After a brilliantly innovative career spanning more than six decades, Tihiro Ohkawa died following a brief illness in La Jolla, California, on 27 September 2014. His scientific ingenuity was wide-ranging, but he is best known as a longtime champion and early leader of magnetic fusion energy research.
Born to an academic family in Kanazawa, Japan, on 3 January 1928, Tihiro was just 16 when he started out in science, volunteering at a local laboratory during the war years. In 1950 he matriculated at the University of Tokyo, where he studied nuclear physics. His first scientific publication, in 1953, described a new kind of particle accelerator. That led physicist Donald Kerst to invite him to spend a year at the University of Illinois at Urbana-Champaign and another at the University of Wisconsin–Madison, where Tihiro improved the design of the fixed-field alternating-gradient accelerator from his 1953 paper. He then returned to the University of Tokyo. Meanwhile, Kerst joined General Atomics (GA), a General Dynamics division that was trying to develop peaceful atomic energy.
After a year at CERN in 1959, Tihiro joined Kerst at GA in San Diego, California, and changed his focus to fusion energy research. Thus began what would be a highly successful 40 years spent seeking to bring fusion energy to realization.
Hydrogen nuclei fusing in the Sun and other stars are confined by gravity. Tihiro was particularly intrigued by the prospect that magnetic confinement fusion on Earth could give humanity an endless supply of energy. His early experiments with Kerst in small toroidal machines were designed to demonstrate that fusion reactions might occur in scaled-up devices.
Kerst returned to Wisconsin after a funding cut at GA in 1967, but Tihiro was ultimately able to obtain government funding to expand GA’s research effort. Confinement research was key because several early experiments suggested that magnetic confinement in toroidal plasmas could be maintained no longer than the Bohm time—in which case magnetic fusion would not be practicable. The first major triumph from Tihiro and his group was the demonstration, in their 3-meter-high dc octopole, that the Bohm time was not an upper limit to confinement.
Tihiro saw that stably confining sufficient plasma pressure demanded highly shaped, vertically elongated plasma cross sections. He designed an elongated tokamak with a peanut-shaped cross section that he called a doublet, which he tried first in a tabletop version before building the larger Doublet II. Early results from those tokamaks were so encouraging that the group won a contract in 1973 to build a 9-meter-tall experimental tokamak, Doublet III.
By the end of the 1970s, Doublet III was a major national effort that employed more than 200 experimentalists, theoreticians, engineers, and technicians. To extend the program and obtain major additional funding, Tihiro secured participation from the Japan Atomic Energy Research Institute and thus formed the first of many international collaborations that now characterize the GA fusion energy effort. In 1979 Tihiro received the James Clerk Maxwell Prize for Plasma Physics from the American Physical Society.
Doublet III was later upgraded to DIII-D, which continues as a leading facility in international fusion research. Tihiro’s legacy is evident in the vertically elongated shapes of modern tokamaks.
In 1980, with funding from GA and Phillips Petroleum, Tihiro tried another configuration, similar to a reversed-field pinch, which he called ohte (Japanese for “checkmate” in chess). The ohte machine ran for eight years, produced good results, and advanced the reversed-field pinch concept. While retaining his interest in fusion energy, in 1986 Tihiro broadened his research endeavors at GA. With a chosen group of scientists, he formed an “institute for the development of advanced technology.” He explored many disciplines, including biotechnology, high-Tc superconductivity, and low-frequency communications.
He left GA in 1994 and spent the next 20 years developing innovative solutions to many problems. He formed three companies, notably the Archimedes Technology Group, which focused on a new method of remediating nuclear waste by using plasma processing. Another concentrated on biotechnology developments, and the third, formed with colleagues in Japan, centered on other spinoffs of plasma-physics technology. That period was in many ways his most productive. In all, he held more than 80 patents and was the primary author of more than 170 scientific publications.
We and his other close associates cherish our memories of him—his deep intellect, his originality, his contests to spur creativity in others, and his vast interest in all forms of innovation. Physics was clearly his passion, but he participated in a range of other activities. He followed local professional sports teams and played golf, tennis, and soccer. He enjoyed annual family skiing and Las Vegas trips. His broad intellectual reach and his internationalism made him truly a citizen of the world, a consummate scientist who excelled at transcending boundaries.