November 20, 2023

Engineering high-frequency fusion

Photo of woman with dark hair and skin in a navy blue blouse smiling at the camera while standing in front of a large piece of electrical hardware

Vidya Nalajala and her team are developing Zap’s advanced repetitive power supply: the high-voltage spark plug that will drive hundreds of thousands of fusion pulses a day.

Electric current is critical to a Zap fusion core’s performance. On principle, the stronger the current, the more fusion energy the device can yield. Repeatability is also important, since more frequent reactions lead to more net energy to the grid. The power supply that converts individual fusion bursts into utility-scale electricity will need to marry both – an incredibly strong current discharged as frequently as the physics will allow.

The team engineering the heartbeat of the fusion plant

At Zap Energy, Vidya Nalajala is the leader of the advanced repetitive pulsed power team developing that technology: their high-voltage power supply will fire hundreds of times every minute, with each megaamp pulse lasting between 100 to 200 millionths of a second. To support baseload power needs, the power supply will spark fusion reactions hundreds of thousands of times a day, for months on end.

“The challenges involved with making this power supply are enormous. Nobody has done anything like this before,” says Nalajala.

The power supply that pulses current into the Z pinch is the largest component of the fusion energy system being developed by Zap.

High energy density science in the high desert

Before joining Zap in 2022, Nalajala worked for more than 15 years at the massive Zebra Pulsed Power Lab (or ZPPL, previously known as the Nevada Terawatt Facility) at the University of Nevada, Reno. ZPPL houses research in high-energy-density physics, which involves subjecting plasma to the extreme conditions found inside stars.

The huge laboratory complex is home to the nation's largest university laser and pulsed-power accelerator combination. Donated by the Los Alamos National Laboratory, and installed in partnership with Sandia National Laboratories, “Zebra” is capable of driving two million volts of electric current through a target and turning it into plasma as hot as the interior of the sun.

Repetitive pulsed power is a relatively small niche within electrical engineering since batteries and supercapacitors discharge electricity quickly enough for most commercial applications. But decades of working at ZPPL gave Nalajala experience with cutting-edge research at the intersection of pulsed power, plasma, Z pinches and fusion energy itself. The thesis for her master’s degree at UNR also focused on compact Z-pinch plasma machines.

Beginning in 2005, Vidya Nalajala worked on dozens of research projects at the Zebra Pulsed Power Lab at the University of Nevada, Reno. Photo credit: Vidya Nalajala, 2018.

Nalajala’s time at ZPPL also honed her leadership style, requiring her to train and lead teams of undergraduates in UNR’s physics department to execute complex research projects.
“For years, I was training 18-year-olds who might not know what a wrench or Phillips-head screwdriver was,” she recalls. “But I like to interact with young brains a lot. I like to listen to their ideas.”

Getting the details wired in

One of Nalajala’s frequent collaborators is Matt Aubuchon, who leads the directorate developing Zap’s pulsed power components. Aubuchon says Nalajala thrives in the ambiguity of a startup environment, describing her as strategic about engaging her teammates to force clarity.

“Vidya is very humble: no attitude, low ego. She can see a long way out what kind of work something will require, and she’s really good at organizing both people and processes to execute over a long timeframe. She sets a good example for the company on how to get stuff done.”

Building a power supply capable of billions of shots over its lifetime means prioritizing repeatability and durability in every conceivable aspect of the project including topology, instrumentation, insulation and cooling. Nalajala sees her role as responsible for maintaining the high-level vision while also nailing the tiniest details.

Daily team standups move quickly from component selection and testing to construction timelines and discussion of systems integration. She has been known to spot-check the gauge of a particular wire and stays in close contact with supply chain colleagues to help expedite critical components.

Engineer Brad Maynard explains the components of the first generation 100 kW Power Supply (100kWPS-01) in Zap’s facility in Mukilteo, Washington.

In the past year, one of her team’s most important accomplishments was the integration of a new pulsed transformer to the power supply. Nalajala lights up while describing the effort: although none of them had ever worked on transformers before, her engineers designed it in house, piece by piece. To test initial versions, they were wrapping, winding and testing components by hand until they achieved the performance they were looking for. The transformer tripled the existing current and enabled them to reach a new high-water mark in pulse repetition rate.

“I don't know how to put it a better way — the vibe is good,” she says. “We come together to solve problems.”

Cabling and a high voltage differential probe at Zap Energy’s facility in Washington.

Envisioning the future of fusion

Earlier this year, Zap’s first prototype of an advanced power supply discharged one thousand consecutive high-voltage pulses at a rate of roughly one pulse every 10 seconds without failure. Since then, the team has been building toward the next milestone: an iteration of the power supply tied to the dynamic load of a plasma, designed to operate in more realistic conditions to better simulate a true power plant environment. They’ve already executed test shots on the new system.

Now, after a year and a half at Zap, Nalajala remains confident that her team will continue to push their technology forward. She points to the attitude they bring to the lab every day as the key to their consistent progress.

“Call it the tenacity, the determination, maybe the hunger for finding solutions, right? This team has thirst to say, ‘I'm going to get this done no matter what.’”