Electrostatic Turbulence and Transport in the Velocity Shear Layer of a Reversed Field Pinch Plasma

Abstract

The electrostatic turbulence in the edge plasma of the RFX reversed field pinch experiment has been studied using Langmuir probes and a homodyne reflectometer. The radial particle flux driven by electrostatic fluctuations has been measured in the region where a double E × B velocity shear layer occurs. It is found that almost 100% of the particle flux at the edge is driven by electrostatic fluctuations. The naturally occurring E × B velocity shear has been shown to be close to that required Biglari-Diamond-Terry criterion for turbulence radial decorrelation

Magnetic and electrostatic structures measured in the edge region of the RFX-mod experiment

“…Due to the presence of a radial electric field, and to a magnetic field essentially poloidal, B $ B h , the edge region is characterized by an average toroidal E Â B flow velocity, that has been found to be of the order of 10 4 m/s [16].…”

Turbulence and Anomalous Transport in Magnetized Plasmas: Hints from the Reversed Field Pinch Configuration

“…Substituting the experimental values, it has been shown that in both experiments the velocity shear has values close to those required for turbulence suppression or reduction [35,36].…”

On the probability distribution function of particle density at the edge of fusion devices

“…The picture (3) is, however, too simplified when compared with real experimental scenarios (apart for the obvious fact that it deals with electron density and not ion density). We mention just a few references: 1) in RFX, the rms of φ/T fluctuations, ∆ φ/T , stays almost constant when entering the plasma, while the same quantity for n, ∆ n , decreases 20 ; 2) in RFX 17 and Frascati Tokamak Upgrade 21 (FTU), measurements of the cross-correlations (∆n t , ∆φ t ) yielded rather low values ( ∼ 0.5), not compatible with (Eq. 3); 3) finally, in a review devoted to this subject, Endler 22 remarked that several experiments were confirming that the relative phase angle of the fluctuations in φ and n lies between π/4 and π/2.…”

“…[17]. Here, we limit to some basic informations: the sampling frequency of the probe was 1 MHz, with a total of about 40,000 measurement points for each shot.…”