Overview of the Langmuir probe system on the Mega Ampere Spherical Tokamak (MAST) Upgrade

P J Ryan; S D Elmore; J R Harrison; J Lovell; R Stephen

doi:10.1063/5.0152680

Overview of the Langmuir probe system on the Mega Ampere Spherical Tokamak (MAST) Upgrade

Rev Sci Instrum. 2023 Oct 1;94(10):103501. doi: 10.1063/5.0152680.

Authors

P J Ryan¹, S D Elmore¹, J R Harrison¹, J Lovell², R Stephen¹

Affiliations

¹ United Kingdom Atomic Energy Authority, Culham Centre for Fusion Energy, Culham Science Centre, Abingdon, Oxon OX14 3DB, United Kingdom.
² Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA.

PMID: 37782217
DOI: 10.1063/5.0152680

Abstract

A detailed description of the Langmuir probe system on Mega Ampere Spherical Tokamak Upgrade is presented. The system features 850 tile-embedded probes and 40 bespoke electronic modules that each have the capability to drive and acquire data from up to 16 probes in a time-multiplexed manner. The system provides spatiotemporal-resolved measurements (1 cm and ∼1 ms, respectively) in the divertor region of ion saturation current, electron temperature, and floating potential. The standard interpretation of current-voltage (IV) characteristics is to apply a four-parameter fit, based on unmagnetized probe theory, which includes a linear model for the ion saturation region. To mitigate the effect of the magnetic field, analysis is restricted to the region of the IV characteristic, which is sensitive to only the tail of the electron energy distribution function.