Comparison of Doppler back-scattering and charge exchange measurements of <i>E</i> × <i>B</i> plasma rotation in the DIII-D tokamak under varying torque conditions
Quinn Pratt, T. L. Rhodes, C. Chrystal, Troy Carter
Abstract
Abstract Measurements of the E × B toroidal angular velocity, <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mi>ω</mml:mi> <mml:mrow> <mml:mi>E</mml:mi> <mml:mo>×</mml:mo> <mml:mi>B</mml:mi> </mml:mrow> </mml:msub> <mml:mo>=</mml:mo> <mml:msub> <mml:mi>E</mml:mi> <mml:mrow> <mml:mi mathvariant="normal">r</mml:mi> </mml:mrow> </mml:msub> <mml:mrow> <mml:mo>/</mml:mo> </mml:mrow> <mml:mi>R</mml:mi> <mml:msub> <mml:mi>B</mml:mi> <mml:mi>θ</mml:mi> </mml:msub> </mml:math> ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mi>E</mml:mi> <mml:mrow> <mml:mi mathvariant="normal">r</mml:mi> </mml:mrow> </mml:msub> </mml:math> is the radial electric field, B θ is the poloidal magnetic field), are made using the Doppler back-scattering (DBS) and charge-exchange recombination (CER) spectroscopy diagnostics. DBS uses the Doppler shift of wavenumber-resolved density fluctuations while CER uses the Doppler shift of impurity emission lines to independently measure plasma parameters for calculating the local radial electric field. DBS and CER profiles of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mi>ω</mml:mi> <mml:mrow> <mml:mi>E</mml:mi> <mml:mo>×</mml:mo> <mml:mi>B</mml:mi> </mml:mrow> </mml:msub> </mml:math> as a function of normalized toroidal flux ( ρ ) are compared at various levels of neutral beam applied torque on the plasma. Under standard neoclassical theory <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mi>ω</mml:mi> <mml:mrow> <mml:mi>E</mml:mi> <mml:mo>×</mml:mo> <mml:mi>B</mml:mi> </mml:mrow> </mml:msub> </mml:math> is a flux surface quantity, making it appropriate to compare across diagnostics. DBS and CER generally show good agreement when comparing <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mi>ω</mml:mi> <mml:mrow> <mml:mi>E</mml:mi> <mml:mo>×</mml:mo> <mml:mi>B</mml:mi> </mml:mrow> </mml:msub> </mml:math> profiles at different levels of neutral beam injection-applied torque. Furthermore, the DBS values have close to the same precision as CER values when averaged over a similar time-scale and effects, such as prompt-torque are considered. DBS is able to observe the rapid ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mo><</mml:mo> </mml:math> 10 ms) modification of the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mi>E</mml:mi> <mml:mrow> <mml:mi mathvariant="normal">r</mml:mi> </mml:mrow> </mml:msub> </mml:math> profile by the diagnostic neutral beam ‘blips’. This modification is most pronounced when the blip applies a large relative change in torque on the plasma. Overall, these results could have implications on transport analysis and suggests using DBS and CER in conjunction to constrain values of the E × B -shear (sometimes called <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mi>γ</mml:mi> <mml:mrow> <mml:mi>E</mml:mi> <mml:mo>×</mml:mo> <mml:mi>B</mml:mi> </mml:mrow> </mml:msub> </mml:math> ).