Dokument: A Study of Edge Localized Mode Control with Resonant Magnetic Perturbation Fields
| Titel: | A Study of Edge Localized Mode Control with Resonant Magnetic Perturbation Fields | |||||||
| URL für Lesezeichen: | https://docserv.uni-duesseldorf.de/servlets/DocumentServlet?id=27595 | |||||||
| URN (NBN): | urn:nbn:de:hbz:061-20131111-103923-3 | |||||||
| Kollektion: | Dissertationen | |||||||
| Sprache: | Englisch | |||||||
| Dokumententyp: | Wissenschaftliche Abschlussarbeiten » Dissertation | |||||||
| Medientyp: | Text | |||||||
| Autor: | Dr. Pearson, Jonathan [Autor] | |||||||
| Dateien: |
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| Stichwörter: | Plasma Phyics, Tokamak | |||||||
| Dewey Dezimal-Klassifikation: | 500 Naturwissenschaften und Mathematik » 530 Physik | |||||||
| Beschreibung: | Edge-localized modes (ELMs) cause fast quasi-periodic collapses of a magnetically confined plasma edge, resulting in a loss of energy confinement and an increase in the radial transport. These events can lead to large transient heat and particle loads on the plasma facing components as well as reducing the pedestal energy confinement by ~10-20%. However, it should be noted that these events also act to clean the plasma of impurities. Hence, a complete physical understanding of the ELM, and how to control such events, is required for future magnetically confined fusion devices. The application of resonant magnetic perturbations (RMPs) to a plasma is one such control mechanism which has been shown to be able to mitigate or even suppress the ELMs. However, the exact mechanism behind these observations, and how to optimise this technique for future devices, is still under debate and forms an important topic of present fusion research.
This study will contribute to this field by investigating the effect of RMPs on ELMs through both modelling, using a unique current relaxation model, and experiments on the JET and TEXTOR tokamaks. The current relaxation model represents an ELM driven by a set of peeling modes, which are current driven modes highly localized at the edge of the plasma as predicted in ideal magneto-hydrodynamics. The model is formulated and implemented in order to focus on the effects of changes in the current density and edge safety factor on the ELM behaviour. This model is chosen due to a high dependence of the ELMs on the edge safety factor, which is a known feature of peeling modes. On TEXTOR, the dynamic ergodic divertor is extensively used in this study to investigate the influence of rotating RMPs, especially looking at differences between alternative phases of the applied fields. A previous observation from JET, of a multi-resonance in the dependence of ELM frequency on the edge safety factor when RMPs are applied, is thoroughly investigated and compared to similar experiments on TEXTOR. This highlights the similarities and differences of the influence of RMPs on ELMs across the two machines, indicating what mechanism is present. It is found that the current relaxation model can explain certain features of ELM control, including the multi-resonant dependence observed on JET and new observations on TEXTOR. The agreement comes when the edge current density is decreased allowing the term associated with the distance from the plasma edge to the nearest rational surface to play an active role in the peeling mode stability. This leads to a new interpretation, which suggests that the dependence of the ELMs on the edge safety factor has three regimes dependent on the balance between the current density and position of the rational surface. These parameters are being affected by the plasma stability changing due to the application of the RMPs. It is also shown that the way the RMPs affect the stability depends on a wide range of parameters sensitive to the machine design and types of ELMs occurring. However, on both tokamaks investigated, it is concluded that the effect of RMPs on the edge transport is not the dominant mechanism for altering the ELM behaviour. It is observed that when the rotating RMPs are applied with a phase and frequency closest to the resonance condition for field penetration, a higher sensitivity on the plasma is seen. A Stronger influence in the ELM behaviour, and larger screening effects occur, when the RMP fields are applied close to this resonant condition. This condition strongly depends on the difference between the rotation frequency of the applied RMPs and the electron perpendicular rotation. These observations state that the ELM control is highly dependent on the peeling mode stability when the edge current density drops. This is due to a large decrease in the edge pressure decreasing the bootstrap current, thus allowing the plasma stability to move towards the peeling stability boundary. It is also stated that optimisation of the effect of RMPs is possible by choosing a phase and frequency which consider the resonant condition for the field penetration. | |||||||
| Lizenz: |  Urheberrechtsschutz | |||||||
| Fachbereich / Einrichtung: | Mathematisch- Naturwissenschaftliche Fakultät » WE Physik » Experimentalphysik Mathematisch- Naturwissenschaftliche Fakultät » WE Physik » Theoretische Physik | |||||||
| Dokument erstellt am: | 11.11.2013 | |||||||
| Dateien geändert am: | 11.11.2013 | |||||||
| Datum der Promotion: | 21.10.2013 |
