The structure of the edge radial electric field {ital E}{sub {ital r}} inferred from the poloidal rotation velocity is compared with that of the particle and thermal transport barrier for {ital H}-mode plasmas in JFT-2M. Both {ital E}{sub {ital r}} and its gradient {partial derivative}{ital E}{sub {ital r}}/{partial derivative}{ital r} in the thermal transport barrier are found to become more negative at the {ital L}-{ital H} transition. On the other hand, {partial derivative}{ital E}{sub {ital r}}/{partial derivative}{ital r} is more positive outside of the separatrix. The shear of the radial electric field and poloidal rotation velocity in the {ital H} mode is localized within the order of an ion poloidal gyroradius near the separatrix, in the region of ion collisionality {nu}{sub *{ital i}}{approx}20--40.

Edge electric field profiles of H-mode plasmas in JFT-2M tokamak

The neutral-beam induced D(α) emission spectrum contains a wealth of information such as deuterium ion temperature, toroidal rotation, density, beam emission intensity, beam neutral density, and local magnetic field strength magnitude |B| from the Stark-split beam emission spectrum, and fast-ion D(α) emission (FIDA) proportional to the beam-injected fast ion density. A comprehensive spectral fitting routine which accounts for all photoemission processes is employed for the spectral analysis. Interpretation of the measurements to determine physically relevant plasma parameters is assisted by the use of an optimized viewing geometry and forward modeling of the emission spectra using a Monte-Carlo 3D simulation code.

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Active spectroscopic measurements of the bulk deuterium properties in the DIII-D tokamak (invited).

Bulk ion toroidal rotation plays a critical role in controlling microturbulence and MHD stability as well as yielding important insight into angular momentum transport and the investigation of intrinsic rotation. So far, our understanding of bulk plasma flow in hydrogenic plasmas has been inferred from impurity ion velocity measurements and neoclassical theoretical calculations. However, the validity of these inferences has not been tested rigorously through direct measurement of the main-ion rotation in deuterium plasmas, particularly in regions of the plasma with steep pressure gradients where very large differences can be expected between bulk ion and impurity rotation. New advances in the analysis of wavelength-resolved Dα emission on the DIII-D tokamak [J. L. Luxon et al., Fusion Sci. Technol. 48, 807 (2002)] have enabled accurate measurements of the main-ion (deuteron) temperature and toroidal rotation. The Dα emission spectrum is accurately fit using a model that incorporates thermal deuterium char...

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Measurements of the deuterium ion toroidal rotation in the DIII-D tokamak and comparison to neoclassical theorya)

Measurements of the Deuterium Ion Toroidal Rotation in the DIII-D Tokamak and Comparison to Neoclassical Theory

A regime of very high confinement (VH-mode) has been observed in neutral beam-heated deuterium discharges in the DIII-D tokamak with thermal energy confinement times up to [approx]3.6 times that predicted by the ITER-89P L-mode scaling and 2 times that predicted by ELM-free H-mode thermal confinement scalings. This high confinement has led to increased plasma performance, n[sub D] (0)T[sub i](0)[tau][sub E] = 2 [times] 10[sup 20] m[sup [minus]3] keV sec with I[sub p] = 1.6 MA, B[sub T] = 2.1 T, Z[sub eff] [le] 2. Detailed transport analysis shows a correspondence between the large decrease in thermal diffusivity in the region 0.75 [le] [rho] [le] 0.9 and the development of a strong shear in the radial electric field in the same region. This suggests that stabilization of turbulence by sheared E [times] B flow is responsible for the improved confinement in VH-mode. A substantial fraction of the edge plasma entering the second regime of stability may also contribute to the increase in confinement. The duration of the VH-mode phase has been lengthened by feedback controlling the input power to limit plasma beta.

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Confinement and stability of VH-mode discharges in the DIII-D tokamak

In this chapter we discuss the various diagnostic techniques in which active spectroscopy plays a role. The use of an injected neutral beam - either a dedicated diagnostic beam or the main heating beams - to localize and enhance the spectroscopic measurements described in Chap. 5 has been exploited for a number of key physics measurements, in particular detailed profile information on ion parameters, the radial electric field, plasma current density, and turbulent transport. The ability to make these detailed measurements has been a key element in the development of improved plasma performance. The neutral beam techniques have been extended by the use of such beam analogs as laser beams, gas puffs, and pellet injection for specific measurements. In each case we describe the general principle behind the measurement and include several successful examples of their implementation, briefly touching on some of the more important physics results. We conclude with a few remarks about the relevance and re...

E. L. Foley

Papers

Chapter 6: Active Spectroscopy