Measurements made using flush-mounted Langmuir probes (FMPs) in tokamaks are difficult to interpret when operating at grazing angles of magnetic field incidence due to the effects of sheath expansion on the probe collection area. The super-X divertor on the upgraded Mega Ampere Spherical Tokamak (MAST-U) will have very shallow angles of magnetic field incidence to plasma facing components (1-10◦), making the use of conventional flush-mounted probes problematic. A novel FMP tip geometry, based on the angled-tip design used successfully on JET and DIII-D, has therefore been used in MAST-U to mitigate sheath expansion effects by increasing the projected probe extent. To verify whether the new design of probe tip allows temperature (Te) and density (ne) measurements to be performed accurately at low angles of incidence, a 4-probe array was taken to Magnum-PSI. Parameter scans were made on a range of hydrogen plasmas in conditions comparable to those possible in MAST-U. The measured temperatures and densities were compared to measurements made by the Thomson scattering system on Magnum-PSI. The measured plasma parameters show that the standard MAST-U FMP tip design successfully mitigates the effects of sheath expansion at low angles of magnetic field incidence. The standard MAST-U Langmuir probe also shows an upper operational limit of θ= 8◦. This covers the vast majority of expected plasma configurations in MAST-U when running both conventional and Super-X configurations.
Angular Dependence Measurements of Magnum-PSI Plasmas Using MAST-U Flush-Mounted Langmuir ProbesAngular Dependence Measurements of Magnum-PSI Plasmas Using MAST-U Flush-Mounted Langmuir Probes https://scientific-publications.ukaea.uk/wp-content/themes/blade/images/empty/thumbnail.jpg 150 150 UKAEA Opendata https://secure.gravatar.com/avatar/679db0b751d3e5fa797cd4b46afe6f58?s=96&d=mm&r=g
The published version of this paper is currently under embargo and will be available on 22/02/2023