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Home > About us > Media > Archived news > 2020 > Make tokamak plasmas rotate by small axisymmetric magnetic disturbances

Make tokamak plasmas rotate by small axisymmetric magnetic disturbances

La rotation du plasma joue un rôle crucial dans le confinement de chaleur et de particules dans les tokamaks, y compris dans l’apparition du mode H de confinement amélioré.

Plasma rotation plays a crucial role on heat and particle confinement in tokamaks including the appareance of the H (high confinement) mode.

The classical equilibrium equation for tokamak plasma is the Grad-Shafranov equation, that neglects the plasma velocity and involves the pressure gradient although pressure is just a passive scalar and not an actuator. We must then go further to consider the issue of plasma velocity within a magnetohydrodynamic framework.

In the article just released Oueslati, Firpo, Physics of Plasmas 27, 102501 (2020), the axisymmetric steady states of the visco-resistive magnetohydrodynamic equations, including the non-linear (v.∇)v term, have been computed using the finite element method.

Playing on boundary conditions with external magnetic perturbations offers a way to break the natural up-down symmetry of the system and produce a net toroidal flow.

Using realistic parameters, some numerical results indicate that small perturbations of the magnetic configuration may be used to increase steady-state speeds and promote tokamak plasma confinement while preserving axisymmetry (which is a good way to prevent turbulence).

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Root-mean square toroidal and poloidal velocities in Alfven units as a function of the Hartmann number H. In a fusion burning tokamak plasma, H is expected to reach about 108.
The effect of a small disturbance of the magnetic configuration on the stationary toroidal velocity of a tokamak plasma at large H is visible by comparing the brown (with pertubation) and navy (without disturbance) curves. In the absence of disturbance, the toroidal velocity field is up-down antisymmetric. We clearly see that the disturbance breaks the symmetry and makes it possible to rotate the plasma much faster.

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