Scientists at Texas A&M University in the U.S. and collaborators at ETH in Switzerland have found an innovative way to obtain lithium-6, a critical component for fusion fuel for some reactor designs. The conventional sourcing method COLEX uses mercury and is banned in the U.S. This prompted scientists to find new ways to source the isotope as the race for unlocking fusion energy accelerates.

Nuclear fusion technology has gathered much attention in recent years as the world seeks cleaner ways to power its economic functions. Decades of research in this area have now reached the point where engineers can replicate reaction conditions that occur in the Sun and attain a net energy gain.

In nuclear fusion, hydrogen isotopes deuterium and tritium are combined to yield helium-3 and lots of energy. Since tritium is radioactive, rare, and expensive to source, fusion facilities have to set up breeder reactors where the isotope is produced by bombarding lithium blankets with neutrons.

Researchers Sarabjit Banerjee and Andrew Ezazi, who were involved with this work said that lithium isotopes, lithium-6, and lithium-7, can both be used for breed tritium, but the reaction with lithium-6 is much more efficient.

Currently, lithium-6 is produced with the COLEX separation process. Liquid mercury is used to isolate it from the commonly occurring isotope lithium-7. Since 1963, a U.S.-imposed ban on the use of liquid mercury due to pollution concerns means that the country cannot produce lithium-6 anymore.

Since then, the U.S. has been operating with a steadily diminishing stockpile of lithium-6 maintained at the Oak Ridge National Laboratory (ORNL).

Banerjee explained in the email, “There is no publicly available information on the stockpiles of 6Li that the United States maintains. It is a closely guarded secret as it is tied to the ability to produce thermonuclear warheads and the amount of said weapons. However, if nuclear fusion were to become a reality, plants would need tons/day of lithium-6.”

Banerjee and his team discovered a mercury-free approach to isolating lithium-6 while working on a project to clean “produced water” in West Texas.

During oil and gas drilling, groundwater that rises to the surface must be cleaned before it is pumped back down. Using a cement membrane, the researchers were able to filter out silt and residual oil but found that the wastewater still had high lithium levels. This was a result of the lithium-binding capabilities of zeta-vanadium oxide (V2O5). V2O5 is lab-synthesized inorganic material.

Banerjee added in the email, “We found that zeta-V2O5 is indeed a highly selective host for Li-ion insertion and we could capture lithium even though the hypersaline wastewater had many orders of magnitude more sodium-, magnesium-, and calcium-ions. The researchers tested the specificity of the material between lithium-6 and lithium-7 and found that it was useful in enriching the lithium-6 isotope.”

The integration of lithium ions into the zeta-V2O5 changes its color from bright yellow to dark olive green, allowing the isolation to be monitored visually. A single electrochemical cycle enriches lithium by five and seven tenths’ percent. Thirty percent enrichment is a minimum requirement for fusion fuel. This can be achieved by reusing the membrane twenty-five times.

Banerjee said, “Zeta-V2O5 is not expensive to produce, and in fact is now commercially available from a startup company. The material can be repeatedly cycled with no loss in selectivity – in fact it was explicitly designed this way. While we have demonstrated proof-of-concept, with a sufficient number of loops, we expect to get to ninety percent enriched lithium-6 within forty cycles.”

The team is currently working to scale their method to an industrial level. Banerjee said in a press release, “I think there’s a lot of interest in nuclear fusion as the ultimate solution for clean energy. We’re hoping to get some support to build this into a practicable solution.”

Texas A&M

Scientists may be close to unlocking the virtually unlimited energy of nuclear fusion due to the development of a cutting-edge device that can superheat plasma.

Japan-based Kyoto Fusioneering has developed a one-megawatt gyrotron. It is a device that generates high-power microwave radiation required for heating and controlling plasma in nuclear fusion reactors. The new tool could be the key to helping Tokamak Energy, a private fusion power company in the United Kingdom, achieve sustainable, commercially viable fusion energy.

Tokamak Energy said in a press release, “The new gyrotron will generate high-power electromagnetic waves for controlling and heating a hydrogen plasma many times hotter than the center of the sun. It will also be used to start up and drive plasma current.”

The company received the gyrotron from Kyoto Fusioneering in late December and plans to install it on its spherical tokamak ST40 this year. Once the fuel-heating technology is operational, Tokamak Energy and several of its partners, including the U.S. Department of Energy, will begin testing lithium on the inner wall of the ST40 for a future fusion pilot plant.

