Topics in Magnetohydrodynamics

To understand plasma physics intuitively one need to master the MHD behaviors. As sciences advance, gap between published textbooks and cutting-edge researches gradually develops. Connection from textbook knowledge to up-to-dated research results can often be tough. Review articles can help. This book contains eight topical review papers on MHD. For magnetically confined fusion one can find toroidal MHD theory for tokamaks, magnetic relaxation process in spheromaks, and the formation and stability of field-reversed configuration. In space plasma physics one can get solar spicules and X-ray jets physics, as well as general sub-fluid theory. For numerical methods one can find the implicit numerical methods for resistive MHD and the boundary control formalism. For low temperature plasma physics one can read theory for Newtonian and non-Newtonian fluids etc

Physics through the 1990s: Plasmas and fluids

The volume contains recommendations for programs in, and government support of, plasma and fluid physics. Four broad areas are covered: the physics of fluids, general plasma physics, fusion, and space and astrophysical plasmas. In the first section, the accomplishments of fluid physics and a detailed review of its sub-fields, such as combustion, non-Newtonian fluids, turbulence, aerodynamics, and geophysical fluid dynamics, are described. The general plasma physics section deals with the wide scope of the theoretical concepts involved in plasma research, and with the machines; intense beam systems, collective and laser-driven accelerators, and the associated diagnostics. The section on the fusion plasma research program examines confinement and heating systems, such as Tokamaks, magnetic mirrors, and inertial-confinement systems, and several others. Finally, theory and experiment in space and astrophysical plasma research is detailed, ranging from the laboratory to the solar system and beyond. A glossary is included

Excitation of Alfvén waves in magnetized plasmas: the reversed-field pinch configuration case

In this thesis Alfven waves in different geometries are analyzed and characterized, comparing the theoretical models obtained from the ideal MHD model and the results of numerical simulations, performed with a non-linear 3D code, called SpeCyl. In particular, the configurations are analyzed with: uniform axial magnetic field and uniform density first and then a variable one; slightly variable magnetic filed, Tokamak-like, with uniform density; RFP-like magnetic field without the reversal of he field at the edge, with uniform density and various density profiles; finally, a realistic and dinamic RFP field, which evolves in time, with uniform and variable density. Thanks to the results obtained, the experimental spectra of the RFX-mod experiment, in which alfvenic fluctuations were observed in the discharges in the plasmas, were qualitatively compared and interpreted. The physical mechanism from which the experimentally observed Alfven waves originate and a possible identification between the observed and theoretical modes is provided: SAW, CAE, GAE

