BEGIN:VCALENDAR VERSION:2.0 CALSCALE:GREGORIAN PRODID:UW-Madison-Physics-Events BEGIN:VEVENT SEQUENCE:0 UID:UW-Physics-Event-8052 DTSTART:20221205T180000Z DURATION:PT1H0M0S DTSTAMP:20260414T073858Z LAST-MODIFIED:20221202T151838Z LOCATION:1610 Engineering Hall SUMMARY:Disruptive Tearing Modes In DIII-D IBS Discharges\, Plasma Phy sics (Physics/ECE/NE 922) Seminar\, Professor Emeritus James D. Callen \, UW-Madison DESCRIPTION: In seeking maximum plasma performance in magnetically con fined burning plasmas\, physics parameters are pushed to conditions wh ere neoclassical tearing modes (NTMs) can grow and precipitate major p lasma current disruptions. In recent ITER baseline scenario (IBS) disc harges in the DIII-D experiment\, the “safety factor” q_95 is redu ced to near 3 and plasma beta_N is increased to about 2 or more. The m ost problematic tearing instabilities occur at the q = 2/1 rational su rface because they are the furthest out radially (and hence closest to the magnetic separatrix)\, and are the lowest m/n modes. Their induce d growing magnetic island widths produce resistive wall drag\, mode lo cking to the wall and ultimately plasma disruption. Recent benchmarkin g studies of IBS-type discharges in DIII-D demonstrate robustly growin g 2/1 tearing instabilities that evolve into locked modes and then dis ruptions are pressure-gradient-driven NTMs which ultimately grow algeb raically (~ t) in time. The inherently nonlinear NTMs are seeded by MH D transients (e.g.\, ELMs\, sawtooth crashes\, or three tearing mode r esonances). Responses to them are correctly modeled by a modified Ruth erford equation. [Classical tearing modes (CTMs) would grow quadratica lly in time ~ t^2 and are negligible]. In ITER\, order of magnitude sm aller MHD transients are predicted to seed 2/1 NTMs.
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\n J. D. Callen is an Emeritus Professor in the Departme nts of Engineering Physics and Physics at UW-Madison. He received his B.S. and M.S. degrees in Nuclear Engineering at Kansas State Universit y in 1962 and 1964\, with the intervening 1963 academic year spent at the Technische Hogeschool Te Eindhoven in the Netherlands on a Fulbrig ht fellowship. He received his Ph.D. in Nuclear Engineering from Massa chusetts Institute of Technology (MIT) in 1968. Thereafter\, he had a NSF Postdoctoral Fellowship at the Institute for Advanced Study in Pri nceton\, NJ where Marshall Rosenbluth was his mentor. Then\, he was an Assistant Professor of Aeronautics and Astronautics at MIT in 1969-19 72\, followed by 7 years in the Fusion Energy Division at Oak Ridge Na tional Laboratory where in the last 4 years he served as the Head of t he Plasma Theory Section. In 1979 he accepted an offer to become a Pro fessor 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 th e TFTR project at Princeton Plasma Physics Laboratory 1991-1992. He re tired from his academic role in 2003\, but is still active in research . Throughout his career he has focused on theory\, modeling and experi mental validation of descriptions of magnetically confined plasmas\, m ostly tokamaks. URL:https://www.physics.wisc.edu/events/?id=8052 END:VEVENT END:VCALENDAR