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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 benefit 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. 

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.  


## 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_