Energy. Laser fusion project alters goals, fueling concern over its strategy.

23 NEWS&ANALYSIS The hopes of fusion researchers worldwide are pinned to the fortunes of the National Ignition Facility (NIF), a $3.5 billion laser center at Lawrence Livermore National Laboratory in California, which is trying to show that it is possible to create a self-sustaining fusion reaction that could serve as a source of energy. But a change in its milestones, revealed in an internal NIF document Science has seen, has highlighted the concerns of some in the fi eld that the path NIF researchers have taken may not be the right one. Funded by the U.S. Department of Energy (DOE), NIF aims to use a huge laser, the highest energy laser in the world, to crush a tiny fuel capsule to temperatures and pressures higher than in the center of the sun. The goal is to spark a fusion fi re in the center of the fuel to start it burning. But the fuel is not considered ignited until high-energy alpha particles produced by the fusion burn heat the surrounding fuel enough to keep the burn going until a sig-nifi cant fraction of the fuel is used. Until last month, NIF was scheduled to show evidence of signifi cant alpha-particle heating by the end of March, then prove by the end of June that fusion can produce as much energy as the laser provided (known as gain=1), and fi nally produce an overall energy yield of 5 megajoules (MJ) by the end of Sep-tember—the end of NIF's initial research program called the National Ignition Campaign (NIC). But a document known as a Baseline Change Proposal, signed by NIF Director Edward Moses on 21 December 2011, would delete this third goal from the NIC schedule and push its two remaining milestones back by 3 months each. Moses said this week that the changes were a scheduling, not a physics, issue. NIF has other priorities apart from fusion ignition: It simulates nuclear explosions to help ensure the effectiveness of the nuclear stockpile and is also used for basic science experiments. Moses says there is high demand from these other users. " People wanted more nonignition shots in [early 2012], " he says, so he had to negotiate a new schedule with NIF's funders in the National Nuclear Security Administration. Moses also downplays the signifi cance of eliminating the 5-MJ milestone. Gain=1 has, since the early planning of NIF in the 1990s, been …