Inertial fusion 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.[6]
• Drivers which are used to compress and create a shock wave that squeezes the target. This compression wave pushes the material down to 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.

The basic mechanism for Inertial Confinement Fusion using a simple direct drive.

Net energy in ICF comes from getting fusion reactions to chain together in a process known as ignition.[7] 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:

1. Keeping the plasma very cold, squeeze it together.
2. Heat the plasma only after it is squeezed; ideally inside a “hot spot”.
3. 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.

Mockup of a golden hohlraum used in laser inertial confinement.

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.[8]
• 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.[9]
• NIKE Laser was built at the Naval Research Laboratory to study excimer (gas-based) lasers.[10]
• Electra Laser was built at the Naval Research Laboratory to study excimer (gas-based) lasers.[11]
• PALS laser facility in the Czech Republic was established to research ICF laser implosions.[12]
• 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.[13] Alternatively, Los Alamos built a large, excimer laser facility called Aurora in the late 1980s.[14] 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.

Glass Shell Targets

Coating round ICF targets is hard - above is a model of PDMA overcoating in a chamber

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.[15] 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.

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.

There are many kinds of targets that have been developed for ICF research - but a power plant would require thousands if not millions of identical targets to be fired repeatedly. This will be exceedingly challenging. At present, the Department of Energy contracts with General Atomics to produce ICF targets for the national laboratories. These targets are partially built at GA and then shipped across the country to the ICF facility for a shot day. The Laboratories maintain hardware and staff onsite to complete the last steps to prepare the targets for a shot.[19]

Cryogenic Targets

Keeping Cryogenic targets frozen while delivering them to target center is hard. At the LLE the target is held inside a cryogenic chamber and raised up to target chamber center on an elevator. Once the shroud is dropped from around the target it is exposed to air and starts melting. A laser pulse is then immediately required to compress it.

There are several ways to get tritium and deuterium into an already-made capsule. High pressure fills work by putting the shells in a chamber with 1 to 100 Atm of gas pressure and having the gas diffuse into the shell.[22] Cryogenic foam shells work can work by wicking in the liquid DT fluid into the foam. This involves getting the delicate shell down in temperature and pressure without damaging it. This is a stepwise process that can take hours to days in time and requires multiple containment chambers and various kinds of pumps. At cryogenic temperatures, the DT gas forms into a fluid which can be wicked into the foam shell. Once filled, operators slowly lower the temperature further to form the ice crystal. Ice can start formation around the equator of the target and then grow into a complete crystal.[23] The ice is embedded with the foam shell structure. Engineers have had problems with ice cracking during this formation process – all of which impacts the performance of the shot. Monitoring of all of this is done using shadow grams, 360 X-ray diagnostics, visual inspection, and other tools; information is all run through software that gets a complete picture of the target during filling.[24]

• Nuclear fusion
• Fusion power
• Inertial electrostatic confinement
• Inertial confinement fusion
• Laser inertial confinement
• Megajoule laser
• National Ignition Facility
• Z-pinch inertial confinement
• Z Pulsed Power Facility
• Project PACER
• List of plasma physics articles

• "La fusion thermonucléaire par confinement inertiel : de la recherche fondamentale à la production d'énergie" (PDF). Archived from the original (PDF) on 2006-11-25. (1.28 MiB) (Université Bordeaux I, November 2005) (in French)
• Tutorial on Heavy-Ion Fusion Energy(Virtual National Laboratory for Heavy-Ion Fusion)
• "Summary Report of the 2nd Research Coordination Meeting on the Element of Inertial Fusion Energy Power Plants" (PDF). Archived from the original (PDF) on 2007-07-10. Retrieved 2006-07-09. (4.82 MiB) (November 2003)
• "Review of the Inertial Fusion Energy Program" (PDF). Archived from the original (PDF) on 2006-09-23. (4.14 MiB) (Fusion Energy Sciences Advisory Committee, March 2004)
• "Overview of fusion nuclear technology in the US" (PDF). (513 KiB) (June 2005)
• Views on neutronics and activation issues facing liquid-protected IFE chambers
• IEEE-USA Position : Fusion Energy Research & Development(June 2006)