Langmuir probes are a versatile diagnostics to measure density, potential and electron temperature inside a plasma. They are used to measure equilibrium profiles and fluctuations. Depending on the problem, the probes can have a variety of different arrangements.
An 8-tip probe array mounted on a manipulator, which can be positioned arbitrarily in the poloidal cross-section. Two dimensional profiles of different plasma parameters can be scanned at the same time.
Probe array used at ASDEX Upgrade. It is mounted on a linear manipulator and can be used in the scrape-off layer of the plasma. The construction is such that the probe can withstand the mechanical forces and heat load while being shot into and pulled back out of the edge plasma.
The two dimensional structure of plasma turbulence is captured within a second using an 8x8 probe array (matrix). The distance between the probes is 1 cm in each direction.
SPIDER: Dynamical changes in the 2D profile are recorded with an array, which uses 32 Langmuir probes to cover the entire poloidal cross-section.
64 probes in the shape of the flux surface in a poloidal cross-section reveal the poloidal structure of turbulence.
The Reynolds-stress array. 128 Langmuir probes are aligned to four adjacent flux surfaces in order to measure the radial derivative of the Reynolds stress on a complete poloidal circumference
The zoom shows, how radial and poloidal components of the electric field can be deduced.
Mirko Ramisch
Dr.Head of Plasma Dynamics and Diagnostics / Library officer