Deuterium plasma discharges of the Divertor Tokamak Test facility (DTT) in different operational scenarios have been predicted by a comprehensive first-principle based integrated modelling activity using state-of-art quasi-linear transport models. The results of this work refer to the updated DTT configuration, which includes a device size optimisation (enlargement to R0 = 2.19 m and a = 0.70 m) and upgrades in the heating systems. The focus of this paper is on the core modelling, but special attention was paid to the consistency with the SOL parameters required to achieve divertor plasma detachment. The compatibility of these physics-based predicted scenarios with the electromagnetic coil system capabilities was then verified. In addition, first estimates of DTT sawteeth and of DTT ELMs were achieved.
Axisymmetric modes in shaped tokamak plasmas are normally associated with vertical displacement events. However, not enough attention has been given to the fact that these modes can be resonant in two different ways. Firstly, for a plasma bounded by a divertor separatrix, a generic n=0 ideal-MHD perturbation, ξ, is singular at the divertor X-point(s), where Beq · ∇ξ = 0, with Beq
the equilibrium magnetic field. As a consequence, n=0 perturbations can give rise to current sheets localized along the divertor separatrix. Secondly, a feedback-stabilized n=0 mode tends to acquire an Alfvénic oscillation frequency. As a result, a resonant interaction with energetic particle orbits can lead to a new type of fast ion instability.
A new type of fast particle instability involving axisymmetric modes in magnetic fusion tokamak plasmas is presented. The relevant dispersion relation involves three roots. One corresponds to a vertical plasma displacement that, in the absence of active feedback stabilization, grows on the wall resistivity time scale. The other two, oscillating close to the poloidal Alfv ́en frequency, are normally damped by wall resistivity. The resonant interaction with fast ions can drive the oscillatory roots unstable. Resonance conditions, stability thresholds and experimental evidence are discussed.
Vertical displacement normal modes in shaped tokamak plasmas are studied analytically, based on the reduced ideal-magnetohydrodynamic model. With the help of quadratic forms, and using the appropriate eigenfunction for vertical displacements with toroidal mode number
$n=0$
and dominant elliptical-angle mode number
$m=1$
, a dispersion relation is derived, including the effects of ideal or resistive walls through a single parameter,
$D_w(\gamma )$
, which is, in general, a function of the complex eigenfrequency
$\gamma = -{\rm i}\omega$
. For the resistive-wall case, the dispersion relation is cubic in
$\gamma$
. One root corresponds to the well-known, non-rotating resistive-wall vertical mode, growing on the resistive-wall time scale. The other two roots are weakly damped by wall resistivity, but oscillate with a frequency below the poloidal Alfvén frequency, which makes them immune to continuum damping, but subject to possible instability due to resonant interaction with fast ions.
Recent progress on the understanding of axisymmetric pertubations in tokamak plasmas is presented, with particular attention on Vertical Displacement Oscillatory Modes (VDOM) that can be driven unstable by their resonance with fast ion orbits, and on the impact of divertor X-points on the stability of vertical displacements.
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