CCFE-PR(16)57

Particle-In-Cell Simulations of the Ball-Pen Probe

Ball-pen probes have been deployed in the SOL of numerous magnetic confinement experiments to make direct measurements of the plasma potential. They have also been used simultaneously with Langmuir probes to make fast measurements of the electron temperature. Despite strong empirical evidence for the success of the BPP it lacks a theoretical underpinning of its collection mechanism. In this paper we investigate the capability of the probe to measure the plasma potential by means of Particle-In-Cell simulations using VSim [C. Nieter et al. J. Comp. Phys, 1, 196 (2004)]. The BPP is found to float at a potential offset from the plasma potential by a factor Te BPP . By simulating BPPs and Langmuir probes, excellent agreement has been found between the measured electron temperature and the specified source temperature. The transport mechanism for both ions and electrons has been determined. E x B drifts are observed to drive electrons and ions down the tunnel. This mechanism is sensitive to the diameter of the probe.

Collection:
Journals
Journal:
Contributions to Plasma Physics
Publisher:
Wiley