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Exceeding 1012 D-D flash neutrons in the 4.5-MA 1-MJ dense plasma focus FAETON-X

The FAETON-X facility, a 4.5-MA, 1-MJ dense plasma focus system developed by Fuse Energy Technologies, has achieved a record-breaking figure of merit of 4.5 MA/MJ and produced a peak D-D neutron yield of approximately 1.27×10¹² per shot, demonstrating superior energy efficiency among megajoule-class fusion devices.

Original authors: Vahid Damideh, J. C. Btaiche, Emile Beaulieu, Isaac Hassen, Sophie Faliero, R. B. Spielman, Jane M. Lehr, T. A. Mehlhorn, Greg Van Dyk, Elahe Aranfar, Hao Xian Tan, Niansheng Qi, Edward Smith, Alexei

Published 2026-08-12

📖 6 min read🧠 Deep dive

CC BY 4.0

Original authors: Vahid Damideh, J. C. Btaiche, Emile Beaulieu, Isaac Hassen, Sophie Faliero, R. B. Spielman, Jane M. Lehr, T. A. Mehlhorn, Greg Van Dyk, Elahe Aranfar, Hao Xian Tan, Niansheng Qi, Edward Smith, Alexei Akoulov, Pierre Tochon, Gabriel Owh, Joong Lee, Eric He, John Deneen, Declan Stanton, Filippa Ljunggren, Dan Lin, Sing Lee

Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). ✨ This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer

The Tiny Star in a Box

Imagine trying to recreate the power of the sun right here on Earth. That's the dream of fusion energy: smashing tiny atoms together so hard they fuse, releasing massive amounts of clean energy. But the sun has gravity to hold everything together; we don't. So, scientists use giant machines to squeeze atoms with magnetic forces, creating a super-hot, super-dense ball of gas called plasma. One of the most clever ways to do this is with a device called a "Dense Plasma Focus." Think of it like a cosmic pinball machine where electricity acts as the flippers, shooting a stream of charged particles into a tight spiral. When they crash into each other in the center, they get squeezed so hard that they fuse, shooting out bursts of neutrons (tiny particles) and X-rays.

Why do we care about these little bursts? Well, they aren't just for making electricity (though that's the ultimate goal). Right now, these machines are like super-powered flashlights that can test how materials and electronics hold up against intense radiation. This is crucial for designing spacecraft that can survive deep space or building electronics that won't fry during a solar storm. The big challenge has always been efficiency: getting the most "bang for the buck" by using as little stored electricity as possible to create the biggest, hottest pinch.

The FAETON-X: A Lightning Storm in a Bottle

In this paper, a team of researchers from Fuse Energy Technologies and several universities introduces a new machine called FAETON-X (or FX for short). They describe it as the most energy-efficient and highest-current machine of its kind in the world. If you've ever seen a lightning storm, you know that the power of a bolt depends on how much voltage it carries and how quickly it can deliver that energy. The researchers wanted to build a machine that could deliver a massive electrical "shout" in a tiny fraction of a second, squeezing plasma tighter than ever before.

The machine is built like a giant capacitor bank (basically a super-charged battery) holding 1 MJ of energy. It uses 20 capacitors to store this power, which is then released all at once. The goal was to push a peak current of 4.5 MA (that's 4.5 million amps!) through the plasma. To put that in perspective, a typical household circuit carries about 15 to 20 amps. This machine is pushing the equivalent of hundreds of thousands of homes' worth of electricity through a tube in a split second.

The secret sauce here is efficiency. The researchers measured a "figure of merit" of 4.5 MA/MJ. This means for every megajoule of energy stored, they get 4.5 million amps of current. This is a record-breaking number for machines of this size, beating out other similar facilities that usually manage between 2.35 and 3.25 MA/MJ. Because the amount of neutrons a machine produces scales with the fourth power of the current (meaning a small increase in current leads to a huge explosion in neutrons), this efficiency boost is a game-changer.

The Results: A Flash of Neutrons

The team didn't just build the machine; they fired it up and watched what happened. They ran 229 shots (trials) during their commissioning campaign, slowly ramping up the power as they learned how to make the machine work better. They found that as they kept firing the machine, the electrodes inside got "conditioned"—essentially cleaned and smoothed out by the repeated blasts—which helped the plasma squeeze tighter and produce more neutrons.

Even though the machine wasn't fully "conditioned" yet (meaning it still has room to get better), it already smashed its own design goals.

