Overview of plasma operation and control studies in the first plasma campaign of JT-60SA

Abstract Stable MA-class divertor plasmas have been achieved in the JT-60SA first plasma campaign based on developed control schemes and careful assessment before the plasma operation. Fundamental plasma characteristics and parameter regimes in the first plasma campaign have been examined. The plasma breakdown was obtained at the low toroidal electric field of <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:mo stretchy="false">|</mml:mo> <mml:mo stretchy="false">|</mml:mo> </mml:mrow> </mml:msub> <mml:mo>∼</mml:mo> </mml:mrow> </mml:math> 0.12–0.15 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mtext> </mml:mtext> <mml:mrow> <mml:mi mathvariant="normal">V</mml:mi> </mml:mrow> <mml:mstyle scriptlevel="0"/> <mml:msup> <mml:mrow> <mml:mi mathvariant="normal">m</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>1</mml:mn> </mml:mrow> </mml:msup> </mml:mrow> </mml:math> with a trapped particle configuration and an Electron Cyclotron Heating (ECH) assist. The EC-assisted low <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:mo stretchy="false">|</mml:mo> <mml:mo stretchy="false">|</mml:mo> </mml:mrow> </mml:msub> </mml:mrow> </mml:math> breakdown was also obtained in a field null configuration by reducing the residual poloidal magnetic field (∼1 mT) and optimizing the initial coil voltage application during the plasma start-up. For the plasma current ramp, the Plasma Current Centroid scheme and the Adaptive Voltage Allocation scheme have been developed and applied. The former one is beneficial when a large eddy current is generated in the vacuum vessel. The latter one adjusts control gains automatically to avoid voltage saturation and unstable plasma control. The divertor configuration with the plasma current of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mi>I</mml:mi> <mml:mrow> <mml:mi mathvariant="normal">P</mml:mi> </mml:mrow> </mml:msub> <mml:mo>∼</mml:mo> </mml:mrow> </mml:math> 1 MA was achieved by using the Cauchy-condition surface scheme and sustained stably (for 3 s in the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mi>I</mml:mi> <mml:mrow> <mml:mi mathvariant="normal">P</mml:mi> </mml:mrow> </mml:msub> </mml:mrow> </mml:math> flat-top) until the flux supplied by the Central Solenoid coils was fully consumed. The plasma has been developed by finding paths to access stable operational regimes to avoid disruptions and critical MHD modes. Power balance analyses showed that the energy confinement time followed the L-mode scaling. A systematic EC wall cleaning has been performed to find suitable conditions for <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mrow> <mml:mi mathvariant="normal">H</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msub> </mml:mrow> </mml:math> gas removal from the first wall. This paper presents the main scientific results of the plasma operation and the plasma control studies in JT-60SA clarifying the issues of starting plasma operation in a new large superconducting machine. The results can make contributions for ITER and DEMO especially in the first operation campaign and commissioning procedures of plasma operation and control systems.