Ronald Davidson *66, an influential plasma physicist and former director of the Princeton Plasma Physics Laboratory, died May 19 in Cranbury, N.J. He was 74. Davidson was an expert in the field of high-intensity charged particle beams. He led PPPL from 1991 to 1996, years when the lab was preparing the Tokamak Fusion Test Reactor for experiments with deuterium and tritium. Davidson was a professor of astrophysics at Princeton for 20 years.