Material migration in tokamak plasmas with a three-dimensional boundary
Material migration in tokamak plasmas with a three-dimensional boundary
In this work, the influence of a 3D boundary induced by resonant magnetic perturbations (RMPs) on the material migration, i.e. the erosion from wall material due to theplasma surface interaction and the transport of these impurities is investigated for the first time. With applied RMPs two new domai...
Saved in:
Personal Name(s): | Laengner, Ruth (Corresponding author) |
---|---|
Contributing Institute: |
Plasmaphysik; IEK-4 |
Published in: | 2013 |
Imprint: |
Jülich
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag
2013
|
Physical Description: |
vi, 140, XVII S. |
Dissertation Note: |
Dissertation, Heinrich-Heine-Universität Düsseldorf, 2013 |
ISBN: |
978-3-89336-924-9 |
Document Type: |
Book Dissertation / PhD Thesis |
Research Program: |
Tokamak physics for ITER and beyond |
Series Title: |
Schriften des Forschungszentrums Jülich Reihe Energie & Umwelt / Energy & Environment
198 |
Subject (ZB): | |
Link: |
OpenAccess |
Publikationsportal JuSER |
In this work, the influence of a 3D boundary induced by resonant magnetic perturbations (RMPs) on the material migration, i.e. the erosion from wall material due to theplasma surface interaction and the transport of these impurities is investigated for the first time. With applied RMPs two new domains occur in the magnetic field structure.Three dimensional SOL flux tubes with predominantly transport parallel to short magnetic field lines and a region of longer stochastic field lines with diffusive gradient driven radial transport. The plasma wall interaction and the material transport in these domains were investigated. A globally higher radial electric field E$_{r}$ as well as local changes in the magnetic field structure such as pressure driven sonic flows or locally higher Er fields can potentially in influence the material transport with applied RMPs. The experiments were performed at the tokamak TEXTOR, the RMPs were induced by the dynamic ergodic divertor (DED). The plasma discharges and DED application was chosen to have a spatially separated 3D structure to be able to investigate the underlying physics. Two spherical carbon test limiters were positioned in different poloidal and toroidal positions which allowed to analyse the material migration in a 3D SOL flux tube and a stochastic region at the same time. Methane doped with 13$^{C}$ was injected through the test limiters during three different plasma scenarios, without RMPs, with static RMPs and an RMP sweep. The test limiters and the injected methane were monitored in situ with different cameras and spectrometers. The deposition of the injected particles was measured post mortem by colourimetry, nuclear reaction analysis and secondary ion mass spectrometry. The most profound change from no RMP to the RMP cases is a 90$^{\circ}$ re-direction of the low ionised carbon C$^{+}$ and C$^{2+}$ into the E$_{r}$xB-drift direction. From a comparison of the experiments and numerical field line tracing it was found that this is a global effect occurring in both 3D domains during applied RMPs. Modelling with the impurity tracing and plasma wall interaction code ERO supports a 2-3 times higher radial electric field at the test limiter positions compared to the unperturbed boundary. Local changes from the plasma geometry do not play a role. Post mortem analysis reveals that the deposition pattern is less in uenced by the higher E$_{r}$xB-drift. ERO modelling shows that the pattern is formed by CH$^{+}_{4}$ and CH$^{+}_{3}$ . Due to the higher mass of the molecules a re-direction is strongly localised close to the injection location. Fist estimations on the material migrationin divertor machines indicate a high potential of RMPs to change the net-deposition in future fusion devices such as ITER. Furthermore, the local deuterium retention increased by a factor of 2-2.4 during RMPs due to a decrease in the surface temperature. Independent from the RMP application, the local deposition efficiency of the injected particles was more than a factor of 10 higher for test limiters with high surface temperatures T$_{surf} \approx$ 2700$^{\circ}$C compared to lower temperatures. A reason for this can be an easier binding of the injected particles to the surface as it is less stable close to the sublimation temperature. |