Investigation of sheath effects on interchange modes in TORPEX plasmas
The TORoidal Plasma EXperiment (TORPEX) at CRPP generates and confines plasmas in a magnetic configuration with open helical magnetic field lines, in which similarly to the SOL of magnetic fusion devices, grad B and magnetic field curvature are at play. In the high vertical magnetic field, Bz, scenario, interchange modes are observed with flute characteristics, k// = 0, and a global character in the perpendicular direction, growing on the largest allowed spatial scale. By further increasing Bz, sheath effects are found to affect strongly the properties of interchange modes, which develop into harmonics with broader spectra and smaller wavelengths. Low temperatures and densities of TORPEX plasmas permit high spatial and temporal resolution measurements over the entire plasma cross-section. These measurements are not achievable in typical fusion experiments. This configuration represents, therefore, a unique starting point to investigate the importance of the sheath in modifying interchange modes and related turbulence with unprecedented diagnostics capabilities. The goal of the present master work is to experimentally investigate how the sheath affects the linear and non-linear properties of interchange modes in TORPEX plasmas.