August 21, 2023

Here’s what happens inside a Zap fusion core

Purple light glows through a window looking into a stainless steel chamber

Part accelerator, part reaction chamber, Zap’s devices are unlike any others in fusion.

Inside a Zap fusion core, a carefully orchestrated sequence of events sets the stage for fusion. Like a symphony, every step must be executed with precision, and in perfect time. This progression creates the intense conditions that lead to fusion, unlocking the potential for a transformative new energy source.

The origins of Zap’s technology can be traced back two decades to Uri Shumlak’s lab at the University of Washington. There, Shumlak theorized a new approach to fusion called a sheared-flow-stabilized Z pinch. Building on that work, he and his collaborators designed and built a series of experimental fusion devices to test his ideas.

“We started at a very low level,” Shumlak says. “But we’ve been able to show in both models and experiments that you can increase the current in a sheared-flow-stabilized Z pinch and if you do it properly, the fusion yield will also increase,” he says.

Shumlak, now Zap Energy’s Chief Science Officer, co-founded the company in 2017 alongside Benj Conway, Zap’s CEO, and Brian A. Nelson, Zap’s Chief Technology Officer. Nelson is also a UW professor emeritus who has engineered and operated every generation of sheared-flow-stabilized Z-pinch fusion device going back to the 1990s.

Today, Zap Energy is building quickly on the foundation of Shumlak and Nelson’s earlier work, with the goal of developing commercially viable fusion energy. As of 2023, the company performs R&D on two devices, named the Fusion Z-pinch Experiment (FuZE) and FuZE-Q.

Anatomy of a Z pinch

The heart of a Zap fusion system is a roughly 10-foot-long cylindrical vacuum chamber where four key steps in the SFS Z-pinch fusion sequence happen in less than one thousandth of a second, resulting in a burst of fusion energy.

Step 1: Ionize

First a puff of deuterium, a gas also known as hydrogen-2, is jolted by a powerful surge of electricity from a bank of capacitors. The electricity ionizes the gas, a process that strips electrons from their nuclei and turns the deuterium from a gas into a plasma.

Step 2: Accelerate

Both the gas and pulse of electricity enter the vacuum chamber on one end. The geometry of the device’s two electrodes creates powerful electromagnetic forces that drive the plasma downstream along the inner electrode.

Step 3: Pinch

As the plasma arrives at the nosecone on the end of the inner electrode, the magnetic fields surrounding the plasma force it inward, until the plasma becomes a thin filament. This rapid compression, called a Z pinch, heats the plasma to the temperatures necessary for fusion. Peak plasma temperatures to date have been measured up to around 60 million degrees Fahrenheit (3 keV in scientific units).

Step 4: Fuse

Finally, under these intense conditions, all of the forces that typically keep nuclei apart are overcome and they begin to fuse together to form helium nuclei. The reactions also release highly energetic neutrons that can be harvested as fusion’s main source of energy. The flow of the plasma resulting from the acceleration step helps maintain the pinch and extend the time for fusion to occur.

The steps are straightforward, but aligning every aspect to make sure the resulting plasma is hot and dense enough, and also stable for long enough, is extremely difficult.

“A plasma is basically this electrically charged gas that’s moving and acting like a fluid, but also heavily influenced by magnetic forces” explains Hannah Meek, a Zap Energy research engineer. “The really tricky part is that it’s incredibly unstable. Slight changes in timing, gas pressures or voltages can completely change its dynamics.”

Progress toward energy gain

Zap has already verified its approach creates fusion energy, and modeling suggests it will continue to intensify as the current in the pinch increases. The success of R&D on FuZE led to the creation of Zap’s latest-generation device, called FuZE-Q, which brings together a more powerful capacitor bank with advances in electrode design, materials, diagnostics and more. Both FuZE and FuZE-Q have already been used to create fusion plasmas thousands of times. By steadily ramping up the current in the pinch and accumulating a mountain of data along the way, Zap is moving closer to the elusive point known as scientific Q=1, where fusion power leaving the plasma equals the power put into the plasma to create the fusion conditions.

FuZE, shown here, is the third generation of Zap's R&D Z-pinch fusion core. The equipment and instrumentation around the device measure the results of scientific tests.

Fortunately, getting to that point and beyond benefits from a strong multiplier effect in a sheared-flow Z-pinch, says Ben Levitt, Vice President of R&D at Zap Energy. In a well-aligned and stable pinch, even a small increase in current leads to a large increase in the temperature and density of the plasma, and ultimately, how many neutrons are produced.

“That multiplier effect is exponential. Doubling the current would yield more than 2,000 times as many neutrons,” Levitt says. “In other words, we're on a really, really steep curve.”

The Z-pinch magnetic field powerfully compresses the plasma into a thin column, producing extreme temperatures and densities. Current devices run horizontally to allow easier access, but future devices will be oriented vertically. The FuZE and FuZE-Q devices are oriented horizontally but future devices are designed to be vertical, like the concept shown in animations.