Recent fusion experiments on the DIII-D tokamak at General Atomics (California, US) and the Alcator C-Mod tokamak at MIT (Massachusetts, US), show that beaming microwaves into the centre of the plasma can be used to control the density in the centre of the plasma, where a fusion reactor would produce most of its power. Several megawatts of microwaves mimic the way fusion reactions would supply heat to plasma electrons to keep the "fusion burn" going.
The new experiments reveal that turbulent density fluctuations in the inner core intensify when most of the heat goes to electrons instead of plasma ions, as would happen in the center of a self-sustaining fusion reaction. Supercomputer simulations closely reproduce the experiments, showing that the electrons become more turbulent as they are more strongly heated, and this transports both particles and heat out of the plasma.
"We are beginning to uncover the fundamental mechanisms that control the density, under conditions relevant to a real fusion reactor," says Dr. Darin Ernst, a physicist at the Massachusetts Institute of Technology, who led the experiments and simulations, together with co-leaders Dr. Keith Burrell (General Atomics), Dr. Walter Guttenfelder (Princeton Plasma Physics Laboratory), and Dr. Terry Rhodes (UCLA).
Read the full report on Science Daily.
–Supercomputer simulation shows turbulent density fluctuations in the core of the Alcator C-Mod tokamak during strong electron heating. Credit: D. R. Ernst, MIT