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Scientists have found a novel way to prevent pesky magnetic bubbles in plasma from interfering with fusion reactions—delivering a potential way to improve the performance of fusion energy devices. And it comes from managing radio frequency (RF) waves to stabilize the magnetic bubbles, which can expand and create disruptions that can limit the performance of ITER, the international facility under construction in France to demonstrate the feasibility of fusion power.

Researchers at the U.S. Department of Energy's (DOE) Princeton Plasma Physics Laboratory (PPPL) have developed the new model for controlling these magnetic bubbles, or islands. The novel method modifies the standard technique of steadily depositing radio (RF) rays into the plasma to stabilize the islands—a technique that proves inefficient when the width of an island is small compared with the characteristic size of the region over which the RF ray deposits its power.

This region denotes the "damping length," the area over which the RF power would typically be deposited in the absence of any nonlinear feedback. The effectiveness of the RF power can be greatly reduced when the size of the region is greater than the width of the island—a condition called "low-damping"—as much of the power then leaks from the island.

Tokamaks, doughnut-shaped fusion facilities that can experience such problems, are the most widely used devices by scientists around the world who seek to produce and control fusion reactions to provide a virtually inexhaustible supply of safe and clean power to generate electricity. Such reactions combine light elements in the form of plasma—the state of matter composed of free electrons and atomic nuclei that makes up 99 percent of the visible universe—to generate the massive amounts of energy that drives the sun and stars.