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Title: Large experiment data analysis collaboration. Final annual progress report for period November 15, 2000 - April 30, 2002

Abstract

Because of the good agreement between theory and experiment (on a number of tokamak experiments) on the nonlinear development, saturation of neoclassical tearing modes (NTMs), the study of NTMs is becoming a mature subject. Thus, our contributions to studies of neoclassical (and regular classical) tearing modes over the past year have focused on a number of particular, more detailed issues: flow shear effects on linear tearing modes, exploring the possibility of NTMs in spherical tokamaks such as NSTX, assisting with classical tearing mode explorations in DIII-D, and fast ion effects on NTMs. In addition, a collaboration with the Institute for Plasma Research group in India was initiated due to their interest in using the NEAR code (developed in part under this grant) to explore neoclassical tearing modes. Finally, a number of talks have been given on basic, current frontier and future extensions of neoclassical tearing mode theory. Our previous identification of the disruption precursor in DIII-D shot 87009 as being due to a global ideal MHD interchange-type instability being driven slowly though its threshold was featured prominently in the DIII-D MHD theory paper at the 2000 IAEA Sorrento meeting. We have also stimulated the application of the NIMROD code tomore » this particular DIII-D disruption precursor and continued to support this code exploration of it. To facilitate quicker evaluations of global-type ideal MHD growth rates and eigenmodes, we have continued our development of a new method for using perturbed equilibria to ''maneuver in delta-W'' space. Since this basic concept for efficiently finding trends in ideal MHD stability using perturbed equilibria has been proven using a screw-pinch geometry, we are now beginning to implement and test the procedure in the GAT0 code for specific DIII-D high beta equilibria. In addition, to analytically explore the ultimate nonlinear evolution of these types of modes, we have begun (primarily on our DOE ''Nonlinear and Nonideal MHD'' theory grant) exploring the growth rate and eigenmode structure of localized interchange instabilities. A surprising aspect of that work is that robust, ideal MHD-like growth rates and radially spread eigenmodes are only obtained when the Suydam/Mercier criteria are exceeded by about a factor of two (D{sub I} > 0.45). A new issue we have begun exploring is how ''thin, isolated'' magnetic islands and their effects can be incorporated into MHD equilibria and hence the EFIT code. In addition, we have given presentations on more general fusion, and MHD topics, which have included some of the results developed under this research grant.« less

Authors:
Publication Date:
Research Org.:
University of Wisconsin-Madison, Madison, WI (US)
Sponsoring Org.:
US Department of Energy (US)
OSTI Identifier:
798782
Report Number(s):
DOE/ER/54139-10
TRN: US200308%%216
DOE Contract Number:
FG02-92ER54139
Resource Type:
Technical Report
Resource Relation:
Other Information: PBD: 14 Jan 2002; PBD: 14 Jan 2002
Country of Publication:
United States
Language:
English
Subject:
43 PARTICLE ACCELERATORS; 70 PLASMA PHYSICS AND FUSION TECHNOLOGY; DATA ANALYSIS; DOUBLET-3 DEVICE; EXPLORATION; GEOMETRY; INSTABILITY; MAGNETIC ISLANDS; NIMROD; PLASMA; PRECURSOR; PROGRESS REPORT; SATURATION; SCREW PINCH; SHEAR; STABILITY

