Alpha particle transport induced by TAE in CFETR steady-state scenario

Abstract In fusion plasmas, α particles are crucial for achieving self-sustained burning conditions. However, toroidal Alfvén eigenmodes (TAE) can induce radial transport of α particles, causing energy loss and potentially quenching the plasma discharge. Recent studies have shown that in the Chinese Fusion Engineering Test Reactor (CFETR) tokamak, the most unstable TAE modes exhibit significantly higher toroidal mode numbers ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mi>n</mml:mi> <mml:mo>=</mml:mo> <mml:mn>7</mml:mn> <mml:mo>∼</mml:mo> <mml:mn>10</mml:mn> </mml:mrow> </mml:math> ) compared to existing devices ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mi>n</mml:mi> <mml:mo>=</mml:mo> <mml:mn>1</mml:mn> <mml:mo>∼</mml:mo> <mml:mn>4</mml:mn> </mml:mrow> </mml:math> ). This implies complex α particle transport with larger radial scales under high- n TAE perturbations. This study investigates the impact of single- n TAE perturbations on α particle transport using the PTC code, focusing on CFETR 2019 steady-state scenario. Three phases of TAE evolution are analyzed: linear growth, weak saturation, and strong saturation. During growth phase, resonant α particles exhibit enhanced energy variations and radial transport compared to non-resonant particles. These particles are transported radially from resonance positions towards the core and boundary of the plasma. In the nonlinear saturated phase, resonant particles form island structures in the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mi mathvariant="normal">Θ</mml:mi> <mml:mo>−</mml:mo> <mml:msub> <mml:mi>P</mml:mi> <mml:mrow> <mml:mi>ϕ</mml:mi> </mml:mrow> </mml:msub> </mml:mrow> </mml:math> phase space, where Θ represents the wave-particle phase, and P φ is the toroidal angular momentum. Notably, island widths <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mi mathvariant="normal">Δ</mml:mi> <mml:msub> <mml:mi>P</mml:mi> <mml:mrow> <mml:mi>ϕ</mml:mi> </mml:mrow> </mml:msub> </mml:mrow> </mml:math> are wider for high- n TAE, indicating increased radial transport. When TAE saturation amplitudes are large, high- n resonance islands overlap radially, leading to substantially enhanced transport scales for associated α particles, particularly pronounced for <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mi>n</mml:mi> <mml:mo>=</mml:mo> <mml:mn>9</mml:mn> <mml:mo>∼</mml:mo> <mml:mn>12</mml:mn> </mml:mrow> </mml:math> modes.