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100 results on '"Chance, M. S."'

1. Generation of nonthermal continuum radiation in the magnetosphere

Author

Okuda, H, Chance, M. S, Ashour-Abdalla, M, and Kurth, W. S

Subjects
Geophysics
Abstract

Generation of electromagnetic continuum radiation from electrostatic fluctuations near the upper hybrid resonance frequency has been calculated by using cold plasma theory in an inhomogeneous plasma near the plasmapause. It is shown that both the polarization and the amplitude of electromagnetic radiation are in good quantitative agreement with spacecraft observations for nonthermal continuum radiation.

Published
1982

2. Finite beta drift Alfven instability

Author

Chance, M. S, Coroniti, F. V, and Kennel, C. F

Subjects
Geophysics
Abstract

We propose a means by which the theory of drift instabilities can be extended to plasmas of arbitrary beta. We then concentrate on the drift Alfven instability driven by an electron temperature gradient, proposed by Coroniti and Kennel (1970) to be a source of Pi 1 micropulsations on auroral lines of force. Even at relatively low beta the full finite beta theory differs considerably from previous low beta theories and produces better agreement with observation.

Published
1973

3. Modeling of feedback and rotation stabilization of the resistive wall mode in tokamaks

Author

Chu, M. S., primary, Bondeson, A., additional, Chance, M. S., additional, Liu, Y. Q., additional, Garofalo, A. M., additional, Glasser, A. H., additional, Jackson, G. L., additional, La Haye, R. J., additional, Lao, L. L., additional, Navratil, G. A., additional, Okabayashi, M., additional, Remierdes, H., additional, Scoville, J. T., additional, and Strait, E. J., additional

Published
2004
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4. Resistive wall mode stabilization with internal feedback coils in DIII-D

Author

Strait, E. J., primary, Bialek, J. M., additional, Bogatu, I. N., additional, Chance, M. S., additional, Chu, M. S., additional, Edgell, D. H., additional, Garofalo, A. M., additional, Jackson, G. L., additional, Jayakumar, R. J., additional, Jensen, T. H., additional, Katsuro-Hopkins, O., additional, Kim, J. S., additional, La Haye, R. J., additional, Lao, L. L., additional, Makowski, M. A., additional, Navratil, G. A., additional, Okabayashi, M., additional, Reimerdes, H., additional, Scoville, J. T., additional, Turnbull, A. D., additional, and Team, DIII-D, additional

Published
2004
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5. Stabilization of the resistive wall mode in DIII–D by plasma rotation and magnetic feedback

Author

Okabayashi, M, primary, Bialek, J, additional, Chance, M S, additional, Chu, M S, additional, Fredrickson, E D, additional, Garofalo, A M, additional, Hatcher, R, additional, Jensen, T H, additional, Johnson, L C, additional, Haye, R J La, additional, Navratil, G A, additional, Reimerdes, H, additional, Scoville, J T, additional, Strait, E J, additional, Turnbull, A D, additional, Walker, M L, additional, and Team, the DIII–D, additional

Published
2002
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7. Modification of high mode pedestal instabilities in the DIII-D tokamak

Author

Ferron, J. R., primary, Chu, M. S., additional, Jackson, G. L., additional, Lao, L. L., additional, Miller, R. L., additional, Osborne, T. H., additional, Snyder, P. B., additional, Strait, E. J., additional, Taylor, T. S., additional, Turnbull, A. D., additional, Garofalo, A. M., additional, Makowski, M. A., additional, Rice, B. W., additional, Chance, M. S., additional, Baylor, L. R., additional, Murakami, M., additional, and Wade, M. R., additional

Published
2000
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21. Ideal MHD stability and performance of ITER steady-state scenarios with ITBs.

Author

Poli, F. M., Kessel, C. E., Chance, M. S., Jardin, S. C., and Manickam, J.

Subjects
STABILITY (Mechanics), MAGNETOHYDRODYNAMICS, PERFORMANCE evaluation, NUCLEAR fusion, OPERATOR theory
Abstract

Non-inductive steady-state scenarios on ITER will need to operate with internal transport barriers (ITBs) in order to reach adequate fusion gain at typical currents of 9 MA. The large pressure gradients at the location of the internal barrier are conducive to the development of ideal MHD instabilities that may limit the plasma performance and may lead to plasma disruptions. Fully non-inductive scenario simulations with five combinations of heating and current drive sources are presented in this work, with plasma currents in the range 7-10 MA. For each configuration the linear, ideal MHD stability is analysed for variations of the Greenwald fraction and of the pressure peaking factor around the operating point, aiming at defining an operational space for stable, steady-state operations at optimized performance. It is shown that plasmas with lower hybrid heating and current drive maintain the minimum safety factor above 1.5, which is desirable in steady-state operations to avoid neoclassical tearing modes. Operating with moderate ITBs at 2/3 of the minor radius, these plasmas have a minimum safety factor above 2, are ideal MHD stable and reach Q ⋩ 5 operating above the ideal no-wall limit. [ABSTRACT FROM AUTHOR]

