Ian Ochs, a 2022 graduate of the Program in Plasma Physics in the Princeton University Department of Astrophysical Sciences, has won the 2023 Marshall N. Rosenbluth Outstanding Doctoral Thesis Award presented by the American Physical Society (APS). The highly competitive honor recognizes “exceptional early-career scientists who have performed original thesis work of outstanding scientific quality and achievement in the area of plasma physics.”
“I was really honored to be recognized, especially given the high standards set by past winners and the graduate research community,” said Ochs, a postdoctoral research fellow in the Department of Astrophysical Sciences. The nationwide award bears the name of Marshall Rosenbluth, a distinguished physicist whose career included research at the U.S. Department of Energy’s (DOE) Princeton Plasma Physics Laboratory (PPPL) from 1967 to 1980.
Surfing the waves
A core part of the 353-page thesis, titled “Controlling and Exploiting Perpendicular Rotation in Magnetized Plasmas,” looks at wave-particle interactions. Ochs uses a surfing analogy to help explain the research. “When you succeed at surfing, you’re going at the same speed as the wave,” he said. “That allows you to exchange a lot of energy with the wave and get pushed along very fast.”
Previous theories have primarily focused on “resonant” particles, he said. However, most surfers are “non-resonant” and are just bobbing along as the wave goes by. His own research “focuses on the way we treat both the resonant particles — the successful surfers — and the non-resonant ones,” he said. This is important because there are a lot of non-resonant particles, and “the very small force on each of them has a disproportionate effect on the plasma as a whole.”
A key feature of the thesis distinguishes between interactions that cause plasma rotation and those that do not. Control of plasma rotation can be extremely useful, not only in fusion physics. Case in point: billions of dollars have been invested in ways to chemically separate high-level radioactive waste from less nasty waste for efficient and safe disposal of the millions of gallons of sludge stored in more than 175 underground tanks in Hanford, Washington.
“But you don’t have to deal with chemical complexities if you convert everything into a plasma, spin it up and remove the highly toxic waste through centrifugal forces,” Ochs said. “Knowing how to control rotation can thus be very important.”
Such concepts are widely appreciated. “Ian’s thesis has had an uncommon impact within several disciplines in our community,” said physicist Nat Fisch, Ochs’ thesis adviser and professor of astrophysical sciences at Princeton University and director of the Program in Plasma Physics. “For example, Ian’s explanations of escaping current and isorotation are being tested on Z-pinch experiments; his theorems on lower hybrid current drive in fusion facilities point to optimizations in tokamak reactors; and his theories of charge extraction by waves in magnetized plasma show how best to rotate plasma for centrifugal applications.”
Enduring educational accomplishment
“But these impacts are far more than additive,” Fisch said. The recognition of common physics themes across these seemingly disparate topics, drawn together with textbook quality derivations and written with engaging clarity, makes this thesis valuable not only as a compilation of many superb advances, but also as an enduring educational accomplishment,” Fisch said.
Ochs’ thesis, supported in part by research grants from the National Science Foundation (NSF), the National Nuclear Security Administration (NNSA) and the DOE Office of Science Fusion Energy Sciences program, has led to fruitful collaborations with researchers in the Weizmann Institute of Science and the Holon Institute of Technology in Israel and the University of Paris and the University of Toulouse in France. The U.S.-Israel Binational Science Foundation, through a joint program with NSF, supported experimental research on related findings at the Weizmann Institute.
The Rosenbluth award marks the most recent high honor for Ochs, a native of Oreland, Pennsylvania. He won a Porter Ogden Jacobus Fellowship — the most prestigious honorific fellowship that Princeton awards annually — for his final graduate school year. As a graduate student, he also held a Princeton Centennial Fellowship and a DOE Computational Science Graduate Fellowship.
Ochs arrived at Princeton with a bachelor’s degree in physics from Harvard University, earned magna cum laude. While at Harvard, he worked with Fisch one summer doing fusion research through the DOE’s National Undergraduate Fellowship in Plasma Physics. “I really loved the work I did that summer,” he recalled. “And going into graduate school, I felt the Program in Plasma Physics gave a lot of freedom to explore different aspects of plasma science while knowing that the work was going toward something that would be useful to humanity.”
Ochs became the ninth graduate of the Program in Plasma Physics to receive the Rosenbluth honor since the APS first awarded it in 1986. Previous winners were Cary Forest, 1992; Michael Beer, 1996; Mark Christopher Herrmann, 2000; Yang Ren, 2008; Jong-Kyu Park, 2010; Jonathan Squire, 2017; Seth Davidovits, 2018; and Yuan Shi, 2020.
The 2023 award includes $2,000 and an invitation to speak at the American Physical Society Division of Plasma Physics (APS-DPP) annual meeting that begins Oct. 30 in Denver. The honor is announced on the APS website.
The Program in Plasma Physics is a graduate program based at PPPL. Students apply directly to the program and are granted degrees through the Department of Astrophysical Sciences.