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PPPL lends General Electric a hand in developing an advanced power switch

Scientists at the U.S. Department of Energy’s (DOE) Princeton Plasma Physics Laboratory (PPPL) are assisting General Electric Co. in developing an electrical switch that could help lower utility bills. The advanced switch “could contribute to a smarter, more advanced, more reliable, and more secure electric grid,” according to the DOE’s Advanced Research Projects Agency-Energy (ARPA-E), which is funding the GE project.

The company is drawing upon PPPL’s know-how in dealing with plasma, the hot, electrically charged gas that researchers control with magnetic fields to fuel fusion reactions. Plasma will form the heart of the proposed GE device, which would use a plasma-filled tube to switch electricity on and off in power-conversion systems.

This gas-filled tube would replace the bulky and costly assemblies of semiconductor switches now used in systems that convert the direct current (DC) coming from long-distance power lines to the alternating current (AC) that lights homes and businesses. Such systems also convert AC current to DC current for transmission between AC power grids.

GE is turning to PPPL for help with these tasks:

• Modeling plasma properties for different magnetic-field configurations and gas pressures. “There aren’t many places with a demonstrated ability to model this type of plasma,” said Timothy Sommerer a physicist at GE Global Research Center who heads the switch project. “These guys [at PPPL] really came through and said they could do it.”

• Developing a method for protecting the cathode — the negative terminal inside the plasma-filled tube — from damage from the positively charged ions, or atomic nuclei, in the dense current that flows through the gas. “You need to operate above a certain current density,” Sommerer said. “But this leads to ion impact that can damage the cathode. So what you want is high current-density and low cathode-damage.”

Sommerer has tapped a team led by physicist Igor Kaganovich, deputy head of the PPPL Theory Department, for the modeling task. The team employs specially designed codes to simulate the plasma, said Kaganovich, who works with physicists Alexander Khrabrov and Johan Carlsson on the project. Joining them for the summer were students Mikhail Khodak of Princeton University and David Keating of the University of California-Berkeley.

For tips on protecting the cathode, GE has been studying PPPL’s use of liquid lithium to prevent damage to the divertor that exhausts heat in fusion facilities. The flowing liquid metal forms a wet, self-healing barrier that constantly replenishes itself, said physicist Michael Jaworski, an expert on the use of lithium in fusion experiments.

GE is working with cathodes made of liquid gallium for its self-healing properties. Learning of PPPL’s work with liquid lithium was “just serendipitous,” Sommerer said, since GE initially sought the Laboratory’s plasma-modeling skills. But “conditions in the divertor are pretty similar to what the cathode would face,” he noted, making PPPL’s experience quite useful to know. 

U.S. Department of Energy
Princeton Plasma Physics Laboratory is a U.S. Department of Energy national laboratory managed by Princeton University.

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