Study of radial field dependent flows in inboard limited Aditya-U plasmas using EMC3-Eirene simulations

Abstract The intrinsically generated plasma rotation in magnetically confined tokamak plasmas has implications for a number of edge and core phenomena. In recent Aditya-U tokamak circular plasma discharges with plasma current of range (142–170) kA, the toroidal rotation was measured to be finite of the order of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mo>∼</mml:mo> <mml:mo stretchy="false">(</mml:mo> <mml:mn>0</mml:mn> <mml:mo>−</mml:mo> <mml:mn>6</mml:mn> <mml:mo stretchy="false">)</mml:mo> </mml:mrow> </mml:math> km s −1 , which reduced with increasing plasma edge density ranging from (1–3) <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mo>×</mml:mo> <mml:msup> <mml:mn>10</mml:mn> <mml:mrow> <mml:mn>18</mml:mn> </mml:mrow> </mml:msup> </mml:mrow> </mml:math> m −3 . As explored by 3D EMC3-Eirene simulations, the primary driver of the background rotation field in Aditya-U is the pressure gradients maintained by the limiter sink action in the SOL region. In the fresh EMC3-Eirene plasma-neural transport simulations of these inboard limited plasmas, two sets with input power in the SOL, 60 kW and 300 kW are simulated such that they are comparable to phases with and without impurity-injection, respectively. The toroidal velocities in them are compared with the experimental observation of toroidal flows, where measurement of the corresponding radial electric field E r also became available. The velocity of intrinsic toroidal rotation, which was reported as measured using the Doppler shift of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msup> <mml:mi>C</mml:mi> <mml:mrow> <mml:mn>5</mml:mn> <mml:mo>+</mml:mo> </mml:mrow> </mml:msup> </mml:mrow> </mml:math> carbon spectral lines in the edge region, was estimated to be of the order of the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mi>E</mml:mi> <mml:mrow> <mml:mi>r</mml:mi> </mml:mrow> </mml:msub> <mml:mo>×</mml:mo> <mml:mi>B</mml:mi> </mml:mrow> </mml:math> velocity. Although this estimation is validated here by radial electric field strengths computed from the simulated plasma temperature, which was unavailable from the experiments, the gradients are shown to be the driver of the background rotation. This rotation in experiments is conditionally compensated by <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mi>E</mml:mi> <mml:mrow> <mml:mi>r</mml:mi> </mml:mrow> </mml:msub> <mml:mo>×</mml:mo> <mml:mi>B</mml:mi> </mml:mrow> </mml:math> drift such that it is captured only when E r is either dominant or approaches zero because of impurity injection. The E r from the present simulations is additionally obtainable from the temperature profiles even though the drifts generated by it are excluded from the simulations. To highlight the impact of negligible temperature gradients it is preferable to compare low-power cases with the impurity injection phases of experiments. The missing impact of impurity injection is thus accounted for in terms of the background temperature profile potentially modified by them, while the original interpretation assumed negligible temperature variation under all conditions.