Magnetohydrodynamic stability analysis of the pedestals of ASDEX Upgrade plasmas

openThe high confinement mode (H-mode) dramatically improves the confinement properties of present tokamak plasmas and is therefore the scenario envisioned for future fusion reactors. The main characteristic of this scenario is the formation of a pedestal, a zone of steep temperature and density gradients, at the edge of the plasma, by means of a transport barrier. The height of the pedestal is limited by the onset of edge localised modes (ELMs), quasi-periodic explosive instabilities at the plasma edge which expel particles and energy on millisecond time-scales. While ELMs in present day machines pose no danger, when scaled to a fusion reactor device they are predicted to cause significant damage to the machine components. As such, the understanding and exploitation of alternative regimes with high confinement, but without ELMs, is of significant interest. The onset of an ELM can be described by magnetohydrodynamic (MHD) stability codes. The aim and project of the current thesis carried out at Max-Planck-Institut für Plasmaphysik (IPP) in Garching (Germany), involves the automation of a workflow which runs codes to test the pedestal MHD stability, such as MISHKA, starting from a standardised set of experimental information. In addition, the HELENA code is employed as a high resolution equilibrium solver through the calculation of the Grad-Shafranov equation for a toroidal axisymmetric plasma. Once the workflow is implemented, it is applied to a database of experimental data from the ASDEX Upgrade tokamak to study the properties of the pedestal through stability diagrams. It is particularly important to provide an estimate of the distance to the MHD stability boundary in the various ELM-free regimes to understand how robust these regimes are and the margin a given regime has before a large ELM is triggered. Various deuterium and helium plasma discharges are studied in this regard.The high confinement mode (H-mode) dramatically improves the confinement properties of present tokamak plasmas and is therefore the scenario envisioned for future fusion reactors. The main characteristic of this scenario is the formation of a pedestal, a zone of steep temperature and density gradients, at the edge of the plasma, by means of a transport barrier. The height of the pedestal is limited by the onset of edge localised modes (ELMs), quasi-periodic explosive instabilities at the plasma edge which expel particles and energy on millisecond time-scales. While ELMs in present day machines pose no danger, when scaled to a fusion reactor device they are predicted to cause significant damage to the machine components. As such, the understanding and exploitation of alternative regimes with high confinement, but without ELMs, is of significant interest. The onset of an ELM can be described by magnetohydrodynamic (MHD) stability codes. The aim and project of the current thesis carried out at Max-Planck-Institut für Plasmaphysik (IPP) in Garching (Germany), involves the automation of a workflow which runs codes to test the pedestal MHD stability, such as MISHKA, starting from a standardised set of experimental information. In addition, the HELENA code is employed as a high resolution equilibrium solver through the calculation of the Grad-Shafranov equation for a toroidal axisymmetric plasma. Once the workflow is implemented, it is applied to a database of experimental data from the ASDEX Upgrade tokamak to study the properties of the pedestal through stability diagrams. It is particularly important to provide an estimate of the distance to the MHD stability boundary in the various ELM-free regimes to understand how robust these regimes are and the margin a given regime has before a large ELM is triggered. Various deuterium and helium plasma discharges are studied in this regard

The JOREK non-linear extended MHD code and applications to large-scale instabilities and their control in magnetically confined fusion plasmas

JOREK is a massively parallel fully implicit non-linear extended magneto-hydrodynamic (MHD) code for realistic tokamak X-point plasmas. It has become a widely used versatile simulation code for studying large-scale plasma instabilities and their control and is continuously developed in an international community with strong involvements in the European fusion research programme and ITER organization. This article gives a comprehensive overview of the physics models implemented, numerical methods applied for solving the equations and physics studies performed with the code. A dedicated section highlights some of the verification work done for the code. A hierarchy of different physics models is available including a free boundary and resistive wall extension and hybrid kinetic-fluid models. The code allows for flux-surface aligned iso-parametric finite element grids in single and double X-point plasmas which can be extended to the true physical walls and uses a robust fully implicit time stepping. Particular focus is laid on plasma edge and scrape-off layer (SOL) physics as well as disruption related phenomena. Among the key results obtained with JOREK regarding plasma edge and SOL, are deep insights into the dynamics of edge localized modes (ELMs), ELM cycles, and ELM control by resonant magnetic perturbations, pellet injection, as well as by vertical magnetic kicks. Also ELM free regimes, detachment physics, the generation and transport of impurities during an ELM, and electrostatic turbulence in the pedestal region are investigated. Regarding disruptions, the focus is on the dynamics of the thermal quench (TQ) and current quench triggered by massive gas injection and shattered pellet injection, runaway electron (RE) dynamics as well as the RE interaction with MHD modes, and vertical displacement events. Also the seeding and suppression of tearing modes (TMs), the dynamics of naturally occurring TQs triggered by locked modes, and radiative collapses are being studied.Peer ReviewedPostprint (published version

High Energy Electron Confinement in a Magnetic Cusp Configuration

We report experimental results validating the concept that plasma confinement is enhanced in a magnetic cusp configuration when beta (plasma pressure/magnetic field pressure) is order of unity. This enhancement is required for a fusion power reactor based on cusp confinement to be feasible. The magnetic cusp configuration possesses a critical advantage: the plasma is stable to large scale perturbations. However, early work indicated that plasma loss rates in a reactor based on a cusp configuration were too large for net power production. Grad and others theorized that at high beta a sharp boundary would form between the plasma and the magnetic field, leading to substantially smaller loss rates. The current experiment validates this theoretical conjecture for the first time and represents critical progress toward the Polywell fusion concept which combines a high beta cusp configuration with an electrostatic fusion for a compact, economical, power-producing nuclear fusion reactor.Comment: 12 pages, figures included. 5 movies in Ancillary file