Turbulence in closed field line configurations

Figure showing the TORPEX configuration with the wire

In fusion oriented devices, a deeper understanding of particle, momentum and heat transport in the core region with closed flux surfaces and in the Scrape-Off Layer (SOL) is required. In TORPEX, to study plasma turbulence and instabilities in magnetic configurations closer to that of a tokamak, a poloidal magnetic field must be included. A toroidal in-vessel copper conductor was developed and installed on TORPEX to generate the required poloidal magnetic field component with the current flowing through it. On the left, a picture of the system installed in the middle of the TORPEX vacuum chamber is shown. One of the junctions joining the four toroidal copper arcs forming the toroidal conductor is indicated, as well as one vertical and lateral support to keep the it suspended inside the vacuum vessel [Fasoli NF 2013].

Backgrounds profiles

The inclusion of a poloidal magnetic field changes the plasma shape as can be see in the lower figure, where time-averaged data are provided in the presence and without the poloidal component. During the current flat-top the plasma density peaks in the region of higher poloidal magnetic field close to the toroidal conductor, forming regions of almost constant density along the flux surfaces. The white arrows correspond to the simulated magnetic field lines. Background plasma parameters, including electron density, temperature and plasma potential, have been fully characterized in a configuration with closed flux surfaces, produced by 900A of current flowing in the toroidal wire.

Figure showing k-spectrum

Plasma fluctuations

In order to understand the basic physical driving mechanisms of plasma instabilities and turbulence, spectral characterization of dominant coherent modes is performed and compared to the numerical studies of the SPC theory group. The movie on the bottom shows conditionally sampled data of fluctuating electron density [Avino PoP 2014].

Figure showing fast camera movie