Untersuchungen der Plasmarandschichtstruktur im Tokamak TEXTOR-94 mittels der Heliumdiagnostik
Untersuchungen der Plasmarandschichtstruktur im Tokamak TEXTOR-94 mittels der Heliumdiagnostik
The investigation of plasma-surface-interaction plays a significant role in high temperatureplasma research. The problem of energy and particle exhaust is of great importancefor a future fusion reactor. The knowledge about the plasma edge parameter is fundamentalfor the understanding of the relevant...
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Personal Name(s): | Lehnen, Michael (Corresponding author) |
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Contributing Institute: |
Publikationen vor 2000; PRE-2000; Retrocat |
Imprint: |
Jülich
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag
2000
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Physical Description: |
II, 117 p. |
Document Type: |
Report Book |
Research Program: |
ohne Topic |
Series Title: |
Berichte des Forschungszentrums Jülich
3835 |
Link: |
OpenAccess OpenAccess |
Publikationsportal JuSER |
The investigation of plasma-surface-interaction plays a significant role in high temperatureplasma research. The problem of energy and particle exhaust is of great importancefor a future fusion reactor. The knowledge about the plasma edge parameter is fundamentalfor the understanding of the relevant physical processes.The aim of the present work is to analyse the plasma edge structure in the tokamakTEXTOR-94 and to give a correlation between the edge parameters and the predefineddischarge parameters as well as to investigate the transport mechanisms in the plasmaedge. A comparison of the experimental findings with a one-dimensional analytic modeland the results of two-dimensional numerical calculations using the fluid-code TECXYshows the importance of drift motions and particle sources for the spatial distribution ofthe plasma edge parameters.Radial profiles of the electron density and temperature in the edge are obtained byspectroscopic observation of a thermal Helium beam injected at three different poloidalpositions: at both sides of the toroidal belt limiter, i.e. at the outer side and at thebottom of the circular plasma in TEXTOR-94, as well as on the inner side. Additionallya measurement of the poloidal ion velocity and temperature has been possible with thehelium beam diagnostic at the outer position by the use of charge exchange processes.The drift motions due to electrical fields and pressure gradients in the plasma edgehave strong influence on the radial and poloidal density distribution. Radial drifts lead toan increase respectively a decrease of the density gradients, depending on the drift orientation. Poloidal drifts change in a complex manner the parallel transport and thus lead toan asymmetric density distribution along the field lines. An increase of the heating poweror a decrease of the pitch angle of the magnetic field lines causes a higher asymmetry. Theexistance of two poloidal counter-rotating layers is proven by the velocity measurementsof C$^{6+}$. An inversion of the magnetic fields leads to an inversion of the drift motions andis therefore a tool to investigate the effects caused by the drifts. The measurements show,that the particle source distribution in the plasma edge has strong influence on the radialdensity profiles. In high density discharges a local maximum of the density is observed inthe vicinity of the main limiter due to the ionisation of neutral particles. The outboarddensity in such a discharge is twice as high as at the inner position. The measurementsof the radial decay length indicate, that the plasma edge of TEXTOR-94 is a region ofsignificant ionisation in high density discharges.The investigations presented here show, that drift motions and particle sources mustnot be neglected in the description of the plasma edge. This is especially true for theestimation of transport coefficients or the observation of local processes nearby the wallsurface. |