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Tokamak GOLEM project web

# Ball-Pen probe diagnostic

## Objectives

The final aim of the experiment will be to improve our understanding of the Ball-Pen probe and its benefits in the measurements in magnetized plasmas.

## Description

The Ball-Pen probe was developed in the tokamak GOLEM [1] to improve the measurement of the plasma potential in the reactor. Basically, it is a Langmuir probe with a movable shield, this shield can moderate the incidence of electrons into the probe taking advantage of the Larmor radii [4]. 

This theory is not completely satisfactory because some research [1][2] has shown that there is always electron current in the probe, also when the probe is deep inside the shield which is in contradiction with the theory. It was found that the E × B drift motion of electrons moving along the equipotential surface plays an essential role in the measurement [7]. To solve this problem, it has been proposed that the shield have the same potential as the probe collector itself. 

## Methodology 

The experiment will consist in measurement of the I-V characteristic curves for different positions of the probe inside the shield, the saturation line will give us the parameter R, which is the ratio between the saturation currents of electrons and ions



## Bibliography

[1] J. Adámek et al, _A novel approach to direct measurement of the plasma potential_

[2] J. Adámek et al, _Comparative measurements of the plasma potential with the ball-pen and emissive probes on the CASTOR tokamak_

[3] R. Schrittwieser, C. Ionita, _Direct measurements of the plasma potential by katsumata–type probes_

[4] Itsuo Katsumata and Moroe Okazaki, _Ion Sensitive Probe-A New Diagnostic Method for Plasma in Magnetic Fields_

[5] J. Adámek et al, _Simultaneous Measurements of Ion Temperature by Segmented Tunnel and Katsumata Probe_

[6] Jana Brotánková, _Study of high temperature plasma in tokamak-like experimental devices_

[7] N. Ezumi, _PIC Simulation of the Motion of Plasma around Ion Sensitive Probes_