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Strauss H.R.,HRS Fusion | Paccagnella R.,CNR Institute of Ionized Gas | Breslau J.,Princeton Plasma Physics Laboratory
Physics of Plasmas | Year: 2010

Nonlinear simulations with the M3D code [W. Park, Phys. Plasmas 6, 1796 (1999)] are performed of disruptions produced by large scale magnetohydrodynamic instabilities. The toroidally asymmetric wall forces produced during a disruption are calculated in an ITER [T. Hender, Nucl. Fusion 47, S128 (2007)] model. The disruption is produced by a vertical displacement event and a kink mode. Expressions are derived for the wall force, including the sideways force, using a thin conducting wall model. The scaling of wall force with γ τw is obtained, where γ is the kink growth rate and τw is the wall penetration time. The largest force occurs with γ τw ≈1. A theory is developed of the wall force produced by kink modes. The theory is in qualitative agreement with the simulations and Joint European Torus [V. Riccardo, Nucl. Fusion 49, 055012 (2009)] experiments. In particular, the theory and simulations give dependence of the sideways on γ τw, correlation of sideways force with sideways plasma displacement, and correlation of toroidally varying plasma current with toroidally varying vertical displacement. © 2010 American Institute of Physics.

Strauss H.,HRS Fusion | Sugiyama L.,Massachusetts Institute of Technology | Paccagnella R.,CNR Institute of Ionized Gas | Breslau J.,Princeton Plasma Physics Laboratory | Jardin S.,Princeton Plasma Physics Laboratory
Nuclear Fusion | Year: 2014

Toroidal rotation can be produced by disruptions, as observed in several experiments. There is a concern that rotating asymmetric forces during an ITER disruption might resonate with the blanket and other structures surrounding the plasma. Here it is shown, both computationally using the M3D code, and analytically, that toroidal rotation is produced by magnetohydrodynamic turbulence. In particular, rotation is produced during an asymmetric vertical displacement event (AVDE) disruption. Toroidal and poloidal rotation are also produced during edge localized modes (ELMs), and may be consistent with a scaling law found for intrinsic toroidal rotation in H-mode tokamaks. © 2014 IAEA, Vienna.

Olofsson K.E.J.,KTH Royal Institute of Technology | Soppelsa A.,CNR Institute of Ionized Gas | Bolzonella T.,CNR Institute of Ionized Gas | Marchiori G.,CNR Institute of Ionized Gas
Control Engineering Practice | Year: 2013

Input-output datasets from two magnetic confinement fusion (MCF) experiments of the reversed-field pinch (RFP) type are examined. The RFP datasets, which are samples of the distributed magnetic field dynamics, are naturally divided into many smaller batches due to the pulsed-plasma operation of the experiments. The two RFP experiments considered are (i) EXTRAP T2R (T2R) with 64 inputs and 64 outputs and (ii) RFX-mod (RFX) with 192 inputs and 192 outputs. Both T2R and RFX are magnetohydrodynamically unstable and operates under magnetic feedback with optional dither injection. Using subspace system identification techniques and randomised cross-validation (CV) methods to minimise the generalisation error, state-space orders of the empirical systems are suggested. These system orders are compared to "stabilisation diagrams" commonly used in experimental modal analysis practice. The relation of the CV system order to the decay of the singular values from the subspace method is observed. Both (i) stable vacuum diffusion and (ii) unstable plasma response datasets are analysed. Apparent simulation and prediction errors are quantified for both cases using a deviation-accounted-for index. These results are purely data-driven. A simple approach towards exploitation of the subspace techniques for finite-element model refinement and data confrontation is presented. © 2013 Elsevier Ltd.

Bellan P.M.,Applied Materials | Paccagnella R.,CNR Institute of Ionized Gas
Physics of Plasmas | Year: 2015

The value of the safety factor on the magnetic axis of a finite-beta spheromak is shown to be a function of beta in contrast to what was used in Bellan, Phys. Plasmas 9, 3050 (2002); this dependence on beta substantially reduces the gradient of the safety factor compared to the previous calculation. The method for generating finite-beta spheromak equilibria is extended to generate equilibria describing toroidal magnetic "bubbles," where the hydrodynamic pressure on the magnetic axis is less than on the toroid surface. This "anti-confinement" configuration can be considered an equilibrium with an inverted beta profile and is relevant to interplanetary magnetic clouds as these clouds have lower hydrodynamic pressure in their interior than on their surface. © 2015 AIP Publishing LLC.

Paccagnella R.,CNR Institute of Ionized Gas
Physics of Plasmas | Year: 2014

This paper presents a model for an ohmically heated plasma in which a feedback exists between thermal conduction and transport, on one side, and the magneto-hydro-dynamical stability of the system, on the other side. In presence of a reconnection threshold for the magnetic field, a variety of periodical or quasi periodical oscillations for the physical quantities describing the system are evidenced. The model is employed to interpret the observed quasi periodical oscillations of electron temperature and perturbed magnetic field around the so called "Single Helical" state in the reversed field pinch, but its relevance for other periodical phenomena observed in magnetic confinement systems, especially in tokamaks, is suggested. © 2014 Euratom.

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