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The program in Theory and Simulation of Fusion Plasmas at General Atomics (GA) supports the OFES's overarching goals of advancing fundamental understanding of plasmas, resolving outstanding scientific issues and establishing reduced-cost paths to more attractive fusion energy systems, and advancing understanding and innovation in high-performance plasmas including burning plasmas. As the lead institution of the DIII-D National Fusion Facility, the GA theory group works in close partnership with the experiment in identifying and addressing key physics issues relevant to the OFES goals.
Analytic theories are developed to model physical effects, and numerical codes are implemented to treat realistic geometries and to integrate interrelated complex phenomena, and validate theoretical calculations against experimental data in order to achieve this objective. The research interests of the staff are divided into several main areas: Magnetohydrodynamics and Stability, Confinement and Transport, Plasma Heating/Fueling and Non-inductive Current Drive, Innovative Confinement Concepts, and Integrated Modeling. Summaries of the currently active areas of research are given in the accompanying pages.
The GA Theory Group has a distinguished history of seminal contributions to fundamental understanding and innovative ideas in magnetic confinement physics:
Pioneering contributions to the peeling-ballooning model and its numerical implementation in the ELITE code, through which a successful explanation of the observed pedestal constraints and numerous ELM characteristics has been obtained
- First investigation of the effect of toroidal plasma flow and flow shear on global MHD modes stability; and the coupling of rotational shear with wall and feedback stabilization
- Shape and profile optimization of tokamak stability properties and elucidating the role of triangularity and higher order shape
- Explanation of the transport bifurcation from L- to H-mode and the further confinement improvement in the DIII-D VH-mode edge using a theory based on ExB rotational shear driven by changes in the diamagnetic flows at the plasma edge
- Analytic calculation showing that zonal flows do not damp as a result of linear collisionless processes, invalidating assumptions in gyrofluid calculations predicting somewhat poorer ITER performance.
- New insight into how the fundamental processes determining the size and field strength scaling of confinement can be obtained from dimensionally similar tokamak discharges
- Development of a comprehensive transport model (fit to gyrokinetic stability and gyrofluid nonlinear simulations with ExB rotational shear stabilization), which gives a good non-adjusted fit to the Transport Profile Database and core confinement barriers
- Development of the first global gyrokinetic continuum code, GYRO, with full physics including trapped-passing ions and electron kinetics, ExB shear stabilization, finite beta and general geometry; and successful validation against DIII-D L-mode discharges
- Formulated a gyrokinetic theory for wave-induced particle transport in a rotating tokamak plasma, which was used to implement a quasi-linear wave diffusion operator in a Monte-Carlo drift orbit code for the study of finite orbit physics in ICRH plasmas
- Developed a comprehensive mechanism for NTM onset in which the time dependent linear drive is a crucial element
- Created a new model for the radial movement of pellet ablation material that explains the enhanced penetration of pellet fuel during high field side or inner wall pellet injection
A unique and historical strength of the theory program is the close connection to the experimental program. The theory group works closely with the DIII-D Team and shares its major research goals:
- To lead a national effort to understand the basic physics processes by which plasma turbulence produces cross-field transport and to use that knowledge to improve confinement
- To establish that the limit to plasma pressure in a tokamak can be substantially increased by the effects of a nearby conducting wall and plasma rotation, as predicted by theory
- To understand the flows and exchanges of fuel and impurity particles between the plasma and the material surfaces of the confining chamber for fuel and impurity control
- To develop the basis for steady-state operation of a tokamak in which the large majority of plasma current is self-generated
- Proceeding from the base of the above scientific building blocks, to implement sufficient plasma control to assess the degree of achievable simultaneous optimization of the tokamak.
A common vision of developing a comprehensive predictive capability for fusion plasmas is shared with the DIII-D program. The theory program is also known for its extensive collaborations with other institutions. Collaborative programs are aggressively planned and initiated to focus external resources on physics issues important to fusion. Participants have come from national laboratories, universities, and foreign institutions. The GA Theory group is also a leading contributor to national and international working groups supporting fusion research such as the Transport Task Force (TTF), the Snowmass Summer Study, and the International Tokamak Physics Activities (ITPA).
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