Abstract
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 charge exchange, beam emission, and fast ion Dα (FIDA) emission spectra. Simultaneous spectral measurements of counter current injected and co current injected neutral beams permit a direct determination of the deuterium toroidal velocity. Time-dependent collisional radiative modeling of the photoemission process is in quantitative agreement with measured spectral characteristics. L-mode discharges with low beam ion densities and broad thermal pressure profiles exhibit deuteron temperature and toroidal rotation velocities similar to carbon. However, intrinsic rotation H-mode conditions and plasmas with internal transport barriers exhibit differences between core deuteron and carbon rotation which are inconsistent with the sign and magnitude of the neoclassical predictions.
Highlights
Plasma toroidal rotation is generally considered a stabilizing mechanism for deleterious magnetohydrodynamic (MHD) instabilities such as the resistive wall mode (RWM)1,2 and neoclassical tearing mode (NTM),3–5 as well as contributing to E Â B shear stabilization of turbulence6 through the radial electric field Er
Intrinsic rotation may play a crucial role in determining the stability and transport of future larger devices, such as ITER, with relatively low torque provided by neutral beam injection
Preliminary measurements which demonstrated the feasibility of deuterium main-ion toroidal rotation measurements in the core of DIII-D plasmas utilized a comprehensive spectral fit model which incorporated all photoemission sources, and complementary views of co and counter current directed neutral beams
Summary
Plasma toroidal rotation is generally considered a stabilizing mechanism for deleterious magnetohydrodynamic (MHD) instabilities such as the resistive wall mode (RWM) and neoclassical tearing mode (NTM), as well as contributing to E Â B shear stabilization of turbulence through the radial electric field Er. Preliminary measurements which demonstrated the feasibility of deuterium main-ion toroidal rotation measurements in the core of DIII-D plasmas utilized a comprehensive spectral fit model which incorporated all photoemission sources, and complementary views of co and counter current directed neutral beams.. A profile diagnostic which covers the plasma region from magnetic axis to edge has been constructed to directly test the neoclassical theory of differential toroidal rotation between bulk ions and impurities in DIII-D. Measurements of ion temperature and toroidal velocity of deuterium and carbon in an L-mode discharge are presented in Sec. IV, including the demonstration of atomic corrections to the results of spectral fitting.
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.