Boeing Just Patented a Laser Fusion Jet Turbine

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US Navy Laser Propels Projectile 1/300th the Speed of Light

The Nike krypton fluoride (KrF) laser at the U.S. Naval Research Laboratory (NRL; Washington, DC) has earned the coveted Guinness World Records title for achieving "Highest Projectile Velocity" of greater than 1,000 km/s, a speed equivalent to two-and-a-quarter million miles per hour.

The previous record was held by researchers at Osaka University's Institute of Laser Engineering in Japan, who in 2006 used a neodymium glass (Nd:glass) laser to accelerate a target to 700 km/s. The record, currently held by NRL, was achieved in collaboration with the NRL Plasma Physics Division and the group from Japan, demonstrating the advantages of the high uniformity and short wavelength of the KrF laser technology.

"The impact of the highly accelerated target on a stationary foil generated thermonuclear fusion neutrons whose energy spread indicated that a gigabar--that's the pressure of a billion atmospheres--was achieved in the collision," said Max Karasik, NRL Laser Plasma Branch. "The results highlight the advantages of a krypton-fluoride laser in efficiently generating uniform pressures required for fuel compression in inertial confinement fusion."

In the experiments, thin plastic foils were accelerated to 1,000 km/s over a distance of less than a millimeter. The moving foils then collided with a stationary foil, generating thermo-nuclear temperatures and neutrons from fusion reactions. The high ablative pressure applied to compress and accelerate targets is used in inertial confinement fusion and high energy density research.

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Break Even Energy Output Exceeded Four Times at LLNL's National Ignition Facility Since September

Fuel gain exceeding unity in an inertially confined fusion implosion

Authors:

Hurricane et al

Abstract:

Ignition is needed to make fusion energy a viable alternative energy source, but has yet to be achieved. A key step on the way to ignition is to have the energy generated through fusion reactions in an inertially confined fusion plasma exceed the amount of energy deposited into the deuterium–tritium fusion fuel and hotspot during the implosion process, resulting in a fuel gain greater than unity. Here we report the achievement of fusion fuel gains exceeding unity on the US National Ignition Facility using a ‘high-foot’ implosion method which is a manipulation of the laser pulse shape in a way that reduces instability in the implosion. These experiments show an order-of-magnitude improvement in yield performance over past deuterium–tritium implosion experiments. We also see a significant contribution to the yield from α-particle self-heating and evidence for the ‘bootstrapping’ required to accelerate the deuterium–tritium fusion burn to eventually ‘run away’ and ignite.

LLNL NIF: There was Probably Break Even Fusion, but...

One unintended effect of the U.S. federal shutdown is that helpful press officers at government labs are not available to provide a reality check to some of the wilder stories that can catch fire on the Internet. They would have come in handy this week, when a number of outlets jumped on a report on the BBC News website. The National Ignition Facility (NIF) at Lawrence Livermore National Laboratory in California, it reported, had passed a "nuclear fusion milestone." NIF uses the world's highest energy laser system to crush tiny pellets containing a form of hydrogen fuel to enormous temperature and pressure. The aim is to get the hydrogen nuclei to fuse together into helium atoms, releasing energy.

The BBC story reported that during one experiment last month, "the amount of energy released through the fusion reaction exceeded the amount of energy being absorbed by the fuel - the first time this had been achieved at any fusion facility in the world." This prompted a rush of even more effusive headlines proclaiming the "fusion breakthrough." As no doubt NIF's press officers would have told reporters, the experiment in question certainly shows important progress, but it is not the breakthrough everyone is hoping for.

A memo sent out on 29 September to collaborating labs from NIF Director Ed Moses—which has been seen by Science—describes a fusion shot that took place at 5:15 a.m. on 28 September. It produced 5x1015 neutrons, 75% more than any previous shot. Neutrons are a product of fusion reactions, so they are used as a measure of success.

[...]

One requirement for ignition is that energy output should exceed the energy input from the laser, i.e., that gain (output divided by input) should be greater than 1. NIF's laser input of 1.8 MJ is roughly the same as the kinetic energy of a 2-tonne truck traveling at 160 km/h (100 miles/h). The output of the reaction—14 kJ—is equivalent to the kinetic energy of a baseball traveling at half that speed. Numerically speaking, the gain is 0.0077. The experiment “is a good and necessary step, but there is a long way to go before you have energy for mankind,” Campbell says.

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BBC Report: Livermore's National Ignition Facility Has Broken Even

Harnessing fusion - the process that powers the Sun - could provide an unlimited and cheap source of energy.

