Largest Laser in the World is Picking up Speed

Ninety-six NIF beamlines have been fired together for the first time, with “excellent” control system and laser stability, according to National Ignition Facility (NIF) & Photon Science Principal Associate Director – Ed Moses. In 2008 the facility’s injection laser systems, which initiate the laser pulses, were fired for 144 beamlines.

New Laser Packs More Power than Nova Laser

A total infrared energy of more than 2.5 megajoules has now been fired. This is more than 40 times what the Nova laser (NIF’s predecessor) typically operated at the time it was the world's largest laser.

Ed Moses, Principal Associate Director, National Ignition Facility

Figure 1. The Target Alignment Sensor system is mounted on a retractable arm inside the 30-meter diameter NIF target chamber.

Back in 2008 tests and sophisticated computer simulations predicted that NIF, at that time under construction at Lawrence Livermore National Laboratory in northern California, was on the way to reach its design specification of 1.8 million joules of ultraviolet energy. This was when all beamlines were completed in 2009 (NIF’s infrared laser energy is converted to ultraviolet for laser fusion experiments to minimize energy loss). A few years later in March 2012, the NIF laser system set an energy record when it fired 1.9 million joules of energy. Even this record was topped in 2018 when the laser system fired 2.15 million joules of energy to its target chamber. Not only is this a new fascinating world record, but it is also an improvement over NIF’s design specification of 1.8 million joules, and more than 10% energy increase compared to the 2012’s 1.9 million joules record.

Lasers Meet Operational and Performance Requirements

The first of the facility’s two 96-beam laser bays was commissioned at the end of July 2007. Each of the 96 beams fired an infrared output energy of about 22,000 joules, more than enough to meet NIF’s operational and performance requirements. Since then six more eight-beam “bundles” have been commissioned in the second laser bay.

This is a significant event as we move towards completion of the National Ignition Facility. The day is coming soon when we will be able to simulate the conditions of extreme temperature and pressure approaching those existing in nuclear explosions.

Thomas D'Agostino, Administrator, National Nuclear Security Administration (NNSA)

2300 High Quality Optics Needed to Fire the Beams

The laser shots last about 25 billionths of a second, a tiny fraction of the time it takes to blink an eye. Firing the beams requires operation of 2,300 high-quality optics and instrumentation modules and nearly 400 computers running a million lines of control system code.

The tests measure the quality of each beam’s spatial profile and temporal pulse shape. Even though each shot is exceedingly short in time, its energy output and frequency is designed to vary significantly throughout its duration, depending on the type of experiments being conducted.

Chris Haynam, the physicist responsible for modeling and testing the quality and performance of the lasers, pointed out that only about a dozen people on NIF’s overnight “owl” shift participated in the control room activities marking completion of commissioning activities for the first laser bay.

This is a good thing. In fact, physicists and chief engineers do not have to be there. The details were worked out far ahead of time. We gave them the plan. The operators executed the plan per the schedule. And it went off without a hitch.

Chris Haynam, Physicist, National Ignition Facility

Meanwhile, data gathered from experiments conducted at NIF in 2003-2004 have enabled sophisticated computer simulations that confirm NIF’s ability to reach the energy levels and beam quality required to produce the world’s first demonstration of inertial confinement fusion.

The NIF Early Light Experiments

The “NIF Early Light” experiments included four shots using four laser beams at high energy on a full-scale target for the first time. Simulations of the experiments on LLNL’s world-class supercomputers matched the actual experimental data to an unprecedented degree. The experiments and simulations indicated that NIF’s laser beams will propagate effectively in plasma-filled targets designed to achieve fusion ignition and thermonuclear burn.

When NIF is operating, the infrared energy from its 192 laser beams is converted to 1.8 million joules (as per design specification) of ultraviolet energy and delivered to millimeter-sized targets at the center of its target chamber in a pulse lasting about ten nanoseconds (billionths of a second). This is equivalent to 1,000 times the electrical generating power of the United States in the same brief time period.

Figure 2. Half of NIF's 192 beamlines are located in Laser Bay 2.

Laser Beams Compress Hollow Shell Filled with Deuterium and Tritium

The laser beams compress a hollow shell filled with the hydrogen isotopes deuterium and tritium to up to 100 times the density of lead. The results are temperatures of more than 100 million degrees Celsius and pressures as much as 100 billion times the Earth's atmosphere. In these conditions the fuel core ignites and thermonuclear burn quickly spreads through the compressed fuel, releasing many times more energy than the amount deposited by the laser beams.

Inertial confinement fusion experiments at NIF create conditions similar to those inside an exploding thermonuclear weapon or in the cores of stars and giant planets. The resulting information obtained via the many experiments happening at NIF will be used to help insure the reliability and safety of the nation’s nuclear stockpile without underground testing. The data is further hoped to also reveal new details about the nature and structure of the universe.

The Gold Hohlraum

NIF experiments from 2009 focused 96 beams on a gold hohlraum (the eraser-sized capsule containing the fusion target) filled with a light gas mixture. Dubbed “Eos” for the Greek goddess of dawn, the experiments used the first set of beams from the first laser bay, traveling to the center of the ten-meter diameter target chamber. They are designed to help validate key aspects of the full-scale ignition campaign that began in 2010.

Figure 3. NIF Hohlraum

This article was updated on the 28^th January, 2020