Published
2012
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22. High poloidal beta equilibria in the Tokamak Fusion Test Reactor limited by a natural inboard poloidal field null

Author

Sabbagh, S. A., primary, Gross, R. A., additional, Mauel, M. E., additional, Navratil, G. A., additional, Bell, M. G., additional, Bell, R., additional, Bitter, M., additional, Bretz, N. L., additional, Budny, R. V., additional, Bush, C. E., additional, Chance, M. S., additional, Efthimion, P. C., additional, Fredrickson, E. D., additional, Hatcher, R., additional, Hawryluk, R. J., additional, Hirshman, S. P., additional, Janos, A. C., additional, Jardin, S. C., additional, Jassby, D. L., additional, Manickam, J., additional, McCune, D. C., additional, McGuire, K. M., additional, Medley, S. S., additional, Mueller, D., additional, Nagayama, Y., additional, Owens, D. K., additional, Okabayashi, M., additional, Park, H. K., additional, Ramsey, A. T., additional, Stratton, B. C., additional, Synakowski, E. J., additional, Taylor, G., additional, Wieland, R. M., additional, Zarnstorff, M. C., additional, Kesner, J., additional, Marmar, E. S., additional, and Terry, J. L., additional

Published
1991
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23. Control of plasma shape and performance of the PBX‐M tokamak experiment in high‐βt /high‐βp regimes

Author

Bell, R. E., primary, Asakura, N., additional, Bernabei, S., additional, Chance, M. S., additional, Duperrex, P.‐A., additional, Fonck, R. J., additional, Gammel, G. M., additional, Greene, G., additional, Hatcher, R. E., additional, Holland, A., additional, Jardin, S. C., additional, Jiang, T.‐W., additional, Kaita, R., additional, Kaye, S. M., additional, Kessel, C. E., additional, Kugel, H. W., additional, LeBlanc, B., additional, Levinton, F. M., additional, Okabayashi, M., additional, Ono, M., additional, Paul, S. F., additional, Powell, E. T., additional, Qin, Y., additional, Roberts, D. W., additional, Sauthoff, N. R., additional, Sesnic, S., additional, and Takahashi, H., additional

Published
1990
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25. Active feedback stabilization of the resistive wall mode on the DIII-D device.

Author

Okabayashi, M., Bialek, J., Chance, M. S., Chu, M. S., Fredrickson, E. D., Garofalo, A. M., Gryaznevich, M., Hatcher, R. E., Jensen, T. H., Johnson, L. C., La Haye, R. J., Lazarus, E. A., Makowski, M. A., Manickam, J., Navratil, G. A., Scoville, J. T., Strait, E. J., Turnbull, A. D., and Walker, M. L.

Subjects
MAGNETOHYDRODYNAMICS, TOKAMAKS, CONTROLLED fusion
Abstract

A proof of principle magnetic feedback stabilization experiment has been carried out to suppress the resistive wall mode (RWM), a branch of the ideal magnetohydrodynamic (MHD) kink mode under the influence of a stabilizing resistive wall, on the DIII-D tokamak device [Plasma Phys. Controlled Fusion Research (Intemational Atomic Energy Agency, Vienna, 1986), p. 159; Phys. Plasmas 1, 1415 (1994)]. The RWM was successfully suppressed and the high beta duration above the no-wall limit was extended to more than 50 times the resistive wall flux diffusion time. It was observed that the mode structure was well preserved during the time of the feedback application. Several lumped parameter formulations were used to study the feedback process. The observed feedback characteristics are in good qualitative agreement with the analysis. These results provide encouragement to future efforts towards optimizing the RWM feedback methodology in parallel to what has been successfully developed for the n = 0 vertical positional control. Newly developed MHD codes have been extremely useful in guiding the experiments and in providing possible paths for the next step. [ABSTRACT FROM AUTHOR]

Published
2001

26. A tearing mode energy principle for an axisymmetric force-free plasma.

Author

Chu, M. S., Chance, M. S., Greene, J. M., and Jensen, T. H.

Subjects
*PLASMA gases, *FUNCTIONALS, *PLASMA stability
Abstract

A self-adjoint, gauge invariant stability functional δWTG for determination of a sufficient condition of tearing mode stability is obtained for a plasma with a uniform pressure. The plasma is stable if there is no free energy available to support energy flux into the singular layer. The Δ’ concept, valid in simple geometries, is generalized to reflect variation of equilibrium quantities on the flux surface. The relationship of δWTG to the ideal stability functional and other possible forms of tearing mode stability functionals is clarified through gauge transformations. [ABSTRACT FROM AUTHOR]

Published
1989
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27. Low-n shear Alfvén spectra in axisymmetric toroidal plasmas.

Author

Cheng, C. Z. and Chance, M. S.

