Most people know about solids, liquids, and gases as the three main states of matter. However, there is a fourth state of matter as well. Plasma, which is also known as ionized gas, is the most abundant, observable form of matter in our universe. It is found in our Sun and other celestial bodies.
     Creating the hot mix of freely moving electrons and ions that compose a plasma often requires extreme pressures and/or temperatures. In these extreme conditions, researchers continue to discover the unexpected ways that a plasma can move and evolve.
     By gaining a better understanding of the motion of plasma, scientists gain valuable insights into solar physics, astrophysics, and fusion.
     In a report published in Physical Review Letters, researchers from the University of Rochester, along with colleagues at the University of California, San Diego, discovered a new class of plasma oscillations. These are back-and-forth, wave-like movements of electrons and ions. These findings have implications for improving the performance of miniature particle accelerators and reactors used to create fusion energy on earth.
     John Palastro is a senior scientist at the Laboratory for Laser Energetics, an assistant professor in the Department of Mechanical Engineering, and an associate professor at the Institute of Optics. He said, “This new class of plasma oscillations can exhibit extraordinary features that open the door to innovative advancements in particle acceleration and fusion.”
     One of the important properties that characterizes a plasma is its ability to support collective motion, with electrons and ions moving in unison.
     These oscillations are similar to a rhythmic dance. In the same way as dancers respond to each other’s movements, the charged particles in a plasma interact and oscillate together, creating a coordinated motion.
     The properties of these oscillations have previously been linked to the properties such as the temperature, density, or velocity of the plasma as a whole.
     However, Palastro and his colleagues have determined a theoretical framework for plasma oscillations where the properties of the oscillations are completely independent of the plasma in which they exist.
     Palastro says, “Imagine a quick pluck of a guitar string where the impulse propagates along the string at a speed determined by the string’s tension and diameter. We’ve found a way to ‘pluck’ a plasma, so that the waves move independently of the analogous tension and diameter.”
     In their theoretical framework, the amplitude of the oscillations could be made to travel faster than the speed of light in a vacuum or stop completely, while the plasma itself travels in an entirely different direction. This research has a variety of promising applications. One of most important applications would be in helping to achieve clean-burning, commercial fusion energy.
     Coauthor of the report, Alexey Arefiev, is a professor of mechanical and aerospace engineering at the University of California, San Diego. He says, “This new type of oscillation may have implications for fusion reactors, where mitigating plasma oscillations can facilitate the confinement required for high-efficiency fusion power generation.”
     Dozens of companies world-wide are working on a variety of designs for fusion power reactors. Hopefully, the work of John Palastro and others will speed the development of fusion power.