A new study featured on the cover of the March 2021 issue of Physics of Plasmas is the first published research from WVU’s PHASMA experiment in the Center for Kinetic Experiment, Theory and Integrated Computation Physics.
The PHAse Space MApping experiment, or PHASMA, is a one-of-a-kind facility that uses lasers to measure the speeds and positions of individual ions and electrons in a plasma. The combination of position and velocity information is called phase space.
“The lasers used in PHASMA hit the ions and electrons with light. Either particles absorb the light and send it back out, or it just bounces off of them,” said Earl Scime, the Center’s director and Oleg D. Jefimenko Professor of Physics and Astronomy. “Either way, the light we measure is shifted in color by the motion of the particles, and that tells us their speed. For example, it is the same technique police use to measure the speed of cars on the highway with lasers or microwaves.”
This study investigated what happens inside a flowing tube of plasma when scientists increase the electrical current, which emulates processes on the sun. Plasma is the fourth state of matter and accounts for 99 percent of all visible matter in the universe.
“Consistent with theory, when the current passes a critical level, the entire tube of plasma kinks as an instability grows, creating a corkscrew-like shape,” Scime said. “Now that we know how to create this kinking behavior, we can use it to our advantage in studies of space phenomena such as magnetic reconnection – a process in which energy stored in the magnetic fields in a plasma is converted into heat and flow. This is what happens in large-scale events on the sun.”
The findings in this paper confirmed how much current in a plasma made of argon gas is needed to create the helix-shaped instability, a first in plasma physics.
“This paper was our first attempt to make these tubes of plasma in argon gas, which had not been done before with our style of plasma guns, and see if the instability threshold matched the predictions of theorists – which it does. Because we also measured the temperature of the plasma with our lasers and were able to identify new waves in the plasma after the kink begins, this work established that our facility works as designed and has the capability to make new discoveries,” Scime said. “It was an exciting paper for us because it lays the groundwork for a lot of what we are going to do in the future.”