Events at Physics
Events on Monday, December 5th, 2022
- Plasma Physics (Physics/ECE/NE 922) Seminar
- “Disruptive Tearing Modes In DIII-D IBS Discharges”
- Time: 12:00 pm
- Place: 1610 Engineering Hall
- Speaker: Professor Emeritus James D. Callen, UW-Madison
- Abstract: In seeking maximum plasma performance in magnetically confined burning plasmas, physics parameters are pushed to conditions where neoclassical tearing modes (NTMs) can grow and precipitate major plasma current disruptions. In recent ITER baseline scenario (IBS) discharges in the DIII-D experiment, the “safety factor” q_95 is reduced to near 3 and plasma beta_N is increased to about 2 or more. The most problematic tearing instabilities occur at the q = 2/1 rational surface because they are the furthest out radially (and hence closest to the magnetic separatrix), and are the lowest m/n modes. Their induced growing magnetic island widths produce resistive wall drag, mode locking to the wall and ultimately plasma disruption. Recent benchmarking studies of IBS-type discharges in DIII-D demonstrate robustly growing 2/1 tearing instabilities that evolve into locked modes and then disruptions are pressure-gradient-driven NTMs which ultimately grow algebraically (~ t) in time. The inherently nonlinear NTMs are seeded by MHD transients (e.g., ELMs, sawtooth crashes, or three tearing mode resonances). Responses to them are correctly modeled by a modified Rutherford equation. [Classical tearing modes (CTMs) would grow quadratically in time ~ t^2 and are negligible]. In ITER, order of magnitude smaller MHD transients are predicted to seed 2/1 NTMs.
J. D. Callen is an Emeritus Professor in the Departments of Engineering Physics and Physics at UW-Madison. He received his B.S. and M.S. degrees in Nuclear Engineering at Kansas State University in 1962 and 1964, with the intervening 1963 academic year spent at the Technische Hogeschool Te Eindhoven in the Netherlands on a Fulbright fellowship. He received his Ph.D. in Nuclear Engineering from Massachusetts Institute of Technology (MIT) in 1968. Thereafter, he had a NSF Postdoctoral Fellowship at the Institute for Advanced Study in Princeton, NJ where Marshall Rosenbluth was his mentor. Then, he was an Assistant Professor of Aeronautics and Astronautics at MIT in 1969-1972, followed by 7 years in the Fusion Energy Division at Oak Ridge National Laboratory where in the last 4 years he served as the Head of the Plasma Theory Section. In 1979 he accepted an offer to become a Professor of Nuclear Engineering (coupled with a zero-time appointment in Physics) at UW-Madison. He became the D.W. Kerst Professor of Physics and Engineering Physics in 1986. Subsequently, he had sabbaticals as a Visiting Scientist at the JET project in England 1986-1987, and the TFTR project at Princeton Plasma Physics Laboratory 1991-1992. He retired from his academic role in 2003, but is still active in research. Throughout his career he has focused on theory, modeling and experimental validation of descriptions of magnetically confined plasmas, mostly tokamaks.