Abstract
Studying stationary regimes with high plasma confinement in a tokamak with reactor technologies (TRT) [1] involves calculating the plasma stability taking into account the influence of the current density profiles and pressure gradient in the pedestal near the boundary. At the same time, the operating limits should be determined by the parameters of the pedestal, which, in particular, are set by the stability limit of the peeling–ballooning modes that trigger the peripheral disruption of edge localized modes (ELM). Using simulation of the quasi-equilibrium evolution of the plasma by the ASTRA and DINA codes, as well as a simulator of magnetohydrodynamic (MHD) modes localized at the boundary of the plasma torus based on the KINX code, stability calculations are performed for different plasma scenarios in the TRT with varying plasma density and temperature profiles, as well as the corresponding bootstrap current density in the pedestal region. At the same time, experimental scalings for the width of the pedestal are used. The obtained pressure values are below the limits for an ITER-like plasma due to the lower triangularity and higher aspect ratio of TRT plasma. For the same reason, the reversal of magnetic field shear in the pedestal occurs at a lower current density, which causes the instability of modes with low toroidal wave numbers and reduces the effect of diamagnetic stabilization.
Highlights
The high plasma-confinement mode (H-mode), the regime with a high energy-confinement time in tokamak plasma, is accompanied by the formation of a transport barrier in the outer region of the plasma near the separatrix: improvement in confinement is associated with the pedestal height, i.e., the amount of pressure at the boundary of the transport barrier, which is an area with reduced transport coefficients
The peeling–ballooning modes are ideal magnetohydrodynamic (MHD) instabilities caused by large pressure gradients and the corresponding bootstrap current in the region of the transport barrier near the plasma boundary
The stability limits of such modes in the “pressure gradient–current density” plane greatly depend on the shape of the plasma, and the trajectory in this plane, along which the pedestal parameters evolve, depends on the plasma collisionality parameter ν* [2, 3]
Summary
The H-mode, the regime with a high energy-confinement time in tokamak plasma, is accompanied by the formation of a transport barrier in the outer region of the plasma near the separatrix: improvement in confinement is associated with the pedestal height, i.e., the amount of pressure at the boundary of the transport barrier, which is an area with reduced transport coefficients. Limitations on the height of the pedestal are based on the assumption that the peeling–ballooning modes, localized at the plasma boundary, are the triggering mechanism for the development of ELM. The peeling–ballooning modes are ideal magnetohydrodynamic (MHD) instabilities caused by large pressure gradients and the corresponding bootstrap current in the region of the transport barrier near the plasma boundary. Conclusions are made about the operating limits of TRT plasma
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