The National Ignition Facility - £2.2billion superlab Creating a miniature star on Earth
It may look like any average building but behind closed doors could lie the answer to safe renewable energy of the future. Here at the National Ignition Facility in Livermore California, scientists are aiming to build the world's first sustainable fusion reactor by 'creating a miniature star on Earth'. Following a series of key experiments over the last few weeks, the £2.2 billion project has inched a little closer to its goal of igniting a workable fusion reaction by 2012. According to the National Ignition Facility (NIF) team in Livermore, on November 2 they fired up the 192 lasers beams at the centre of the reactor and aimed them at a glass target containing tritium and deuterium gas.
Inside the National Ignition Facility, a service system lift gives technicians access to the target chamber interior for inspection and maintenance. The chamber is a sphere 10 meters in diameter, assembled from ten-centimeter-thick aluminum panels which were preformed and then welded in place. It is covered with .3 meters of concrete which was injected with boron to absorb neutrons from the fusion reaction. The holes in the chamber permit the 192 laser beams to enter the chamber and to provide viewing ports for diagnostic tools. (NIF/Lawrence Livermore National Laboratory)
The single largest piece of equipment at the National Ignition Facility is its 130-ton target chamber. The design features 6 symmetric middle plates and 12 asymmetric outer plates, which were poured at the Ravenswood Aluminum Mill in Ravenswood, West Virginia. The plates were shipped to Creusot-Loire Industries in France, where they were heated and shaped in a giant press. The formed plates were then shipped to Precision Components Corp. in York, Pennsylvania, where they were trimmed and weld joints prepared. Assembly of the target chamber at Lawrence Livermore National Laboratory (seen here) was then performed in a temporary cylindrical steel enclosure. (NIF/Lawrence Livermore National Laboratory)
After the target chamber was lowered into place, the seven-story walls and roof of the Target Bay were completed. (NIF/Lawrence Livermore National Laboratory)
Construction workers install equipment inside the target chamber at the National Ignition Facility. (NIF/Lawrence Livermore National Laboratory)
Concrete pedestals in the two laser bays support the beampath infrastructure system for NIF's 192 laser beams. This is one of two 96-beam laser bays that were built at the facility. (NIF/Lawrence Livermore National Laboratory)
This photo from January 2002 shows the installation of the National Ignition Facility power-conditioning system, which has more than 160 kilometers of high-voltage cable, which delivers energy to the system's 7,680 flashlamps. (NIF/Lawrence Livermore National Laboratory)
The National Ignition Facility's Laser Bay 2. The laser beams travel more than 1,000 feet before they reach the target chamber. Laser Bay 2 was commissioned on July 31, 2007. (NIF/Lawrence Livermore National Laboratory)
The Seven Wonders of NIF
While construction of the football-stadium-sized National Ignition Facility was a marvel of engineering (see Building NIF), NIF is also a tour de force of science and technology development. To put NIF on the path to ignition experiments in 2010, scientists, engineers and technicians had to overcome a daunting array of challenges.
1. Faster, Less Expensive Laser Glass Production
Laser glass is the heart of the NIF laser system; it's the material that amplifies the laser light to the very high energies required for experiments. NIF's laser glass is a phosphate glass that contains a chemical additive with atoms of neodymium. The NIF laser system uses about 3,070 large plates of laser glass. Each glass plate is about three feet long and about half as wide. If stacked end-to-end, the plates would form a continuous ribbon of glass 1.5 miles long. To produce this glass quickly enough to meet construction schedules, NIF uses a new production method developed in partnership with two companies – Hoya Corporation, USA and Schott Glass Technologies, Inc. – that continuously melts and pours the glass. Once cooled, the glass is cut into pieces that are polished to the demanding NIF specifications.
2. Large Aperture Optical Switches
A key element of the amplifier section of NIF's laser beampath is an optical device called a plasma electrode Pockels cell, or PEPC, Plasma Electrode Pockels Cell that contains a plate of potassium dihydrogen phosphate (KDP). This device, in concert with a polarizer, acts as a switch – allowing laser beams into the amplifier and then rotating its polarization to trap the laser beams in the amplifier section. A thin plasma electrode that is transparent to the laser wavelength allows a high electric field to be placed on the crystal, which causes the polarization to rotate. The trapped laser beams can then increase their energy much more efficiently using multiple passes back and forth through the energized amplifier glass. After the laser beams make four passes through the amplifiers, the optical switch rotates their polarization back to its normal configuration, letting them speed along their path to the target chamber.
