Chinese researchers say that recent advancements in the burgeoning field of inertial confinement fusion are bringing us one step closer to making accessible nuclear fusion a reality.
The new findings, which incorporate innovative new modeling approaches, could open new avenues for the exploration of the mysteries surrounding high-energy-density physics, and could potentially offer a window toward understanding the physics of the early universe.
Harnessing controlled nuclear fusion as a potential source of clean energy has seen several significant advancements in recent years, and the recent research by a Chinese team, funded by the Strategic Priority Research Program of Chinese Academy of Sciences and published in Science Bulletin last month, signals the next wave of insights with what the team calls a “surprising observation” involving supra-thermal ions during observations of fusion burning plasmas at National Ignition Facility (NIF) at Lawrence Livermore National Laboratory in California.
Inertial Confinement Fusion
A primary component driving the pursuit of controlled nuclear fusion as a potential means of generating clean and abundant energy is inertial confinement fusion ICF, which relies on the ignition of fuel packets comprised of deuterium-tritium (DT).
Nuclear fusion, the process that powers stars, involves atomic nuclei fusing to form heavier nuclei, which releases massive amounts of energy. In stars, hydrogen atoms fuse into helium under very extreme naturally occurring conditions, generating self-sustaining reactions.
By comparison, in the laboratory, achieving ignition is more complex, although it represents a major step toward using fusion as a clean, efficient, and sustainable energy source. Fusion-based energy relies on hydrogen as fuel, producing only helium as a byproduct, making it environmentally friendly. If harnessed for electricity generation, it could provide a virtually limitless and eco-conscious alternative to conventional energy sources.
In February 2021, scientists achieved a burning plasma state during internal confinement experiments conducted at the National Ignition Facility, marking a significant step toward the development of fusion energy. Late in August of that same year, the successful achievement of ignition occurred at Lawrence Livermore National Laboratory’s National Ignition Facility, as revealed in three peer-reviewed papers published the following year.
When it comes to DT fusion, neutrons carry most of the released energy, which can thereby be harnessed for electricity generation. At the same time, alpha particles become trapped in the fuel packet, which propels additional fusion reactions. Once the energy from these alpha particles exceeds the energy input produced during the implosion that occurs, the resulting plasma that is generated reaches a self-sustaining burning phase like what occurs naturally on the surface of stars like our Sun.
A Unique Plasma Phenomenon
During the 2021 experiments, scientists noted the observation of a novel physical phenomenon revealed in data involving neutron spectra, where the data revealed a significant deviation from earlier predictions based on hydrodynamics. Namely, the NIF team’s 2021 observations seemed to point to the presence of supra-thermal DT ions.
The discovery was significant, especially since it presented challenges to current models that dictate particle speeds occurring in idealized gases, otherwise recognized as Maxwell-Boltzmann distributions. Further, the findings pointed to non-equilibrium mechanisms and kinetic effects that had previously remained unacknowledged.
Modeling such effects presents challenges to more than just currently accepted physics, as this process can often include significant energy exchanges that make predicting their kinetic effects difficult. Supra-thermal ions are produced when large-angle collisions occur during these processes, which result from the deposition of alpha particles. What results are potentially significant deviations from the equilibrium state, which often evade easy categorization alongside standard hydrodynamic observations.
New Approaches in Modeling Ion Kinetics
The recent Chinese research effort, led by Prof. Jie Zhang from the Institute of Physics of Chinese Academy of Sciences and Shanghai Jiao Tong University, sought to overcome such challenges by employing a novel approach: the team implemented a new model for large-angle collisions, which also factors in the influence of background ions alongside the relative motion of ions present in binary collisions.
The resulting model proposed by the team allowed them to generate a more cohesive framework for understanding the currently elusive elements of ion kinetics. Specifically, the team introduced a hybrid-particle-in-cell LAPINS code which, through integration with their model, allowed the researchers to produce simulations of inertial confinement fusion burning plasmas.
The team’s findings are promising, as they have revealed unprecedented insights that include ignition moment promotion of close to ~10 picoseconds. The research team also notes the presence of supra-thermal D ions below an energy threshold of ~34 kiloelectronvolts (keV), which clocks in at close to double the expected amount of deposition of alpha particle densities. Lastly, the team reports observations of close to a 24% increase of alpha particles densities close to the hotspot center.
The team’s findings appear to agree with separate neutron spectral moment analyses conducted by the NIF during kinetic simulations, with each batch of data now revealing disparities between neutron spectral moment analyses and hydrodynamics predictions, with the latter appearing to rise with overall increases in yield.
The team’s findings are important in the push toward harnessing controlled nuclear fusion, a field which has seen several promising developments in recent months. Last year, a joint research effort between Japanese and European researchers achieved a record-breaking plasma volume, generated by the JT-60SA reactor located in Naka, Japan.
In the United States, the Princeton Plasma Physics Laboratory (PPPL) also made significant advancements in plasma stability with help from artificial intelligence, where researchers developed a reinforcement learning model capable of predicting and preventing tearing mode instabilities in fusion plasmas.
Ultimately, the Chinese research team’s new findings help to further propel the field, and set the course for new research opportunities that will enable finer control of the high energy densities of nuclear burning plasmas. Ultimately, such discoveries could soon pave the way toward abundant new sources of clean energy, in addition to unveiling insights about the evolution of our universe.
The team’s findings were detailed in a paper, “Mechanisms behind the surprising observation of supra-thermal ions in NIF’s fusion burning plasmas” by Yuhan Xue, et al, published in Science Bulletin.
Micah Hanks is the Editor-in-Chief and Co-Founder of The Debrief. He can be reached by email at micah@thedebrief.org. Follow his work at micahhanks.com and on X: @MicahHanks.