Advanced Simulations of Helicon Antennae and Sources

A recent experiment at the DIII-D tokamak has pioneered an innovative and potentially critical actuator for burning plasmas: helicon wave current drive. Steady-state profile maintenance in future burning plasma experiments will require efficient and economically viable sources of off-axis current drive. Promising indications that helicon current drive can fill this need led to the establishment of a high- priority DIII-D research-line focused on exploration of helicon current drive physics, and a low-power prototype helicon antenna was installed in DIII-D and operated to provide an initial exploration of the physics of helicon wave antenna operation. A more sophisticated high-power helicon antenna would be needed to demonstrate application of the helicon concept for actuated plasma control, e.g., to produce measureable driven current. The development of a more detailed theoretical understanding of this current drive source antenna, and its complicated interaction with, and coupling to, the scrape-off layer plasma, in time to be impactful in the design of future experiments is the primary research goal of this project. The project will utilize the time-domain cold plasma modeling capability developed in a DOE sponsored SciDAC project to model the coupling of power to the plasma, including both wave polarizations, evanescent near-fields, and sheath effects. 3D geometric modeling at this detail level has not yet been performed on a helicon antenna-plasma system before in this frequency range. The size of the antenna in the completed experiments should allow for this to be done, e.g., validated, with good confidence in the Phase I. However the size of an eventual high-power antenna makes for a more challenging modeling and research project, and the capability to do this more difficult problem in a useful manner will need to be demonstrated before proceeding to Phase II. Three tasks will focus on the development of the helicon antenna modeling capability. The initial task will set up the simulation input files, ensuring that low power antenna CAD geometry is properly imported. The second task will focus on validation of predicted antenna performance vis-a-vis the experimental results. The third task will set up and demonstrate initial modeling of the high-power antenna, to a degree that one may be confident of usefulness in the Phase II. A fourth task will focus on integration of this type of simulation into the Graphical User Interface of the commercial software package being used to do these simulations, so that antenna coupling to plasma, which is presently not possible with the GUI, is enabled. The ability to model antenna coupling to plasma in a user friendly (GUI-driven) time-domain software package would be a unique feature of the commercial software. Such capability would be of great interest in the design and analysis of a wide range of helicon and industrial plasmas heated by RF antennas.