by Imran H. Khan

nif-1209-18049I was privileged to visit the most powerful laser on the planet at National Ignition Facility(NIF) at Lawrence Livermore National Laboratory this week. NIF was created to generate a controlled Fusion Reaction that happens regularly on stars. The NIF houses a 1.8 Mega Joule laser that will be used to fire a laser pulse at a 2mm target of hydrogen atoms to create Fusion reaction consists of involving deuterium (D) and tritium (T). Deuterium is an isotope of hydrogen, so-called “heavy hydrogen”, and is found in seawater (about 33g per tonne). Tritium is an isotope of hydrogen, and may be produced by neutron reactions with lithium, which is widely available, both from ore from the earth and also from seawater. In each D-T fusion reaction 17.6 MeV of stored energy is released, along with a Helium nucleus (He) and a neutron (n). This is about one million times the amount of energy released from a chemical reaction, such as the burning of fossil fuels. This is how so little fuel can produce so much energy when fusion is employed. The answer to human energy needs may lie at the beginning of the periodic table rather than at its end.

laser_bayThe $4 Billion facility consists of two massive Laser Bays housing 96 lasers each for a total of 192 laser beams. The beam is triggered by a complex shaped very low energy laser pulse. This is then multiplied nearly a million times and split into 192 channels. Each 50 cm x 50 cm wide channel is then further amplified in the two laser bays using neodymium-glass amplifiers. There are 7000 optical components in the laser mechanism. The system’s modular design gives tremendous control of the operation. The beams are grouped in a hierarchical manner. Four beams enter the bay as a quad. Two quads make a bundle. Six 8 beam bundles make a cluster, two clusters make a 96- beam laser bay, and two bays make NIF. Each beam can be controlled separately or as a group.

hohlraum_tmbAll these beams emerge from the two bays and into the spherical target chamber from all directions in rectangular conduits. These conduits have inert argon gas in them. The spherical chamber is housed in a four story building and is something out of science fiction movies. In the final stages the laser beam goes through a number of optical components and is up shifted in frequency to ultra violet light. It enters the target capsule consisting of gold walls. When the ultraviolet light hits the walls, X-rays are generated. It is the intensely powerful X-rays that generate the pressure on the target capsule that triggers the fusion reaction. The key is to make all the 192 channels of light arrive at the target precisely at the same time. If there is even the slightest variation in the time of arrival, the energy field gets distorted and the target squishes in the direction of lesser pressure. The NIF is designed to deliver nearly 2 million joules of ultraviolet laser energy in a billionth-of-a-second pulses onto a target of hydrogen fuel smaller than a match head, heating it up to 100 million degrees while simultaneously subjecting it to pressures 100 billion times Earth’s atmosphere.

Target_chamberThe target chamber has a concrete casing to absorb the neutrons released by the reaction. In March of this the facility cranked up the power to 1.1 MJ, just under 60% of the full output energy. The first full power firing is expected in the fall of this year. The facility runs 24×7 and is expected to fire 250 shots in fiscal 2010 and ramp up to 700 shots per year by 2012. Optical damage is one of the notorious problems when laser operate at these levels of power. There is extensive optical instrumentation to measure the optical path of each laser. Research conducted here in such finely tuned and highly instrumented facility will allow researchers to evolve techniques for shaping the pulses and other damage control techniques for the next generation of such fusion diode pumped solid state lasers that can fire at 10 to 15 pulses per second.

GroupThere are similar facilities in Europe called HiPER (High Power laser Energy Research) facility and also in China and Japan. The future concept based in this technology called LIFE for Laser Inertial Fusion Engine. LIFE has the potential to meet future worldwide energy needs in a safe, sustainable manner without carbon dioxide emissions. LIFE power plants could generate Gigawatts of power 24 hours a day for as long as 50 years without refueling while avoiding carbon dioxide emissions, easing nuclear proliferation concerns and mitigating the concerns associated with nuclear safety and long-term nuclear waste disposal.

NIF is abuzz with researchers working towards nuclear fusion for global energy solution that is environmentally friendly and abundant in nature. Should this promise come true it will change the politics of the world as well as substantially raise the standard of living for all, by providing abundant source of energy. 2010 promises to be an exciting year. Keep your fingers crossed.

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One Response to “Big Science at National Ignition Facility”

  1. imran on April 28th, 2010 4:50 pm