But to be viable, fusion power plants would have to produce more energy than they consume, which has proven elusive.

Now, a breakthrough by scientists at the National Ignition Facility (NIF) could boost hopes of scaling up fusion.

NIF, based at Livermore in California, uses 192 beams from the world's most powerful laser to heat and compress a small pellet of hydrogen fuel to the point where nuclear fusion reactions take place.

The BBC understands that during an experiment in late September, the amount of energy released through the fusion reaction exceeded the amount of energy being absorbed by the fuel - the first time this had been achieved at any fusion facility in the world.

This is a step short of the lab's stated goal of "ignition", where nuclear fusion generates as much energy as the lasers supply. This is because known "inefficiencies" in different parts of the system mean not all the energy supplied through the laser is delivered to the fuel.

But the latest achievement has been described as the single most meaningful step for fusion in recent years, and demonstrates NIF is well on its way towards the coveted target of ignition and self-sustaining fusion.

For half a century, researchers have strived for controlled nuclear fusion and been disappointed. It was hoped that NIF would provide the breakthrough fusion research needed.

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Proposed Cure for the NIF Fusion Problems: Focusing (sorta)

For several decades, researchers have been using the world’s most powerful lasers to try to recreate the fusion reaction that occurs in stars. The process, called inertial confinement fusion (ICF), uses multiple laser beams to compress and heat a small, spherical target containing nuclear fuel, in order to ignite thermonuclear fusion. In principle, the heat released from the reaction could provide an alternative energy source, but the challenges to achieving ignition are many. One, in particular, is to understand and control a process first identified in the mid-1990s  called crossed-beam energy transfer (CBET), in which the laser beams exchange energy with each other as they overlap in the plasma. In laser-driven fusion experiments, CBET occurs just before the laser beams deposit their energy into the target. The effect can therefore modify the finely tuned symmetry of the beams or cause energy to leak out of the target.

Now, Igor Igumenshchev from the Laboratory for Laser Energetics at the University of Rochester in New York and colleagues are proposing a new technique to mitigate the negative effects of CBET. In Physical Review Letters, Igumenshchev et al. use simulations to show that dynamically reducing—or “zooming”—the spot size of the lasers as they interact with the target would reduce energy transfer between the beams, without disrupting the symmetry of the laser illumination—a negative side effect of some existing proposals for correcting CBET.

The CBET process is relatively simple to explain. When two laser beams overlap in a plasma [ed. see above], they create a beat wave. Free charges in the plasma accumulate where the beat wave’s electric field is weakest (a result of what is known as the ponderomotive force) and this accumulation of charges modulates the refractive index, in effect creating a Bragg diffraction grating for the lasers. Because this grating is created by the beat wave, the Bragg condition is, by construction, always satisfied. Moreover, if there is a wavelength separation between the laser beams, or the plasma flows, the grating can move at (or close to) the speed of sound. The moving grating will then scatter light from one beam in the exact direction of the other beam, effectively transferring energy from one laser beam to the other.

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What the Rochester group is proposing now [6] may prove to be an even more effective way of controlling CBET than simply reducing the laser spot size. Igumenshchev et al.’s key insight is that the negative effects of CBET and radiation asymmetry occur at different times during the target’s implosion. The symmetry of the laser illumination is crucial in the first few nanoseconds after the lasers interact with the target, when nonuniformities can drive low-frequency perturbations on the surface of the spherical target, which grow as it implodes and reduce the implosion performance. At later times, though, the plasma corona has sufficiently expanded to smooth out radiation nonuniformities. But it also offers a favorable terrain for CBET to occur. Igumenshchev et al.’s proposal is to drive the first few nanoseconds of the laser pulse with large spots that are roughly the same diameter as the size of the target; then, at later times, switch to spot sizes that are ∼30–40% smaller, in order to reduce CBET and maintain good energy coupling to the target. The authors show, using 2D hydrodynamics simulations, that tailoring the spot size in this way yields an implosion performance that is almost as good as the ideal case: a purely spherically symmetric implosion.

How would this tuning of the spot size be achieved in practice? The authors imagine a new type of optical element called a “zooming phase plate,” which would produce a different spot size depending on whether a laser lands on the central part of the plate or the outer edges. With such a plate, it would be possible to send two consecutive laser pulses toward the plasma: a first pulse that hits only the outer area of the plate and produces a large spot on the target, and a second pulse that covers the center of the plate and produces a 30–40% smaller spot on the target.