Citation Formats

Callen, J. D. Large experiment data analysis collaboration. Final annual progress report for period November 15, 2000 - April 30, 2002. United States: N. p., 2002. Web. doi:10.2172/798782.
Callen, J. D. Large experiment data analysis collaboration. Final annual progress report for period November 15, 2000 - April 30, 2002. United States. doi:10.2172/798782.
Callen, J. D. 2002. "Large experiment data analysis collaboration. Final annual progress report for period November 15, 2000 - April 30, 2002". United States. doi:10.2172/798782. https://www.osti.gov/servlets/purl/798782.
@article{osti_798782,
title = {Large experiment data analysis collaboration. Final annual progress report for period November 15, 2000 - April 30, 2002},
author = {Callen, J. D.},
abstractNote = {Because of the good agreement between theory and experiment (on a number of tokamak experiments) on the nonlinear development, saturation of neoclassical tearing modes (NTMs), the study of NTMs is becoming a mature subject. Thus, our contributions to studies of neoclassical (and regular classical) tearing modes over the past year have focused on a number of particular, more detailed issues: flow shear effects on linear tearing modes, exploring the possibility of NTMs in spherical tokamaks such as NSTX, assisting with classical tearing mode explorations in DIII-D, and fast ion effects on NTMs. In addition, a collaboration with the Institute for Plasma Research group in India was initiated due to their interest in using the NEAR code (developed in part under this grant) to explore neoclassical tearing modes. Finally, a number of talks have been given on basic, current frontier and future extensions of neoclassical tearing mode theory. Our previous identification of the disruption precursor in DIII-D shot 87009 as being due to a global ideal MHD interchange-type instability being driven slowly though its threshold was featured prominently in the DIII-D MHD theory paper at the 2000 IAEA Sorrento meeting. We have also stimulated the application of the NIMROD code to this particular DIII-D disruption precursor and continued to support this code exploration of it. To facilitate quicker evaluations of global-type ideal MHD growth rates and eigenmodes, we have continued our development of a new method for using perturbed equilibria to ''maneuver in delta-W'' space. Since this basic concept for efficiently finding trends in ideal MHD stability using perturbed equilibria has been proven using a screw-pinch geometry, we are now beginning to implement and test the procedure in the GAT0 code for specific DIII-D high beta equilibria. In addition, to analytically explore the ultimate nonlinear evolution of these types of modes, we have begun (primarily on our DOE ''Nonlinear and Nonideal MHD'' theory grant) exploring the growth rate and eigenmode structure of localized interchange instabilities. A surprising aspect of that work is that robust, ideal MHD-like growth rates and radially spread eigenmodes are only obtained when the Suydam/Mercier criteria are exceeded by about a factor of two (D{sub I} > 0.45). A new issue we have begun exploring is how ''thin, isolated'' magnetic islands and their effects can be incorporated into MHD equilibria and hence the EFIT code. In addition, we have given presentations on more general fusion, and MHD topics, which have included some of the results developed under this research grant.},
doi = {10.2172/798782},
journal = {},
number = ,
volume = ,
place = {United States},
year = 2002,
month = 1
}

Technical Report:

