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Fusion technologies | Closing a fusion schism

Historically, inertial confinement and magnetic confinement approaches to fusion have been parallel, separate processes. The ITER Private Sector Fusion Workshop in May showed why that no longer necessarily has to be the case. Fusion historians look back at the 1950s as an age of optimism in the nuclear field.  Scientists, infused with a belief that controlled fusion 'could be mastered by short-term technological pressure just as uncontrolled fusion had been,'¹ identified magnetic confinement as the method by which fusion power would be achieved. Around the world, scientists embarked on a variety of magnetic fusion concepts, from tokamaks to stellarators to mirror configurations. As the first fission power plant began operations in 1957, fusion scientists hoped that they would not be far behind. However, experiments quickly revealed that magnetic confinement fusion was a different beast. The understanding of plasma physics was still rudimentary, and a plasma's myriad instabilities could not yet be controlled magnetically to the extent needed for fusion energy gain. Yet, no viable alternative technique existed. That changed in 1960 with the invention of the laser. Though ubiquitous in the modern world, at the time, the advent of this technology revolutionized fusion science. Scientists such as John Nuckolls in the United States quickly realized that with an implosion system, in which an assortment of lasers simultaneously fire to compress and heat a small amount of fusionable material, fusion-relevant conditions could be created. In 1972, Nuckolls' pioneer paper, 'Laser Compression of Matter to Super-High Densities: Thermonuclear (CTR) Applications,'² created a basic blueprint for how a feasible power plant could operate with this method. Today, it is called 'inertial confinement fusion.' Nuckolls and others' work led to a sort of 'schism' across the fusion community. Magnetic confinement and inertial confinement fusion, while ultimately aimed at obtaining the same goal of usable fusion power, faced powerfully different scientific obstacles. While magnetic confinement programs continued to focus on finding ways to minimize plasma instabilities and optimize confinement, inertial confinement programs had to overcome the enormous technical complexity of laser synchronization as well as implosion instabilities, among other challenges. The timelines of the two technologies gradually progressed, but on parallel paths with little room for collaboration. Indeed, this schism led to a bit of a contest between the two approaches, with experts on both sides at times castigating the other as unrealistic. Magnetic confinement advocates often lamented that inertial designs would be difficult to scale up to power plant efficiency, and argued that the complex configuration of lasers necessary to induce net-gain fusion was unrealistic and expensive. Inertial confinement advocates argued that their approaches are simpler, have a higher energy density, and have a greater level of operational control and repeatability than their magnetic counterparts. However, both sides of the fusion schism have overcome many of these supposed obstacles in recent years. In 2022, the National Ignition Facility at the Lawrence Livermore National Laboratory in the United States attained scientific breakeven for the first time, obtaining 3.15 MJ of energy from 2.05 MJ, resulting in a Qsci of 1.5. Recent shots at the NIF have yielded even higher Q values, and private companies aim to follow in the NIF's footsteps. On the magnetic confinement fusion side, JET produced a fusion record 69 MJ in its final experiment late last year, while ITER's scientific goal is Q≥10. Other private magnetic confinement fusion approaches project scientific breakeven as well in the coming decade. This progress on both sides made a historical collaborative event possible at the first-of-a-kind ITER Private Sector Fusion Workshop. At a panel debate on inertial confinement fusion hosted by the CEO of Fusion Energy Insights Melanie Windridge, Ex-Fusion CEO Kazuki Matsuo and Marvel Fusion CEO Dan Gengenbach discussed avenues in which the two approaches could learn from each other. Signs of schism were nowhere to be found on stage that day. Indeed, it is the very success that both sides have enjoyed in recent years in approaching scientific breakeven that creates collaborative opportunities. After explaining Ex-Fusion's planned pathway to fusion power, in particular the plan for scaling up single-shot approaches to a continuously operating facility, Matsuo explained that the need to capture energy for usable power creates a natural convergence between inertial and magnetic confinement approaches. In particular, Matsuo pointed to the blanket system (which will be largely responsible for the conversion of the fusion process into usable energy) as an area with a significant degree of overlap. 'Our blanket systems are very similar. Technological insight and innovation in this area is considered by our community as a key area for collaboration.' Matsuo continued to explain that collaborating on material challenges, as well as diagnostic advancements made at ITER, would help accelerate his own company's progress. He also believes that the regulatory hurdles ITER has gone through has paved a pathway that could advantage inertial confinement fusion companies like his own. 'As ITER progresses,' Matsuo stated, 'it will help define and establish the international standard for safety at fusion power plants.' For his part, Gengenbach believes that sharing some of the software development that has occurred at ITER could help Marvel Fusion achieve its goals. 'There are certainly some codes we would love to use,' he laughed. He also agreed that there is plenty to learn about the reactor aspect of plant safety regulation, despite 'very different technologies.' Both magnetic and inertial confinement fusion approaches still face challenges on the pathway to commercialization. But as the scientists and engineers on both sides continue to doggedly pursue the answers to the remaining obstacles, the knowledge that there are ways to collaborate across the 'fusion schism' may just accelerate both sides' pursuit of fusion power. ¹ Furth, Harold P., and Post, Richard F. Advanced Research in Controlled Fusion. University of California (p2), 1964. https://doi.org/10.2172/4618103 ² Nuckolls, J., Wood, L., Thiessen, A. et al. Laser Compression of Matter to Super-High Densities: Thermonuclear (CTR) Applications. Nature 239, 139—142 (1972). https://doi.org/10.1038/239139a0

