DIII-D research advancing the physics basis for optimizing the tokamak approach to fusion energy

Publicación con muchos autores, entre ellos la investigadora de la Universidad de Sevilla: Cano Megías, PilarDIII-D physics research addresses critical challenges for the operation of ITER and the next generation of fusion energy devices. This is done through a focus on innovations to provide solutions for high performance long pulse operation, coupled with fundamental plasma physics understanding and model validation, to drive scenario development by integrating high performance core and boundary plasmas. Substantial increases in off-axis current drive efficiency from an innovative top launch system for EC power, and in pressure broadening for Alfven eigenmode control from a co-/counter-Ip steerable off-axis neutral beam, all improve the prospects for optimization of future long pulse/steady state high performance tokamak operation. Fundamental studies into the modes that drive the evolution of the pedestal pressure profile and electron vs ion heat flux validate predictive models of pedestal recovery after ELMs. Understanding the physics mechanisms of ELM control and density pumpout by 3D magnetic perturbation fields leads to confident predictions for ITER and future devices. Validated modeling of high-Z shattered pellet injection for disruption mitigation, runaway electron dissipation, and techniques for disruption prediction and avoidance including machine learning, give confidence in handling disruptivity for future devices. For the non-nuclear phase of ITER, two actuators are identified to lower the L–H threshold power in hydrogen plasmas. With this physics understanding and suite of capabilities, a high poloidal beta optimized-core scenario with an internal transport barrier that projects nearly to Q = 10 in ITER at ∼8 MA was coupled to a detached divertor, and a near super H-mode optimized-pedestal scenario with co-Ip beam injection was coupled to a radiative divertor. The hybrid core scenario was achieved directly, without the need for anomalous current diffusion, using off-axis current drive actuators. Also, a controller to assess proximity to stability limits and regulate βN in the ITER baseline scenario, based on plasma response to probing 3D fields, was demonstrated. Finally, innovative tokamak operation using a negative triangularity shape showed many attractive features for future pilot plant operation.US Department of Energy - Office of Science - Office of Fusion Energy Sciences DE-FC02- 04ER54698 y DE-AC52-07NA2734

Evolution of 2D deuterium and impurity radiation profiles during transitions from attached to detached divertor operation in DIII-D

This paper presents the detailed evolution of conditions along both the inner and outer divertor legs during the transition from attached ELMing H-mode to partially detached divertor (PDD) operation in DIII-D. Visible emission profiles in a poloidal plane show that in ELMing H-mode prior to deuterium gas injection, CIII emission peaks in the inner SOL near the X-point and deuterium emission (from ionization and recombination) peaks at the inner target plate near the inner strike point (ISP). The spatial profiles of the recombination and ionization zones, determined by forming images of the ratio of intensities from simultaneous images of D{sub {alpha}} and D{sub {gamma}} emission, show that recombination dominates the inner leg emission near the target; ionization dominates in a poloidally narrow zone upstream in the inner leg. After deuterium injection, when the PDD transition begins, the profiles of carbon visible emission show first an increase in the inner SOL near the X-point, followed by increases in emission in the lower regions of the outer leg. Deuterium emission at the transition onset decreases at th4e ISP and increases across the private flux region below the X-point. As the transition to PDD conditions proceeds the deuterium emission increases in the private flux region; recombination dominates near the floor and ionization higher near the X-point. Carbon emission appears along both divertor legs and at the X-point. In the final quasi-steady PDD state, the recombination emission in the outer leg is near the separatrix and along the target plate; emission from collisional excitation dominates in the upper part of the outer leg just below the X-point, and carbon emission is localized at the X-point. These results suggest that transport of neutral deuterium between the inner and outer divertor legs through the private flux region plays an important role in the initiation of outer leg detachment in DIII-D

Supervision and Scholarly Writing: Writing to Learn - Learning to Write

This paper describes an action research project on postgraduate students’ scholarly writing in which I employed reflective approaches to examine and enhance my postgraduate supervisory practice. My reflections on three distinct cycles of supervision illustrate a shift in thinking about scholarly writing and an evolving understanding of how to support postgraduate students’ writing. These understandings provide the foundation for a future-oriented fourth cycle of supervisory practice, which is characterised by three principles, namely the empowerment of students as writers, the technological context of contemporary writing, and ethical issues in writing

Doppler coherence imaging and tomography of flows in tokamak plasmas

This article describes the results of spatial heterodyne Doppler "coherence imaging" of carbon ion flows in the divertor region of the DIII-D tokamak. Spatially encoded interferometric projections of doubly ionized carbon emission at 465 nm have been demodulated and tomographically inverted to obtain the spatial distribution of the carbon ion parallel flow and emissivity. The operating principles of the new instruments are described, and the link between measured properties and line integrals of the flow field are established. An iterative simultaneous arithmetic reconstruction procedure is applied to invert the interferometric phase shift projections, and the reconstructed parallel flow field amplitudes are found to be in reasonable agreement with UEDGE modeling

Experimental and Numerical Studies of Separatrix Splitting and Magnetic Footprints in DIII-D

A numerical field line integration code is used to study the structure of divertor footprints produced by small non-axisymmetric magnetic perturbation in the DIII-D tokamak. The numerical modeling results are compared to experimental infrared camera data which show a splitting of the divertor target plate heat flux into several distinct peaks when an n=3 magnetic perturbation from the DIII-D I-coil is applied. The heat flux splitting consistently appears when the n=3 perturbation is applied and disappears when the perturbation is removed. The magnitude of the splitting implied by the numerical modeling is a factor of 3 smaller than the splitting seen in the experimental data. These results suggest that the plasma response to the edge resonant applied n=3 magnetic perturbation produces an amplification of the vacuum magnetic footprint structure on the divertor target plates. These results may have significant implications for the ITER divertor design