Friday, May 5, 2017
Abstract: Particle transport in tokamaks has received much less attention than electron 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 fueling 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. Particle transport has been extensively studied by performing several dimensionally matched collisionality scans in various plasma scenarios on JET and DIII-D. A gas puff modulation technique has been developed with high quality time-dependent density profile measurements to determine particle transport coefficients. Density peaking has been found to increase with decreasing collisionality in all H-mode scenarios while in L-mode, no dependency was found.In September 2016, gas puff modulation in I-mode was performed on C-Mod to study particle transport and density peaking in I-mode. The detailed analysis is on-going, and hopefully C-Mod can also contribute to the multi-machine density peaking studies.
Momentum transport and plasma rotation have also been extensively studied on many tokamaks in recent years. Both experiments and theory have shown that sheared plasma rotation can stabilise turbulence while the rotation itself has beneficial effects on MHD instabilities.
Numerous experimental results, both on momentum transport and intrinsic torque, have been reported on individual devices – yet only few experimental multi-machine momentum transport or intrinsic torque comparisons have been performed. This seminar reports dedicated scans to study momentum transport and intrinsic torque, carried out as dedicated joint experiments on JET, DIII-D, AUG, NSTX and C-Mod within the ITPA framework.
BIO: Dr. Tuomas Tala graduated in the technical physics department at Helsinki University of Technology in Finland. Since then he has spent 9 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.