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

Mathematical Model and Analysis of Drug Addiction among Adolescent’s Populace in Nigeria

Drug addiction has become a menace especially among adolescents which has massively contributed to the social vices perpetrated by youths in Nigeria. We constructed a five-compartment model to explain the transmission dynamics of addiction leading to a non-linear deterministic equation. The next generation approach was employed to obtain the basic reproduction number (R_0). The drug free equilibrium point was obtained and showed to be locally asymptotically stable when the threshold quantity is less than one. A suitable Lyapunov function was constructed for the global stability which was found to be globally asymptotically stable. Sensitivity analysis was conducted to ascertain the behavior of the various parameters on the threshold quantity to deduce a suitable intervention strategy. Numerical simulations are carried out, the analysis is discussed, and the results are presented in graphical form. Keywords: Addiction, model, drug, stability, basic reproduction number, sensitivity analysis

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

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

On the acoustic diffraction by the edges of benthic shells

Author Posting. © Acoustical Society of America, 2004. This article is posted here by permission of Acoustical Society of America for personal use, not for redistribution. The definitive version was published in Journal of the Acoustical Society of America 116 (2004): 239-244, doi:10.1121/1.1675813.Recent laboratory measurements of acoustic backscattering by individual benthic shells have isolated the edge-diffracted echo from echoes due to the surface of the main body of the shell. The data indicate that the echo near broadside incidence is generally the strongest for all orientations and is due principally to the surface of the main body. At angles well away from broadside, the echo levels are lower and are due primarily to the diffraction from the edge of the shell. The decrease in echo levels from broadside incidence to well off broadside is shown to be reasonably consistent with the decrease in acoustic backscattering from normal incidence to well off normal incidence by a shell-covered seafloor. The results suggest the importance of the edge of the shell in off-normal-incidence backscattering by a shell-covered seafloor. Furthermore, when considering bistatic diffraction by edges, there are implications that the edge of the shell (lying on the seafloor) can cause significant scattering in many directions, including at subcritical angles.This research was supported by the U.S. Office of Naval Research (Grant No. N00014-02-1-0095) and the Woods Hole Oceanographic Institution (WHOI), Woods Hole, MA

A Fast Visible Camera Divertor-Imaging Diagnostic on DIII-D

In recent campaigns, the Photron Ultima SE fast framing camera has proven to be a powerful diagnostic when applied to imaging divertor phenomena on the National Spherical Torus Experiment (NSTX). Active areas of NSTX divertor research addressed with the fast camera include identification of types of EDGE Localized Modes (ELMs)[1], dust migration, impurity behavior and a number of phenomena related to turbulence. To compare such edge and divertor phenomena in low and high aspect ratio plasmas, a multi-institutional collaboration was developed for fast visible imaging on NSTX and DIII-D. More specifically, the collaboration was proposed to compare the NSTX small type V ELM regime [2] and the residual ELMs observed during Type I ELM suppression with external magnetic perturbations on DIII-D[3]. As part of the collaboration effort, the Photron camera was installed recently on DIII-D with a tangential view similar to the view implemented on NSTX, enabling a direct comparison between the two machines. The rapid implementation was facilitated by utilization of the existing optics that coupled the visible spectral output from the divertor vacuum ultraviolet UVTV system, which has a view similar to the view developed for the divertor tangential TV camera [4]. A remote controlled filter wheel was implemented, as was the radiation shield required for the DIII-D installation. The installation and initial operation of the camera are described in this paper, and the first images from the DIII-D divertor are presented