Magnetic Humps Research Articles

Modification of Engineering Return-Stroke Models to Include Dispersion Effects

Recently, Baba and Ishii (see ibid., vol.44, p.476-7, Aug. 2002) have presented a method to modify the transmission-line (TL) type model to incorporate current distortion. In this brief, we generalize their method, as well as an exponential decay return stroke speed model, to simple engineering return-stroke models, and investigate the influence of dispersion effects on associated electromagnetic fields. Results show that the proposed modification to the models eliminates the inherent discontinuity in the traveling current source (TCS) model and the Bruce-Golde (BG) model at the upward-moving front. In addition, it turns out that an increase in the current risetime with height does not have significant effect on magnetic hump, electric ramp, and distant zero crossing, while a rapid decrease in return stroke speed with height could affect these features.

New Linked Mirrors

The conceptual project APEX (Adapted Plasma Experiment) is discussed. The APEX objective is the development of a physical foundations for the CW fusion reactor, created on a base of an alternative type of magnetic trap, which could provide a “tokamak scale” confinement time at much higher β. Linked mirrors are the prototypes of this heading. The main idea of DRACON trap – the short circuit secondary plasma currents inside the curve elements (CE) – is kept. The new principle of poloidal pseudosymmetry and the non-traditional scheme of MHD plasma stabilization by “magnetic hump” give a possibility of a new approach to reduce plasma losses.The APEX concept provides for the Experimental Pseudo SYmmetric Linked trap (EPSYLON) design. The whole installation will be have two axisymmetric mirror parts (OME) closed with two CEs. Each OME contains the diverter. CE should have a strongly rippled magnetic field. As far as each OME and each CE is a trap with mirror confinement it is possible to start an investigation of the system from separate experiments with different parts of the whole system. The EPSYLON construction will be adapted to the experimental results. The experiment with OME is chosen now as the first step of the program. The main objective of this first experiment is the investigation of the “magnetic hump” MHD stabilization produced by divertor. EPSILON-OME installation is discussed. The closed system calculations are going in parallel.

Equilibrium magnetic fields and currents in a nonaxisymmetric torus: external magnetic fields in stellarators

The three dimensional (3-D) and axisymmetric (2-D) magnetic fields produced by currents flowing in plasmas that are confined in stellarators with a nearly planar geometrical axis are investigated. Using the Green's function method to solve the 3-D linear equation derived previously, a simple procedure is presented here to determine the structure of plasma induced external magnetic fields in stellarators. A detailed numerical analysis of the values of the external 3-D magnetic fields and their dependences on the plasma profiles is performed. Analytical formulas are derived that could be useful for estimations. The possibility of using the measurements of these fields for the experimental identification of the magnetohydrodynamic (MHD) equilibria is considered. Also discussed are some interesting aspects of the influence of the magnetic hump on the value of the Pursch-Schluter currents (that appear in recent Heliotron-E experiments) and the influence of different features of the vacuum magnetic field on the dipole component of plasma induced field is classified. The results of calculations related to the modern experiments are presented, and the case that may be typical for future experiments is also considered

Equilibrium and Destruction of a REB in a Magnetic Guide

A REB with a relatively small ν/ γ (320 keV, 0.75 kA and 1.0 MeV, 1 kA) is injected into an axial magnetic guide in the injection system of ERA device of IPP-Nagoya. The beam surface envelope reveals an outstanding spatially periodic structure in the uniform field and the wave length and the REB parameters in the guide are found to be well consistent with the values predicted with a particular kind of the equilibrium model, proposed by Diament a few years ago. A rapid destruction of the REB during the passage through a magnetic hump and with an abrupt change of the surrounding metal wall radius is observed and discussed briefly.