A 1D fluid model for the measurement of perpendicular flow in strongly magnetized plasmas

Abstract

We show that it is possible to measure the parallel and the perpendicular flow in a strongly magnetized plasma, using a probe with two current collecting surfaces, inclined with respect to the magnetic field. The method is based on a one-dimensional fluid model, which we use to relate the unperturbed velocity components (the quantities we wish to measure) to the velocity and density perturbations caused by the probe. In this way we are able to establish a link between the electric saturation currents collected by the probe surfaces and the unperturbed velocity. The role of the cross-field transport into a pre-sheath of a collecting probe surface and the boundary condition for the flow velocity at the magnetic pre-sheath entrance are also investigated. § Partner in the Trilateral Euregio Cluster (TEC).

A rotating directional probe for the measurements of fast ion losses and plasma rotation at Tokamak Experiment for Technology Oriented Research

“…Discussions by Goubergen et al 12 pointed out that j depends on the parallel and perpendicular flows j ∼ exp{v /c s − v ⊥ cot(θ )/c s − 1}, where v and v ⊥ are the parallel and perpendicular flow velocities and c s is the ion sound speed. Following this, a consideration of the perpendicular flow is necessary for the calculations of the current density.…”

Oblique ion collection in the drift approximation: How magnetized Mach probes really work

“…, that fits the diffusive solution [10,1]. Third, consideration of the characteristics shows unambiguously that leading faces, for which θ < θ m receive simply the unperturbed flux [Γ = n ∞ c s (M h cot θ−M ∞ )], while trailing faces, even those for which M ∞ − M h cot θ > 1, are governed by the formula (15).…”

“…The approximate one-dimensional diffusive treatment has been generalized [10] to include an additional perpendicular plasma drift velocity, accounting for the boundary-condition modification [11] that the transverse drift causes. Measuring the dependence of the ion collection current-density on orientation of oblique probe faces then allows one to deduce the perpendicular as well as the parallel external drift velocity.…”

Plasma Edge Diagnostics for TEXTOR

“…In order to determine the perpendicular Mach number, the probe model has been extended by taking into account the perpendicular flux into the flux tube and reformulating the Bohm condition at the sheath entrance. 31 The change of the upstream and downstream ion saturation currents R with inclination angle u is obtained from a one-dimensional~1-D! fluid model and has the form ln R ϭ 2.21~M 5 Ϫ M 4 cot u!, where M 5 and M 4 are the parallel and perpendicular Mach numbers.…”