Inertial fusion energy is a proposed approach to building a nuclear fusion power plant based on performing inertial confinement fusion at industrial scale. This approach to fusion power is still in a research phase. ICF first developed shortly after the development of the laser in 1960, but was a classified US research program during its earliest years. In 1972, John Nuckolls wrote a paper predicting that compressing a target could create conditions where fusion reactions are chained together, a process known as fusion ignition or a burning plasma. On August 8, 2021, the NIF at Livermore National Laboratory became the first ICF facility in the world to demonstrate this (see plot). This breakthrough drove the US Department of Energy to create an Inertial Fusion Energy program in 2022 with a budget of 3 million dollars in its first year.
Design of an IFE power plant This kind of fusion reactor would consist of two parts:
Targets which can be small capsules (<7 millimeter diameter) that contain fusion fuel. Although many kinds of targets have been tested including: cylinders, shells coated with nanotubes, solid blocks, hohlraum, glass shells filled with fusion fuel, cryogenically frozen targets, plastic shells, foam shells and materials suspended on spider silk. Drivers which are used to compress and create a shock wave that squeezes the target. This compression wave pushes the material inward, resulting in the temperature and pressure where fusion occurs. Drivers that have been explored are solid-state lasers, excimer lasers, high velocity solid objects, X-rays, beams of ions (heavy ion fusion (HIF)) and beams of electrons.
Net energy in ICF comes from getting fusion reactions to chain together in a process known as ignition. To get there we need to squeeze material to hot and dense conditions for long enough. But a key problem is that after a plasma becomes hot - it becomes hard to compress. The goal then is to avoid getting material hot until after it is compressed. In literature, this is known as the low adiabatic approach to compression. These steps are outlined below:
Keeping the plasma very cold, squeeze it together. Heat the plasma only after it is squeezed; ideally inside a "hot spot". Fusion happens, and the resulting products deposit their energy creating more fusion. Several compression approaches attempt to do this including: Central Hot Spot Ignition, Fast Ignition, Shock Ignition and Magneto-inertial-fusion.
Research institutions
This program was originally established as a way to develop Nuclear weapons, because ICF mimics the compression physics of a fission-fusion bomb. These facilities have been built around the world, below are some examples.
Laser Mégajoule in France was developed in 2002 and upgraded in 2014. Omega Laser was first built in 1992 at the University of Rochester. Omega-EP was first built in 2008 at the University of Rochester as second more powerful laser beam. Gecko Laser was first built at Osaka University in Japan in 1983 but has since been upgraded nearly a dozen times. NIF was first operational in 2009 at the Livermore National Laboratory. NIKE Laser was built at the Naval Research Laboratory to study excimer (gas-based) lasers. Electra Laser was built at the Naval Research Laboratory to study excimer (gas-based) lasers. PALS laser facility in the Czech Republic was established to research ICF laser implosions. Machine 3 was developed by First Light Fusion to accelerate blocks of material to create a shockwave on the target. There have also been multiple ICF facilities built, tested and decommissioned in the past. For example, Sandia National Laboratory pursued a series (<10 machines) of ion-beam and electron-beam driven ICF research program through the 1970s and into the middle 1980s. Alternatively, Los Alamos built a large, excimer laser facility called Aurora in the late 1980s. Livermore National Laboratory built a succession of laser facilities including Nova, Cyclops, 4-PI, SHIVA and other devices. As part of the run up to the NIF opening and achieving ignition, Livermore National Laboratory funded a body of research around the Laser Inertial Fusion Energy program. Under this program, a reactor design was developed, costing, reactor chambers and energy capture programs were explored.
Research programs
IFE development has come in waves within the United States. Below are some government programs that have been funded over the years to push this technology forward:
HAPL The high average laser program was administered by the Naval Research Laboratory from 1999 to 2008. This program doled out grants to target, laser and driver teams across the United States and organized 19 meetings between member organizations. LIFE The Laser Inertial Fusion Energy program was administered by Livermore National Laboratory from 2008 to 2016. This program was funded to develop an IFE fusion power plant based around the National Ignition Facility. SDI The Strategic Defense Initiative (SDI) inadvertently supported many of the IFE laser technologies seen today.
Driver development It is still unclear which driver would work best for an IFE power plant, with supporters of different drivers pushing their favorite approach. Lasers have thus far proven to be the most well researched. Below is a summary of the laser drivers that have been studied. The challenge with implementing laser systems does not just come from the beam, but also the optics, mirrors, amplifiers and gratings that are also needed to put this system in place.
Related technologies Depending on the driver that is being used there are key related technologies that need to be matured; below are some of these:
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