Magnetic flux pumping in 3D nonlinear magnetohydrodynamic simulations

A self-regulating magnetic flux pumping mechanism in tokamaks that maintains the core safety factor at $q\approx 1$, thus preventing sawteeth, is analyzed in nonlinear 3D magnetohydrodynamic simulations using the M3D-C$^1$ code. In these simulations, the most important mechanism responsible for the flux pumping is that a saturated $(m=1,n=1)$ quasi-interchange instability generates an effective negative loop voltage in the plasma center via a dynamo effect. It is shown that sawtoothing is prevented in the simulations if $\beta$ is sufficiently high to provide the necessary drive for the $(m=1,n=1)$ instability that generates the dynamo loop voltage. The necessary amount of dynamo loop voltage is determined by the tendency of the current density profile to centrally peak which, in our simulations, is controlled by the peakedness of the applied heat source profile.Comment: submitted to Physics of Plasmas (23 pages, 15 Figures

Non-linear Simulations of MHD Instabilities in Tokamaks Including Eddy Current Effects and Perspectives for the Extension to Halo Currents

The dynamics of large scale plasma instabilities can strongly be influenced by the mutual interaction with currents flowing in conducting vessel structures. Especially eddy currents caused by time-varying magnetic perturbations and halo currents flowing directly from the plasma into the walls are important. The relevance of a resistive wall model is directly evident for Resistive Wall Modes (RWMs) or Vertical Displacement Events (VDEs). However, also the linear and non-linear properties of most other large-scale instabilities may be influenced significantly by the interaction with currents in conducting structures near the plasma. The understanding of halo currents arising during disruptions and VDEs, which are a serious concern for ITER as they may lead to strong asymmetric forces on vessel structures, could also benefit strongly from these non-linear modeling capabilities. Modeling the plasma dynamics and its interaction with wall currents requires solving the magneto-hydrodynamic (MHD) equations in realistic toroidal X-point geometry consistently coupled with a model for the vacuum region and the resistive conducting structures. With this in mind, the non-linear finite element MHD code JOREK has been coupled with the resistive wall code STARWALL, which allows to include the effects of eddy currents in 3D conducting structures in non-linear MHD simulations. This article summarizes the capabilities of the coupled JOREK-STARWALL system and presents benchmark results as well as first applications to non-linear simulations of RWMs, VDEs, disruptions triggered by massive gas injection, and Quiescent H-Mode. As an outlook, the perspectives for extending the model to halo currents are described.Comment: Proceeding paper for Theory of Fusion Plasmas (Joint Varenna-Lausanne International Workshop), Varenna, Italy (September 1-5, 2014); accepted for publication in: to Journal of Physics: Conference Serie

Electron acceleration in a JET disruption simulation

Runaways are suprathermal electrons having sufficiently high energy to be continuously accelerated up to tens of MeV by a driving electric field [1]. Highly energetic runaway electron (RE) beams capable of damaging the tokamak first wall can be observed after a plasma disruption [2]. Therefore, it is of primary importance to fully understand their generation mechanisms in order to design mitigation systems able to guarantee safe tokamak operations. In a previous work, [3], a test particle tracker was introduced in the JOREK 3D non-linear MHD code and used for studying the electron confinement during a simulated JET-like disruption. It was found in [3] that relativistic electrons are not completely deconfined by the stochastic magnetic field taking place during the disruption thermal quench (TQ). This is due to the reformation of closed magnetic surfaces at the beginning of the current quench (CQ). This result was obtained neglecting the inductive electric field in order to avoid the unrealistic particle acceleration which otherwise would have happened due to the absence of collision effects. The present paper extends [3] analysing test electron dynamics in the same simulated JET-like disruption using the complete electric field. For doing so, a simplified collision model is introduced in the particle tracker guiding center equations. We show that electrons at thermal energies can become RE during or promptly after the TQ due to a combination of three phenomena: a first REs acceleration during the TQ due to the presence of a complex MHD-induced electric field, particle reconfinement caused by the fast reformation of closed magnetic surfaces after the TQ and a secondary acceleration induced by the CQ electric field

Assessment of Alternative Energy/Environment Futures for Austria, 1977-2015: An Executive Summary

This report was prepared to complement a presentation made October 25, 1977 at IIASA. The presentation, titled "An Executive Briefing Session", was designed to present the final results of a thirteen-month study of the Austrian Energy/Environment System to leaders in Austrian government, industry, and science. This written documentation of the results (of which a German translation is also available) presents in a brief form the final conclusions of this study. The study results provide a comprehensive spatial and sectoral description of Austrian energy consumption, and examine alternative energy and environmental policy strategies. This report, however, is only a summary and a more complete description will appear in Research Report form in 1978

Assessment of Alternative Energy/Environment Futures for Austria: 1977-2015

The Austrian Regional Energy/Environment Study is the fourth in a series of IIASA studies on regional energy and environmental systems. The regions studied previously were the German Democratic Republic, the Rhone-Alpes Region in France and the state of Wisconsin in the U.S.A. The Austrian case study, regional in scope, complements the work of the IIASA Energy Systems Program which focuses primarily on global aspects of energy. This report presents the major results of the l5-month, Austrian case study, which examines alternative energy futures and strategies for Austria and some of their environmental implications. A secondary objective is the development of appropriate concepts and methods for energy/environment management and policy design in Austria

Assessment of Alternative Energy/Environment Futures for Austria 1977-2015: Final Summary Report

This study had two primary objectives: (1) To examine alternative energy futures and strategies for Austria and to consider some of their environmental implications. (2) To investigate and apply appropriate concepts and . methodologies for energy/environment management and policy design in Austria. The establishment of these objectives was based upon the conviction that in Austria, as in most regions and nations of the world, there is an urgent need for the development and application of methods for studying regional energy systems and for testing the impact of alternative policies. In view of the major role which energy plays in the determination of environmental quality, this study was designed to aid in the integration of energy and environmental management from a systems perspective. "Regional," in the context of our previous studies, is not strictly defined as subnational or as a specific class of geographic units; rather, it refers to a region, appropriately bounded so that it is possible to speak of energy and environmental systems from a physical, socioeconomic, or administrative perspective, or from all three. At the beginning of this study, we intended to limit its scope to a selected few Austrian Lander (states); we quickly realized that Austria's size and vigorous interregional links precluded anything less than a national study

Three-dimensional non-linear magnetohydrodynamic modeling of massive gas injection triggered disruptions in JET

JOREK 3D non-linear MHD simulations of a D2 Massive Gas Injection (MGI) triggered disruption in JET are presented and compared in detail to experimental data. The MGI creates an overdensity that rapidly expands in the direction parallel to the magnetic field. It also causes the growth of magnetic islands (m=n ¼ 2=1 and 3/2 mainly) and seeds the 1/1 internal kink mode. O-points of all island chains (including 1/1) are located in front of the MGI, consistently with experimental observations. A burst of MHD activity and a peak in plasma current take place at the same time as in the experiment. However, the magnitude of these two effects is much smaller than in the experiment. The simulated radiation is also much below the experimental level. As a consequence, the thermal quench is not fully reproduced. Directions for progress are identified. Radiation from impurities is a good candidate.EURATOM 63305