The Goal: They expected to get about 5 × 10¹¹ neutrons per shot.
The Reality: They consistently got around that number, but on their best shot (shot #224), they measured a peak yield of (1.27 ± 0.27) × 10¹² neutrons.

That's more than double what they hoped for! They achieved this using deuterium gas at a pressure of 10 Torr. The machine also produced a "dynamics-induced pinch voltage" that peaked at 127 kV (kilovolts) just before the plasma stopped moving and got squished. This high voltage is exactly what the team predicted would happen, confirming that their design philosophy works.

What the Data Tells Us

The researchers used a bunch of high-tech tools to watch the action, including special cameras that see X-rays, sensors that measure how fast the plasma moves, and detectors that count the neutrons. They compared what they saw with computer simulations (using something called the "Lee code"). The real-world data matched the computer models very well, especially regarding how the plasma moved and how much energy was transferred.

One interesting finding was about the "current sheath"—the layer of plasma that gets pushed inward. In the beginning of the squeeze, the sheath was a bit "diffuse" or spread out, but as it got closer to the center, it tightened up, with more of the current participating in the final crush. This behavior explained why the neutron yield was so high. The machine also produced photons (light particles) mostly in the 250 to 750 keV range, which is a specific type of high-energy X-ray.

What's Next?

The paper is very clear about what this machine can and cannot do right now. It is currently optimized for D-D (Deuterium-Deuterium) fusion, which is what they tested. However, the design is built to handle D-T (Deuterium-Tritium) fusion as well. The team calculates that if they switch to D-T fuel, the machine could potentially produce around 5 × 10¹³ neutrons per shot. That would be a massive jump, making it a powerful tool for testing how electronics and materials survive extreme radiation.

They also mention that the machine could be tweaked to run with even lower pressures to create fast beams of particles, which could be used to study D-7Li reactions. This would produce even faster neutrons (up to 14 MeV), which are great for simulating the harsh radiation environments found in space or nuclear reactors.

The authors are careful to note that while the results are impressive, the machine is still being "conditioned." They expect that with more shots and fine-tuning of the electrode shapes (they've already tried different anode tips and gaps), the neutron yield will go even higher, potentially reaching their target of 5 MA/MJ efficiency. For now, FAETON-X stands as a proof-of-concept that a compact, highly efficient machine can generate a "flash" of neutrons that rivals much larger, older facilities, opening the door for better radiation testing and fusion research without needing a massive power plant.

Technical Summary: Exceeding 10¹² D–D Flash Neutrons in the 4.5-MA 1-MJ Dense Plasma Focus FAETON-X

Problem and Context
The dense plasma focus (DPF) is a pulsed power device capable of generating intense bursts of fusion neutrons, X-rays, and energetic particle beams. While DPFs are valuable for fusion research, materials science, and radiation effects testing, maximizing neutron yield ( $Y_n$ ) remains a primary challenge. Empirical scaling laws indicate that neutron yield scales approximately as $Y_n \propto I^4$ (where $I$ is the peak pinch current), making peak current the critical lever for performance. Consequently, the figure of merit for energy efficiency in DPF design is the peak discharge current per unit of stored capacitor bank energy (MA/MJ).

Prior to this work, existing Mega-Joule (MJ) class DPF facilities (e.g., PF-1000, Gemini, MJOLNIR) reported peak currents ranging from 2.35 to 3.8 MA for 1–1.3 MJ of stored energy, yielding MA/MJ figures between 2.35 and 3.25. While the MJOLNIR facility achieved a record 1.2 × 10¹² neutrons/shot, it operated at 3.8 MA with 1.3 MJ, and its original goal of 4.5 MA at 2 MJ was not realized due to triggering limitations. There was a need for a facility that could achieve higher current efficiency (MA/MJ) to leverage the $I^4$ scaling law for superior neutron output per joule.

Methodology and Experimental Design
Fuse Energy Technologies designed and commissioned FAETON-X (FX), a direct MJ-class scale-up of their predecessor, FAETON-I. The design philosophy prioritized maximizing the MA/MJ ratio through three key enabling conditions: high direct-charged voltage, fast synchronized multi-module triggering, and minimized static inductance.

