Study of detachment and the processes involved in its dynamics in MAST-U with the IRVB diagnostic
POSTER
Abstract
In a tokamak with a conventional divertor geometry, increasing levels of detachment cause the peak in total radiation emissivity to move from near the divertor targets to around the X-point. The InfraRed Video Bolometer (IRVB) diagnostic recently validated in MAST-U[1] allows accurate mapping of plasma emissivity in the divertor and X-point region with higher spatial resolution than more established methods like resistive bolometers.
The IRVB was used in MAST-U to investigate the correlation between particle flux and radiation detachment in a spherical tokamak. During L-mode ohmic density ramps (Ip=600kA, neup=0.2-1.2x1019 #/m3) the radiation is observed to move off the target first on the inner leg up to the X-point while the particle flux is still increasing on the outer target. Then as the particle flux of the outer target rolls-over, radiation moves upstream off that target as well. The movement is gradual with neup on both legs, contrary to expectations from the analytic DLS model, which predicts an unstable transition on the inner leg[2,3].
During ohmic super-X discharges the IRVB, together with other diagnostics [4,5], was used to show that inside the super-X chamber, during detachment, most of the radiation is hydrogenic, and molecular effects have a significant contribution.
References: [1] F. Federici, et al. Review of Scientific Instruments, 94(3):033502, 2023
[2] B. Lipschultz, F. I. Parra, and I. H. Hutchinson. Nuclear Fusion, 56(5), 2016
[3] C. Cowley, B. Lipschultz, D. Moulton, and B. D. Dudson. Nuclear Fusion, 62(8), 2022
[4] T. A. Wijkamp, et al. Nuclear Fusion, 63(5):056003, 2023
[5] K Verhaegh, et al. Nuclear Fusion, (submitted), 2023
The IRVB was used in MAST-U to investigate the correlation between particle flux and radiation detachment in a spherical tokamak. During L-mode ohmic density ramps (Ip=600kA, neup=0.2-1.2x1019 #/m3) the radiation is observed to move off the target first on the inner leg up to the X-point while the particle flux is still increasing on the outer target. Then as the particle flux of the outer target rolls-over, radiation moves upstream off that target as well. The movement is gradual with neup on both legs, contrary to expectations from the analytic DLS model, which predicts an unstable transition on the inner leg[2,3].
During ohmic super-X discharges the IRVB, together with other diagnostics [4,5], was used to show that inside the super-X chamber, during detachment, most of the radiation is hydrogenic, and molecular effects have a significant contribution.
References: [1] F. Federici, et al. Review of Scientific Instruments, 94(3):033502, 2023
[2] B. Lipschultz, F. I. Parra, and I. H. Hutchinson. Nuclear Fusion, 56(5), 2016
[3] C. Cowley, B. Lipschultz, D. Moulton, and B. D. Dudson. Nuclear Fusion, 62(8), 2022
[4] T. A. Wijkamp, et al. Nuclear Fusion, 63(5):056003, 2023
[5] K Verhaegh, et al. Nuclear Fusion, (submitted), 2023
*Work supported by US DOE DE-AC05-00OR22725 and UK EPSRC Energy Programme [grant number EP/W006839/1].
Presenters
-
Fabio Federici
- UKAEA