Subjects
*SHEAR flow, *AXIAL flow, *MAGNETIC fields
Abstract

In toroidal plasmas, the toroidal magnetic field is nonuniform over a magnetic surface and causes coupling of different poloidal harmonics. It is shown both analytically and numerically that the toroidicity not only breaks up the shear Alfvén continuous spectrum, but also creates new, discrete, toroidicity-induced shear Alfvén eigenmodes with frequencies inside the continuum gaps. Potential applications of the low-n toroidicity-induced shear Alfvén eigenmodes on plasma heating and instabilities are addressed. [ABSTRACT FROM AUTHOR]

Published
1986
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28. Resistive ballooning in the toroidal reversed-field pinch.

Author

Dagazian, R. Y. and Chance, M. S.

Subjects
*REVERSED field pinches, *PLASMA gases
Abstract

Various toroidal reversed-field pinch (RFP) equilibria stable to ideal Mercier and ballooning modes are subjected to resistive ballooning analysis. The stability properties of these configurations are thus investigated as a function of quantities that are experimentally measurable. Resistive ballooning is seen as a likely candidate for the interpretation of a certain class of density fluctuation phenomena observed in these devices. [ABSTRACT FROM AUTHOR]

Published
1985
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29. A numerical study of the high-n shear Alfvén spectrum gap and the high-n gap mode.

Author

Chu, M. S., Greene, J. M., Lao, L. L., Turnbull, A. D., and Chance, M. S.

Subjects
MAGNETOHYDRODYNAMIC waves, TOKAMAKS, PHYSICS
Abstract

The toroidicity-induced gaps of the shear Alfvén wave spectrum in tokamaks are shown to satisfy an envelope equation. The structure of these gaps, and the location of the high-n gap modes, which are localized modes with frequency in the gap, are studied for general numerically generated equilibria. The dependence of the frequencies of the gaps and the gap modes on the equilibrium properties, such as elongation, triangularity, and β of the plasma are explored. [ABSTRACT FROM AUTHOR]

Published
1992
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30. Stabilization of the resistive wall mode in DIII–D by plasma rotation and magnetic feedback

Author

Okabayashi, M, Bialek, J, Chance, M S, Chu, M S, Fredrickson, E D, Garofalo, A M, Hatcher, R, Jensen, T H, Johnson, L C, Haye, R J La, Navratil, G A, Reimerdes, H, Scoville, J T, Strait, E J, Turnbull, A D, Walker, M L, and Team, the DIII–D

Abstract

Suppression of the resistive wall mode (RWM) has been successfully demonstrated in the DIII–D tokamak by using rotational stabilization in conjunction with a close-fitting vacuum vessel wall. The duration of the high-pressure discharge was extended to hundreds of times the wall skin time. Frequently, the plasma pressure reached the ideal-wall magnetohydrodynamic (MHD) kink limit. The confined pressure is up to twice as high as the no-wall ideal MHD kink limit. Near its marginal stability point, the RWM is found to resonate with residual non-axisymmetric fields (e.g. components of the error field). A magnetic feedback system has been used to identify and compensate for the residual non-axisymmetric fields. This is to the best of our knowledge, the first demonstration of the sustainment of a stable plasma with pressure at levels well above the no-wall pressure limit. This technique is expected to be applicable to other toroidal devices.

Published
2002

35. Study of high poloidal beta plasmas in TFTR and DIII-D

Author

Navratil, G. A., Gross, R. A., Michael Mauel, Sabbagh, S. A., Bell, M. G., Bell, R., Bretz, N., Budny, R., Chance, M. S., Fredrickson, E. D., Hatcher, R., Hawryluk, R. J., Janos, A. C., Jardin, S. C., Jassby, D. L., and Mccune, D. C.

36. Neutral-Beam Current-Driven High-Poloidal-Beta Operation of the DIII-D Tokamak

Author

Simonen, T. C., primary, Matsuoka, M., additional, Bhadra, D. K., additional, Burrell, K. H., additional, Callis, R. W., additional, Chance, M. S., additional, Chu, M. S., additional, Greene, J. M., additional, Groebner, R. J., additional, Harvey, R. W., additional, Hill, D. N., additional, Kim, J., additional, Lao, L., additional, Petersen, P. I., additional, Porter, G. D., additional, St. John, H., additional, Stallard, B. W., additional, Stambaugh, R. D., additional, Strait, E. J., additional, and Taylor, T. S., additional

Published
1988
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41. MHD stability in high βTDIII-D divertor discharges

Author

Lao, L L, primary, Strait, E J, additional, Taylor, T S, additional, Chu, M S, additional, Ozeki, T, additional, Howl, W, additional, Stambaugh, R D, additional, Burrell, K H, additional, Chance, M S, additional, DeBoo, J C, additional, Gohil, P, additional, Greene, J M, additional, Groebner, R J, additional, Kellman, A G, additional, Mahdavi, M Ali, additional, Osborne, T H, additional, Porter, G, additional, and Turnbull, A D, additional

Published
1989
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