According to Tokamak Energy, the ST40 tokamak is the “most advanced of its kind in the world.” It achieved a record of more than one hundred and eighty million degrees Fahrenheit plasma ion temperature in 2022. This is more than six times hotter than the sun’s core temperature and is considered to be the threshold for commercial fusion energy.

The ultra-powerful gyrotron will advance Tokamak Energy’s efforts to produce nuclear fusion for commercial use by 2030, as the International Energy Forum (IEF) reported.

The IEF explained that nuclear fusion generates nearly four million times more energy than dirty fuels such as coal, oil, and gas and four times more than nuclear fission. Since it doesn’t produce carbon dioxide, other polluting gases, or long-lived radioactive waste, it is an ideal clean, low-cost energy source to that could power the world in the future.

Gyrotrons will probably play a major role in bringing sustainable fusion power to homes and cities. Gyrotrons offer several benefits that can advance progress in fusion research, including their ability to superheat plasma and transmit microwave radiation through waveguides, allowing for more flexibility in positioning.

The new technology also reduces the size needed for the central solenoid which is a key component in tokamaks that generates a strong magnetic field used to initiate and maintain the plasma current during the fusion process.

Tokamak Energy stated that “A gyrotron, which uses Electron Cyclotron Resonance Heating (ECRH), solves one of the key challenges for a spherical tokamak – limited space for a central solenoid, which would otherwise be required to induce the plasma current”.

Tokamak Energy said it plans to use both its current neutral beam injection heating system and gyrotron heating on the ST40 to improve their understanding of the balance needed for future spherical tokamak pilot plants.

Ross Morgan is the director of strategic partnerships at Tokamak Energy. He said, “We’re excited to work with our partners Kyoto Fusioneering to add this important upgrade to our record-breaking fusion machine, and continue to operate ST40 to test and push new boundaries.”

Tokamak Energy

Part 2 of 2 Parts (Please read Part 1 first)

Gyrokinetic Electromagnetic Numerical Experiment (GENE) is an open-source plasma microturbulence program which can be used to efficiently compute gyroradius-scale fluctuations and the resulting transport coefficients in magnetized fusion/astrophysical plasmas. GENE is comprehensive, well benchmarked, portable, and highly scalable.

If you want to determine the temperature of a body of water, you simply place a thermometer in the water. In fusion research, plasma temperature is usually measured using microwaves emitted by the plasma itself. Fluctuations in the electron temperature can also be derived from these emissions.

In addition, by launching microwaves into the plasma, researchers are able to analyze the backscattered radiation to extract information about fluctuations in the electron density. This information provides the number of electrons per unit volume. Utilizing this approach, Höfler and her team were able to characterize fluctuations in both plasma temperature and plasma density.

Two diagnostic methods played a central role in the experiment. The first consisted of using Doppler reflectometers to measure fluctuations in the plasma density. Using three reflectometers from ASDEX Upgrade’s available diagnostic equipment, the team analyzed vortices of various sizes at different locations. The second method utilized a Correlation-Electron-Cyclotron-Emission (CECE) radiometer from the Massachusetts Institute of Technology (MIT) in the U.S. for precise measurements of electron temperature fluctuations.

The comparative plasma simulations in five-dimensional phase space were carried out using the GENE program which was developed at IPP and is globally recognized as a leading tool for numerically modeling turbulent processes inside plasmas. The complexity of these phenomena is so great that the supercomputers used for this study required two months of computing time to model the observed turbulence over just a few milliseconds.

Close collaboration between experimental and theoretical physicists was very important. It is not enough for GENE calculations to reproduce the plasma turbulence correctly. They also have to simulate the complex measurement process, which the researchers have now achieved after years of work. This is the only way that comparability between experiment and numerical calculation can be established at all.

Höfler recalled, “When I received the simulation results, I was genuinely surprised by how well they matched all the experimental data.” Even phenomena that were not expected intuitively were accurately predicted by GENE software

The research team established different temperature profiles for the two plasma discharges studied at ASDEX Upgrade. In Discharge 1, steeper temperature gradients were applied when compared to Discharge 2. As expected, Discharge 1 exhibited greater temperature fluctuations than Discharge 2. However, unexpectedly, the density fluctuations behaved in the opposite way. This is a result that initially seemed inexplicable. Yet, the GENE simulations reproduced this behavior exactly.

Höfler summarizes, “We have proven that GENE reliably predicts the real behavior of the two plasma discharges”. With respect to fusion research, this means that simulations can be used to optimize plasma scenarios to achieve the highest possible energy confinement time. The concept of a digital twin of a fusion reactor is now more tangible, allowing for improved predictions of reactor plasma performance.

GENE Code