BY ANDREW M. SESSLER AND KEITH R. SYMON

DONALD WILLIAM KERST died on August 19, 1993, at the age of 81. On that day the country lost one of its most influential physicists, one with a remarkable breadth of interests. Kerst will long be remembered for his development of the betatron, but he also made very important contributions to the general design of particle accelerators, nuclear physics, medical physics, and plasma physics.

In addition to these scientific and technical contributions, his deep understanding of physics, his know-how, and his enthusiasm have been a source of education and inspiration both to his students and his colleagues. His many students and junior colleagues during the last forty years have continued to make their own contributions to these fields. He was an enthusiastic and effective mentor who worked hard and expected his students to do likewise, and they did. His students liked and admired him. Thirty-three students completed Ph.D. degrees in the betatron group at the University of Illinois over a period of thirty years. Forty-two students completed their doctorates in the plasma group at the University of Wisconsin during the seventeen years that he led the group. Over the last forty years many of the leading scientists in the fields of accelerator physics, nuclear