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 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. 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 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. 3D geometric modeling at this detail level has not yet been performed on a helicon antenna-plasma system before in this frequency range. The Phase I project demonstrated the ability to model the DIII-D Low Power Antenna loaded into a resistive sheet, and also into plasma, and benchmarked simulations of it to experimental test-bed measurements of loading vs frequency and distance to the resistive sheet. Simulations of a 36 module High Power Antenna configuration on a NERSC supercomputer also show feasibility to handle a problem this large. The Phase II project will focus efforts in three areas: a) modeling and analysis of the helicon antennas and experiments performed and being planned for the DIII-D tokamak, b) improvements to the software to address issues brought to light in the Phase I effort, and c) integration of the modeling capability into a robust user friendly commercial package. The primary research challenge will be modeling of the High Power Antenna array, which has a linear dimension of a couple meters, and yet requires 1 mm scale resolution, such that the modeling effort requires software that can operate effectively at super-computer scale.Commercial Applications and Other BenefitsThe 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.