then at laser MegaJoule with the aim of demonstrating thermonuclear ignition of inertially confined fuel. The above lasers deliver pulses of 1.5-2 MJ of UV light (with wavelength of 350 nm) in a few ns, with peak power of about 500 TW. The concept to be tested is based on indirect drive (i.e. compression of the fuel by X-rays generated and contained in a laser irradiated hohlraum) and central ignition of the fuel. The foreseen experiments rely on the knowledge acquired in about forty years of research in diverse areas such as laser-matter interaction, hydrodynamics, laser sciences, cryogenics, etc. Recent progress, however, has stimulated studies on the feasibility of ignition and substantial energy gain at smaller laser energy. This is the result of i) the introduction of schemes (such as fast ignition, and shock ignition) which separate the compression and ignition stages and relax symmetry requirements; ii) improved understanding of Rayleigh-Taylor instability and of techniques for reducing its growth, which make efficient direct-drive compression possible; iii) developments in laser technology, allowing for smoother beams, and for very high intensity PW beams.
In this talk I will briefly review the above developments, discuss the conditions required to achieve ignition using different schemes, and present a simple model (supported by simulations) to estimate target gain as a function of a small set of parameters. I will then discuss a few key open issues for the feasibility of these advanced schemes. Such topics are currently addressed within the HiPER (High Power Laser for Energy Research) project.
The inertial confinement is alternative to magnetic confinement approach to harnessing of thermonuclear fusion reactions for sustainable energy production. It considers a compression and heating of the deuterium-tritium mixture with the help of high-power, high energy lasers and fusion energy release in 100 ps time. Two laser systems capable to deliver an energy more than one MJ and release power more than 400 TW are the National Ignition Facility in the USA and the Laser Mega Joule in France. The ignition of controlled thermonuclear reactions is planned at the NIF within next two years. The LMJ facility will be operational in next 5 years.
In my talk I will present the basic principles of the IFE and the works that we are doing in France and in our laboratory in particular. Two major pathways are persuaded: the fast ignition of a cone-in-shell fuel assembly target with electrons or ions and the shock ignition of a spherically compressed fuel. The physics of laser plasma coupling will be discussed as well as the conditions needed for ignition. Along with the IFE, the laser matter interaction finds many other applications, which I will discuss briefly in the end of my talk.