Pulsed Power Architecture: FX utilizes a 500 µF capacitor bank composed of twenty 25 µF, 100 kV capacitors. It operates at a charge voltage of 65 kV, storing 1 MJ of energy. The system employs 180 parallel RG-220/U coaxial transmission lines to deliver energy to the focus chamber.
Switching and Inductance: The bank discharges through twenty 120 kV, 750 kA self-mounted rail gap switches filled with SF6. These are triggered by two ten-channel BFMGs with sub-2 ns inter-switch jitter. The system static inductance is minimized to approximately 55 nH.
Electrode Geometry: The device features two coaxial, oxygen-free copper electrodes. The hollow anode is 41.2 cm long with a 15 cm radius, tapering to 10 cm. The cathode consists of 36 copper bars (20 mm diameter, 61.5 cm long) arranged at a 21 cm radius. The anode-cathode gap is 5 cm, separated by a 9 cm long quartz insulator.
Diagnostics: The facility is equipped with a comprehensive diagnostic suite, including:
- Three Rogowski-coil systems for current measurement (total and segmented).
- High-voltage resistive dividers and CVRs for anode-cathode voltage.
- Diamond-based photo-conducting detectors (PCDs) for X-ray timing.
- Photodiode arrays to measure current sheath velocity.
- Neutron diagnostics: Indium foil activation (for fast and thermal components), neutron time-of-flight (nToF) using PMT-scintillators at 5 m and 8 m, and BTI bubble detectors for dose.
- A sampling calorimeter with alternating absorber and image plate layers for photon spectrum reconstruction via Bayesian unfolding.
Simulation: Experimental data was correlated with the Lee Model Code, a current-based simulation tool that uses fitted mass ( $f_m$ ) and current ( $f_c$ ) fractions to model plasma dynamics and radiation yields.

Key Results
The FAETON-X facility achieved a peak discharge current exceeding 4.5 MA at 65 kV, resulting in a figure of merit of 4.5 MA/MJ. This represents the highest reported MA/MJ ratio for any MJ-class DPF, significantly surpassing contemporaneous peers (2.35–3.25 MA/MJ).

Neutron Yield: During the commissioning campaign (229 shots), the facility demonstrated a clear upward trend in yield as the machine conditioned. While the initial design goal was ~5 × 10¹¹ D-D neutrons/shot, the facility achieved a peak recorded yield of $(1.27 \pm 0.27) \times 10^{12}$ neutrons/shot at 10 Torr deuterium. This yield was achieved before the machine was fully conditioned.
Dynamics and Voltage: Analysis of Shot #224 (the peak yield shot) using the Lee Code revealed a strong correlation between measured and simulated current waveforms. The dynamically induced pinch voltage reached a measured peak of 127 kV just prior to stagnation. The code computed a neutron yield of $1.4 \times 10^{12}$ for this shot, consistent with the measured value.
Plasma Characteristics: The radial current fraction ( $f_{cr}$ ) was fitted at 0.35 initially, increasing to 0.7 in the second part of the radial phase, indicating a complex current sheath behavior where the rearward part of the sheath caught up with the frontal part. The system converted approximately 26.8% of the initial stored energy (270 kJ) into plasma work during the radial phase.
Radiation: Photon spectra reconstructed from the calorimeter showed dominant energies between 250 and 750 keV. Neutron time-of-flight measurements confirmed a neutron energy of $2.48 \pm 0.45$ MeV, consistent with D-D fusion.

Significance and Claims
The paper claims that FAETON-X represents a "step-change" in energy efficiency for the MJ-class DPF category. By achieving 4.5 MA/MJ, the facility demonstrates that the high-voltage design philosophy (high voltage, low inductance, fast triggering) successfully scales to the MJ level.

The authors state that the facility is not yet fully conditioned and that continued conditioning is expected to further increase neutron production, potentially reaching design goals of $>2 \times 10^{12}$ D-D neutrons/shot at 12 Torr. Furthermore, the paper highlights the platform's potential for D-T operation, noting that with fast beam ion energies around 115 keV (near the peak of the D-T fusion cross-section), the facility is designed to produce approximately $5 \times 10^{13}$ D-T neutrons per shot.

The significance of FAETON-X lies in its role as a compact, controllable fast-neutron source for pulsed power fusion R&D and radiation effects testing. It is positioned to support the evaluation of electronics and materials against displacement damage and single-event effects, offering a laboratory-scale alternative to reactor irradiation or underground nuclear testing. The facility is also designed to support D-7Li operations for generating fast neutrons up to ~14 MeV.

In conclusion, the paper presents FAETON-X as the world's most energy-efficient and highest-current MJ-class DPF to date, validating the correlation between dynamics-induced pinch voltage and neutron yield established in smaller-scale predecessors, and setting a new benchmark for neutron production in the dense plasma focus field.

The Tiny Star in a Box

The FAETON-X: A Lightning Storm in a Bottle

The Results: A Flash of Neutrons

What the Data Tells Us

What's Next?

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