1,734,720 research outputs found
Sideways force due to coupled rotating kink modes in tokamaks
No full textThe possibility of generation of the rotating sideways force on the wall by the kink modes is analytically investigated. The approach is basically the same as that developed earlier in (Mironov and Pustovitov 2017 Phys. Plasmas 24 092508) for the locked modes, but now their rotation is allowed. Its main elements are ∂b/∂t ≠ 0 (described by the growth rate γ and angular rotation frequency ω of the magnetic perturbation b), resistive dissipation in the wall, and the requirement of zero sideways force on the plasma. These make the approach greatly different from those resulting in the so-called Noll's formula. The result is also different; it predicts a force an order of magnitude smaller. Nevertheless, such a force can be dangerous at the resonance frequency of the vacuum vessel. The derived relations show that the rotating force must be maximal at ωτ w = O(1), where τ w is the resistive wall time. For the faster modes it decreases roughly as ∼1/ω
On the computation of the disruption forces in tokamaks
No full textThe currents and forces induced in the tokamak vacuum vessel (wall) during the disruption are calculated for different values of wall resistivity. Several consequences and new developments are derived from the general result that the global disruption force acting on the perfectly conducting wall must be exactly opposite to the similar force acting on the plasma, which is inherently small in tokamaks. This theoretical prediction is tested and confirmed here for the ITER tokamak with disruption modelled as the fast thermal quench followed by slower current quench that develops into the vertical displacement event. The plasma is simulated by the evolutionary equilibrium code CarMa0NL. One of the results is that the computed integral force on a perfectly conducting wall is zero at each instant during a disruption. This in turn highlights the importance of having good models for the plasma (in which the equilibrium constraint is explicitly imposed) and for the structures (able to correctly describe the induced currents and the resistive effects). The dependence of the disruption force on the magnetic field penetration through the wall is demonstrated. Also the concept of a disruption force damper is proposed, able to 'absorb' a significant part of the force that would arise on a resistive wall during a disruption
Vornehmer v.d. Nation Ottowa
No full textVORNEHMER V.D. NATION OTTOWA
Vornehmer v.d. Nation Ottowa ( -
Alt Dresden. Frauenkirche v.d. Terrase
No full textALT DRESDEN. FRAUENKIRCHE V.D. TERRASE
Alt Dresden. Frauenkirche v.d. Terrase ( -
München // Karlsplatz v.d. Protest. Kirche gesehen
No full textMÜNCHEN // KARLSPLATZ V.D. PROTEST. KIRCHE GESEHEN
München // Karlsplatz v.d. Protest. Kirche gesehen ( -
Global forces on the COMPASS-U wall during plasma disruptions
No full textFirst, it is shown that during electromagnetic transients in COMPASS-U the poloidal field coils must drain sizeably the current from the vessel and, therefore, reduce disruption forces and their duration. Next, the role of poloidal eddy current (which is absent in some approaches) in the dynamics of vertical and radial forces is found to be essential. Finally, to verify the CarMa0NL modelling for COMPASS-U, the numerical results are cross-validated with general analytical predictions (Pustovitov 2015 Nucl. Fusion 55 113032): the computed vertical force on the tokamak wall is found to be almost zero during rapid ( jump-like) transients, as it should be because of strong skin-effect. This test proves the credibility of the simulation model and computational realization 2021 IAEA, Vienna
Magnetic Diagnostics: General Principles and the Problem of Reconstruction of Plasma Current and Pressure Profiles in Toroidal Systems
No full text"The restrictions of the magnetic diagnostics are discussed. Being related to the integral nature of the measurable quantities, they follow from the fundamental laws of electromagnetism. A series of particular examples demonstrating the strength of these restrictions is given and analyzed. A general rule is emphasized that the information obtained from external magnetic measurements is obviously insufficient for the reliable evaluation of plasma current and pressure profiles in tokamaks or in stellarators. The underlying reason is that outside the plasma the own field of the equilibrium plasma currents is determined by the boundary conditions on the plasma surface only."research repor
Suppression of Pfirsch-schluter Current by Vertical Magnetic Field in Stellarators
No full text"This article is devoted to the problem whether it is possible to make stellarator configuration insensitive to plasma pressure using external vertical magnetic field as a control parameter. Conventional stellarators with a planar circular axis are analyzed. It is shown that for these systems the condition of Pfirsch-Schluter current suppression can be formulated as a two-dimensional equation with all values expressed through the vacuum magnetic field only. The major advantage of this formulation is that it allows to solve the problem without solving equilibrium equations. It is used as a basis to show that complete suppression of Pfirsch-Schluter current by means of the vertical field is possible, in principle, either in shear-free systems or in stellarators with l geq 3. In l=2 stellarators with a shear it is possible to get significant reduction of the current and to suppress pressure-induced plasma column shift. This can be called an integral independence on beta in contrast to the true local independence in other cases. In all cases large inward shift of plasma column is necessary. It is out of operational range in all existing devices except Heliotron E. In recent experiments in Heliotron E the state ""integrally"" independent on beta was almost achieved. The present study was stimulated by this result."research repor
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