TY - JOUR

T1 - Nonlinear trapping in the bounce-Transit and drift resonance and neoclassical toroidal plasma viscosity in tokamaks

AU - Shaing, K. C.

AU - Garcia-Munoz, M.

AU - Viezzer, E.

N1 - Publisher Copyright:
© 2020 IAEA, Vienna.

PY - 2020

Y1 - 2020

N2 - Bounce-Transit and drift resonance is one of the resonances in tokamaks with broken toroidal symmetry. It plays an important role in the wave-particle interactions. The nonlinear consequence of the resonance is the nonlinear particle trapping in the magnetic well, created by the radial drift motion resulting from the perturbed magnetic fields. These nonlinearly trapped particles form superbananas. When the effective collision frequency is less than the bounce frequency of the superbananas, the resonance is resolved by the nonlinear orbits. The transport theory for the superbananas is developed by solving the drift kinetic equation using the Eulerian approach. The neoclassical toroidal plasma viscosity, and the non-Axisymmetric transport coefficients have a scaling, which can be significant even for weakly perturbed tokamaks. Here, is the collision frequency, r is the minor radius, is the typical magnitude of the perturbed magnetic field strength, B is the equilibrium magnetic field strength, and U is a function of the magnetic shear parameter, mode numbers, and with being the poloidal gyro-radius. The magnitude of the energy flux can be comparable to that of the axisymmetric tokamaks for energetic alpha particles when ∼ 0.1. Thus, the theory sets a maximum magnitude of the tolerable perturbed magnetic field strength in fusion reactors, when nonlinear trapping is significant.

AB - Bounce-Transit and drift resonance is one of the resonances in tokamaks with broken toroidal symmetry. It plays an important role in the wave-particle interactions. The nonlinear consequence of the resonance is the nonlinear particle trapping in the magnetic well, created by the radial drift motion resulting from the perturbed magnetic fields. These nonlinearly trapped particles form superbananas. When the effective collision frequency is less than the bounce frequency of the superbananas, the resonance is resolved by the nonlinear orbits. The transport theory for the superbananas is developed by solving the drift kinetic equation using the Eulerian approach. The neoclassical toroidal plasma viscosity, and the non-Axisymmetric transport coefficients have a scaling, which can be significant even for weakly perturbed tokamaks. Here, is the collision frequency, r is the minor radius, is the typical magnitude of the perturbed magnetic field strength, B is the equilibrium magnetic field strength, and U is a function of the magnetic shear parameter, mode numbers, and with being the poloidal gyro-radius. The magnitude of the energy flux can be comparable to that of the axisymmetric tokamaks for energetic alpha particles when ∼ 0.1. Thus, the theory sets a maximum magnitude of the tolerable perturbed magnetic field strength in fusion reactors, when nonlinear trapping is significant.

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U2 - 10.1088/1741-4326/ab7595

DO - 10.1088/1741-4326/ab7595

M3 - Article

AN - SCOPUS:85082853118

SN - 0029-5515

VL - 60

JO - Nuclear Fusion

JF - Nuclear Fusion

IS - 5

M1 - 056002

ER -