Determination of velocity shears in a simple magnetized torus by means of a combined Langmuir and Mach probe

Abstract

We present a multiple electric probe setup for diagnostics of plasmas which is aimed to simultaneously measure the fluctuations of the ion velocity field along one direction and the ͑E ϫ B͒ flux perpendicular to it. The probe design is based on combining a Mach probe with two slightly spatially separated Langmuir probes. The probe has been prepared to operate in the turbulent regime of the simple magnetized torus Blaamann. Experiments have been focused on the measurements of shear in the velocity along the magnetic field and on its correlation with the radial flux. Preliminary results are showing the effectiveness of the proposed diagnostics as well as the relevance of velocity fluctuations and correlations in plasma turbulence and in anomalous transport.

Asymmetry reversal of ion collection by mach probes in flowing unmagnetized plasmas

“…This approach has been successful in magnetized plasmas for a wide range of parameters. [1][2][3][4][5]. Mach probes have not been used extensively in unmagnetized plasmas.…”

The role of sheath and acceptance angle in front of a retarding field energy analyzer for plasma flow analysis

“…Hence, measurement of plasma flow is of key interest in a number of plasma environments. In laboratory magnetized plasmas, the directional Langmuir or Mach probe is a well-proven "in-situ" diagnostic tool to obtain the flow velocity [1,2]. However, in nonmagnetized or weakly magnetized plasmas, this method does not readily yield reliable velocity measurements, as it has been shown by numerical and experimental studies [3,4] that the collection of upstream ions to the rearward probe surface can be significant.…”

On the Use of a Retarding Field Energy Analyzer for Plasma Flow Analysis

“…the flow speed in terms of ion sound speed c s . This method is well proven and widely adopted in magnetized plasmas [10]; while in non-magnetized plasmas it is more disputed [11]. The other method is a straightforward measurement of the plasma potential, taking the difference of the potential measured in the anti-parallel direction and in either the perpendicular or parallel direction to flow.…”