Three PPPL scientists win competitive awards


image: Physicists Sam Cohen, left, Yevgeny Raitses and Erik Gilson have received DOE grants totaling more than $ 3 million over three years for cutting-edge plasma science projects.
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Credit: Photos by Elle Starkman / Collage by Kiran Sudarsanan

World-class expertise in the study of plasma – the hot, charged state of matter made up of free electrons and atomic nuclei, or ions, which makes up 99% of the visible universe – has won science projects from tip for three physicists from the US Department of Energy (DOE) Princeton Plasma Physics Laboratory (PPPL). The three-year awards provide leading PPPL research physicists Sam Cohen, Erik Gilson and Yevgeny Raitses $ 330,000 each per year to pursue projects ranging from studying plasma particles thousands of times thinner than a hair human to the formation of heavenly bodies. PPPL projects represent three of the nine projects awarded by the DOE.

These awards, based on competitive peer review, aim to expand key areas of plasma science. “A better understanding of the properties of plasma has many important scientific and technological applications, including high power lasers, advanced microelectronics, and astrophysics,” said James W. Van Dam, associate director of the DOE Bureau of Science for fusion energy sciences. “The research, led by the DOE National Laboratory teams, funded as part of this announcement, will help ensure continued US leadership in this critical area. “

Here is an overview of the designated projects.

Explore energetic electrons. The energetic electrons are, unexpectedly, very hot particles (over 100 M ° C) produced during the radiofrequency heating of magnetized plasmas. Such electrons were found by graduate student Peter Jandovitz and former graduate student Charles Swanson, now a PPPL physicist, in low-temperature, low-power magnetic mirror plasmas. “The issue is with such a low power, which can eventually cause the creation of energetic electrons,” said physicist Sam Cohen, who studies this phenomenon.

Project results could apply to plasma processing in the field of microelectronics in which energetic electrons can bombard semiconductor materials and create defects, Cohen said.

He plans to study high-temperature electron creation in his Princeton Field-Reversed Configuration (PFRC) device, which uses magnetic mirrors to create the magnetic field that confines the plasma. The project will explore the basic physics of the process and seek answers to questions such as where electrons grow, the shape of magnetic fields, and why the properties of plasma affect them. Cohen will use X-ray detectors to measure and analyze these electrons.

To explain the formation of highly energetic cosmic rays, physicist Enrico Fermi theorized 72 years ago that a charged particle increases energy when it bounces between moving magnetic interstellar clouds. Fermi argued that a series of particle collisions with a magnetic field perpendicular to the particles like a moving wall would produce energetic cosmic rays.

However, research by scientists on the PFRC revealed the energetic behavior of the particles in which the particles moved. parallel to the magnetic field of mirror configuration.

Investigation of star formation. Funding for the magneto-rotational instability (MRI) experiment at PPPL will help research a phenomenon that could explain the formation of stars and planets. Scientists speculate that MRI could explain the observed rates of dust and other material swirling in so-called accretion discs around cosmic objects like stars and black holes and how this material is collapsing inward and freezes in celestial bodies.

“Our recent experiments and the simulations that accompany them have shown intriguing and unexpected signs of instability; this funding will allow us to take our research on this instability to the next level, ”said Gilson.

The MRI experiment aims to replicate the instabilities that are believed to cause the swirling dust clouds to collapse in the growing bodies they orbit. The experimental set-up consists of two nested cylinders with the space between them filled with a liquid metal alloy. The cylinders rotate at different speeds, mimicking the different rotational speeds of the material in the accretion discs.

Gilson and his colleagues will use the funding to modify the MRI experiment to allow for greater variation in liquid metal conditions. Scientists will examine whether the top and bottom caps and walls of the device could be causing the unexpected results.

Gilson noted that the project team includes Princeton University professor and PPPL distinguished researcher Hantao Ji, as well as Princeton University professor Jeremy Goodman, and that the funding will support Yin Wang, a postdoctoral researcher who will do most of the research. The funding will also support related computer simulations produced by Wang and PPPL theoretical physicist Fatima Ebrahimi. This new funding will also support graduate students interested in working with the IRM experience for a thesis project.

Measurement of dusty plasmas. Dusty plasmas harbor charged non-plasma particles of a few nanometers to several microns. These particles are known to influence a wide range of plasma behavior. “Dusty plasma is a huge field,” said Raitses, the principal investigator who shares leadership with PPPL physicist Shurik Yatom and Mikhail Shneider, principal investigator at Princeton University. “Dusty plasma is relevant for fields ranging from space physics to microelectronics,” said Raitses.

The researchers aim to measure the charge of dust particles, which have a major influence on the properties and dynamics of dusty plasma. The project will study low-temperature, or cold, plasmas that compare to the million-degree fusion plasmas that have been the hallmark of PPPL research. The determination of the royalty is an essential scientific and practical problem.

While the majority of the dusty plasma measurements have been indirect, the new company “will meet the challenge of [on-site] and real-time measurements of particle charge and mass, ”said the PPPL proposal. The researchers plan to develop and combine two laser techniques in coordination with electron density measurements to meet the challenge.

These techniques are technically referred to as “Laser Stimulated Photo Detachment (LSPD)” and “Laser Induced Incandescence (LII)”. The first is a method of removing electrons from dust while the second will measure the size and density of foreign particles in the plasma and a microwave probe will detect changes in particle density.

Yatom developed the LII diagnostic for a previous project on nanosynthesis that researchers are now exploiting. “The three diagnoses together will allow us to infer the load using a model to be developed by Shneider,” said Raitses.

The three-year project aims to integrate theoretical and experimental studies of LSPD electron detachment that can be applied to the measurement of particle charges in a wide range of dusty plasmas. The project will collaborate with a number of dusty plasma research groups at the University of Auburn and the University of Minnesota. The co-PIs also hope that the project will attract graduate students to conduct their research on the difficult problems of diagnosing dusty plasmas.

PPPL, at the Forrestal campus of Princeton University in Plainsboro, New Jersey, is dedicated to creating new knowledge in the physics of plasmas – ultra-hot charged gases – and developing practical solutions for creating fusion energy. The laboratory is managed by the University for the Office of Science of the United States Department of Energy, who is the biggest proponent of basic physical science research in the United States, and strives to address some of the most pressing challenges of our time. For more information, please visit

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