Image of the week | The platform's quasi-final appearance

Since preparation work began in 2007 on the stretch of land that was to host the 42-hectare ITER platform, regular photographic surveys have been organized to document the progress of the installation's construction. Using helium balloons, helicopters, ultra-light fixed-wing aircrafts and taking advantage of the recent development of easily maneuverable drones, aerial photography experts (and sometimes ITER staff flying by the worksite on an aerial tour) have captured both the expanse and the minute details of the construction site. In this most recent image, taken on a bright, cloudless day in late June, 14 years after construction was launched, the platform has acquired its quasi-final appearance. Civil works are now complete and the only 'missing' structure is the Hot Cell & Radwaste Facility that will sit next to the Tokamak Complex. The progress accomplished can be measured by viewing this series of photographs, taken in March 2013, August 2015, April 2016, August 2017 and December 2017. Impressive to say the least.

Cryopumps | Preparing for the cold tests

Before being delivered to ITER, the torus and cryostat cryopumps are submitted to a  comprehensive series of factory acceptance tests. This is not sufficient, however, to guarantee that these most complex of components, designed to operate at temperatures as low as 4.5 K and as high as 200 °C, will perform as expected. To remove all uncertainty, a test facility was created within the ITER cryoplant, allowing each pump to be tested through a whole range of operating temperatures and pumping scenarios. On 19 June, a 'cryojumper,' was installed to connect the test facility to the cryoplant's fluids distribution unit. 'A cryojumper is not just a pipe and a flange,' explains Alessandra Iannetti, the test facility project manager. 'It is a sophisticated component that transports helium at the temperature of outer space while keeping thermal losses to a minimum. It is equipped with a 'magic' flange, called a 'Johnston coupling,' which will allow easy insertion and removal every time we test a new cryopump.' The cryopump that will undergo the first round of cold tests is a pre-production component that will not be installed in the ITER machine. By cold testing it thoroughly however, the vacuum team will be able to refine the procedures that will be applied to the actual torus and cryostat cryopumps. Testing will verify the pump's performance in operational conditions, something that has not been done yet. The cryopumps will be cycled exactly as they will be cycled during actual operation, going through all the different temperature steps from 4 K (minus 269 °C) to 300 K (ambient temperature), each step corresponding to the capture of specific gas molecules. Even higher temperature—up to 470 K (200 °C)—will be required for the deep cleaning maintenance phases. Whether all eight cryopumps will be tested is not yet decided. The decision will depend in part on the availability of the cryogenic distribution system, which will be partly mobilized by the testing of the machine's toroidal field coils. Cold testing an ITER cryopump is a two- to three-month long procedure. As the integrated commissioning of the cryoplant is set to begin early next year, the testing of the pre-production pump is not anticipated before May 2025.

of-interest

2024 Distinguished Career Awards (FPA)

The Board of Directors of Fusion Power Associates (FPA) has announced the recipients of its 2024 Distinguished Career Awards. The awards will be presented at Fusion Power Associates 45th Annual Meeting and Symposium, Fusion Energy: Progress, Challenges and Promise, 2-3 December 2024 in Washington, D.C. E. Michael Campbell is recognized for his decades of scientific and managerial leadership of inertial confinement fusion programs at LLNL, General Atomics and the University of Rochester, and consulting/advisory contributions at many other institutions. The Board especially notes the seminal early roles he played that led to the construction of the National Ignition Faciiity, that then led to the recent first laboratory demonstration of fusion ignition. Bruno Van Wonterghem is recognized for his decades of tenacious dedication to scientific and operational excellence in bringing both the LLNL Beamlet and NIF facilities to completion and successful operations. The Board especially notes his many scientific  publications contributing to understanding laboratory inertial confinement fusion and his managerial expertise that has enabled thousands of groundbreaking laser-plasma experiments. FPA Distinguished Career Awards have been given annually since 1987 to recognize individuals who have made distinguished lifelong career contributions to fusion energy development. A list of previous recipients is at https://fusionpower.org and click on Awards.

press

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EU Fusion Business Forum unveils new market opportunities

European steel for Test Blanket Modules arrives in Korea

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Ion temperature saturation observed in current fusion machines, a risk for ITER?

Завершена поставка катушек тороидального поля для реактора ITER

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ニュートン別冊 核融合 最前線

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