Lawrence Livermore National Laboratory technicians John Hollis (right) and Jim McElroy install a SIDE camera in the target bay of the NIF in January of 2009. The camera was the last of NIF's 6,206 various opto-mechanical and controls system modules called "line replaceable units" or LRUs to be installed. The first LRU, a flashlamp, was installed on Sept. 26, 2001. (NIF/Lawrence Livermore National Laboratory)
3. Stable, High-Gain Preamplifiers
NIF uses 48 preamplifier modules, or PAMs, each of which provides laser energy for four NIF beams. The PAM receives a very low energy (billionth of a joule) pulse from the master oscillator room and amplifies the pulse by a factor of about a million, to a millijoule.Technician Installing Preamplifier Module It then boosts the pulse once again to a maximum of about ten joules by passing the beam four times through a flashlamp-pumped rod amplifier. To perform the range of experiments needed on NIF, the PAMs must perform three kinds of precision shaping of the input laser beams.
Workers on the NIF target bay floor just outside the target chamber. (NIF/Lawrence Livermore National Laboratory/Jacqueline McBride)
4. Deformable Mirrors
The deformable mirror is an adaptive optic that uses an array of actuators to bend its surface to compensate for wavefront errors in the NIF laser beams. There is one deformable mirror for each of NIF's 192 beams.Deformable MirrorAdvances in adaptive optics in the atomic vapor laser isotope separation (AVLIS) program at Lawrence Livermore National Laboratory demonstrated that a deformable mirror could meet the NIF performance requirement at a feasible cost. Livermore researchers developed a full-aperture (40-centimeter-square) deformable mirror that was installed on the Beamlet laser in early 1997. Prototype mirrors from two vendors were also tested in the late 1990s. The first of NIF's deformable mirrors were fabricated, assembled and tested at the University of Rochester's Laboratory for Laser Energetics and installed and successfully used on NIF to correct wavefronts for the first beams sent to target chamber center (see NIF Early Light).
A technician inspects the final optics inspection (FODI) system for the NIF. When the FODI is extended into the 10-meter diameter target chamber from a diagnostic instrument manipulator, it can produce images of all 192 beamline final optics assemblies. (NIF/Lawrence Livermore National Laboratory)
5. Large, Rapid-Growth Crystals
NIF's KDP crystals serve two functions: frequency conversion and polarization rotation (see Optical Switch). The development of the technology to quickly grow high-quality crystals was a major undertaking and is perhaps the most highly publicized technological success of the NIF project.KDP CrystalNIF laser beams start out as infrared light, but the interaction of the beams with the fusion target is much more favorable if the beams are ultraviolet. Passing the laser beams through plates cut from large KDP crystals converts the frequency of their light to ultraviolet before they strike the target. The rapid-growth process for KDP, developed to keep up with NIF's aggressive construction schedule, is amazingly effective: Crystals that would have taken up to two years to grow by traditional techniques now take only two months. In addition, the size of the rapid-growth crystals is large enough that more plates can be cut from each crystal, so a smaller number of crystals can provide NIF with the same amount of KDP.
6. Target Fabrication
To meet the needs of NIF experiments, NIF's millimeter-sized targets must be designed and fabricated to meet precise specifications for density, concentricity and surface smoothness. When a new material structure is needed, materials scientists create the necessary raw materials. Fabrication engineers then determine whether those materials – some never seen before – can be machined and assembled. Manufacturing requirements for all NIF targets are extremely rigid. Prototype Ignition Target Components must be machined to within an accuracy of one micrometer, or one-millionth of a meter. In addition, the extreme temperatures and pressures the targets will encounter during experiments make the results highly susceptible to imperfections in fabrication. Thus, the margin of error for target assembly, which varies by component, is strict. Throughout the design process, engineers inspect the target materials and components using nondestructive characterization methods to ensure that target specifications are met and that all components are free of defects. Together, this multidisciplinary team takes an experimental target from concept to reality.
The final optics assemblies, shown here mounted on the lower hemisphere of the target chamber, contain special optics for beam conditioning, color conversion, and color separation. They also focus the beams from 40-by-40 centimeter squares of light to a spot on the target only .2 to 2 millimeters in diameter. (NIF/Lawrence Livermore National Laboratory)
7. Integrated Computer Control System
Fulfilling NIF's promise requires one of the most sophisticated computer control systems in government service or private industry. Every NIF experimental shot requires the coordination of complex laser equipment. In the process, some 60,000 control points for electronic, high voltage, optical and mechanical devices – such as motorized mirrors and lenses, energy and power sensors, video cameras, laser amplifiers, pulse power and diagnostic instruments – must be monitored and controlled. The NIF Control Room The precise orchestration of these parts by NIF's integrated computer control system will result in the propagation of 192 separate nanosecond (billionth of a second)-long bursts of light over a one-kilometer path length. The 192 separate beams must have optical pathlengths equal to within nine millimeters so that the pulses can arrive within 30 picoseconds (trillionths of a second) of each other at the center of a target chamber ten meters in diameter. Then they must strike within 50 micrometers of their assigned spot on a target measuring less than one centimeter long – an accuracy comparable to throwing a pitch over the strike zone from 350 miles away.
The exterior of the National Ignition Facility in in Livermore, California. Construction of the facility was completed in March 2009 and it was dedicated on May 31, 2009. (NIF/Lawrence Livermore National Laboratory)
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