Laser driven inertial fusion: the physical basis for current and recently proposed ignition experiments

Posted April 14, 2010

Prof. Stefano Atzeni
Dipartimento di Energetica, UniversitĘĄ di Roma "La Sapienza", Roma, Italy
Time: May 28th, 2010 9:30am
Place: Lecture Hall 111, Department of Physics
Title: Laser driven inertial fusion: the physical basis for current and recently proposed ignition experiments

Abstract: 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.

I thank A. Schiavi (CNISM) and all members of the HiPER WP9 group for discussions and collaboration. This work is partially supported by the HiPER project (EC FP7 project number 211737).


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