Speaker
Description
Steven Thomas1,*, Jerry W. Hughes1, Alex Tookey2, Davis Easley3, Yacopo Damizia4,
Bart Lomanowski3, Saskia Mordijck4, Ekin Öztürk4, Scott Silburn2,
and the MAST Upgrade Team2,†
1MIT Plasma Science and Fusion Center, Cambridge, MA 02139, USA
2UKAEA, Culham Campus, Abingdon, Oxfordshire, OX14 3DB, UK
3Oak Ridge National Laboratory, Oak Ridge, TN 37831-6169, USA
4William & Mary, Williamsburg, VA 23185, USA
*email: sthoma@mit.edu; †See author list of [1]
Recent work [2] has optimised the high-speed video (HSV) diagnostic on MAST Upgrade to obtain absolutely calibrated line-of-sight-integrated emission from neutral deuterium. The HSV is a wide-angle, high sampling rate (≥ 30 kHz) optical camera, fitted with an optical interference filter to isolate Dα line emission (n = 3 → 2). HSV data, interpreted using a collisional-radiative model, is used to infer radial profiles of ionization source rate, Sion, and neutral density, n0. Furthermore, Sion is used to obtain radial ion flux profiles, Γ.
Future fusion pilot plants will operate with burning plasmas to achieve high fusion power output, which requires high core pressures. As core transport is stiff, the maximum achievable pressure in the core relies on large edge pedestal gradients [3]. Therefore, predictions of plasma core performance require good predictions of the pedestal density and gradients, ne and ∇ne, respectively, which are set by a balance between Γ and Sion through the continuity equation:
∂t ne = −∇ · Γ + Sion. In the edge, sources from cold neutrals are plentiful and are the dominant contribution to the flux [2].
The data from HSV provides an excellent resource for validating codes and testing models on MAST-U. For example, Γ is used in a diffusive-convective ansatz to infer diffusive and convective flux transport coefficients which are used as inputs to SOLPS-ITER and the Sion output directly compared to the experimental Sion inference. Preliminary attempts to model MAST-U discharges with KN1D [4] show disagreement between the simulated neutral penetration length and the inferred n0 profile from HSV. We use this opportunity to discuss the new edge neutral inferences in MAST Upgrade and how they can be used to constrain and test modelling of the plasma exhaust.
Acknowledgements: Work supported by DOE Awards DE-SC0023289, DE-SC0023372, and DE-AC05-00OR22725, and by the Engineering and Physical Sciences Research Council [grant number EP/W006839/1].
References
[1] J. R. Harrison et al., Nucl. Fusion, vol. 64, p. 112017, 2024.
[2] S. Thomas et al., "(Submitted) The poloidal fuelling location and its effect on H-mode plasma performance in MAST Upgrade," Plasma Phys. Control. Fusion, 2026.
[3] J. E. Kinsey et al., Nucl. Fusion, vol. 51, p. 083001, 2011.
[4] B. LaBombard, "KN1D: A 1-D Space, 2-D Velocity, Kinetic Transport Algorithm for Atomic and Molecular Hydrogen in an Ionizing Plasma," Tech. Rep. PSFC Research Report PSFC/RR-01-3, 2001.