Part 2 of 2 Parts (Please read Part 1 first)
     Helion says that its approach is different from other fusion power reactor designs in three important ways. First, it utilizes a pulsed, non-ignition fusion system. The company explains, “This helps us overcome the hardest physics challenges, build highly energy-efficient devices, and allows us to adjust the power output based on need by adjusting the pulse rate.”
     The second major difference is that the Helion system is built to directly recover all unused and new electromagnetic energy efficiently. The company says, “Other fusion systems heat water to create steam to turn a turbine, which loses a lot of energy in the process.”
     The third important difference is that the Helion fusion reactor uses a deuterium and helium-3 fuel mixture. Deuterium-helium-3 fusion results in charged particles that can be directly recaptured as electricity. The company points out that “This helps keep our system small and efficient, allowing us to build faster and at a lower cost. This fuel cycle also reduces neutron emissions, substantially reducing many of the engineering challenges faced by users of deuterium-tritium fusion fuel.”
     Helion has constructed six prototype fusion reactors over the years. Trenta is its most recent prototype. The company claims that it ran nearly every day for two years. Trenta reportedly completed ten thousand high-power pulses and operated under vacuum for sixteen months. The company says, “With Trenta, Helion became the first private organization to reach plasma temperatures of one hundred eighty million degrees Fahrenheit (9 keV).” After successful test campaigns, Helion shut down Trenta in January of 2023.
     Helion is now focused on constructing its seventh fusion reactor prototype, called Polaris. According to Helion, Polaris is designed to demonstrate the production of a small amount electricity. It will have a higher magnetic field strength and an increase repetition rate when compared to Trenta. Helion hopes to begin the operation of Polaris by early 2024.
     Helion also notes several other technical milestones it has achieved. Among these milestones, the company claims that its magnets operate at over ninety percent energy efficiency. In addition, Helion says that its magnets have achieved compression fields over ten Tesla. It has also achieved sustained plasmas with lifetimes greater than one millisecond. The company says that “With every machine we build, we learn more about the capabilities of our science and technology. With rapid iteration and testing, we have been able to learn quickly and apply what we’ve learned to our next machines.”
     Earlier this year, Microsoft signed a power purchase agreement with Helion to buy electricity from Helion’s first commercial fusion power plant. That unit is expected to produce at least fifty megawatts after an initial ramp-up period. It is projected to come online in 2028.
     David Kirtley is the CEO of Helion. He said in a statement announcing the collaboration with Nucor that “A project like this is only made possible by working with a forward-looking company like Nucor, which is committed to decreasing its carbon emissions.”
     Topalian said that “This project marks a tremendous milestone in the potential for the use of nearly limitless clean electricity for industrial manufacturing. By entering this agreement, we are demonstrating our commitment to be the cleanest steel producer in the world, while setting an example for all manufacturing companies.”

     Researchers under the direction Chang Liu of Princeton Plasma Physics Laboratory (PPPL) have discovered a promising approach to mitigating damaging runaway electrons created by plasma disruptions in tokamak fusion reactors. This approach harnesses a unique type of plasma waves that bears the name of astrophysicists Hannes Alfvén, a 1970 Nobel laureate.
     Alfvén waves have long been known to loosen the confinement of high-energy particles in tokamak reactors. This permits some particles to escape and reduces the efficiency of the donut-shaped fusion reactors. However, the new findings by Chang Liu and his team at General Atomics, Columbia University and PPPL have uncovered new techniques to deal with runaway electrons.
    The researchers found that such loosening can diffuse or scatter high-energy electrons before they can turn into avalanches that damage tokamak components. This process was determined to be circular. The runaway electrons create plasma instabilities that give rise to Alfvén waves that keep avalanches from forming.
     Chang Liu is a staff researcher at PPPL and the lead author of a paper that details the results of his work in the journal Physical Review Letters. He said, “The findings establish a distinct link between these modes and the generation of runaway electrons.”

     Researchers have derived a theory for the circularity of these interactions. The results of their experiments align well with runaway electrons in experiments on the DIII-D National Fusion Facility which is a Department of Energy (DoD) tokamak that General Atomics operates for the U.S. DoE Office of Science.
     Felix Parra Diaz is the head of the Theory Department at PPPL. He said, “Chang Liu’s work shows that the runaway electron population size can be controlled by instabilities driven by the runaway electrons themselves. His research is very exciting because it might lead to tokamak designs that naturally mitigate runaway electron damage through inherent plasma instabilities.”
    Plasma disruptions begin with sharp drops in the multi-million-degree temperatures required initiate and sustain fusion reactions. These drops in temperatures are called “thermal quenches”. They release avalanches of runaway electrons similar to earthquake-produced landslides. Liu said, “Controlling plasma disruptions stands as a paramount challenge to the success of tokamaks,”
     Plasmas are the hot, charged states of matter composed of free electrons and atomic nuclei called ions. Fusion reactions combine light elements in the form of plasmas to release vast amounts of energy. Fusion processes power the Sun and stars. Mitigating the risk of plasma disruptions and runaway electrons would provide a significant benefit for tokamak facilities designed to reproduce the fusion process on Earth.
     The new approach could have implications for the advancement of the International Thermonuclear Experimental Reactor (ITER). ITER is the international tokamak project under construction in France to demonstrate the practicality of fusion energy and could mark a key step in the development of commercial fusion power plants.
     Liu said, “Our findings set the stage for creating fresh strategies to mitigate runaway electrons.” Experimental campaigns in which all three research centers aim to further develop the important findings with respect to runaway electrons.