Diamagnetic energy measurements and evaluation of poloidal beta and internal inductance during the first operational phase at JT-60SA

Abstract This paper reports on the evaluation of the diamagnetic energy using diamagnetic loops in JT-60SA, the largest operating tokamak in the world, and revisits the physics behind the evaluation of poloidal beta ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mi>β</mml:mi> <mml:mrow> <mml:mi mathvariant="normal">p</mml:mi> </mml:mrow> </mml:msub> </mml:mrow> </mml:math> ) and internal inductance ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mi>l</mml:mi> <mml:mrow> <mml:mi mathvariant="normal">i</mml:mi> </mml:mrow> </mml:msub> </mml:mrow> </mml:math> ). During the first operation phase of JT-60SA, diamagnetic measurements were utilized in assessing parameters related to plasma equilibrium, such as stored energy, <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mi>β</mml:mi> <mml:mrow> <mml:mi mathvariant="normal">p</mml:mi> </mml:mrow> </mml:msub> </mml:mrow> </mml:math> , and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mi>l</mml:mi> <mml:mrow> <mml:mi mathvariant="normal">i</mml:mi> </mml:mrow> </mml:msub> </mml:mrow> </mml:math> . The evaluated stored energy is above 200 kJ with 1 MJ electron cyclotron heating, and we observed the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mi>l</mml:mi> <mml:mrow> <mml:mi mathvariant="normal">i</mml:mi> </mml:mrow> </mml:msub> </mml:mrow> </mml:math> rise from around unity to above 2 during the plasma current ramp-down phase. The diamagnetic measurements successfully operated throughout the discharge duration, which is above 10 s, with low measurement errors. The correction of the error arising from the interaction between diamagnetic measurements and superconducting coils, as well as the detailed estimation of these errors, are discussed in detail. Furthermore, the physics behind the rise in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mi>l</mml:mi> <mml:mrow> <mml:mi mathvariant="normal">i</mml:mi> </mml:mrow> </mml:msub> </mml:mrow> </mml:math> is revealed by using both the JT-60SA experiment and numerical simulations.