Reciprocating Mach Probe (X-point)

[Objectives]
A fast reciprocating Langmuir (electrostatic) probe system (RPS) was installed at the W-shaped divertor (Photo from VV) in 1997 during the pumping divertor installation.

Upstream divertor plasma data, i.e. profiles of electron temperature, ion saturation current and floating potential from the divertor nose to the private region, have been measured in order to investigate heat and particle transport in the divertor region.

Mach probe (two double-probes ) measurement determines the SOL plasma flow (Mach number) along the field lines.

The SOL plasma flow and plasma detachment have been studied in the W-shaped divertor with pumping system.

[Specifications]

Langmuir probes:

Two double probes for Te, Is measurement at up-stream and down-stream sides of the field lines (i.e. Mach probe), and a floating probe for potential measurement. Head and 5 electrodes are made of carbon fiber composite (CFC).

Spatial resolution:

1-2 mm in radial direction.
It has provided high spatially resolved profiles of the local electron temperature (Te), ion saturation current (Is) for ion- and electron-side of the probe head.

Scanning speed:

25cm for ~0.5s (~50 cm/s)

Driving component:

a compact pneumatic cylinder and steel springs.
Total mass of the moving components is about 25kg.

Position: P-9 section, divertor port

(2005) Probe head and electrodes were replaced.

Position: P-9 section: X-point Reciprocating probe system and W-shaped divertor

[References]
[1] S. Sakurai et al., J. Nucl. Matter.266-269 (1999) 1191.
[2] N. Asakura et al., J. Nucl. Matter,266-269 (1999) 182.
[3] N. Asakura et al., Nucl. Fusion, (1999) 1983.
[4] N. Asakura et al., Physical Review Letters, Vol.84 (2000) 3093.
[5] N. Asakura et al., J. Nucl. Matter, 290-293 (2001) 825.
[6] N. Asakura et al., Plasma Phys. Control. Fusion 44 (2002) A313.