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How controllable is nuclear fusion?

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The control of nuclear fusion in order to harness its energy is an extremely challenging task that we have been struggling to achieve ever since its theoretical conception by Houtermans in 1929. There are many, many problems in controlling the mechanisms for nuclear fusion, so I will briefly talk about some of the accomplishments that we have managed to achieve so far.

First tokamaks are currently the most promising method for controlling fusion. There have been several advances in recent decades:

  • 1997 - The JET tokamak in the UK set the current world record for the most fusion power produced, 16 MW.
  • 1998 - The JT-60 tokamak in Japan set the current world record for Q with Q=1.25. Q is called the gain factor and is the ratio of fusion power to the power needed to maintain the plasma in a stead state. Q=1 is referred to break even.
  • 2013 - East tokamak sets the world record for plasma confinement in the high confinement mode, 30 seconds.

While these examples of controlling fusion have been with magnetic confinement techniques there are others that are used.

For example, Inertial confinement fusion (ICF) heat and compresses a target to the point of fusion. The most successful ICF devices almost always use lasers. In 2014 the NIF in California used an ICF device to extract more energy from controlled nuclear fusion than was absorbed by the fuel to trigger it. They are the only facility to achieve a 'fuel energy gain' via nuclear fusion.

ICF conditions are very similar to those created in a thermonuclear weapon. In fact the largest bombs in existence, hydrogen bombs, heat and compress materials with a fission primary explosion. Then this initiates a fusion reaction that releases a tremendous amount of energy. ICF may pave the way for a 'pure fusion weapon'. This is when no primary fission reaction is required and therefore no radioactive material is needed to build the weapon. This would then reduce fallout from radioactive damage after the blast.

As you can see the power to control nuclear fusion has already come far on a long road that will certainly be of importance in the future.

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