Coaxial helicity injection in open-flux low-aspect-ratio toroidal discharges

Redd, A. J.; Jarboe, T. R.; Nelson, B. A.; O’Neill, R. G.; Smith, R. J.

doi:doi:10.1063/1.2800863

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Spontaneous quasi single helicity regimes in EXTRAP T2R reversed-field pinch

In recent years, good progress toward a better understanding and control of the plasma performance in reversed-field pinch devices has been made. These improvements consist both of the discovery of spontaneous plasma regimes, termed the quasi single helicity (QSH) regime, in which part of the plasma core is no longer stochastic, and of the development of techniques for active control of plasma instabilities. In this paper, a systematic study of spontaneous QSH in the EXTRAP T2R device [ P. R. B...

Unified linear response function for zonal flows with full finite orbit effects

A new formulation of the linear response function of electrostatic potential to nonlinear drive (due to turbulence) is presented in this paper; zonal flows play important roles in the self-regulation of turbulence and their basic physics are contained in response functions. Two branches of zonal flows [stationary zonal flow and geodesic acoustic mode (GAM)] are known to exist in the low and high frequency ranges. However, they have been analyzed separately using different approximations due the...

Open-flux low-aspect-ratio toroidal discharges generated and sustained by coaxial helicity injection (CHI) in the Helicity Injected Torus device (HIT-II) are described. The discharges in this study are flux tubes directly connected to the CHI electrodes, with poloidal flux less than or equal to the CHI injector flux, and no possibility of a significant closed-flux plasma core. Theoretically derived scalings for the dependence of CHI injector current on the toroidal field current and magnitude of the injector flux are experimentally confirmed, and empirical models are developed for the poloidal magnetic field and toroidal plasma current in open-flux discharges. In particular, the toroidal plasma current is independent of the toroidal magnetic field, both theoretically and empirically. Variations in injector flux geometry demonstrate that the CHI injector current leaves the electrode surfaces at the flux strike points, and that the relative width of the CHI injector determines whether the dominant observed relaxation mechanism is a harmonic mode at the plasma edge or reconnection near the CHI electrodes. In the case of an effective interelectrode distance approximately equal to the device minor radius, the ratio of toroidal plasma current to CHI injector current is maximized. Global magnetic equilibrium quantities and local magnetic measurements are consistent with modelling these open-flux discharges as thin current sheets connected to the CHI electrodes.

Article Outline

INTRODUCTION
THEORETICAL BACKGROUND
THE HIT-II DEVICE AND EXPERIMENTAL METHODS
HIT-II CHI DISCHARGES
HIT-II EMPIRICAL DATABASE RESULTS
DISCUSSION OF THE RESULTS
CONCLUSIONS

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KEYWORDS and PACS

Keywords

magnetic reconnection, plasma magnetohydrodynamics, plasma toroidal confinement, Tokamak devices

PACS

52.55.Fa

Tokamaks, spherical tokamaks
52.30.Cv

Magnetohydrodynamics (including electron magnetohydrodynamics)
52.35.Vd

Magnetic reconnection

ARTICLE DATA

Digital Object Identifier

http://dx.doi.org/10.1063/1.2800863

PUBLICATION DATA

ISSN

1070-664X (print)

1089-7674 (online)

Publisher

$abstract.society.value is a Member of CrossRef

American Institute of Physics

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