Researchers are starting to discover the curing powers of plasma—bringing the ion-based form of matter into medical realms. A kind of plasma called non-equilibrium atmospheric pressure plasma can help heal wounds, destroy cancer cells and kill harmful bacteria.

The jets of plasma that doctors might use, however, often become turbulent with the direction and velocity changing dramatically. Now, researchers have found this turbulence likely emerges from heat-induced sound waves generated at the plasma electrodes. This new insight is critical for more consistent and effective medical therapies.

“Now that we understand where the induced turbulence in atmospheric pressure plasma jets is coming from, it may be possible to better control it,” said Amanda Lietz of the University of Michigan, who is an author of a new report discussing these results, based on computer simulations, appearing as the cover article this week in the journal Applied Physics Letters.

A plasma is an ionized gas consisting of the positively charged ions and free-flowing electrons. They tend to be extremely hot, like those found in fusion devices. Non-equilibrium atmospheric pressure plasma jets, however, are cool to the touch.

In a typical medical device, atmospheric pressure plasma is made from a noble gas such as helium. An electric field ionizes the helium by removing an electron from each atom, creating a plasma that’s not only at atmospheric pressure, but is also near room temperature.

The plasma flows through a handheld, pen-sized instrument and exits as a high-speed jet. The jet mixes with ambient air, which is filled with chemical species such as oxygen, nitrogen and water vapor molecules. The fast-moving electrons in the plasma slam into these molecules, producing highly reactive species such as hydroxyl and nitric-oxide molecules. These radicals, as they’re also called, are therapeutic.

Scientists still aren’t entirely sure why these plasma-produced radicals are so beneficial in human therapies. They hypothesize that the reactive particles may induce an immune response in the body or modify the biochemical signaling agents between cells. In the case of cancer, the radicals might also trigger an oxidative stress response. Because cancer cells are already in a more stressed state than healthy cells, the radicals may push the cancer cells over the edge, killing them while healthy cells remain unharmed.