The NIF target chamber is coated with a 16-inch-thick neutron shielding concrete shell. The entire assembly weighs about one million pounds.
World's Largest Laser Meets World's Fastest Computers
April / May 2007
Volume 5 Number 2
Barry Zito, the superstar pitcher signed last year by the San Francisco Giants, warms up for games with a "long toss" routine, throwing strikes from centerfield to a catcher positioned at third base.
Pretty impressive—€”but imagine hitting the strike zone with a baseball thrown from 350 miles away.
That's the level of precision required of the computerized control system for the National Ignition Facility (NIF), the world's largest and most energetic laser now nearing completion at Lawrence Livermore National Laboratory. The price tag is $3.5 billion.
When completed in 2009, NIF will use 192 laser beams to compress eraser-sized fusion targets to conditions required for thermonuclear ignition and burn. This will enable scientists to study the physics of matter at densities, pressures and temperatures that exist only in the interior of stars and in exploding nuclear weapons.
In the process, more energy will be liberated than is used to initiate the fusion reactions. By demonstrating the ability to attain fusion ignition in the laboratory, NIF will provide the basis for future decisions about fusion's long-term potential as a clean, virtually boundless energy source—€”the same energy that powers the sun and the stars.
Every NIF experimental shot requires the coordination of complex laser equipment. In the process, 60,000 control points of electronic, 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 precise orchestration of these parts will result in the propagation of 192 separate nanosecond (billionth of a second)-long bursts of light over a 1-kilometer path length. These 192 beams must arrive within 30 picoseconds (trillionths of a second) of each other at the center of a target chamber 10 meters in diameter, and they must strike within 50 micrometers of their assigned spot on a target measuring less than 1 centimeter long.
Fulfilling NIF's promise requires a large-scale computer control system as sophisticated as any in government service or private industry. Conceived and built by a team of 100 software developers, engineers and quality control experts, NIF's integrated computer control system (ICCS) software, now nearly 85 percent complete, will soon have about 1.6 million lines of code running on more than 850 computers. ICCS, which is operated from a main control room, fires the laser and conducts these experiments automatically.
"We want NIF operations to be as efficient and automated as possible," says Paul VanArsdall, associate project manager for ICCS, citing the success the system's developers achieved in aligning NIF's beams automatically. The alignment control system software determines the position of NIF's laser beams on the optics by analyzing sensor video images with a variety of computer-vision algorithms.
Motor control robotics software uses the sensor information to remotely position more than 9,000 stepping motors and other actuators. These devices point the beams through pinholes, center them on mirrors and lenses and focus them onto the target—€”achieving greater precision and effectively eliminating the need for personnel to adjust the beamlines manually.
ICCS already has proved itself during almost-daily test shots using beams from the first "bundles" of eight beams—€”the basic modular unit of NIF—€”as they were installed. Last December, the first "cluster" of six bundles became operationally qualified when all 48 beams in the cluster were fired simultaneously. ICCS was able to fire the entire shot cycle, including shot setup, data archiving, shot data analysis and post-shot amplifier cooling, in a little more than three hours.
All subsystems participated in the shots to test NIF's end-to-end functionality. At least one of every type of hardware device was successfully monitored and controlled by ICCS. Among its many accomplishments, the control system demonstrated that it can use deformable mirrors to maintain the optical quality in laser beams, synchronize the beams' arrival at their targets and align the laser's optical elements to ensure that beams hit their targets precisely.
Over the next two years, as the rest of the laser bundles are completed, computers and software that were fielded for the initial bundles will be replicated. NIF's independent bundle architecture simplifies the task of controlling the laser because each bundle is prepared for the upcoming shot independently. The bundles are synchronized just before shot time so that even the most complex experiments can be carried out efficiently with a short turnaround time.
VanArsdall emphasizes the importance of this concept: "With the bundle approach, we have a highly manageable way to bring additional lasers on line. We designed each bundle to be controlled by its own software segment running on a set of computers dedicated to that bundle. As a result, performance remains constant regardless of the number of bundles installed." A more traditional approach would have resulted in a control system of overwhelming complexity because software would have to be scaled up to control all 192 laser beams simultaneously.
"Instead, we just have to deploy 24 copies of the control system," says VanArsdall. "We've demonstrated the architecture during extensive commissioning shots and user experiments. Once we control one bundle, it is a straightforward task to extend controls to all. In this way, we've simplified our design and dramatically improved the performance of ICCS."
The modular control system concept dovetails well with plans for NIF experiments. For example, although achieving ignition will require all 192 beams, many experiments will require fewer laser beams.
"We started building the first software prototypes for NIF in 1997 with a team of about eight people," recalls Bob Carey, lead software architect and one of the original eight developers. From that modest group, the organization grew to include many additional software developers, information technologists, systems engineers, quality control managers and an independent testing group. Computer scientists and engineers on the team average 20 years of experience in such fields as database design, real-time controls, test engineering, graphics user interfaces and object-oriented programming.
NIF was designed to be operational over a 30-year lifetime. Therefore, control software must be flexible and easy to update. "We wanted an architecture that provided an integrated control system we could maintain for the foreseeable future," says Larry Lagin, associate project manager for software engineering and a division leader in LLNL's Computation Directorate.
ICCS's architecture is hierarchical in nature. The two main layers are a front-end or bottom layer consisting of about 800 front-end processors (FEPs) and a supervisory or top layer of more than 50 powerful computers—€”all managed in the main NIF control room from an ensemble of 14 operator consoles. The supervisory layer includes operator-controlled graphics displays and automated controls that work with the FEPs to coordinate components in all 192 beams.
Databases and common services incorporated into the supervisory layer support control system operation.
