Edge radial electric field in positive and negative triangularity plasmas in the TCV tokamak

Abstract We present the first edge E r measurements in negative triangularity (NT) plasmas in the Tokamak à Configuration Variable (TCV). The Doppler backscattering measurements of <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:mo>≈</mml:mo> <mml:msub> <mml:mi>E</mml:mi> <mml:mi>r</mml:mi> </mml:msub> <mml:mrow> <mml:mo>/</mml:mo> </mml:mrow> <mml:mi>B</mml:mi> </mml:mrow> </mml:math> reveal a significant impact of triangularity on the E r well: in Ohmic, neutral beam injection, and electron cyclotron resonance heated discharges, the E r well and associated <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mi>E</mml:mi> <mml:mi>r</mml:mi> </mml:msub> <mml:mo>×</mml:mo> <mml:mi>B</mml:mi> </mml:mrow> </mml:math> shear are stronger in NT-shaped plasmas compared to their positive triangularity (PT) counterpart. This suggests a connection to the concomitant NT performance gain relative to PT L-mode.