Abstract
In order to realize high performance burning plasmas in magnetic-confinement fusion devices, such as tokamaks, both bulk plasma transport and that of energetic fusion alpha-particles, which result from different scale fluctuations with different free energy sources, have to be reduced simultaneously. Utilizing the advantage of global toroidal non-linear simulations covering a whole torus, here, we found a new coupling mechanism between the low-frequency micro-scale electromagnetic drift-wave fluctuations regulating the former, while the high-frequency macro-scale toroidal Alfven eigenmode (TAE) regulates the latter. This results from the dual spread of micro-scale turbulence due to the macro-scale TAE not only in wavenumber space representing local eddy size but also in configuration space with global profile variations. Consequently, a new class of turbulent state is found to be established, where the turbulence is homogenized on the poloidal cross-section with exhibiting large-scale structure, which increases fluctuation levels and then both transports, leading to deterioration in the fusion performance.
Highlights
Study of plasma confinement is going to enter a new regime, that is, burning plasmas [1], which produce energetic alpha particles by the fusion reaction
In this letter, we study nonlinear interactions between the toroidal Alfven eigenmode (TAE) driven by high energy particles, which is a macro-scale MHD instability characterized by the high frequency of Alfvén waves, and the DW turbulence driven by a temperature gradient in the electromagnetic regime, which is characterized by the low-frequency Alfvénic ion–temperature gradient modes [18, 19] by means of the global gyrokinetic simulation code GKNET [20, 21], which covers a whole torus plasma from the core to the edge with the profile variation of plasma density and temperature
DW mode through the geometrical damping effect. These two processes, one in spectral space causing a large-scale structure and enhancing transport, while the other is in configuration space causing a damping of the dominant DW mode and reducing the transport, are not independent but coupled exhibiting synergistic interaction, leading to a new class of turbulent state in burning plasmas. These processes cause the increase of the fluctuation amplitude over a wide range of wavenumbers and enhancement of both bulk plasma transport and energetic particle transport, so that the interaction is found to lead to unfavorable effects on the performance of burning plasmas
Summary
Study of plasma confinement is going to enter a new regime, that is, burning plasmas [1], which produce energetic alpha particles by the fusion reaction. DW mode through the geometrical damping effect These two processes, one in spectral space causing a large-scale structure and enhancing transport, while the other is in configuration space causing a damping of the dominant DW mode and reducing the transport, are not independent but coupled exhibiting synergistic interaction, leading to a new class of turbulent state in burning plasmas. These processes cause the increase of the fluctuation amplitude over a wide range of wavenumbers and enhancement of both bulk plasma transport and energetic particle transport, so that the interaction is found to lead to unfavorable effects on the performance of burning plasmas
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