Beside the familiar solid, liquid, and gas, matter has a fourth state: plasma, an immensely hot state of matter where electrons are stripped from gas atoms. Very hot flames and lightning are made up of plasma, as are the sun and the stars. Here on Earth, the field of plasma physics marches forward. A mechanical engineering Ph.D. student has created a small device that creates plasma that can be studied, with results that can be extrapolated to the larger scale. Cold plasmas, another area of study, particularly for medical applications, are created by trapping and cooling neutral atoms and then ionizing the atoms.
Marc Ramsey, a Vanderbilt University mechanical engineering Ph.D. student, has created a tabletop device that produces high-energy-density plasma. He worked at the newly renovated Vanderbilt University mechanical engineering laboratory on the project with Prof. Robert Pitz. The tabletop device generates plasma at more than one million atmospheres at the center of a collapsing bubble, creating conditions relevant to physics and astrophysics, and difficult and expensive to create by other means, Pitz said.
At those kinds of pressures, there are no solids or liquids, only plasma.
The tabletop device generates plasma at more than one million atmospheres at the center of a collapsing bubble, creating conditions difficult and expensive to create by other means. Image: Vanderbilt University
Plasmas at the conditions created in the device exist at the centers of giant planets such as Jupiter and occur during some astrophysical events, he said. Such conditions have been created at only a few facilities around the world, at Sandia National Laboratories in Albuquerque, NM, for instance, by its Z machine, a pulse power X-ray and gamma ray generator.
While Ramsey’s device cannot recreate every experiment conducted at the large facilities, it sits on a table and can fire several times per minute, much more frequently than the large facilities can perform. The power supply is the size of a shoebox.
“The types of conditions this can produce are a small subset of what those other facilities can produce,” Ramsey said. “But this at least gets into the ballpark for thousands or millions of times less money, time, and energy. It will allow us to study the properties of these types of plasmas at a very small scale and mathematically scale it up to the larger events.”
The device works by pumping water to a vacuum and nucleating a bubble from a low-energy laser pulse. Raising the pressure quickly then causes the bubble to collapse, creating plasma that emits an intense burst of light and then a shock wave. Generating a similar event in the large facilities requires thousands or even millions of joules of energy, while the Vanderbilt lab’s device requires little more than one joule, Ramsey said.
More features and capabilities of the device are described in an article, “Energetic Cavitation Collapse Generates 3.2 Mbar Plasma with a 1.4 J Driver,” published April 10, 2013, by Physical Review Letters.
Read the most recent issue of Mechanical Engineering.
It [the device] will allow us to study the properties of these types of plasmas at a very small scale and mathematically scale it up to the larger events.
Marc Ramsey, Vanderbilt University