Magnetohydrodynamic instabilities are responsible for geo- and astrophysical phenomena such as reversals of the geomagnetic field, sunspots, solar flares, and accretion disk dynamics. Two particular types of these instabilities were experimentally investigated in rotating spherical and cylindrical apparatus using the eutectic alloy GaInSn as a working fluid. The spherical apparatus, Hydromagnetic Experiment with Differentially Gyrating sphEres HOlding GaInSn (HEDGEHOG), was used to investigate the magnetised spherical Couette (MSC) flow for a range of the imposed axial magnetic field corresponding to Hartmann numbers of 0 to 40 and for a Reynolds number of 1000. A wave with an azimuthal wavenumber of 2 was observed at a Hartmann number of 0, which changed its azimuthal wavenumber to 3 at Hartmann numbers of 5 and 10. For Hartmann numbers between 10 and 22.5, the experimental flow displayed no temporal dependence, since the MSC flow was in its base state. In the remainder of the investigated range of Hartmann numbers, rotating waves with azimuthal wavenumbers of 2, 3, and 4 manifested, with some dependence on whether the Hartmann numbers were fixed or continuously varied. For the magnetised Taylor-Couette (MTC) flow investigated using the Potsdam ROssendorf Magnetic InStability Experiment (PROMISE), thermal convection was found to influence the azimuthal magnetorotational instability (AMRI) in two major ways. Firstly, it reduced the critical Hartmann number required for the onset of AMRI. Secondly, it broke the symmetry of the AMRI travelling waves so that they either travelled upwards or downwards depending on the direction of the radial heat flux.
| Identifer | oai:union.ndltd.org:DRESDEN/oai:qucosa:de:qucosa:93797 |
| Date | 25 October 2024 |
| Creators | Ogbonna, Jude |
| Contributors | Eckert, Kerstin, Hollerbach, Rainer, Stefani, Frank, Technische Universität Dresden |
| Source Sets | Hochschulschriftenserver (HSSS) der SLUB Dresden |
| Language | English |
| Detected Language | English |
| Type | info:eu-repo/semantics/publishedVersion, doc-type:doctoralThesis, info:eu-repo/semantics/doctoralThesis, doc-type:Text |
| Rights | info:eu-repo/semantics/openAccess |
| Relation | info:eu-repo/grantAgreement/European Research Council/European Union Horizon 2020 research and innovation programme/787544/ |
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