For nearly a century, scientists have been tantalized by the prospect of attaining an inexhaustible source of energy through nuclear fusion. Unfortunately, engineering a controlled environment where atomic nuclei can continuously fuse under extreme pressure and temperature to produce energy that we can capture is very difficult, but that doesn't mean exciting advances aren't being made. Here we take a look at some of the different approaches to nuclear fusion, and the reasons why some appear more promising than others.

Fusion and fission are different processes for producing nuclear energy. Where nuclear fusion seeks to combine separate atoms into a larger one, nuclear fission relies on breaking apart an atom (usually Uranium 235) by striking it with a neutron. Both processes release huge amounts of energy, though fusion produces more.

This energy produced by nuclear fission is captured inside reactors, like those at Fukushima and Chernobyl, and used to heat water into steam, which spins a turbine and generates electricity. But this process creates waste products that can remain radioactive for millions of years, which, as we have seen at Fukushima and Chernobyl, can become a disaster when things go awry.

Fusion, on the other hand, would produce no long-lasting nuclear waste, with the necessary materials able to be recycled within 100 years. There is also no danger of a meltdown or nuclear accident because it relies on high-temperature reactions that cool within seconds when disrupted. And because these reactions use relatively small amounts of fuel, there is no danger of them being harnessed to produce nuclear weapons.

The field of nuclear nuclear fusion research involves scientists solving all sorts of problems, but all are working towards the same goal, which is recreating the processes that the Sun itself uses to produce monumental amounts of energy. Huge gravitational forces confine hydrogen from the Sun's atmosphere and use intense heat and pressure to convert the gas to plasma, in which nuclei collide at high velocity to form helium and release energy.

"Solar power is really fusion power, just at a distance," Matthew Hole, a nuclear fusion expert and research fellow at Australian National University, tells New Atlas. "All this power is just fusion reactions coming from the Sun, that's all a solar array is doing from the edge of the reactor. But the reactor happens to be eight light minutes away."

Another key factor is gravity. The Sun's tremendous gravitational forces are around 28 times greater than here on Earth, which means we've had to get creative with the way we confine our fuel for nuclear fusion reactions. The favored approach as it stands is through the use of magnetic fields, which can be used to confine two heavy forms of hydrogen, deuterium and tritium, in a donut-shaped device called a tokamak.

Attack of the tokamaks

Tokamaks are one example of a magnetic confinement system for nuclear fusion, and is the one Hole considers the most feasible in terms of net power generation. These consist of a neat series of coils placed around a torus-shaped reactor, where a plasma is heated to millions of degrees with the help of a strong internal current. The idea is to hold the plasma in place for long enough for the fusion of nuclei to occur.

The first tokamaks were designed in the 1950s, and in 1991 the Joint European Torus (JET) tokamak in the UK became the first device to achieve a controlled release of fusion power. It then set a power output record for a tokamak device with a 16-MW effort in 1997. Despite the achievement, it still required 24 MW of power to heat the plasma, meaning the experiments fell well short of the net gain energy generation needed to make nuclear fusion feasible.