FAQ - The core theory of D-D fusion's history

[Richard Hull]

With the recent movie on Oppenheimer, it turns out he was obliquely involved in fusion physics in a paper which is considered one of his two greatest papers. It was a 1938 paper in collaboration with a fellow female physicist, Melba Phillips. The paper resulted in an explanation as to why deuterons can bombard various atoms at energies far below the predicted energy needed and yet fuse in a number of ways known by experiment to actually happen. This strange reaction is now know as the Oppenheimer-Phillips reaction. It is how we do fusion.

As quantum physics matured, we now know that quantum tunneling can occur just in a probabilistic manner at energies far below theoretical considerations. This is especially true of low z atoms bombarded by deuterons. This is the very basis of modern fusion physics.

In our case we are bombarding deuterons and fast deuterium neutrals with other deuterons. This is not ideal as evidenced by our pitiable fusion energy returns. We get results ultimately based on quantum tunneling which is what the Oppenheimer-Phillips reaction made manifest.

Quantum tunneling probability increases only up to a point where the energy applied to the deuteron reaches a peak. This is where we use what is called the capture cross section graph to determine the ideal energy for best fusion. For all deuteron/low Z bombardments a crescendo of fusion occurs at a given energy as noted.

Any increase in energy beyond this peak energy point and the fusion reactions fall off as the deuteron is ripped apart at an increasing rate rather than fuse with its target. This is called stripping. Further increases in deuteron energy will see stripping as the only reaction taking place and all fusion, effectively, ceases.

History of D-D fusion

1932 - Using a crude accelerator, by accident, Mark Oliphant created the first laboratory demonstration of fusion. The reaction could not be explained by the physics of the day using the very limited energy available during the experiment.

1938 - In a paper submitted to physics review Robert Oppenheimer and Melba Phillips determined that via quantum physics a D-P reaction could occur, where deuterons of low energy might fuse with a low Z nuclei releasing a proton. As in one half of the Oliphant D-D reaction D+D = N + 3He.

1950's Both the Soviet Union and the US used liquid Deuterium to boost fission yields in fission bombs to supply large amounts of fast neutrons via D-D fusion to assist in fission and to fission the surrounding depleted Uranium bomb casing. Teller referred to this process as alarm clock boosting.


After thought on the D-D reaction

The D-D fusion reaction is a fabulous example of how the O-P reaction can do a reaction D+D = N + 3He to create a new element fusing the proton to make Helium, but might also do a reaction D+D = P + T making a new isotope of hydrogen, Tritium

Beyond this history, D-D fusion is currently only used as a limited rather portable commercial neutron source for activation analysis.
D-D fusion is not being investigated as a source of fusion energy as the D-T reaction is far more energetic and vastly easier to accomplish using less energy than is demanded in D-D fusion.
Amateur fusion uses the D-D reaction As it within their energy accessibility and the deuterium fuel is easy to obtain and is not regulated by the NRC in the United States.

I present a paper in the FAQS in some detail for the amateur level understanding of the D-D found here.

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Richard Hull