Extreme plasma theories put to the test

The first controlled studies of extremely hot, dense matter have overthrown the widely accepted 50-year-old model used to explain how ions influence each other's behavior in a dense plasma. The results should benefit a wide range of fields, from research aimed at tapping nuclear fusion as an energy source to understanding the inner workings of stars.

The peaks on this chart represent key energy signatures produced in a dense ultrahot plasma, which for the first time allow detailed measurements of the effects of this plasma environment. Read... (Image courtesy of Sam Vinko, University of Oxford)

The study also demonstrates the unique capabilities of the Linac Coherent Light Source (LCLS) X-ray laser at the U.S. Department of Energy (DOE)'s SLAC National Accelerator Laboratory. While researchers have created extremely hot and dense plasmas before, LCLS allows them to measure the detailed properties of these states and test a fundamental class of plasma physics for the first time ever.

Plasma is sometimes referred to as the fourth state of matter – alongside solid, liquid and gas – and in this case it was hundreds of times hotter than the surface of the sun (2 million kelvins or 3.6 million degrees Fahrenheit). These measurements, reported by an international team of researchers and published this week in Physical Review Letters, contradict the prevailing model that scientists have used for a half-century to understand the conditions inside plasmas.

"We don't think this could have been done elsewhere,'' said Justin Wark, leader of a group at Oxford University that participated in the study. ''Having an X-ray laser is key."

The international research team, which made the plasma by targeting super-thin aluminum with X-rays at LCLS, reported its initial results in January. Now, in a second study based on a new analysis of data from the same experiment, the group tackled another question: How are atoms in such a hot, dense plasma affected by their environment?

The researchers were able to pinpoint how much energy it takes to knock electrons from highly charged atoms in a dense plasma. "That's a question no one's been able to test properly before," said Orlando Ciricosta of Oxford University and lead author of the study, which included scientists from three DOE national laboratories.