The National Ignition Facility: enabling fusion ignition for the 21st century
Summary (3 min read)
- The installation of all 192 ultra-clean and precision aligned beampath enclosures in NIF's two laser bays was completed in September 2003.
- When completed in 2008, NIF will provide 192 energetic laser beams to compress deuterium-tritium fusion targets to conditions in which they will ignite and burn, liberating more energy than is required from the laser to initiate the fusion reactions.
- NIF experiments will be conducted in a well-controlled laboratory setting to precisely study physical processes at a range of temperatures and pressures approaching up to 100 million K and 100 billion times atmospheric pressure.
- The 10-meter diameter target chamber sets the scale for the facility.
2. THE NIF LASER SYSTEM ARCHITECTURE
- NIF's main laser system consists of two large amplifier units -the power amplifier, and the multi-pass or main amplifier.
- 3 Experience gained with earlier laser systems at LLNL, e.g., the Shiva 10 kJ infrared laser 26 , and the Nova 30 kJ ultraviolet laser 27 allowed researchers to specify the requirements for the NIF laser architecture.
- 28 During initial operation, NIF is configured to operate in the "indirect drive" configuration, which directs the laser beams into cones in the upper and lower hemispheres of the target chamber.
- This configuration is optimized for illuminating the fusion capsule mounted inside cylindrical hohlraums using x-rays generated from the hot walls of the hohlraum to implode the capsule.
3. NIF OPTICS
- Among the many challenges in designing and building NIF has been the design, engineering, construction, and commissioning of what is arguably the largest precision optical instrument ever built.
- There are more than 7500 large optics of 40 cm or greater transverse size including laser amplifier glass slabs, lenses, mirrors, polarizers, and crystals.
- An additional 26,000 smaller optical components are used in NIF.
- The total area of precision optical surfaces in NIF is nearly 4,000 square meters.
- Currently NIF's finishing vendors have finished approximately 30% of the optics required for NIF's 192 laser beams.
4. ACTIVATION OF NIF'S FIRST LASER BEAMS
- In October 2001 the first laser light from NIF's master oscillator was generated in the master oscillator room.
- This master oscillator has demonstrated the required pulse shaping stability and accuracy for high contrast ignition pulses and other types of laser pulses that are of interest to NIF experimenters.
- A separate target chamber, known as the Precision Diagnostic System (PDS), which is located in one of NIF's switchyards, has also been used to fully characterize NIF's 1 , 2 , and 3 laser beam energy, power, and wavefront to validate and enhance computer models that predict laser performance.
- NIF's highest 3 single laser beam energy to date is 10.4 kJ, equivalent to 2 MJ for a fully activated NIF, exceeding the NIF energy point design of 1.8 MJ.
- High power campaigns have also been completed with drive power reaching 7 terawatts or about 5 gigawatts/cm 2 .
5. EXPANDING SCIENTIFIC HORIZONS USING THE NATIONAL IGNITION FACILITY
- The National Academy of Sciences in the United States has recently recognized the exciting scientific frontiers becoming available at the next generation of high-energy-density experimental facilities.
- NIF can explore the physics of matter at temperatures approaching those that existed in the very early universe.
- 42 NIF's high-energy laser beams can be tailored for driving relatively large, uniform volumes.
- Currently there is no theory that adequately describes WDM.
- Isochoric heating with fusion ignition neutrons or high energy petawatt laser-generated ion beams when they become available in the coming decade provides an additional capability for shocking and heating materials to exotic physical states.
6. LABORATORY ASTROPHYSICS
- Laboratory-based astrophysics experiments, simulating extreme physics phenomena heretofore inaccessible, are now becoming feasible for the first time on NIF.
- 7 . Radiative shocks such as supernova blast waves can be simulated using scaled gas-filled targets illuminated by energetic laser beams.
- 49 Figure 8 displays examples of these phenomena and associated laser-driven analog experiments performed on Nova and Omega.
- Additional examples of scaled astrophysical phenomena that can be simulated using lasers.
- On the right the visually striking structures seen in the Eagle nebula (Hubble Space Telescope photograph courtesy of NASA STScI, Release Number : STScI-1995-44) are compared with similar RT structures generated using the Nova Laser.
7. IGNITION ON NIF
- One of the key missions of NIF is to generate and study thermonuclear ignition and energy gain using the 192 lasers of NIF to compress and heat small capsules containing a mixture of the heavy hydrogen isotopes of deuterium and tritium.
- Precisely focused temporally-shaped laser beams are directed into the hohlraum through the ends and deliver their energy to the inside walls, generating intense x-rays that uniformly illuminate the capsule.
- 53 Recent studies by LLE researchers are also looking at "polar" direct drive options, in which beam positioning and timing using NIF's indirect drive configuration of lasers can be optimized to directly drive fusion capsules.
- In addition, significant progress has been made at LANL and at LLE in fabricating smooth and beryllium/copper and plastic capsules that nearly meet these new design specifications.
8. FIRST PHYSICS FROM NIF
- Over the past year nearly 200 full system shots have been carried out on NIF.
- In addition a sophisticated suite of experimental diagnostics has been fielded on the 10-meter diameter target chamber and become available for use.
- The x-ray images compare favorably with sophisticated calculations of laser-plasma interactions.
- This data is compared with computer models that show qualitative agreement.
