3D passive stabilization of n = 0 MHD modes in EAST tokamak

Abstract

Evidence is shown of the capability of non-axisymmetrical conducting structures in the Experimental Advanced Superconducting Tokamak (EAST) to guarantee the passive stabilization of the n = 0 MHD unstable mode. Suitable numerical modeling of the experiments allows a clear interpretation of the phenomenon. This demonstration and the availability of computational tools able to describe the effect of 3D conductors will have a huge impact on the design of future fusion devices, in which the conducting structures closest to plasma will be highly segmented.

Comparison of different linearized plasma response models on the EAST tokamak

“…A set of 58 shots has been considered in the present paper, which comprises 27 low confinement mode (L-mode) shots [10] corresponding to the old geometry of EAST and 31 shots referring to the new geometry, containing different L mode shots [11], high confinement mode (H-mode) shots and quasisnowflake (QSF) [13] divertor shots. In these shots, the feedback control of the vertical instability has been intentionally switched off at a given time instant, giving rise to a vertical displacement event (VDE), in which the plasma's axisymmetric vertical position evolves with an exponentially unstable behaviour.…”

“…In this paper, we will investigate with such tools the behavior of the experimental advanced superconducting tokamak (EAST) [9], which will be described in detail in the following section. Extensive work on this subject [10,11] has shown that a highly satisfactory agreement can be achieved with experimental results (in terms of the growth rate of vertical instability) with a linearized modelling including an accurate description of the 3D structures surrounding the plasma, while standard axisymmetric models have proved largely inadequate. Based on this positive result, it was also possible to find an equivalent two-dimensional (2D) model providing similar results in the range of our parameters of interest [12].…”

Whispering Gallery Effect in Relativistic Optics

“…An established branch of high-energy density laser-matter interaction physics combines geometrical and material properties of the targets used in order to absorb most of the laser energy and to redistribute it with the highest efficiency into directional electron or ion currents, shock waves, quasistatic fields, radiation, or other daughter effects. Several approaches have been already proved to be very efficient in terms of laser radiation absorption: nanoclusters [1,2], foams [3,4,5], structured targets [6,7,8,9], or more tricky setups [10]. There, a target design defines predominant channels for efficient energy deposition.…”

Disruptive plasma simulations in EAST including 3D effects

“…Figure 10 shows a pictorial representation of the plasma configuration, the halo current injected in the structure and the corresponding current density flowing in various parts of the conducting structures. The inherently 3D current density pattern, already reported in [15,17], is clearly represented.…”

“…Given the specific properties of this device, the three-dimensional (3D) features of the plasma facing components (PFCs) must be necessarily taken into account in disruption simulations, since the toroidally continuous conducting structures are relatively far from the plasma [15]. Indeed, a linearized version of the CarMa0NL code [16] has been utilized in the past to estimate the growth rate of VDEs in EAST [15,17,18] and demonstrated that 3D features must be necessarily considered to obtain reliable estimates. This peculiarity will be probably shared by future devices like DEMO [2].…”