Inertial confinement fusion

Conversely, the nuclear force increases with the number of nucleons, so isotopes of hydrogen that contain additional neutrons reduce the required energy.

Not only would the fission triggers be expensive to produce, but the minimum size of such a bomb is large, defined roughly by the critical mass of the plutonium fuel used.

[13] Much of the work since the 1970s has been on ways to create the central hot-spot that starts off the burning, and dealing with the many practical problems in reaching the desired density.

Early calculations suggested that the amount of energy needed to ignite the fuel was very small, but this does not match subsequent experience.

Lasers have scaled up from a few joules and kilowatts to megajoules and hundreds of terawatts, using mostly frequency doubled or tripled light from neodymium glass amplifiers.

[citation needed] Heavy ion beams are particularly interesting for commercial generation, as they are easy to create, control, and focus.

It included three primary concepts; energy generation under Project PACER, the use of nuclear explosions for excavation, and for fracking in the natural gas industry.

PACER was directly tested in December 1961 when the 3 kt Project Gnome device was detonated in bedded salt in New Mexico.

Further studies designed engineered cavities to replace natural ones, but Plowshare turned from bad to worse, especially after the failure of 1962's Sedan which produced significant fallout.

[21] Another outcome of Atoms For Peace was to prompt John Nuckolls to consider what happens on the fusion side of the bomb as fuel mass is reduced.

[23] In 1956 a meeting was organized at the Max Planck Institute in Germany by fusion pioneer Carl Friedrich von Weizsäcker.

At this meeting Friedwardt Winterberg proposed the non-fission ignition of a thermonuclear micro-explosion by a convergent shock wave driven with high explosives.

[24] Further reference to Winterberg's work in Germany on nuclear micro explosions (mininukes) is contained in a declassified report of the former East German Stasi (Staatsicherheitsdienst).

In 1967, research fellow Gurgen Askaryan published an article proposing the use of focused laser beams in the fusion of lithium deuteride or deuterium.

[28] Through the late 1950s, and collaborators at Lawrence Livermore National Laboratory (LLNL) completed computer simulations of the ICF concept.

Funding for fusion research was stimulated by energy crises produced rapid gains in performance, and inertial designs were soon reaching the same sort of "below break-even" conditions of the best MCF systems.

The realization that exploding pusher target designs and single-digit kilojoule (kJ) laser irradiation intensities would never scale to high yields led to the effort to increase laser energies to the 100 kJ level in the ultraviolet band and to the production of advanced ablator and cryogenic DT ice target designs.

Shiva was a "proof of concept" design intended to demonstrate compression of fusion fuel capsules to many times the liquid density of hydrogen.

However, due to the laser's coupling with hot electrons, premature heating of the dense plasma was problematic and fusion yields were low.

NIF's main objective is to operate as the flagship experimental device of the so-called nuclear stewardship program, supporting LLNLs traditional bomb-making role.

When the implosion reaches maximum density (at the stagnation point or "bang time"), a second short, high-power petawatt (PW) laser delivers a single pulse to one side of the core, dramatically heating it and starting ignition.

Several projects are currently underway to explore fast ignition, including upgrades to the OMEGA laser at the University of Rochester and the GEKKO XII device in Japan.

Challenges to this approach include relatively low drive temperatures, resulting in slow implosion velocities and potentially large instability growth, and preheat caused by high-energy x-rays.

[61][62][63] In April 2017, clean energy startup Apollo Fusion began to develop a hybrid fusion-fission reactor technology.

[73] In March 2022, Australian company HB11 announced fusion using non-thermal laser pB11, at a higher than predicted rate of alpha particle creation.

These devices were to deliver multiple targets per second into the reaction chamber, using the resulting energy to drive a conventional steam turbine.

If the driver energy misses the fuel pellet completely and strikes the containment chamber, material could foul the interaction region, or the lenses or focusing elements.

One concept, as shown in the HYLIFE-II design, is to use a "waterfall" of FLiBe, a molten mix of fluoride salts of lithium and beryllium, which both protect the chamber from neutrons and carry away heat.

Cooling is provided by a molten ceramic, chosen because of its ability to absorb the neutrons and its efficiency as a heat transfer agent.

[81][82] Funding for the NIF in the United States is sourced from the Nuclear Weapons Stockpile Stewardship program, whose goals are oriented accordingly.

The 10 beam LLNL Nova laser , shortly after its completion in 1984. In the late 1970s and early 1980s the laser energy per pulse delivered to a target using inertial confinement fusion went from a few joules to tens of kilojoules, requiring very large scientific devices for experimentation.
Schematic of the stages of inertial confinement fusion using lasers. The blue arrows represent radiation; orange is blowoff; purple is inwardly transported thermal energy.
  1. Laser beams or laser-produced X-rays rapidly heat the surface of the fusion target, forming a surrounding plasma envelope.
  2. Fuel is compressed by the rocket-like blowoff of the hot surface material.
  3. During the final part of the capsule implosion, the fuel core reaches 20 times the density of lead and ignites at 100,000,000 ˚C.
  4. Thermonuclear burn spreads rapidly through the compressed fuel, yielding many times the input energy.
Plot of NIF results from 2012 to 2022
Plot of NIF target gain from 2012 to 2022, on a logarithmic scale. Note the 10× increase in gain in 2021 due to the achievement of ignition, followed by the achievement of target gain greater than 1 in 2022.
Indirect drive laser ICF uses a hohlraum which is irradiated with laser beam cones from either side on its inner surface to bathe a fusion microcapsule inside with smooth high intensity X-rays. The highest energy X-rays can be seen leaking through the hohlraum, represented here in orange/red.
Mockup of a gold plated National Ignition Facility (NIF) hohlraum
An Inertial confinement fusion target, which was a foam filled cylindrical target with machined perturbations, being compressed by the Nova Laser. This shot was done in 1995. The image shows the compression of the target, as well as the growth of the Rayleigh-Taylor instabilities. [ 17 ]
An inertial confinement fusion fuel microcapsule (sometimes called a "microballoon") of the size used on the NIF which can be filled with either deuterium and tritium gas or DT ice. The capsule can be either inserted in a hohlraum (as above) and imploded in the indirect drive mode or irradiated directly with laser energy in the direct drive configuration. Microcapsules used on previous laser systems were significantly smaller owing to the less powerful irradiation earlier lasers were capable of delivering to the target.
National Ignition Facility target chamber
The Electra Laser at the Naval Research Laboratory demonstrated more than 90,000 shots over 10 hours at 700 joules. [ 76 ]
An inertial confinement fusion implosion in Nova, creating "micro sun" conditions of tremendously high density and temperature rivaling even those found at the core of the Sun .