Focused Energy and Xcimer Energy: DOE’s inertial fusion pilot picks

June 21, 2023, 12:00PMNuclear News

Focused Energy and Xcimer Energy are two of the eight fusion developers the Department of Energy selected in late May for funding under the public-private Milestone-Based Fusion Development Program, and the only developers using an inertial confinement concept. The Milestone program, announced in September 2022, was open to any fusion developer willing to undergo a competitive merit-review process, regardless of fusion confinement concept. But the prospects for inertial fusion concepts might have gotten a boost from Lawrence Livermore National Laboratory’s December 2022 achievement of scientific breakeven at the National Ignition Facility (NIF), which was announced shortly before the application window for the Milestone program closed.

Xcimer Energy announced on May 31 that it had received a substantial $9 million of the total $46 million in Milestone program funds for the first 18 months of work. (Focused Energy has not yet announced its Milestone funding.) As we did for Realta Fusion and Zap Energy, the DOE’s “innovative concept” picks, Nuclear Newswire is taking a look at what these two companies have in common (besides lasers), how their technologies distinguish them from other fusion developers and each other, and how they got started.

NIF points way to laser fusion: Scientists at NIF use multiple laser beams to compress and ignite spherical targets containing deuterium-tritium fuel, and the inertial fusion energy (IFE) companies’ concepts plan to do the same. But NIF was designed for experimental flexibility, not energy production. In an inertial fusion power plant, individual targets would not be housed inside a cylindrical hohlraum as at NIF—instead, both Milestone awardees are opting for “direct-drive” compression of targets and a high repetition rate. The energy released as neutrons from the fusion of D-T fuel would heat the fusion chamber wall, and that heat would drive a power plant.

Both Focused Energy and Xcimer Energy were founded in 2021, the year when, on August 8, NIF recorded what was at the time a record-breaking laser shot generating 1.3 megajoules of fusion energy. Both companies include former LLNL staff among their employees and executives. And both would depart from NIF’s design for lasers and targets in pursuit of lower costs and higher repetition rates.

Focused Energy’s target design. (Image: Focused Energy)

Focused Energy’s German target work: Focused Energy describes itself as “a German American company spun off from the Technical University of Darmstadt in 2021 that will enable safe, clean, and virtually inexhaustible energy production through laser-based nuclear fusion in just a few years.” Focused Energy proposes to get there by combining direct-drive laser fuel compression with “proton fast ignition.”

Focused Energy founders include physicists Markus Roth, of TU Darmstadt in central Germany, who is the company’s chief science officer, and Todd Ditmire, of the University of Texas–Austin, who had previously founded the laser company National Energetics. Focused Energy was incorporated in the United States with an operations base in Darmstadt and U.S. staff based in Austin, Texas.

Focused Energy announced in a LinkedIn post that the company was “delighted to be selected” by the DOE. “Focused Energy’s approach to #FusionEnergy relies on the same laser-based nuclear fusion and deuterium and tritium fuel as used by Livermore. Some of Livermore’s leading scientists are now working for Focused Energy,” the company said. That would include U.S.-based scientific director Patel Pravesh, formerly a senior scientist at LLNL, who is named as the principal investigator in the DOE’s funding announcement.

“New, better laser systems are being developed that will operate more efficiently than those used in Livermore. The targets with the fuel are also continuously developed in Darmstadt, resulting in a significant increase in efficiency,” continued the company’s statement.

The BB-sized synthetic diamond target capsules LLNL uses in NIF are produced in southern Germany by Diamond Materials GmbH through a partnership with LLNL and General Atomics. Focused Energy’s capsules would be different. The diamond shell of NIF’s targets would be replaced with two layers of plastic and an outer coating of metal around the 2-millimeter target. The target shell would—like the NIF targets—enclose a layer of D-T ice surrounding D-T gas.

“We are developing the technology for high-repetition-rate laser-driver systems of increased reliability and reduced cost by mass manufacturability,” Focused Energy says on its website. The company also markets its laser-driven radiation sources that can produce neutron, X-ray, and muon beams as diagnostic tools for industrial users.

A rendering of Xcimer Energy’s fusion chamber. (Image: Xcimer Energy)

Xcimer Energy’s gas laser approach: Xcimer is located in Redwood City, Calif., on the San Francisco Peninsula and about an hour’s drive from LLNL. The company says it “proposed to DOE a development plan aimed at resolving the major engineering challenges needed to construct a fusion pilot plant by the 2030s.”

Xcimer Energy would use excimer laser technology—originally pioneered for missile defense, according to the company—to drive its inertial fusion concept. Excimer lasers use high-pressure gas—typically a combination of a noble gas and a reactive gas such as fluorine or chlorine. (Xcimer’s fusion energy concept would use a combination of krypton and fluorine.) When the pressurized KrF is stimulated by electricity, the gas mixture gives off laser light in the ultraviolet range. According to Xcimer, “Our system delivers light at orders of magnitude lower cost and up to [ten times] higher energy than the NIF. By incorporating technologies developed in other fields, the laser eliminates the disadvantages of conventional approaches to IFE.”

An electron beam pumped laser dubbed Electra, developed at the Naval Research Laboratory, holds the records for repetition rate and lifetime for an excimer laser. Douglas Weidenheimer, Xcimer’s director of pulsed power engineering, led design and delivery of the pulsed power systems for the program at NRL while working for L3-Harris, according to Xcimer.

Xcimer Energy envisions a sequence of the potential advantages from the use of excimer lasers: “A low-cost laser enables economical production of laser energies of tens of megajoules, which allows direct scaling of the hotspot ignition mechanism proven at the NIF to larger, more reliable, higher-yield fuel capsules. The higher energy output from larger capsules permits operation of a power plant at a repetition rate of under one shot per second, significantly reducing engineering risk relative to other IFE concepts. Together, these innovations allow the adoption of the well-studied HYLIFE chamber concept developed at Lawrence Livermore National Laboratory, which allows a 30-year facility lifetime without first-wall replacement and the accompanying waste generation and material science R&D challenges.”

Conner Galloway, chief executive officer and cofounder of Xcimer, and the PI named on the company’s Milestone award, said that “Xcimer’s innovations directly address the remaining challenges in deploying laser-driven inertial fusion energy and enable the fastest and lowest-risk path to put fusion power on the grid.”

Look for more: Look for Newswire coverage of DOE’s six other picks for the milestone fusion program featuring "innovative concepts" (Realta Fusion and Zap Energy), stellarators (Princeton Stellarators and Type One Energy), and tokamaks (Commonwealth Fusion Systems and Tokamak Energy).

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