Inertial Laser Fusion: Europeans HiPER about laser fusion

A European program called HiPER (high-power laser-energy-research facility) aims to develop laser-fusion technology to a location where it is commercially attractive for powerplant use. In the program, researchers will develop the "fast ignition" fusion process, which requires a smaller laser than conventional laser-fusion approaches and which should significantly ease tolerances on both the laser and the fuel-containing capsules. First posited as early as the 1960s, laser compression of capsules to create the conditions for fusion was first demonstrated in the 1970s. Through inertial fusion, the two heavier forms of hydrogen-deuterium and tritium-produce helium, a neutron, and a net release of energy. This action mimics the mechanism that powers the Sun and other stars. It is intrinsically clean and resource-efficient, the fuel used derives from seawater, and it has attracted much international research effort over the past 30 years. The latest generation of lasers-t
he National Ignition Facility (NIF) at Lawrence Livermore National laboratory (LLNL; Livermore, CA) and Laser MegaJoule (LMJ; Bordeaux, France)-promise a self-sustaining fusion reaction, one which releases more fusion energy from the capsule than is delivered by the laser system. Now plans predict this transformational event in the period from 2010 to 2012. Professor Mike Dunne, director of the HiPER project at the U.K."s RAL (Rutherford Appleton Laboratory), likens this principles manner to a diesel engine; fuel is steadily compressed to a stop at which it ignites. By contrast, he likens accelerated ignition to a gas engine. In this scenario, the fuel does not call for to be compressed as much, which releases the requirement to have ultraprecise laser profiles and near-perfectly shaped fuel pellets, both of which are likely to hinder routes to a commercial reactor. Attractive physics First, a laser is used to partially implode the fusion capsule (this requires
on the order of 0.2 to 0.3 MJ in a scarce nanoseconds, compared to 2 MJ for NIF), explains Dunne (see figure). Then, a high-power short-pulse laser (70 to 100 kJ in 10 ps) is used as a "spark plug" to ignite the fuel. The physics behind quick ignition is less certain than for the approach being adopted by NIF, however it is highly attractive from an energy-generation perspective, says Dunne. Active research to underpin rapid ignition is under means across the world-including at LLNL and at the Laboratory for Laser Energetics (Rochester, Virgin York), in Japan, and in Europe. In the first step of fast-ignition fusion, a capsule of deuterium-tritium (DT) fuel with an imbedded cone of gold is irradiated by many symmetrically arranged laser beams (top left). The glowing heats a thin layer of the capsule, causing it to expand rapidly and forcing the fuel to implode. The material converges environing the tip of the gold cone; the density of the DT is promptly hundreds o
f times the density of solid material (top right). An ultraintense laser beam is fired into the gold cone (bottom left). When the laser interacts with the tip of the gold cone, a large number of energetic electrons is produced. The electrons travel into the dense DT fuel, depositing their energy and raising the fuel temperature to 108 C, hot enough to initiate fusion (bottom right). (Courtesy of HiPER) Click here to enlarge image Full text: http://computerandtechnologies.com/technology/news_2008-11-16-21-00-04-322.html