NBI fueling and particle transport between ICRH and NBI identity shots in JET with GENE and TGLF validation

Tuomas Tala

University of Technology, Finland

Wednesday, December 1, 2021



PSFC Seminars

Abstract: Particle transport in tokamaks has received much less attention thanelectron and ion heat transport channels. It is still often not treated self-consistently in transport modelling and predictions for future tokamaks. As a consequence, particle transport and fuelling remain one of the major open questions in understanding ITER physics. The shape of the density profile has a significant influence on fusion performance and impurity transport. The uncertainties in the particle transport limit our predictive capability for future fusion devices. Density peaking has been studied between an ICRH and NBI identity plasma on JET. The comparison shows that 8MW of NBI heating/fueling increases the density peaking by a factor of two, being R/Ln=0.45 for the ICRH pulse and R/Ln=0.93 for the NBI one averaged radially over ρtor=0.4‒0.8. The dimensionless profiles of q, ρ*, Ï *, βn and Ti/Te≈1 were matched within 5% difference except in the central part of the plasma (ρtor<0.3). The difference in the curvature pinch (same q-profile) and thermo-pinch (Ti=Te) between the ICRH and NBI discharges is virtually zero. This verifies that the factor of 2 increase in density peaking is indeed solely due to the NBI fuelling.  This result of R/Ln increasing by 0.5 per 8MW of NBI power is valid for the ITG dominated low power H-mode plasmas. However, some of the physics processes influencing particle transport, like rotation, turbulence and fast ion content scale with power, and therefore, the simple scaling on the role of the NBI fuelling is not necessarily the same under high power (30MW) JET conditions and in larger devices.

Bio: Dr. Tuomas Tala graduated in the technical physics department at Helsinki University of Technology in Finland. Since then he has spent 10 years in JET (currently the largest fusion research laboratory and tokamak in the world) working on tokamak heat, momentum and particle transport. Earlier he developed models for understanding the physics of Internal Transport Barriers (ITBs) that are crucial elements when trying to achieve steady-state fusion plasma operation. Recently he has concentrated on comparative multi-tokamak studies on particle and momentum transport topics within the ITER project framework. This has included longer and
shorter visits to numerous plasma physics laboratories worldwide. He has also executed two experiments on C-Mod at MIT, one on momentum transport and one on particle transport. He is also the director of the Finnish
fusion research unit.