Alex McColgan

It means the probability of proton-proton reactions happening, where we have much less plasma and much less time, is essentially zero.

Indeed, the reaction has never been experimentally measured.

In fact, looking at the problem in the most basic and fundamental way, it is statistically impossible to achieve proton-proton fusion on Earth in any meaningful way.

So what are all these fusion researchers doing?

Why do we even bother trying?

Well, they are not attempting to fuse protons.

Instead, they are trying to fuse alternative combinations of nuclei that are much more reactive.

Back in the 1930s, Mark Oliphant, a student of Ernest Rutherford, conducted a series of experiments.

He fired deuterium nuclei at one another, generating other exotic hydrogen and helium isotopes, and thus proving that heavy hydrogen nuclei could be made to react with one another.

Today, fusion scientists favour a combination that was first put to use in the H-bomb.

one that is 24 orders of magnitude more reactive than protons alone.

It is deuterium, remember this is classic heavy hydrogen consisting of one proton and one neutron, and tritium, the even heavier isotope of hydrogen with one proton and two neutrons in its nucleus.

The reason this combination is so much more reactive is that these extra neutrons lead to a greater strong force, and there is no need for one proton to undergo weak force mediated beta decay into a neutron.

Now, deuterium and tritium aren't just more reactive than the protons that power the sun, they also give rise to different reaction products.

Instead of generating an alpha particle and two protons, they make an alpha particle and a neutron.

But like the proton-proton reaction chain, they still produce a ton of energy.

Energy that we can use to generate electricity.

Just one gram of deuterium tritium fuel holds energy equivalent to 2,400 gallons of oil.

So, if we've identified more reactive starting materials that give us plenty of energy out, what's the problem now?

Well, it's not one problem, but problems.