Large experiment data analysis collaboration. Annual progress report for period November 15, 1999 - November 14, 2000
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 the 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.
- Research Organization:
- University of Wisconsin-Madison, Madison, WI (US)
- Sponsoring Organization:
- US Department of Energy (US)
- DOE Contract Number:
- FG02-92ER54159
- OSTI ID:
- 798781
- Report Number(s):
- DOE/ER/54139-9; TRN: US200308%%215
- Resource Relation:
- Other Information: PBD: 10 Jul 2000; PBD: 10 Jul 2000
- Country of Publication:
- United States
- Language:
- English
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