CFD Research, UAH plasma model shows manufacturing uses

HUNTSVILLE – Manufacturers using plasma processes in semiconductor production and materials processing will have a new tool developed by the University of Alabama in Huntsville and CFD Research Corp.

“The striations we are talking about are visible in noble gases in some contexts,” said Dr.
Vladimir Kolobov, a principal research scientist in the Center for Space Plasma and Aeronomic Research at UAH. He has been studying them for 30 years; the noble gases are helium, neon, argon, krypton, xenon and mixtures of them.

For example, striations are invisible to the naked eye as they move fast through the neon
gas used inside fluorescent light tubes, he says, but they can be easily visualized using a
stroboscopic technique.

“What we are talking about is something that for 200 years people could see, but only very
recently could they be seen in computer simulations,” Kolobov said.

In fact, he said, the bright and dark layers of striations have been observed in gas discharges long before Dr. Irving Langmuir introduced the term plasma.

“We have used a self-consistent hybrid model of collisional plasma to obtain moving
striations in DC discharges of noble gases,” Kolobov said. “The calculated properties of self-excited waves in neon and argon agreed with available experimental data, and the origin of a helium plasma stability due to stratification was clarified.

“A simplified two-level excitation-ionization model has been used, neglecting the nonlinear effects due to stepwise ionization, gas heating and Coulomb interactions among electrons.”

The new model provides insights into the conditions under which stratifications form.

“When you can develop a computer model and reproduce them, then you know that you
understand this process,” Kolobov said.

The research was funded by the National Science Foundation’s Established Program to Stimulate Competitive Research (EPSCoR) Future Technologies enabled by Plasma Processes initiative and its predecessor, Connecting the Plasma Universe to Plasma
Technology in Alabama. Both grants are led by UAH.

The work relates to space science studies at CSPAR because solar wind plasma is wholly
ionized. However, its properties have commonalities with weakly ionized gas discharge plasmas, so the model can also be applicable to space weather forecasting.

“We have previously shown that electron kinetics in solar wind plasma has many aspects in
common with electron kinetics in gas discharges,” Kolobov said. “The grid-based kinetic
solvers can be used for collisional gas-discharge plasma and collision-less magnetized
space plasmas. They have already been demonstrated for electron kinetics in the solar
wind.”

“The dual utility of plasma models such as this illustrates the both the strengths of the UAH
and CFDRC partnership and the importance of cross-disciplinary collaboration, which is
one of the important goals underlying the FTPP grant that supports nine institutions across
Alabama, including UAH and CFDRC,” said Dr. Gary Zank, the Aerojet Rocketdyne chair of
UAH’s Department of Space Science, director of CSPAR and the principal investigator for
the FTPP and CPU2AL grants.

“The development of an electron kinetic model for the solar wind led to a significant
advance in our understanding of how energetic electrons created in the atmosphere of the
sun carry energy to the Earth and beyond. It’s gratifying to see related theory and modeling being successful when applied to practical manufacturing problems involving gas discharges.”

The research was made possible by developing grid-based kinetic solvers for electrons in
low-temperature collisional plasmas. The advancement of hybrid kinetic-fluid solver
models is one of the foundational research focus areas in the new FTPP project.

“We have pursued the development of such solvers for almost 25 years at CFD Research
Corp. and UAH,” said Kolobov. “Finally, we have developed something that was not
possible when I started studying this plasma stratification problem 30 years ago in my PhD
work, which is why I am so excited about it.”