The NIF will produce up to 1. 8 MJ of 351-nm laser light—which is higher
than that produced by any previous laser system by a factor of 50.
laser energy required to drive the implosion. The initial ignition capsule will use a Be ablator that contains a 100-µm-thick
DT ice shell. The demonstration of ICF ignition on the NIF is
the highest priority near-term HED goal.
The pursuit of ignition on the NIF is a project managed
through the National Ignition Campaign (NIC), which is
executed by a national team including LLNL, LLE, Los
Alamos National Laboratory, General Atomics and Sandia
National Laboratories. It includes the ignition campaign on
the NIF and supporting experiments, primarily carried out on
the OMEGA laser facility. The goals of the NIC are to carry
out the first “credible” ignition attempt in 2010, leading to the
development of robust ignition by 2012.
The NIF laser system
The NIF is the largest, most complex and most expensive
optical system ever built. It has 192 beamlines arrayed in 48
quads (four neighboring beamlines) to irradiate the inside of
a hohlraum target with cylindrical symmetry to achieve ICF
ignition with indirect drive. The resulting X-ray irradiation
will compress the capsule to ignition conditions. The NIF will
deliver up to 1. 8 MJ of ultraviolet energy in an approximately
20-ns pulse, allowing the ignition hohlraum to reach a radiation temperature of 3,300,000 degrees C (300 eV) and driving
the capsule to ignition conditions.
The system requires exquisite pulse shaping, pointing and
beam-to-beam co-timing and co-pointing. To meet these stringent requirements, new technologies were developed, and the
laser system architecture was completely rethought.
The NIF architecture uses a multipass laser system that
extracts a much larger fraction of the energy stored in the
amplifiers than was possible with previous high-energy inertial
fusion lasers. The NIF laser amplifies light from the master
oscillator by a factor of 10.
The NIF multipass design
is enabled by a number
of major technological
advances, including devel-
opment of large full-beam
plasma-based optical Deformable
switches (Pockels cell) and
deformable mirrors, 48
stable, high-gain preampli- Main
fiers (one for each of four filter (CSF)
beams) capable of high-precision spatial, temporal,
and spectral pulseshaping,
and a highly sophisticated computer control system capable of
monitoring more than 60,000 individual control points.
The multipass design allows the laser beam to make four
passes through the main amplifier while maintaining the
spatial uniformity required for effective amplification and,
ultimately, frequency conversion to 0.35-mm light at the target
chamber. Like all large inertial fusion laser systems in the
world, the entire NIF laser—from master oscillator to just
outside the target chamber—operates at the fundamental laser
wavelength of 1,053 nm. The 351-nm ultraviolet light used in
NIF experiments is produced by nonlinear optical frequency
conversion of the 1,053-nm fundamental harmonic.
This conversion is performed by using full-aperture potassium dihydrogen phosphate crystals, which are located just
outside of the 10-meter-diameter target chamber. This nonlinear frequency conversion scheme was first developed at LLE
and is now in use at all major laser fusion facilities worldwide.
The NIF is now complete, with all optics installed. The
Department of Energy formally certified completion of the
NIF on March 27, 2009. The NIF has fired all 192 beams in
the infrared and has demonstrated an equivalent full system
energy of more than 4 MJ of infrared laser energy.
LLNL scientists are now in the process of ramping up the
laser to full energy ( 1. 8 MJ operation) in the ultraviolet. A
single bundle of eight beams has been fired a number of times
at an energy of 78 kJ, which is equivalent to 1. 8 MJ for the
entire system. The first 192 ultraviolet target shot occurred on
February 26, 2009, and a total 192-beam ultraviolet energy
of 1. 1 MJ to target chamber center was demonstrated on
March 10, 2009. NIF will commence 192 beam target experiments at 1-MJ energy later this year, with operation at 1. 8 MJ
expected by 2011. The system has met or exceeded all of its
performance requirements, including producing the high-contrast ignition pulse shape.
The NIF uses 192 beamlines arrayed in 48 quads.