New insights into plasma oscillations are paving the way for improved particle accelerators and commercial fusion energy.
Most people know about solids, liquids, and gases as the main three states of matter, but a fourth state of matter exists as well. Plasma鈥攁lso known as ionized gas鈥攊s the most abundant, observable form of matter in our universe, found in the sun and other celestial bodies.
Creating the hot mix of freely moving electrons and ions that compose a plasma often requires extreme pressures or temperatures. In these extreme conditions, researchers continue to uncover the unexpected ways that plasma can move and evolve. By better understanding the motion of plasma, scientists gain valuable insights into solar physics, astrophysics, and fusion.
In a published in Physical Review Letters, researchers from the , along with colleagues at the University of California, San Diego, discovered a new class of plasma oscillations鈥攖he back-and-forth, wave-like movement of electrons and ions. The findings have implications for improving the performance of miniature particle accelerators and the reactors used to create fusion energy.
鈥淭his new class of plasma oscillations can exhibit extraordinary features that open the door to innovative advancements in particle acceleration and fusion,鈥 says , a senior scientist at the , an assistant professor in the聽, and an associate professor at the聽.
Plasma waves with a mind of their own
One of the properties that characterizes a plasma is its ability to support collective motion, where electrons and ions oscillate鈥攐r wave鈥攊n unison. These oscillations are like a rhythmic dance. Just as dancers respond to each other鈥檚 movements, the charged particles in a plasma interact and oscillate together, creating a coordinated motion.
The properties of these oscillations have traditionally been linked to the properties鈥攕uch as the temperature, density, or velocity鈥攐f the plasma as a whole. However, Palastro and his colleagues determined a theoretical framework for plasma oscillations where the properties of the oscillations are completely independent of the plasma in which they exist.
鈥淚magine a quick pluck of a guitar string where the impulse propagates along the string at a speed determined by the string鈥檚 tension and diameter,鈥 Palastro says. 鈥淲e鈥檝e found a way to 鈥榩luck鈥 a plasma, so that the waves move independently of the analogous tension and diameter.鈥
Within their theoretical framework, the amplitude of the oscillations could be made to travel faster than the speed of light in a vacuum or come to a complete stop, while the plasma itself travels in an entirely different direction.
The research has a variety of promising applications, most notably in helping to achieve clean-burning, commercial fusion energy.
Coauthor , a professor of mechanical and aerospace engineering at the University of California, San Diego, says, 鈥淭his new type of oscillation may have implications for fusion reactors, where mitigating plasma oscillations can facilitate the confinement needed for high-efficiency power generation.鈥
The Office of Fusion Energy Sciences, the Department of Energy National Nuclear Security Administration, and the New York State Energy Research Development Authority supported this research.
4