TY  - THES
U1  - Dissertation / Habilitation
A1  - Bohlin, Hannes
T1  - Global dynamics of magnetic reconnection in VINETA II
N2  - Magnetic reconnection is a fundamental plasma process where a change in field line connectivity occurs in a current sheet at the boundary between regions of opposing magnetic fields. In this process, energy stored in the magnetic field is converted into kinetic and thermal energy, which provides a source of plasma heating and energetic particles. Magnetic reconnection plays a key role in many space and laboratory plasma phenomena, e.g. solar flares, Earth’s magnetopause dynamics and instabilities in tokamaks. A new linear device (VINETAII) has been designed for the study of the fundamental physical processes involved in magnetic reconnection. The plasma parameters are such that magnetic reconnection occurs in a collision-dominated regime. A plasma gun creates a localized current sheet, and magnetic reconnection is driven by modulating the plasma current and the magnetic field structure. The plasma current is shown to flow in response to a combination of an externally induced electric field and electrostatic fields in the plasma, and is highly affected by axial sheath boundary conditions. Further, the current is changed by an additional axial magnetic field (guide field), and the current sheet geometry was demonstrated to be set by a combination of magnetic mapping and cross-field plasma diffusion. With increasing distance from the plasma gun, magnetic mapping results in an increase of the current sheet length and a decrease of the width. The control parameter is the ratio of the guide field to the reconnection magnetic field strength. Cross-field plasma diffusion leads to a radial expansion of the current sheet at low guide fields. Plasma currents are also observed in the azimuthal plane and were found to originate from a combination of the field-aligned current component and the diamagnetic current generated by steep in-plane pressure gradients in combination with the guide field. The reconnection rate, defined via the inductive electric field, is shown to be directly linked to the time-derivative of the plasma current. The reconnection rate decreases with increasing ratio of the guide field to the reconnection magnetic field strength, which is attributed to the plasma current dependency on axial boundary conditions and the plasma gun discharge. The above outlined results offer insights into the complex interaction between magnetic fields, electric fields, and the localized current flows during reconnection.
N2  - Die globale Dynamik der magnetischen Rekonnexion in VINETA II ist untersucht worden. Die magnetischen und elektrischen Felder und die Plasmaströme während magnetischer Rekonnexion wurden charakterisiert. Insbesondere wurde ihre Beeinflussung durch das magnetische Führungsfeld analysiert.
KW  - Magnetische Rekonnexion
KW  - Plasmaphysik
KW  - Plasma
KW  - Laborexperiment
KW  - Magnetfeld
KW  - Magnetfelddiagnostik
KW  - Magnetic reconnection
KW  - Plasma
KW  - Magnetic field diagnostics
KW  - Laboratory experiment
KW  - Magnetic fields
Y2  - 2014
U6  - https://nbn-resolving.org/urn:nbn:de:gbv:9-002125-8
UN  - https://nbn-resolving.org/urn:nbn:de:gbv:9-002125-8
ER  -