Key discoveries about plasma

Prof. Nathaniel Fisch

For Nathaniel Fisch, a professor of astrophysical sciences, and director of the Plasma Physics Program at Princeton, grants from the NSF-BSF partnership have enabled a current collaboration with Professor Yitzhak Maron from the Weizmann Institute as well as the continuation of a long-term research partnership with Professor Amnon Fruchtman of the Holon Institute of Technology. Before the NSF-BSF partnership was created, Fisch and Fruchtman received two BSF grants, first in 1998, and again in 2008.

Fisch and Fruchtman first met by chance in an airplane when Fisch was a postdoc and Fruchtman was a graduate student. They discovered they had a common interest in plasma physics. According to Fisch, they immediately started looking for ways to collaborate and found ways to do so over many years. Since Fruchtman was Israeli, one of the ways was through a BSF grant. “The BSF has certainly enabled our partnership to continue,” Fisch said. “More than that, through collaboration with Professor Fruchtman, I was personally introduced to a number of fascinating topics new to me but of particular interest in Israel, including the current NSF-BSF partnership that Professor Fruchtman and I have with the team of Professor Yitzhak Maron. In 2013, I spent a `mini-sabbatical’ at Weizmann, where I learned about certain fascinating findings in experiments carried out by Maron and Dr. Eyal Kroupp on the Weizmann Z-pinch.”

Prof. Amnon Fruchtman

That led to a joint proposal by the Princeton, Weizmann and Holon team to explain these curious results. In a special NSF-BSF program, the NSF supports the US researchers while the BSF supports the Israeli researchers, with the aim of a teamed effort.

The team focuses on one of the key mysteries involving plasma. Mention plasma, and most people (at least those who watch medical dramas) probably think of blood. However, that’s just one example. Plasma is superheated matter – so hot that the electrons are ripped away from the atoms forming an ionized gas. In the night sky, plasma glows in the form of stars, nebulas, and auroras. That branch of lightning that cracks the sky is plasma, so are the neon signs along city streets. In fact, plasma comprises more than 99 percent of the visible universe – and discovering more about it can have a transformative impact on just about every form of science.

Prof. Yizhak Maron

Very dense plasma can be compressed in a device called a Z-pinch (a plasma confinement system that uses an electrical current in the plasma to generate a magnetic field that compresses it). The recent experiments at the Weizmann Institute suggested that the energy in a Z-pinch plasma is dominated by the motion of hydrodynamic turbulent eddies. The further compression of this motion appears to increase the energy in these eddies, rather than the ion temperature. This finding about compression differs substantially from the prevailing one, in which the ions simply get hotter. These investigations led to a variety of insights, and a new model for turbulence in compressing plasma.

Fisch is particularly proud that the joint investigations stimulated by the findings by the Weizmann team have now led to a significant recognition for a promising young member of his Princeton research team. Seth Davidovits, a 2017 graduate of the Program in Plasma Physics in the Princeton University Department of Astrophysical Sciences, won the 2018 Marshall N. Rosenbluth Outstanding Doctoral Thesis Award presented by the American Physical Society. Davidovits’ dissertation focused on the theory and simulation of turbulence in compressing fluids, with an emphasis on effects unique to plasma, such as a novel sudden viscous dissipation mechanism. Fisch was his thesis advisor.

“Through the support of the NSF and the joint NSF-BSF program, Seth was also able to work with the Weizmann group to develop a new way of accounting for turbulence in interpreting data,” Fisch said. “That led to greater internal compatibility within multiple methods of measurement, which in turn lent additional support for the unusual results previously reported by Weizmann. With this grounding in experiment, Seth’s thesis is now positioned to be unusually influential.”

The Princeton-Weizmann-Holon effort is an example of how the NSF-BSF partnership provides opportunities for US scientists to work with Israeli scientists, with benefits not only for today’s US and Israeli scientists, but for tomorrow’s scientists as well.