Fusion

If hydrogen fusion (including deuterium and tritium) was easy, we wouldn't be here. Very small masses of hydrogen would have "burned" to iron very early in the formation of our galaxy; not enough time for complex life to form.

"Cold Fusion" aka "Low Energy Nuclear Reactions" assumes that deuterium fusion is easy - that is, it can happen with electron-chemistry energy levels (electron-volts) and solid-matter atomic spacings (nanometers) rather than the 300 KeV, 300 femtometer deuteron spacings encountered (for tens of nanoseconds) in 100 million Kelvin temperature fission-fusion weapons, or the vastly slower (gigayear rates) proton-proton reactions that occur in the dense 15 million Kelvin temperature cores of gigameter-diameter stars like our Sun.

It isn't the "temperature" that really matters, what matters is the particle energy and velocity. Thermal velocity in this case, particle accelerators and lasers can also make high energy particles. For a hot gas, the thermal energy of the particle is 1.5kT.

• k is Boltzmann's constant, 8.62E-5 eV/Kelvin. eV electron-volts is the appropriate energy unit for atomsn-m

So, the energy per particle in a thermonuclear blast is 1.5*8.62E-5*1E8 eV = 13 KeV, and a head-on collision of two opposite-direction particles is 26 KeV.

For comparison, the temperature of a welding torch flame is around 3500 Kelvins, about 0.5 eV, and boiling water is 370 Kelvins, about 0.05 eV.

How much energy is needed to fuse two deuterons?