Picture of the probe head. The probe consists of nine segments with two and five segments with no Langmuir probe pins. The Langmuir probe pins are labelled with T1, T2, T3, … (seen in the picture) and B1, B2, … on the opposite side of the probe head.
Typical time-traces for a fast ion losses experiment with the rotating directional probe at TEXTOR. From top to bottom: the plasma current (I p ), the electron density (n e ), the power of the NBI 2 (P NBI2), the radial probe position (r), and the rotation angle (θ).
Sketch of a segment of the rotating directional probe. One segment contains two Langmuir probe pins (orange). Both probe pins are facing into opposite directions to measure the co- and counter-going particle fluxes, ΓCo and ΓCtr, simultaneously. The probe head rotates anti-clockwise (looking towards the core of the device). I p and B t give the toroidal plasma current and toroidal magnetic field direction, B ∥ indicates the direction of the parallel component of the magnetic field, and r is the direction of the minor radius. θ is the rotation angle and θ0 is the reference angle when the probe pin areas are perpendicular to the parallel flux.
Example for an ion saturation current measured by one Langmuir probe pin during the rotation of the probe head by 360° with non-zero parallel flow. I sat is the measured ion saturation current and θ is the rotation angle of the probe. The two maxima are proportional to the parallel particle flux in co- (ΓCo) and counter-current (ΓCrt) directions.
Data of the rotating directional probe for two opposite facing Langmuir probe pins at r = 45.2 cm inside of the LCFS. The dots show the measurement, and the solid and dashed lines give the fitting curves. The dashed curve corrects for gyration hits of passing ions. The view is limited to half a turn of the probe head, since this contains the whole information on the plasma flow.
Sketch of (a) the velocity distributions in the SOL of a beam heated plasma with a dominant fast ion losses contribution and (b) the velocity distribution in the edge of a counter rotating ohmic plasma. The hatched and cross-hatched regions correspond to the particle amount flowing in counter- and co-current direction, respectively. See Fig. 3 for further information on the flow directions with respect to the probe head geometry.
Measured fast ion losses in a co-beam heated plasma. The dependence of fast ion losses on the plasma current is shown. A reference without beam induced fast ions is shown by the stars.
Plasma edge and SOL Mach number measured in an ohmic plasma.
Cross-correlation between the signal measured at r = 47.6 cm with signals measured further away from the plasma. The cross-correlations indicates the radial outward propagation of ion losses with a speed of about 200 m s−1 (marked by dashed line).
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