Editing Inertial confinement fusion (section)

====United States====
ICF history began as part of the "[[Atoms for Peace|Atoms For Peace]]" conference in 1957. This was an international, UN-sponsored conference between the US and the [[Soviet Union]]. Some thought was given to using a hydrogen bomb to heat a water-filled cavern. The resulting steam could then be used to power conventional generators, and thereby provide electrical power.{{sfn|Nuckolls|1998|p=1}}

This meeting led to [[Operation Plowshare]], formed in June 1957 and formally named in 1961. 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&nbsp;kt [[Project Gnome]] device was detonated in bedded salt in New Mexico. While the press looked on, radioactive steam was released from the drill shaft, at some distance from the test site. Further studies designed engineered cavities to replace natural ones, but Plowshare turned from bad to worse, especially after the failure of 1962's [[Sedan (nuclear test)|Sedan]] which produced significant [[fallout]]. PACER continued to receive funding until 1975, when a 3rd party study demonstrated that the cost of electricity from PACER would be ten times the cost of conventional nuclear plants.<ref>F.A. Long, [https://books.google.com/books?id=4QsAAAAAMBAJ "Peaceful nuclear explosions"], ''Bulletin of the Atomic Scientists'', October 1976, pp. 24-25.</ref>

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. This work suggested that at sizes on the order of milligrams, little energy would be needed to ignite the fuel, much less than a fission primary.{{sfn|Nuckolls|1998|p=1}} He proposed building, in effect, tiny all-fusion explosives using a tiny drop of D-T fuel suspended in the center of a hohlraum. The shell provided the same effect as the bomb casing in an H-bomb, trapping x-rays inside to irradiate the fuel. The main difference is that the X-rays would be supplied by an external device that heated the shell from the outside until it was glowing in the x-ray region. The power would be delivered by a then-unidentified pulsed power source he referred to, using bomb terminology, as the "primary".{{sfn|Nuckolls|1998|p=2}}

The main advantage to this scheme is the fusion efficiency at high densities. According to the Lawson criterion, the amount of energy needed to heat the D-T fuel to break-even conditions at ambient pressure is perhaps 100 times greater than the energy needed to compress it to a pressure that would deliver the same rate of fusion. So, in theory, the ICF approach could offer dramatically more gain.{{sfn|Nuckolls|1998|p=2}} This can be understood by considering the energy losses in a conventional scenario where the fuel is slowly heated, as in the case of [[magnetic fusion energy]]; the rate of energy loss to the environment is based on the temperature difference between the fuel and its surroundings, which continues to increase as the fuel temperature increases. In the ICF case, the entire hohlraum is filled with high-temperature radiation, limiting losses.{{sfn|Nuckolls|1998|p=3}}