Scientists at the Naval Research Laboratory, the University of Rochester and elsewhere have long advocated "direct drive", i.e., shining the laser light directly onto the capsule surface. Techniques were proposed and demonstrated to "smooth out" the intensity of the laser beam in order to make it more comparable to that of the uniformity of the X-ray technique. Indeed, as long ago as 1988, scientists at the University of Rochester achieved compression of deuterium-tritium fuel capsules to 100-200 liquid density using direct drive and only 2 kilojoules of laser light (approximately 700-1000-fold compression is needed for fusion power plants). Similar compressions had been achieved earlier at LLNL using indirect drive with about 4 kilojoules of laser light. It was recognized that achieving the full desired compression to ignition using direct drive (so-called "hot spot ignition") would be difficult, so techniques for igniting lower compression fuels using supplementary energy pulses (so-called "fast ignition" and "shock ignition") began to be proposed and studied.

Although some in the U.S. have proposed that NIF should change course from indirect to direct drive, this idea has not caught on, in part because it would require expensive and time consuming changes to the NIF configuration and also because sub-ignition experiments are currently adequate for weapons physics experiments at LLNL. There are ideas, however (called polar direct drive), for carrying out direct drive experiments on NIF that would lessen the time and cost of doing so (see http://fire.pppl.gov/FPA13_McCrory_LLE.pdf).

In France, a laser called Laser Megajoule (LMJ), similar in capability to NIF, will begin operation in 2014. In a paper prepared for presentation at Fusion Power Associates 34th annual meeting and symposium (posted at http://fire.pppl.gov/FPA13_Batani_ILP_CEA.pdf), Dimitri Batani of the Institute of Laser Plasmas in France indicated a formal plan to study "inertial fusion for energy production" using direct drive on LMJ, including study of "advanced ignition schemes" like shock ignition and fast ignition. The experiments would use the PETAL high intensity short pulse companion laser, currently under construction, for the ignition tests. Batani indicated that an "agreement between CEA (the French atomic energy authority that owns and operates LMJ primarily for weapons physics research) and Region Aquitaine implies that 20 to 30 percent of (LMJ) installation time will be dedicated to Civilian Research performed by the European Academic Community". Direct drive experiments on LMJ would start in 2017 using about 30 kilojoules of LMJ's 2 Megajoules and 3.5 kilojoules from PETAL. Batani stated, "we will have a full-scale facility where it will be possible to demonstrate shock ignition of fusion targets." He said, the goal is "performing shock ignition demonstration experiments within the next decade".

Batani can be reached at: batani@celia.u-bordeaux1.fr
McCrory can be reached at: rmcc@lle.rochester.edu