World's largest laser blasted over fusion plan
Apr 12, 2010 - Jeff Hecht - NewScientist
The world's largest laser is meant to spark off a fusion reaction this year – but don't bank on it. So says the US government's watchdog in a critical report about the huge laser array at the National Ignition Facility (NIF).
Despite crucial success in evenly compressing fusion fuel pellets earlier this year, the Lawrence Livermore National Laboratory's $3.5 billion array in Livermore, California, faces problems in repeating that success at the higher power needed for fusion, says a US Government Accountability Office (GAO) report.
First proposed in 1962, laser fusion seeks to heat and compress hydrogen isotopes to the temperatures and pressures of the sun's interior, triggering nuclear fusion. Livermore's version uses a two-stage process that mimics the triggering of a hydrogen bomb by firing synchronised pulses from 192 laser beams to generate a burst of X-rays that compress the fuel.
The symmetrical implosion requires a combined laser pulse energy of 0.7 megajoules. Livermore physicists have said they hope to reach "ignition" – generating as much fusion energy as is contained in the laser pulse – at a laser energy of 1.2 to 1.3 megajoules, well short of NIF's 1.8-megajoule capacity.
But the GAO says that many independent researchers think that ignition may require at least 1.8 megajoules, because plasma instabilities could deflect light away from the target. The outside experts also warn that firing on full power could damage crucial high-power optics in the machine.
The GAO also complains that Livermore dragged its feet in commissioning an outside review panel that it recommended in 2005.
Still, the GAO does not criticise NIF's operators as harshly as it did in 2000. It slammed the NIF for management failures that put it years behind schedule and billions over its original budget.
Lawrence Livermore told New Scientist that they are confident that they can achieve fusion with no more than 1.5 megajoules.