Different Approaches to Inertial Confinement Fusion

A couple of weeks ago, The Fusion Report covered the various types of lasers and their uses in fusion energy systems (“Lasers for Fusion Energy – The Basics”) – to say that there were a lot of Reddit comments on the inefficiency of “current” lasers systems would be an under-statement! As was pointed out by more than a few readers, the Lawrence Livermore National Laboratory (LLNL) National Ignition Facility (better known as “NIF”), in spite of being the first Q>1 fusion experiment, was never built as a fusion energy research facility. Rather, NIF was built to support nuclear weapon maintenance and design by enabling the study of materials and matter when subjected to nuclear explosions. As another Reddit contributor noted, NIF’s lasers are pumped by flashlamps (a 1990s technology), and these lasers were not designed for efficiency. Which raises the question “what is the state of inertial confinement fusion (ICF) in 2025?”, which is what this blog will explore.

Inertial Confinement Fusion

To refresh everyone’s memories, the approach of ICF is to bombard a target (usually a tiny deuterium-tritium iceball) with a number of focused, coherent energy sources (again, usually a laser). The goal is to compress and heat the target enough that fusion occurs. While lasers are one of the better-known methods of inertial confinement, other energetic/coherent beams could also be utilized, such as ion beams (heavy ions or light ions), or X-rays. In all cases, the challenge is always to minimize energy loss in creating the beams and coupling the energy
into the target, whether the target is heated through indirect drive (via a hohlraum such as in NIF) or directly by the beams.

From a systems perspective, there are several places where energy can be lost, which reduces ICF efficiency and requires a higher Q to achieve engineering break-even (let alone economic break-even). The diagram above, though specific to an indirect-drive laser ICF, captures most of the areas in an ICF fusion machine where energy can be lost. In particular, the major areas of loss include the following:

1. Generating the Beam: It takes energy to create and focus a high-energy laser beam. While NIF’s lasers are only 0.5% efficient, modern diode-pumped solid state neodymium (Nd) glass lasers can generate near-infrared (NIR) beams at efficiencies of up to 20%.
2. Frequency-Shifting the Beam: NIR beams, while efficient to generate, shorter wavelength light such as ultraviolet couple better with the targets in indirect-drive ICF systems. This typically has efficiencies of between 50% and 100%.
3. Generating X-Rays and Compressing the Target: For indirect-drive systems, the hohlraum (the capsule surrounding the fuel) must be irradiated with x-rays to cause ablation and compression of the fuel. The generation of x-rays from UV laser light tends to be about 85% efficient, while the ablation process tends to be about 15% efficient, for an overall efficiency of 12%. For direct-drive systems directly irradiating a target, efficiencies of about 10% are realized.
4. Overall Efficiency for Laser Based ICF Systems: Looking at the steps in a laser-based system, efficiencies of about 1%-2% are “state of the art” today. Approaches to improve this today are focusing on how to better couple the laser energy to the target. One of the leading approaches is known as shock-augmented ignition, which could significantly improve target energy coupling and the overall efficiency of laser-based ICF systems, as will improvements in direct-drive solutions.
5. Particle Beam ICF Systems: In comparison, particle accelerators can produce ion beams at efficiencies of 30%-40%, though achieving the needed power density required can be challenging. To reach the power required, a couple of approaches are being explored, including utilizing lithium ions (light-ion beam direct-drive), as well as using lead or bismuth (heavy-ion beam direct-drive).

What Companies on the Private Side are Evaluating ICF?

While magnetic confinement fusion (and variations on it) is the leading approach for fusion machines today, there are several companies that are working on inertial confinement, with most of them involving lasers. Below is a quick overview of these companies and the approach they are taking on ICF:

• First Light ($113.5M raised to date): First light is a UK fusion energy company based in Oxfordshire. Of the inertial confinement companies funded to date, First Light is the only one not (necessarily) using lasers. The heart of First Light’s approach is a mechanical “amplifier” (shown at right), which channels and increases mechanical pressure to achieve fusion in a fuel target at the apex (bottom) of the amplifier cone. They have two machines in place today to test their approach: “Machine 3”, with a peak impact speed of 20km/sec and a projectile acceleration of 1 billion Gs (each “G” of acceleration is about 9.8 meters/sec2); and “BFG”, a two-stage gas gun which can achieve projectile velocities of 7 km/sec.

• Marvel Fusion ($123M raised to date): Marvel, which is headquartered in Munich Germany, is utilizing lasers to fuse hydrogen protons and boron-11 to produce aneutronic fusion. The company is building a $150M laser fusion facility in Colorado in conjunction with Colorado State University which should be completed by 2026. The facility will be capable of producing fusion energies in the hundreds of megawatt range.

• Xcimer Energy ($100M raised to date): Xcimer Energy is a Denver/Bay Area company that is focused on deuterium-tritium fusion energy (no pun intended! 😊). Founded in 2021, their approach is to utilize a 10+ MJ Krypton Fluoride excimer gas laser to power their fusion machine. Their indirect-drive approach is similar to NIF, but with larger targets to improve performance and reduce repetition rates to under 1 Hz. The system surrounds the chamber with liquid lithium salts to protect the chamber and to create tritium.

  

• Focused Energy ($82M raised to date): Focused Energy is a Bay Area company that is utilizing deuterium and tritium (D-T) fuel for inertial fusion. Focused Energy recently signed an agreement with the government of the state of Hesse in Germany to put a fusion power plant at the site of the former Biblis nuclear fission power plant. It is interesting to note that of the three laser-based inertial confinement in this article (Marvel, Focused Energy, and HB11), only Focused Energy is working on utilizing D-T as their fuel.

• HB11 Energy ($23M raised to date): As their name implies, HB11 energy, like Marvel, is using hydrogen protons and boron-11 for their fusion process, avoiding the large-scale creation of fast neutrons. The company is working with the University of Adelaide on an Australian-based laser facility to support their fusion efforts, which will focus on improving the “wall-plug” efficiency of its lasers, avoiding the efficiency issues experienced with NIF’s lasers. While HB11’s funding level is a concern relative to their ability to build an entire fusion machine, hopefully the company can make some advances on its lasers that will be useful to the rest of the ICF companies.
  
  

Conclusion: Laser-Based Fusion’s Future Still Looks Bright

Despite NIF’s achievement of Q>1 in 2022, inertial confinement fusion still lags behind magnetic confinement fusion when it comes to private funding of fusion companies, as well as on the technology maturity side. This isn’t surprising, given that the concept of a tokamak was proposed in 1951 and the first one built in 1958, while the first laser wasn’t built until 1960 (and it wasn’t for fusion). In fact, the first lasers that were capable of being used for fusion were not built until the mid-1970s, and UV lasers (the best ones for ICF) were not built and tested until the Nova laser in 1984 (25 years after the first tokamak was built). However, advances in laser and target designs should help improve the efficiency of ICFs, much in the same way that high-temperature superconductor (HTS)-based magnets improved the performance and feasibility of MCF machines. This is a space that we will keep watching for you 😊!