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  • Neoclassical tearing modes have now entered the mainstream of tokamak research. One indication of this was the featuring of it in the ITER MHD instabilities paper at the 1998 Yokohama meeting, of which we (along with many colleagues throughout the world) were co-authors. In addition, this past year a number of talks were given on various aspects of neoclassical tearing modes and their impacts in tokamak plasmas. At present, we are anxiously awaiting the DIII-D electron cyclotron heating and current drive feedback experiments to see if neoclassical tearing modes can be stabilized according to our theoretical model, or if themore » theory needs to be modified. A major question in the application of neoclassical tearing mode theory to realistic aspect ratio toroidal plasmas such as DIII-D is: what is the effect of shear in the toroidal flow velocity on toroidicity-induced mode coupling? Both differential rotation between surfaces and flow shear at the rational surfaces can be important both in determining the linear growth rates of tearing modes and in the nonlinear excitation of tearing modes induced by sawtooth crashes. To explore these effects we have been developing an efficient new code NEAR that is based on the FAR code and the Generalized Reduced MHD (GRMHD) equations. The primary work this year has been on running tearing mode and 1/1 resistive kink mode benchmark cases against the full FAR and reduced FAR codes. After correcting some coding, the NEAR code has been shown to be more accurate than the reduced FAR code, and much faster and at least as accurate as the full FAR code. A summary of these results and plans for using the NEAR and NIMROD codes to explore DIII-D type plasmas over the next year are summarized. This past year our joint paper on the disruption precursor model for L-mode NCS high beta DIII-D plasmas was published. This work has also been used to buttress the validity of the application of the ideal MHD instability model to DIII-D and tokamak burning plasmas. In this model ideal MHD instabilities are driven slowly through their instability threshold. Then, the instability grows linearly as exp(t{sup 3/2}) until the magnetic topology of the equilibrium plus perturbation begins to overlap. A code was developed to implement this model using the GATO linear eigenmode structure to try to ascertain the radial region of the plasma where the model first breaks down and the plasma disruption begins; unfortunately, while it seemed that the breakdown may have been occurring first at the edge, neither the ECE signals nor magnetic topology calculations were accurate enough to derive a firm conclusion. Finally, because of the need for investigating ideal MHD instability and growth rates and eigenmode structure in the vicinity of the instability threshold and the fact that well-resolved GATO runs take a lot of computer time, we have begun exploring an idea put forth by Steve Cowley some years ago to determine these changes perturbatively in delta-W space.« less
  • This is the second annual progress on the three-year Large Experiment Data Analysis Collaboration DOE grant DE-FGO2-92ER54139, which succeeded a previous four-year grant under the same grant number. This year most of the collaboration effort shifted from being with the TFTR program, to being with the DIII-D program, and most new research focused on the properties, causes and possible amelioration of neoclassical tearing modes. In addition, our studies of nonlocal electron heat transport in TFTR have attracted wider attention, and are now being transferred to similar research on DIII-D.
  • Studies of neoclassical tearing modes have remained the dominant area of research on this grant. This year articles and reports on our previous research projects in collaboration with GA colleagues on a new nonlinear tearing mode model, seed island excitation from geometrically coupled perturbations, the combination of flow shear and viscosity on magnetic islands, and ITER projections got published. A major new theoretical achievement by our group was the development of generalized reduced MHD equations that include flow shear effects. The potential importance of this work was recognized by its having been selected for an invited oral talk at themore » most recent Sherwood Theory Conference. These new equations facilitate a self-consistent treatment of the effects of flow shear on neoclassical tearing modes, the study of which is just beginning. It is anticipated that the subcontract sublet to S.E. Kruger will allow him to continue this research work in close collaboration with C.C. Hegna and GA colleagues, and in particular to apply the resultant theory to DIII-D data on such effects. In addition, seed island formation induced by geometrically coupled perturbations was simulated using the neofar code, and the neoclassical tearing mode in DIII-D shot 86144.02250 was simulated using the NIMROD code. Also, RF stabilization of tearing modes was modeled. Finally, a couple of summary-type talks were given in Japan on the status of neoclassical tearing mode studies. The model we have constructed in collaboration with DIII-D colleagues for the temporal development of disruption precursors in NSC L-mode DIII-D plasmas has been published as a General Atomics report and is in the process of being published in the Physics of Plasmas. This simple model is based on the temporal development of an ideal MHD instability as its beta is driven slowly through the instability threshold. Unfortunately, rather than being ''the'' mechanism for disruptions, it seems to be just one of many such mechanisms. In order to explore the topology of the magnetic flux surfaces just before the major disruption for our model, we have begun to use a signal analysis code developed previously to compare ECE signals with theoretical predictions for these disruption precursors--in particular their radial dependence, and the implications for the flux surface geometry and topology.« less
  • Studies of neoclassical tearing modes have remained the dominant area of research on this grant. Our major role in their development was recognized through an invited paper at the 1998 Pittsburgh DPP-APS meeting and through our inclusion as coauthors on some major TFTR and DIII-D papers. During this past year, prior work has been published on DIII-D experiment-motivated theories of stabilization of tearing modes via localized current-drive and heating and on effects of geometry on these modes (elongation and triangularity effects should be small in DIII-D), and on experimental studies of the imposed beta limits and direct, internal measurements ofmore » the critical classical tearing mode stability parameter (delta-prime). Also, linear and nonlinear theory and computation studies of classical tearing modes via the ''almost ideal MHD'' constraint has been the subject of a number of meeting presentations and has recently been published. Recent work has been concerned with developing a theoretical model for the magnitude of seed island perturbations due to, geometrically coupled magnetic perturbations (e.g., ELMS or sawtooth crashes) and simulations thereof, exploring the effects of external perturbations, development of a simulation model for flow shear effects, studies of the effect of the combination of flow shear and perpendicular viscosity in distorting the magnetic island structure and producing the phase shift in ECE signals across a magnetic island, simulations of feedback stabilization of tearing mode islands, and exploring what aspects of tearing modes need to be calculated for DIII-D. Our continuing role in transient transport and nonlocal electron heat transport was recognized by an invited paper at the June 1997 EPS Berchtesgaden meeting which was published this past year. In addition, further details of nonlocal electron heat transport, primarily on TFTR, have been the subject of meeting presentations and are being published. Since Dr. Kissick left this research group for UCLA in April 1998 and Prof. Callen is in the process of transferring leadership of the TTF Transient Transport Working Group to Prof. Gentle (U. Texas), it is anticipated that this grant research area will be substantially diminished in the future. Stimulated in large part by the excellent internal fluctuation diagnostics (primarily ECE and BES) for studying MHD modes in the interior of DIII-D, we have begun work in a new area: disruption precursors induced by MHD modes being driven slowly through their ideal stability boundaries. In particular, we have constructed a new model for the temporal development of such precursors and shown that it provides a very good fit to DIII-D data. Also, we are in the process of developing codes for comparing the spatial profile of the disruption precursors with those predicted from the GATO ideal MHD instability code.« less
  • The research performed during the third year of this grant concentrated on a few key TFTR experimental data analysis issues: (1) characterization of MHD mode activity in TFTR; (2) comparison of low mode number MHD modes with neoclassical MHD theory; (3) further developments in local electron heat transient transport measurements; and (4) some other topics. Emphasis is placed on differences in these characteristics in DT and DD plasmas.