Advancing Fusion Theory
The U.S. Department of Energy has chosen a major new project led by PPPL to be part of a national initiative to develop the next generation of supercomputers for the benefit of U.S. economic competitiveness, national security and scientific discovery. Known as the Exascale Computing Project, the initiative will include a focus on next-generation high-performance software and applications and workforce training.
Theoretical physicist Fatima Ebrahimi has for the first time produced computer simulations of the efficiency of a novel technique for starting up doughnut-shaped fusion facilities called tokamaks. The pioneering technique, known as coaxial helicity injection (CHI), could eliminate the large central solenoid coil that is needed to make “a star in a jar” in tokamaks today.
Runaway electrons form a searing, laser-like beam of electric current released by plasma disruptions. These beams could damage the interior walls of future tokamaks the size of ITER, the international fusion experiment under construction in France.
Controlling instabilities called Alfvén waves can lead to higher temperatures within tokamaks and more efficient fusion processes. A number of institutions have recently conducted research, led by Gerrit Kramer at PPPL, that suggests that applying magnetic fields to fusion plasmas can calm these waves. "You want to suppress the Alfvén waves as much as possible so the fast ions stay in the plasma and help heat it," Kramer said.
"Chirp, chirp, chirp." The familiar sound of birds is also what researchers call a wave in plasma that breaks from a single note into rapidly changing notes. This behavior, which often has frequencies far above what the human ear can hear, can cause heat in the form of high energy particles — or fast ions — to leak from the core of plasma inside the doughnut-shaped tokamaks that house fusion reactions.
A computer program that can limit instabilities that reduce the performance of fusion plasmas has been developed by Imène Goumiri, a former Princeton University graduate student and now a researcher at the University of Wisconsin-Madison. The more instabilities there are, the less efficiently doughnut-shaped fusion facilities called tokamaks operate.
