Nuclear fusion is used every day in the oil industry and elsewhere. They use small fusion devices known as neutron generators that accelerate deuterium ions and smash them into tritium atoms; fusion occurs and neutrons are emitted. (1 tritium + deuterium yields 1 helium nucleus + 1 neutron.) See the Wikipedia article Neutron generator.

For the oil industry, all this occurs down in the well using a neutron generator that is only a few inches in diameter. The device then measures the number of neutrons that scatter off the rock and return, as a function of energy, and the induced gamma rays from the rock. This device is very useful for measuring porosity and other features of the rock.

Is this “cold fusion”? Yes, in a sense, since the device can operate at room temperature. It certainly is not thermonuclear fusion, the fusion that takes place at very high temperatures. However, it is not the notorious cold fusion that was (mis)reported by Pons and Fleishman; to read about that sorry story, you can look at the Wikipedia article on Cold fusion.

Why don’t more people know about this? Controlled nuclear fusion, at room temperature, available for practical applications today! The simple reason is that this kind of fusion takes more energy to produce than is emitted by the fusion (mostly in kinetic energy of the neutrons). Strong electric fields are needed to accelerate the deuterons into the tritium. So this approach works as an energy consumer, not as an energy producer. It produces useful neutrons, but not enough energy to be useful.

Such neutron generators are used in industry and medicine for other applications that require neutrons.