Ronald C. Davidson, who oversaw one of the biggest advances in fusion energy research, attempting to replicate the power of the sun, died on May 19 at his home in Cranbury, N.J. He was 74.

The cause was complications from pneumonia, said the Princeton Plasma Physics Laboratory, where Dr. Davidson was director from 1991 to 1996.

Fusion is the process that powers the sun, generating energy through the merging of atoms, and, for decades, scientists have tried to reproduce that on earth. During Dr. Davidson’s tenure, the Princeton lab made major advances toward that goal, studying ways to make the fusion self-sustaining.

In 1993, the laboratory’s immense Tokamak Fusion Test Reactor began a series of runs using a mix of deuterium and tritium, two heavier forms of hydrogen. (“Tokamak” is an acronym of three Russian words that mean “toroidal magnetic chamber,” referring to the doughnut-shaped reactor that housed the ultrahot gases.)