- Two NIF beams were used to drive this experiment, while the other two beams provided separately delayed x-ray backlighter sources.
9. THE PATH FORWARD TO FULL NIF
- Completion of all 192 laser beams is scheduled for September 2008.
- The increasing symmetry and energy available as the number of beams increases enables a variety of target configurations including planar targets, horizontal and vertical half-hohlraums , and vertical hohlraums with 4-fold and 8-fold symmetry.
- After project completion, NIF is expected to ramp up to approximately 700 shots per year for a wide variety of experimental users as a national user facility.
- As NIF matures, the authors fully expect the facility to evolve to include exciting new capabilities, some of which are mentioned briefly here.
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Frequently Asked Questions (21)
Q1. What contributions have the authors mentioned in the paper "The national ignition facility: enabling fusion ignition for the 21st century" ?
NIF provides a scientific center for the study of inertial confinement fusion and the physics of matter at extreme energy densities and pressures. This paper provides a detailed look the NIF laser systems, laser and optical performance, and results from laser commissioning shots. The authors also discuss NIF ’ s high –energy density and inertial fusion experimental capabilities, the first experiments on NIF, and plans for future capabilities of this unique facility.
Q2. What are the other capabilities of the NIF program?
In addition to diagnostics, the NIF Program includes support for building and commissioning facility capabilities in diffractive optics (phase plates), cryogenic target systems, and target area operations.
Q3. How many picoseconds of beam-to-beam synchronization have been measured?
Beam-to-beam synchronization has also been measured and adjusted to better than 6 picoseconds, which corresponds to approximately 1 part in 150,000 of the total beampath in NIF.
Q4. How many joules of laser energy will be delivered in a specially shaped pulse?
For inertial fusion studies the beams will deliver 1.8 million joules (approximately 500 trillion watts of power) in a specially shaped pulse of laser energy in the near-ultraviolet (351 nanometer wavelength).
Q5. How many megajoules of energy is stored in the power conditioning system?
The Power Conditioning System located on either side of each laser bay stores up to 500 Megajoules of electrical energy for the 7,680 flashlamps used in NIF’s large glass amplifier sections.
Q6. How many slabs are used in the power amplifier?
Recent optimization studies indicate that three slabs per beam in the power amplifier are sufficient to meet NIF’s power and energy requirements, while allowing for additional capability in the future.
Q7. What is the purpose of the NIF target chamber and final focusing system?
The NIF target chamber and final focusing system is designed with maximum flexibility for experimental users and includes over 100 diagnostic instrumentation and target insertion ports.
Q8. How will the NIF laser system be controlled?
NIF experiments will be conducted in a well-controlled laboratory setting to precisely study physical processes at a range of temperatures and pressures approaching up to 100 million K and 100 billion times atmospheric pressure.
Q9. How many shots per year is expected to be performed?
After project completion, NIF is expected to ramp up to approximately 700 shots per year for a wide variety of experimental users as a national user facility.
Q10. What is the way to design a fusion capsule?
Designs supporting indirect-drive, or x-ray drive of ignition capsules in hohraums are becoming more robust as better physics understanding and better modeling capability, including full 3-dimensional modeling of capsules and hohlraums, allows design trade-off studies to be rapidly performed and design spaces to be optimized.
Q11. What is the purpose of the laser?
The 60- beam Omega laser at the University of Rochester Laboratory for Laser Energetics (LLE) is configured to study direct drive ICF and has been performing ignition experiments for many years.
Q12. What is the design of the capsule?
The capsule is suspended in a hollow gold cylinder called a hohlraum that has laser entrance windows on each end of the cylinder.
Q13. How many optics are being produced per month?
NIF meter-scale optics suitable for high fluence operation with the required wavefront specification are being manufactured at a production rate of over 100 optics per month and the authors are following a schedule for completing production for all the necessary optics for 192 beam lines by 2007.
Q14. How many shots per year will NIF provide?
A shot campaign conducted on NIF in 2003 provided three target shots per day over a three-day period, giving us confidence in NIF’s ability to meet the planned 700 shots per year when it is fully operational.
Q15. How many beams can be directed to the target chamber center?
Laser physicists have determined how NIF’s current injection laser, main amplifier, and beam transport system could be modified to allow up to 20 high-energy petawatt-class (HEPW) beams to be directed to target chamber center.
Q16. What are the other conditions that exist in the interior of stars and planets?
Other NIF experiments will study physical processes at temperatures approaching 108 K and 1011 bar; conditions that exist naturally only in the interior of stars and planets.
Q17. What are the design options for a fusion capsule?
These designs include extremely narrow micron-diameter fill tubes and graded-dopant beryllium capsules that ease the filling and maintenence of cryogenic DT in the capsule.
Q18. How many system shots have been conducted?
These beams are being regularly used for laser performance and physics experiments and to date nearly 250 system shots have been conducted.
Q19. How much energy can be added to a capsule?
58 Figure 11 shows recent calculations suggesting that as much as 1.5 MJ of energy may couple to a capsule at 250- eV drive temperature.
Q20. What is the name of the lab?
NIF is housed in a 26,000 square meter environmentally controlled building and is the world’s largest and most energetic laser experimental system.
Q21. What is the recent development of the NIF point design?
54A NIF “point design” ignition hohlraum and capsule has been developed using increasingly sophisticated 3D computer calculations.