The earliest DT nuclear fusion discoveries

TL;DR

This paper reviews the historical development of DT fusion cross section measurements, highlighting key discoveries from the 1940s and 1950s that advanced fusion energy research, including early experiments, resonance effects, and conceptual insights.

Contribution

It uncovers the earliest measurements of DT fusion, their historical context, and new insights into prior experiments and theoretical concepts used by Fermi.

Findings

Los Alamos measurements revealed a resonance enhancing fusion cross section by 100x.

Early measurements were reasonably accurate given technological limitations.

The paper suggests DT fusion was first reported in 1938, predating common references.

Abstract

We describe the earliest measurements of the DT fusion cross section commissioned by the Manhattan Project, first at Purdue University in 1943 and then at Los Alamos 1945-6 and later, in 1951-2. The Los Alamos measurements led to the realization that a 3/2$^+$ resonance in the DT system enhances the fusion cross section by a factor of one hundred at energies relevant to applications. This was a transformational discovery, making the quest for terrestrial fusion energy possible. The earliest measurements were reasonably accurate given the technology of the time and the scarcity of tritium, and were quickly improved to provide cross section data accurate to just a few percent. We provide a previously-unappreciated insight: that DT fusion was first reported in Ruhlig's 1938 University of Michigan experiment and likely influenced Konopinski in 1942 to suggest its usefulness for thermonuclear technologies. We report on preliminary work to repeat the 1938 measurement, and our simulations of that experiment. We also present some work by Fermi, from his 1945 Los Alamos lectures, showing that he used the S-factor concept about a decade before it was introduced by nuclear astrophysicists.