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Photoacoustics Aid Search for Fusion Materials


In the 1920s Arthur Eddington proposed that the process of fusing small nuclei together, or fusion, released large amounts of energy and was in fact what powered the stars. Since that time fusion power has been an important area of study, but despite nearly 100 years of research, controlled fusion remains elusive.

In recent years, the plasma-wall interaction within fusion devices has become an increasingly important area of research. To date, an ideal material for the interior walls of fusion devices has not yet been found—but the work of Zhili Zhang, associate professor of mechanical, aerospace, and biomedical engineering, may help change that.

Zhili Zhang, associate professor of mechanical, aerospace, and biomedical engineering“Controlled fusion has some problems. Basically you have to create a very hot gas, so you generate ionized gases called plasmas,” said Zhang. “The plasmas will bombard a metal wall and the wall will be etched. The goal is to find a material to hold the plasma, so now the big research problem is the plasma-wall interaction.”

Zhang’s JDRD project proposes to provide more accurate measurements of plasma-wall interactions in the new ORNL Proto-MPEX, an experimental facility designed to help test materials for their fusion containment capabilities. Zhang’s team will contribute to this goal by providing real-time measurement data for the testing materials.

“You know the material will be impacted by the plasma. It’s a very fast process. Plasma will etch the wall within almost a millisecond, so how can you provide in situ measurements of the plasma-wall interactions?” said Zhang.

Theodore Biewer, Zhang’s partner and a senior research scientist at ORNL, will be investigating this problem by taking surface measurements while his team takes gas phase measurements.

“We also propose to use photoacoustics,” said Zhang. “So the laser will hit the wall and some of the energy will be absorbed, which will increase the local temperature on the surface. That will generate a pressure increase, which will lead to an acoustic wave, so you can hear it. This is a good way to do nondestructive detection on the surface.”

Zhang’s team has constructed a much smaller version of the facility in his lab in order to test their ideas before moving to the Proto-MPEX. He hopes this will allow for improved efficiency in the testing process, which he believes will generate scientifically significant information.

The LDRD team has submitted a proposal to the US Department of Energy based on the preliminary research and design of the project. The proposal, which if funded could also benefit Zhang’s work, has passed through the first round of eliminations and is under consideration for approval.