Behaviour of electron density profiles and particle transport analysis in the RFX reversed field pinch

Abstract

Density profiles measured in RFX by a 13 chord mid-infrared (MIR) interferometer are found to be flat or hollow. Density gradients are large only in a region typically of the order of 2 to 4 cm from the edge. A detailed investigation of the form of the electron density profile during the current flat-top phase in different experimental conditions has been performed. The shape of the profile seems to depend only on the I/N (plasma current/line density) parameter, varying from flat or slightly peaked at high I/N to clearly hollow at low I/N. The systematic existence of stationary hollow density profiles implies the presence of an outward directed fluid velocity. A one dimensional (1-D) particle transport code has been used to simulate the profile behaviour in order to obtain quantitative information on the form of the diffusion coefficient and of the `anti-pinch' velocity. The results are compatible with a transport mechanism based on parallel transport along stochastic magnetic field lines in a large part of the plasma core region. In this framework, the apparent anti-pinch term would be driven by the temperature gradient.

Nonlocal Transport in the Reversed Field Pinch

“…Experimentally the pinch is large close to the particle sources and directed against the density gradient [13][14][15], showing a similarity with our simple case. The reduction of magnetic chaos is crucial in reducing D and cancelling the pinch: this happens e.g.…”

“…This has given support to the application of this formalism to the empirical transport coefficients found in experiments [13][14][15].…”

“…where D and v are fit to observed transport in tokamaks [9][10][11][12] and reversed-field pinches (RFP) [13][14][15]. By making a detailed study of ion transport in the RFX we have found a link between pinch velocity and a magnetic chaotic topology [16].…”

Feasibility of electron Bernstein wave coupling via O-X-B mode conversion in the RFX-mod reversed field pinch device

“…Typical values of L B are shown in Fig. (1), whereas L n in RFX is approximately 2 cm for I p up to 0.8 MA [21]. In Fig.…”

A statistical analysis of pulsed poloidal current drive in the Reversed Field eXperiment

“…[2][3][4] In the MH regime, magnetic fluctuations are nonetheless detrimental to confinement: They cause magnetic chaos in the plasma core, [5][6][7] which allows for an enhanced particle and energy transport. 8,9 This might not be the case in the single helicity ͑SH͒ regime, when a single mϭ1 mode takes place, therefore, allowing for a more laminar ͑and less turbulent͒ dynamo mechanism. 10,11 The reduction of the energy transport associated to the magnetic fluctuations is one of the major tasks of RFP research.…”