A high-performance network, with a throughput of 1 gigabit per second, interconnects these computers for passing commands, assessing bundle status and retrieving diagnostics data. The network also carries video images of the laser beams generated by more than 300 high-resolution digital cameras that serve as the eyes of the control system for monitoring and adjusting the laser alignment automatically.
The FEPs, which attach to the laser hardware, operate as real-time applications running on industrial-grade microprocessors. They are organized to support hardware in NIF's functional systems: injection laser, beam controls, laser diagnostics, pulse power and target diagnostics.
Different types of FEPs optimize the control of similar devices, such as beam motion or the main power supplies. Installed in racks, the FEPs interface to devices such as stepping motors, transient digitizers, calorimeters and photodiodes. For example, a single beam control FEP drives as many as 100 motors to precisely adjust the laser beam so that the laser is kept on course within 50 micrometers (about half the width of a human hair). In keeping with the independent bundle concept, these FEPs are wired to control devices associated with a single bundle.
Supervisor systems run on servers and workstations located near the main NIF control room and provide operators with system status and other data from the FEPs. Operators access supervisor-system data through a hierarchy of on-screen graphics interfaces. Operators can also view video images of the laser beams from any of the hundreds of sensor cameras located throughout the complex.
Daily operation of NIF is managed by the on-duty shot director, who oversees control room activities and operates the laser and target systems for conducting shot experiments. The ICCS team developed shot-supervisor software that assists the shot director and the control room staff to prepare and fire each shot by automatically sequencing the system's many functions. "The software puts everything within each bundle in a specific time sequence and makes sure all the components play together to achieve the required laser performance," says Dave Mathisen, lead designer of the shot-supervisor software. The shot director interacts with this software to ensure that experiments run successfully.
In designing the NIF central control room, VanArsdall studied the layout of the National Aeronautics and Space Administration (NASA)'s mission control room in Houston, Texas. NIF laser physicist and former NASA astronaut Jeff Wisoff notes that both control rooms have operator stations corresponding to different hardware systems. In NIF's case, each console corresponds to a functional system on the laser. Similar to NASA operators in the Launch Center control room, operators located in the NIF control room continuously track data on their monitors.
Wisoff, the deputy associate director for NIF Operations, sees other similarities between executing a NIF shot and launching a Space Shuttle. "Launch of a Space Shuttle is controlled by software centered in the Launch Center control room until T minus 31 seconds—€”or 31 seconds before liftoff," says Wisoff. "Then computers onboard the shuttle take over." Similarly, countdown for a NIF shot includes computer checks of every subsystem, and the control system will automatically stop events from proceeding unless all conditions are satisfactory. At T minus 2 seconds, the ICCS software turns over control to a high-precision integrated timing system designed to trigger thousands of laser modules and diagnostics at exactly the right instant.
"We've established disciplined software engineering to deliver a majority of the software, and we've proven the control system architecture," says VanArsdall. The team is increasingly confident that NIF will be a vital resource for keeping the U.S. nuclear stockpile safe and reliable, advancing scientific knowledge of the physics of matter under extreme conditions and taking the next steps in fusion energy toward achieving ignition. "Many of us have devoted most of our careers to achieving ignition in the laboratory," says Lagin. "It's a grand challenge, and it's also a great privilege to be part of the team working to achieve it."
Arnie Heller is a technical communications specialist at Lawrence Livermore National Laboratory.
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About the National Ignition Facility
Ground was broken for the National Ignition Facility, a stadium-sized complex, in 1997. When complete, the $3.5-billion project will contain a 192-beam, 1.8-megajoule, 700-terawatt laser system adjoining a 10-meter-diameter target chamber with room for nearly 100 experimental diagnostics. NIF's beams will compress and heat small capsules containing a mixture of hydrogen isotopes of deuterium and tritium. These fusion targets will ignite and burn, liberating more energy than is required to initiate the fusion reactions. NIF experiments will allow scientists to study physical processes at temperatures approaching 100 million kelvins and 100 billion times atmospheric pressure—€”conditions that exist naturally only in the interior of stars and in nuclear weapon detonations.
A cornerstone of the National Nuclear Security Administration's Stockpile Stewardship Program, NIF will help ensure the reliability of the U.S. nuclear weapons stockpile by allowing scientists to validate computer models that predict age-related effects on the stockpile. Access to these regimes will also make possible new areas of basic science and applied physics research.
NIF's 192 beams are organized in quads, bundles and clusters. Quads are four beams with the same pulse shape. Each NIF bundle—€”an upper and lower quad—€”is controlled independently from the others.
In July 2001, the NIF project began working on an accelerated set of milestones leading to NIF Early Light, a campaign to demonstrate NIF's capability to deliver high-quality laser beams to the target chamber in support of early experiments. The first quad was activated in December 2002. On May 30, 2003, NIF produced 10.4 kilojoules of ultraviolet laser light in a single laser beamline, setting a world record for laser performance. By the end of the Early Light campaign, in October 2004, more than 400 shots had been performed. During that time, NIF met performance criteria for beam energy and power output, beam-to-beam uniformity and timing and delivery of shaped pulses for ignition and nonignition experiments. The first cluster of 48 beams became operational on Dec. 7, 2006, and achieved more than a megajoule of infrared laser energy, demonstrating NIF's capability of achieving 4.2 megajoules in the infrared.
When all beams are operating, NIF will deliver more than 60 times the energy of Livermore's Nova laser, which was decommissioned in 1999, or the OMEGA laser at the University of Rochester's Laboratory for Laser Energetics. NIF will make significant contributions to astrophysics, hydrodynamics, materials science and plasma physics. Experiments will create physical regimes never before seen in any laboratory setting—€”to benefit maintenance of the U.S. nuclear weapons stockpile, spur advances in fusion energy and open new vistas in basic science.
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