Plasma transport analysis, the study of how plasma particles, heat and momentum drift across magnetic field lines, is a necessary first step for understanding how well fusion reactors are performing. Teams of scientists from the U.S. Department of Energy's (DOE) Princeton Plasma Physics Laboratory (PPPL) and General Atomics (GA) have joined forces to bring PPPL's premier transport code, TRANSP, to beginning users and experts alike.
Using the workflow manager OMFIT developed by GA scientists, the team has created a TRANSP module that streamlines data preparation for TRANSP analysis and couples TRANSP to other widely used software. While TRANSP analysis of international tokamak experiments has been available for more than 30 years, the new interface through OMFIT has produced a new user base, modern visualization and increased productivity.
Expanding the global community
The result has been expansion of a global community. "From a technical point of view, OMFIT is a workflow manager that can couple physics codes, execute them in complex workflows, and provide them with streamlined interfaces," says Orso Meneghini, a GA physicist. "Perhaps more importantly, OMFIT is a growing community effort, which is gathering the contribution of many physicists across domestic and international institutions, and is supporting the research of over two hundred scientists worldwide."
In recent years, the number of TRANSP users on DIII-D, the National Fusion Facility that GA operates for the DOE, has expanded from a handful to nearly 40 researchers by the end of 2016. While most are new users, legacy users have also migrated to the OMFIT platform. "What used to be a complex and cumbersome process to generate TRANSP runs that was mastered by only a few has now become available to all users with powerful and intuitive drivers and visualizations," says physicist Brian Grierson, a PPPL researcher on DIII-D who developed the TRANSP module in OMFIT with PPPL physicists Shaun Haskey and Nikolas Logan.
Logan points out the utility of the module. "Through OMFIT, we have created a community-based platform for developing scientific analysis software, where expert users can develop and oversee critical physics analysis with results available for the wider community," he says.
Benchmarked on U.S. tokamaks
Researchers have used the new TRANSP interface in OMFIT to study fusion plasmas in three U.S.-based tokamaks: DIII-D; the National Spherical Torus Experiment (NSTX) at PPPL prior to its recent upgrade; and Alcator C-Mod at MIT, which ceased operation at the end of 2016. The interface was benchmarked on the U.S. experiments and is now being used to analyze data gathered from domestic and international tokamaks.
Multiple scientists presented TRANSP analysis results obtained through OMFIT at the 2016 International Atomic Energy Agency (IAEA) Fusion Energy Conference in Kyoto, Japan. "I used the new OMFIT workflow to efficiently analyze transport in an ITER-like DIII-D discharge with TRANSP," says Chris Holland of the University of California, San Diego. ITER is an international tokamak under construction in France.
"The TRANSP output and uncertainty analysis was then used as input for massively parallel multiscale GYRO simulations" that model plasma turbulence at the microscopic scale in fusion reactors, Holland said. Results of the simulations, published in the journal Nuclear Fusion in May, matched experiments showing that turbulence caused by electron transport takes place at multiple scales of time and space.
PPPL, on Princeton University's Forrestal Campus in Plainsboro, N.J., is devoted to creating new knowledge about the physics of plasmas -- ultra-hot, charged gases -- and to developing practical solutions for the creation of fusion energy. The Laboratory is managed by the University for the U.S. Department of Energy's Office of Science, which is the largest single supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time. For more information, please visit science.energy.gov.