Turbulence at the boundary of toroidal plasmas with open and closed magnetic flux surfaces
Event details
| Date | 25.09.2015 |
| Hour | 10:30 › 11:30 |
| Speaker | Dr. Fabio Avino, CRPP-EPFL |
| Location |
PPB 019
|
| Category | Conferences - Seminars |
The control and confinement of fusion plasmas are currently limited by a lack of understanding of the physical mechanisms behind the evolution of the turbulent transport experienced by particles and energy. In-situ investigations of plasma turbulence is more accessible in basic plasma physics devices, with the possibility of rigorously validating numerical codes. One of these experiments is TORPEX, in which a comprehensive characterization of plasma turbulence has been conducted in the presence of open helical magnetic field lines in toroidal geometry. Closed magnetic flux surfaces can now be obtained by driving a current inside the toroidal conductor recently installed on TORPEX, which generates the required poloidal magnetic field. This allows studying plasma turbulence in magnetic geometries of increasing complexity. The simplest configuration of quasiconcentric flux surfaces is first explored, with a detailed spectral characterization of the measured electrostatic quasi-coherent fluctuations. Measurements of the toroidal and poloidal mode numbers reveal field-aligned modes. These present a poloidal localization indicating a clear ballooning feature that is in agreement with the results of a linear fluid code. The first experimental measurements of plasma blobs in the presence of a single-null X-point are performed. Blobs radially propagating outwards across the X-point are conditionally sampled, which allows us to track and analyze in detail the corresponding dynamics. The ExB drifts induced by the background potential gradients and the fluctuating potential dipole are both responsible for the measured blob acceleration in the X-point region. The contribution of the potential dipole is explained on the basis of an analytical model, in which the variation of the magnetic field intensity close to the X-point plays a key role. This results in a blob speed scaling that is in good agreement with the measured values.
Practical information
- Informed public
- Free
Organizer
- Prof. P. Ricci
Contact
- Prof. P. Ricci