# What is the lowest possible theoretical temperature that nuclear fusion can occur at?

I am not talking about the pseudo-science of so called cold fusion I am interested in what temperature you can get away with to produce fusion reaction. I was thinking in terms of micro-fusion or at least at levels below the huge tokamaks being produced because obviously small scale devices couldn't handle millions of degrees of temperature. Or correct me if I am wrong please as I am no expert just a curious student!!

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Even at absolute zero there is a small probability for two nuclei to fuse due to quantum tunneling, but the rate for this is incredibly low. So really the question is "what is the minimum temperature for practically usable fusion?" That is both much harder and more interesting to answer. :) –  Michael Brown May 3 '13 at 9:58
You can do low-temperature fusion, you just can't do it efficiently enough to get energy out of it. A tabletop fusor (en.wikipedia.org/wiki/Fusor) uses an electric field to accelerate ions. Because the ions aren't in thermal distribution, it doesn't make sense to say they are at a high temperature. –  BowlOfRed May 12 at 22:11

ITER is aiming for 150.000.000K. Please note that this temperature of the plasma, i.e. average kinetic energy of the ions is in electron volts

For example, a typical magnetic confinement fusion plasma is 15 keV, or 170 megakelvins .

15 KeV is enough to assure that the plasma does not neutralize itself and the bare nuclei have a high enough statistical and quantum mechanical probability of interaction/fusion by overcoming the coulomb repulsion of two positive nuclei.

The electrostatic force between the positively charged nuclei is repulsive, but when the separation is small enough, the attractive nuclear force is stronger. Therefore the prerequisite for fusion is that the nuclei have enough kinetic energy that they can approach each other despite the electrostatic repulsion.

The temperatures necessary for the various fusion reactions:

The fusion reaction rate increases rapidly with temperature until it maximizes and then gradually drops off. The DT rate peaks at a lower temperature (about 70 keV, or 800 million kelvin) and at a higher value than other reactions commonly considered for fusion energy.

This is in a nutshell the status for thermodynamic/plasma fusion.

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+1 for the data, though I should point out that some stars are powered entirely by deuterium burning at temperatures of only $10^6$ K. You don't need to be at the peak of the curve to get substantial energy output - I can only assume engineers focus on such high temperatures (far higher than any in the Sun even) for practical purposes, as strange as that may sound. –  Chris White May 3 '13 at 18:55
@ChrisWhite I suppose a star can afford low output since there is so much mass in it. :) –  anna v May 4 '13 at 3:38