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

Abstract

This work discusses a new directional probe designed for measurements of fast ion losses and the plasma rotation with a high angular resolution in magnetically confined plasmas. Directional and especially Mach probes are commonly used diagnostics for plasma flow measurements, and their applicability for the fast ion losses detection has been demonstrated. A limitation of static Mach probes is their low angular resolution. At the Tokamak Experiment for Technology Oriented Research, the angular resolution is strongly restricted by the finite number of available measurement channels. In a dynamic plasma, where instabilities can lead to local changes of the field line pitch-angle, plasma flow, or fast ion losses, a low angular resolution makes a precise data analysis difficult and reduces the quality of the measured data. The new probe design, the rotating directional probe, combines the features of early directional probes and Mach probes. It consists of two radially aligned arrays of nine Langmuir probe pins with each array facing opposite directions. During the measurement the probe head rotates along its axis to measure the ion saturation current from all directions. As a result, the rotating directional probe simultaneously provides an angular dependent plasma flow and fast ion losses measurement at different radial positions. Based on the angular dependent data, a precise determination of the current density is made. In addition, the simultaneous measurement of the ion saturation current at different radial positions allows for resolving radially varying field line pitch-angles and identifying the radial dynamic of processes like fast ion losses.

On the effects of magnetic perturbations on fast ion losses studied at TEXTOR

“…These are below 12% along the entire profile and show that no correlation in the toroidal direction is present. The different behaviour strongly supports the assumptions of the analysis method presented in [18,21]: fast ions are only detected from one side.…”

“…The rotating directional probe [18] is mounted on the reciprocating probe [19,20] and inserted from the low-field side (LFS) along the mid-plane into the scrape-off layer (SOL) to a final position of r = 47 cm touching the plasma edge at a toroidal angle φ ≈ 346°; see figure 1. The probe head is equipped with two arrays of nine Langmuir probe pins facing in opposite directions for simultaneous measurement of particles from both directions.…”

Diagnostic set-up and modelling for investigation of synergy between 3D edge physics and plasma-wall interactions on Wendelstein 7-X

“…By adjusting the applied grid potentials, it is not only possible to determine ion parameters but also to use the probe head for multi-channel electron parameter measurements or high-energy particle loss measurements. Here, the physics design of two back to back oriented RFA modules is aiming for the measurement of fast particle loss which comes from one direction to the probe [12].…”

Modelling and application of a new method to measure the non-thermal electron current in the edge of magnetically confined plasma

“…The directional probe usually consists of two collectors located on the two sides of a central insulator. Directional probe has been applied on the measurements of parallel ion flow and floating potential in the magnetically controlled plasmas [29][30][31][32][33][34][35]. Herein we propose a new type of directional probe which has the capability to measure parallel electron current, and consequently this new probe is named directional electron probe (DEP).…”