(BSc/MSc) Measurement of electron-temperature dynamics in TJ-K plasmas
Turbulent heat transport in magnetized plasmas is co-determined by temperature fluctuations. In order to quantitatively record the dynamics in the electron temperature, a triple probe diagnostics is to be set up and tested. The evaluation for temperature fluctuations is carried out according to the literature. The measured time series are examined for statistical or turbulent properties. Of particular interest is the correlation between fluctuations in temperature and density. This is analyzed depending on the radial position.
(BSc/MSc) OML extension for analyses of probe characteristics
Previous evaluations of the probe characteristics at TJ-K are based on the theory of ideal probes. This way, a robust estimate of the electron temperature is possible, but absolute values of the plasma density are too vague due to non-saturating currents at high probe bias. An improvement could be achieved by utilizing the so-called OML theory. This is to be tested for TJ-K plasmas. Density measurements from interferometry are used for comparison.
(BSc/MSc) Power distribution over turbulence scales
In turbulent flows, the power in the turbulent fluctuations follows a typical spectral distribution. In order to determine a wavenumber spectrum (k-spectrum), extensive simultaneous measurements of the fluctuating variables are necessary. The so-called pseudo-k method allows the estimation of wavenumber spectra from simpler two-point measurements. Using plasma fluctuation measurements with multi-probe arrays at TJ-K, pseudo-k spectra are examined for comparability with real wavenumber spectra.
(BSc/MSc) PIC simulation of electrostatic waves in TJ-K plasmas
A variety of waves exist in a plasma. This work deals with electrostatic and electromagnetic waves in a plasma and how they can be coupled. The free PIC code EPOCH is meant to be used for these investigations. For this purpose, it is necessary to make adjustments to the input parameters of the program such that it represents the plasma in the TJ-K stellarator. Furthermore, the propagation of electrostatic waves over a wide range of plasma parameters (magnetic field, heating power, plasma density) will be studied.
(BSc oder MSc) Effect of plasma density fluctuations on wave coupling
Plasma density fluctuations can deflect a microwave beam injected into a plasma and on average lead to a broadening of the beam. The effect on the coupling processes of electromagnetic with electrostatic waves is to be quantified with a code available at the institute. Thereby, the fluctuation amplitude, its spatial localization as well as the correlation length (average structure size) shall be varied. Finally, the results are to be transferred to existing experiments in order to estimate the degradation of the coupling efficiency there.