Studying Ignition Schemes on European Laser Facilities

Full text: First experiments on the National Ignition Facility in the United States have successfully begun in 2009 which give confidence in demonstrating ignition and net energy gain within the next two years. Such an achievement - likely to be confirmed a few years later on the Laser MegaJoule in France - will be a major step towards determining the feasibility of Inertial Confinement Fusion. The current status of the LMJ programme, from the laser facility construction to the indirectly-driven central ignition target design, will be first presented, as well as experimental campaigns, conducted on the Ligne d'Integration Laser and on LULI2000, as part of this programme. Special attention will be paid to experiments aiming at characterizing high-energy laser interaction with under-dense plasmas and to supporting theoretical analysis and simulations. The viability of the Inertial Fusion Energy (IFE) approach strongly depends on our ability to address the salient questions related to efficiency of the target design and laser driver performances. In the overall framework of the European HiPER project, two alternative schemes both relying on decoupling target compression and fuel heating - fast ignition (FI) and shock ignition (SI) - are currently considered. After a brief presentation of the HiPER project's objectives, FI and SI target designs will be discussed. Theoretical analysis, 2D radiation-hydrodynamics, hybrid and PIC simulations, performed at the Polytechnic University of Madrid (Spain) and the University Bordeaux 1 (France) will help understanding the key unresolved issues of the two schemes. The on-going European experimental effort to demonstrate the viability of the two schemes on various laser facilities will finally be described. Two FI-relevant problems will be tackled: (i) influence of plasma density scale-lengths on the laser-to-electron energy transfer and (ii) fast electron beam transport in pre-compressed matter. Preliminary experimental results on shock ignition will also be presented. These studies have been partly funded through the EURATOM IFE KiT programme, the HiPER Preparatory Phase and the LASERLAB-Europe II transnational access programme. (author)