Survey of the edge radial electric field in L-mode TCV plasmas using Doppler backscattering

Abstract A Doppler backscattering (DBS) diagnostic has recently been installed on the Tokamak à Configuration Variable (TCV) to facilitate the study of edge turbulence and flow shear in a versatile experimental environment. The dual channel V-band DBS system is coupled to TCV’s quasi-optical diagnostic launcher, providing access to the upper low-field side region of the plasma cross-section. Verifications of the DBS measurements are presented. The DBS equilibrium <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mi>v</mml:mi> <mml:mo>⊥</mml:mo> </mml:msub> </mml:mrow> </mml:math> profiles are found to compare favorably with gas puff imaging (GPI) measurements and to the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mi>E</mml:mi> <mml:mtext mathvariant="italic">r</mml:mtext> </mml:msub> </mml:mrow> </mml:math> inferred from the radial force balance of the carbon impurity. The radial structure of the edge <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mi>E</mml:mi> <mml:mtext>r</mml:mtext> </mml:msub> <mml:mo>×</mml:mo> <mml:mi>B</mml:mi> </mml:mrow> </mml:math> equilibrium flow and its dependencies are investigated across a representative set of L-mode TCV discharges, by varying density, auxiliary heating and magnetic configuration.