The recent breakthrough at the National Ignition Facility (NIF) in December 2022, where a laser experiment achieved a net energy gain in fusion, has sent ripples of excitement through the scientific community. This milestone, coupled with significant private investment, has propelled fusion energy research into the spotlight. Yet, the path to harnessing fusion as a viable energy source remains fraught with challenges. Enter the High Energy Density Science (HEDS) division at SLAC National Accelerator Laboratory, a powerhouse of innovation tackling these obstacles head-on.
SLAC’s journey in fusion research is underpinned by its rich history of scientific advancements. From housing the Stanford Linear Accelerator to pioneering the Linac Coherent Light Source (LCLS), the world’s first X-ray Free Electron Laser, SLAC has consistently pushed the boundaries of scientific exploration. The LCLS, with its ultrafast, high-intensity X-ray pulses, has revolutionised our understanding of ultrafast processes in materials, from photosynthesis to viral proteins. Now, SLAC is leveraging this technology to probe the extreme conditions of fusion plasmas.
The Matter in Extreme Conditions (MEC) instrument at SLAC, equipped with high-power optical lasers, creates pressures and temperatures akin to those found in the heart of the Earth and the solar corona. This extreme environment is a playground for researchers to test and refine their models of planetary formation and fusion reactions. The X-ray beam from LCLS penetrates these extreme states, providing a real-time window into their dynamic evolution. This capability is crucial for advancing fusion science, as it allows researchers to directly probe matter under high-pressure, high-temperature conditions.
X-ray diagnostics, a critical aspect of fusion research, provide essential insights into these extreme states. X-ray diffraction, for instance, captures atomic-scale structural changes, revealing how materials rearrange under extreme compression. This technique has already shown how hydrocarbon chains can transform into diamonds under conditions similar to those within Uranus and Neptune. X-ray scattering, on the other hand, offers a detailed view of interactions within high-temperature states, helping researchers understand how materials respond to pressure and radiation. X-ray imaging, with its nanometer spatial-scale resolution, enables ultrafast imaging of laser-driven samples, observing lattice dynamics and instabilities in hot plasma.
The future of fusion science at SLAC is poised for even greater advancements with the advent of LCLS-II. This major upgrade includes a superconducting accelerator capable of delivering millions of X-ray pulses per second, with a unique pulse train feature enabling sequential X-ray snapshots. This will allow researchers to track the behaviour of fusion fuel capsules in unprecedented detail, moving closer to understanding the conditions necessary for sustained fusion reactions. The upgraded laser system at the Matter in Extreme Conditions endstation will be capable of driving samples to the brink of fusion, allowing researchers to study how matter traverses into and through the high-energy density phase space.
The HEDS division at SLAC is not just focused on X-ray diagnostics. They are also using beams from across the electromagnetic spectrum to understand fusion targets. Optical probes, for instance, use interferometry to see how quickly a laser-driven shockwave moves through fusion fuels, while terahertz radiation allows measurements of electrical conductivity, influencing how electric fields are generated and propagated inside the extreme states. This multi-faceted approach is essential for understanding the heating and laser coupling to fusion targets.
The implications of SLAC’s work are profound. As the world grapples with the urgent need for clean, sustainable energy, fusion energy offers a tantalising prospect. However, the journey from laboratory breakthroughs to commercial viability is long and fraught with challenges. SLAC’s innovative technologies and approaches are not just pushing the boundaries of fusion science; they are also shaping the future of energy development. The ability to probe and understand the extreme conditions of fusion plasmas is a significant step towards harnessing fusion energy. As SLAC continues to innovate, it is not just advancing fusion science; it is also inspiring a new generation of scientists and engineers to tackle the energy challenges of the future. The sector is on the cusp of a revolution, and SLAC is at the forefront, driving the change with its groundbreaking research and innovative technologies.
