Fusion Energy Sciences Workshop ON TRANSIENTS IN TOKAMAK PLASMAS Report on Scientific Challenges and Research Opportunities in Transient Research June 8-11, 2015 Fusion Energy Sciences Transient Events in Tokamak Plasmas FUSION ENERGY SCIENCES WORKSHOP ON TRANSIENTS IN TOKAMAK RESEARCH Report on Science Challenges and Research Opportunities for Transient Events in Tokamak Plasmas Chair: Charles M. Greenfield, General Atomics Co-Chair: Raffi Nazikian, Princeton Plasma Physics Laboratory FES Contact: Mark S. Foster, U.S. Department of Energy ELM Leads: Raffi Nazikian, Princeton Plasma Physics Laboratory John Canik, Oak Ridge National Laboratory Natural ELM Free Operating Scenarios Jerry Hughes, Massachusetts Institute of Technology Wayne Solomon, Princeton Plasma Physics Laboratory ELM Mitigation or Suppression with 3D Magnetic Perturbations Max E. Fenstermacher, Lawrence Livermore National Laboratory Oliver Schmitz, Univ. of Wisconsin, Madison ELM Pacing Larry Baylor, Oak Ridge National Laboratory Gary Jackson, General Atomics Disruption Leads: Charles M. Greenfield, General Atomics Dylan Brennan, Princeton University Disruption Prediction Steven A. Sabbagh, Columbia University Chris Hegna, University of Wisconsin, Madison Disruption Avoidance Edward J. Strait, General Atomics David Gates, Princeton Plasma Physics Laboratory Disruption Mitigation Valerie Izzo, University of California, San Diego Robert Granetz, Massachusetts Institute of Technology 2 Transient Events in Tokamak Plasmas ELM Panel Members Natural ELM Free Operating Scenarios Keith Burrell, General Atomics Andrea Garofalo, General Atomics Jerry Hughes, Massachusetts Institute of Technology Dennis Mansfield, Princeton Plasma Physics Laboratory John Rice, Massachusetts Institute of Technology Wayne Solomon, Princeton Plasma Physics Laboratory ELM Mitigation or Suppression with 3D Magnetic Perturbations Joon-Wook Ahn, Oak Ridge National Laboratory Choong-Seock Chang, Princeton Plasma Physics Laboratory Todd Evans, General Atomics Max E. Fenstermacher, Lawrence Livermore National Laboratory Nathaniel Ferraro, General Atomics Rick Moyer, UC San Diego Oliver Schmitz, Univ. of Wisconsin, Madison Carlos Paz-Soldan, General Atomics Raffi Nazikian, Princeton Plasma Physics Laboratory Jong-Kyu Park, Princeton Plasma Physics Laboratory Francois Waelbroeck, University of Texas, Austin ELM Pacing Larry Baylor, Oak Ridge National Laboratory Alessandro Bortolon, Princeton Plasma Physics Laboratory Nicolas Commaux, Oak Ridge National Laboratory Stephanie J. Diem, Oak Ridge National Laboratory Gary Jackson, General Atomics Dennis Mansfield, Princeton Plasma Physics Laboratory Robert Lunsford, Princeton Plasma Physics Laboratory Daisuke Shiraki, Oak Ridge National Laboratory Zhehui Wang, Los Alamos National Laboratory Ex officio Alberto Loarte, ITER Organization Guido Huijsmans, ITER Organization Disruption Panel Members Disruption Prediction N. Ferraro, Princeton Plasma Physics Laboratory J. Ferron, General Atomics R. Granetz, Massachusetts Institute of Technology Chris Hegna, University of Wisconsin, Madison Scott Kruger, Tech-X Corporation R. La Haye, General Atomics David A. Maurer, Auburn University 3 Transient Events in Tokamak Plasmas Steven A. Sabbagh, Columbia University Benjamin Tobias, Princeton Plasma Physics Laboratory K. Tritz, Johns Hopkins University Ex officio Peter deVries, ITER Organization Disruption Avoidance David Gates, Princeton Plasma Physics Laboratory Stephan P. Gerhardt, Princeton Plasma Physics Laboratory Jeremy M. Hanson, Columbia University David A. Humphreys, General Atomics E. Kolemen, Princeton University Robert J. La Haye, General Atomics Matthew J. Lanctot, General Atomics Steven A. Sabbagh, Columbia University Edward J. Strait, General Atomics Michael L. Walker, General Atomics Ex officio Joseph A. Snipes, ITER Organization Disruption Mitigation Nicolas Eidietis, General Atomics Robert Granetz, Massachusetts Institute of Technology Valerie Izzo, University of California, San Diego Roger Raman, University of Washington David Rasmussen, Oak Ridge National Laboratory Ex officio Michael Lehnen, ITER Organization Joseph A. Snipes,, ITER Organization Cover design: Kyle Palmer, Princeton Plasma Physics Laboratory Technical Editing: John Greenwald, Princeton Plasma Physics Laboratory Fusion Energy Sciences Office of Science 4 Transient Events in Tokamak Plasmas U.S Department of Energy Cover page image credits Top left: Visible fast camera image of edge filaments ejected from the plasma by an ELM event in NSTX (shot 141307 at 505.486 ms). In this figure the separatrix is the dashed line and the limiter (RF antenna) shadow is the dotted line. Courtesy: B. Davis, R. Ma- queda, S. Zweben. R.J. Macqueda, et al., Phys. Plasmas 16, 056117 (2009). Middle: Visible image of brehmstrahlung radiation from confined runaway electrons in DIII-D. C. Paz-Soldan, et al., Phys. Plasmas 21 022514 (2014). Top right: Visible image obtained during a major disruption in Alcator C-MOD. Streaks are trails of particles released from surfaces during the disruption event. Courtesy: Ian Faust and Robert Granetz (MIT Plasma Science and Fusion Center). Bottom right: The nonlinear ELM magnetic tangle, shown by a single magnetic field line (white) traced many times around the torus, approximately follows the temperature con- tours of the ELM (yellow/blue) near the lower X-point during a large Type I ELM. (DIII- D shot 119690, resistive MHD simulation with M3D code). L.E. Sugiyama and H.R. Strauss, Phys. Plasmas 17, 062505 (2010). Bottom left: Contrast-enhanced fast image of ELM filament in the Pegasus Toroidal Ex- periment at University of Wisconsin-Madison. Courtesy: M.W. Bongard and R.J. Fonck (University of Wisconsin). 5 Transient Events in Tokamak Plasmas Table of Contents Executive Summary 7 I. Overview of the Transients Challenge 14 I.0 Introduction 14 I.1 Disruptions in Tokamak Plasmas 15 I.2 Edge Localized Modes in Tokamak Plasmas 18 I.3 Linkages to other Plasma Science 22 I.4 Resource Documents 23 I.5 Transient Workshop Process and Report Organization 24 I.6 Note to the Reader 26 II. The Disruption Challenge 27 II.0 Introduction 28 II.1 Subpanel report on Disruption Prediction 34 II.2 Subpanel report on Disruption Avoidance 99 II.3 Subpanel report on Disruption Mitigation 166 III. The ELM Challenge 201 III.0 ELM Physics: Progress since ReNeW, Gaps and Research Needs 202 III.1 ELM mitigation requirements for fusion reactors 209 III.2 Subpanel report on naturally ELM stable and ELM mitigated regimes 212 III.3 Subpanel report on ELM Mitigation or Suppression with Three-Dimensional Magnetic Perturbations 245 III.4 Subpanel report on ELM pacing 297 IV. Appendices 319 A. Charge Letter from FES 320 B. Community Input Workshop speakers 323 C. Transients Workshop agenda 325 D. List of Workshop Participants 328 E. List of submitted white papers 330 6 Transient Events in Tokamak Plasmas Executive Summary A series of community workshops was held under the direction of the Office of Fusion Energy Sciences to identify research opportunities addressing the challenges of potential- ly damaging transient events in tokamak fusion reactors, specifically Edge-Localized Modes (ELMs) and disruptions. The findings and recommendations identify and address the research gaps and needs for the U.S. fusion program to maintain leadership in this rapidly evolving area, to meet the ITER challenge in time for ITER operation and to de- velop the physics basis to inform the design of future tokamaks beyond ITER. A main goal of tokamak research is to develop the means of operating high-pressure fu- sion plasmas within the bounds of stability and controllability while avoiding the occur- rence of transient events that can degrade or terminate the plasma discharge and poten- tially damage the facility. Various events in a tokamak plasma can lead to the sudden re- lease of thermal and magnetic stored energy to the walls. Two events of particular con- cern are ELMs and disruptions. First, ELMs can drive repetitive (approx. 1 Hz) pulses of up to 10 percent or more of the plasma stored energy to the walls in ITER. Second, dis- ruptions can rapidly release significantly more plasma energy than ELMs or completely terminate the discharge, releasing all of the plasma’s thermal and magnetic energy into the first wall, vessel components, and the device support structure. Disruptions can also produce a runaway electron population that can cause concentrated, local damage to components. It is critical for the success of ITER and future tokamaks to gain full under- standing and control of these events. Moreover, success on this challenging scientific re- search path is essential for the long-term viability of the tokamak approach to fusion en- ergy. Present estimates indicate that sustained fusion performance in ITER and later reactors will require very large reductions in the magnitude and frequency of both ELMs and ma- jor disruptions based on extrapolations from current experiments. For example, in a high fusion power ITER plasma, ELMs can release in excess of 30 MJ of stored energy to the wall in a fraction of a millisecond and this can repeat hundreds of times in a single high power discharge. Minor disruptions can release 300 MJ or more, and major disruptions can release the predicted total plasma stored energy – up to 500 MJ, and produce runa- way electrons. The consequences can be significant, ranging from melting of the first wall and other device components and accelerated material erosion limiting the lifetime