Reconstruction of current profiles from external magnetic and MSE measurements on DIII-D

Abstract This work introduces a new current model into the EFIT code for plasma current profile reconstruction. Using this model, edge-localized current density profiles are reconstructed solely from external magnetic measurements. Quantitative comparisons show that edge current profiles obtained with the new current model align closely with those from kinetic equilibrium reconstruction. The new model enables current density reconstruction with fewer diagnostics than kinetic equilibrium reconstruction (Lao et al 1990 Nucl. Fusion 30 1035–49), demonstrating that edge-localized current density information can be obtained from external magnetic measurements only, without the help of kinetic profiles and internal diagnostics, and without using the bootstrap current model. Furthermore, with the constraints of external magnetic and MSE measurements, current profiles in full radius obtained from the new model are in good agreement with the results of kinetic equilibrium reconstruction, which not only improves the efficiency of current reconstruction but also helps avoid possible errors caused by different kinds of diagnoses. Possible applications are also discussed, and a brief analysis of the evolution of the full-radius current density is performed. Noticeable decreases in both the magnitude and gradient of the edge current around the time of ELM bursts are observed. Moreover, analysis of the full radius current density profiles ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mrow> <mml:msub> <mml:mi>ρ</mml:mi> <mml:mi>N</mml:mi> </mml:msub> </mml:mrow> <mml:mo>=</mml:mo> <mml:mn>0</mml:mn> <mml:mo>−</mml:mo> <mml:mn>1.0</mml:mn> </mml:mrow> </mml:math> , <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mrow> <mml:msub> <mml:mi>ρ</mml:mi> <mml:mi>N</mml:mi> </mml:msub> </mml:mrow> <mml:mrow> <mml:mtext> </mml:mtext> </mml:mrow> </mml:mrow> </mml:math> denotes to square root of the normalized toroidal flux) reveals that as the edge current changes, the inner current also changes following a sinusoidal-like pattern at almost all time slices during four type-I ELMs in discharge 161493. The current evolution in the inner region ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mrow> <mml:msub> <mml:mi>ρ</mml:mi> <mml:mi>N</mml:mi> </mml:msub> </mml:mrow> <mml:mo>=</mml:mo> <mml:mrow> <mml:mtext> </mml:mtext> </mml:mrow> <mml:mn>0.2</mml:mn> <mml:mo>−</mml:mo> <mml:mn>0.6</mml:mn> </mml:mrow> </mml:math> ) is synchronized with the boundary region ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mrow> <mml:msub> <mml:mi>ρ</mml:mi> <mml:mi>N</mml:mi> </mml:msub> </mml:mrow> <mml:mo>=</mml:mo> <mml:mrow> <mml:mtext> </mml:mtext> </mml:mrow> <mml:mn>0.89</mml:mn> <mml:mo>−</mml:mo> <mml:mn>1.0</mml:mn> </mml:mrow> </mml:math> ), while the intermediate region ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mrow> <mml:msub> <mml:mi>ρ</mml:mi> <mml:mi>N</mml:mi> </mml:msub> </mml:mrow> <mml:mo>=</mml:mo> <mml:mrow> <mml:mtext> </mml:mtext> </mml:mrow> <mml:mn>0.6</mml:mn> <mml:mo>−</mml:mo> <mml:mn>0.89</mml:mn> </mml:mrow> </mml:math> ) shows opposite behavior. This sinusoidal-like variations in full-radius current density profile indicates strong core-pedestal coupling, suggesting ELMs significantly affect core plasmas, though current changes manifest differently across radial regions.