Like atoms coming together to release their power, fusion researchers worldwide are joining forces to unravel the world’s energy crisis. Harnessing the facility of fusing plasma as a reliable energy source for the facility grid isn’t any easy task, requiring global contributions.
The Princeton Plasma Physics Laboratory (PPPL) — a U.S. national laboratory funded by the Department of Energy (DOE) — is leading several efforts on this front, including collaborating on the design and development of a brand new fusion device on the University of Seville in Spain. The SMall Aspect Ratio Tokamak (SMART) strongly advantages from PPPL computer codes in addition to the Lab’s expertise in magnetics and sensor systems.
“The SMART project is an incredible example of us all working together to unravel the challenges presented by fusion and teaching the subsequent generation what we now have already learned,” said Jack Berkery, PPPL’s deputy director of research for the National Spherical Torus Experiment-Upgrade (NSTX-U) and principal investigator for the PPPL collaboration with SMART. “We’ve got to all do that together or it isn’t going to occur.”
Manuel Garcia-Munoz and Eleonora Viezzer, each professors on the Department of Atomic, Molecular and Nuclear Physics of the University of Seville in addition to co-leaders of the Plasma Science and Fusion Technology Lab and the SMART tokamak project, said PPPL gave the look of the perfect partner for his or her first tokamak experiment. The following step was deciding what form of tokamak they need to construct. “It needed to be one which a university could afford but in addition one that might make a novel contribution to the fusion landscape on the university scale,” said Garcia-Munoz. “The concept was to place together technologies that were already established: a spherical tokamak and negative triangularity, making SMART the primary of its kind. It seems it was a incredible idea.”
SMART should offer easy-to-manage fusion plasma
Triangularity refers back to the shape of the plasma relative to the tokamak. The cross section of the plasma in a tokamak is usually shaped just like the capital letter D. When the straight a part of the D faces the middle of the tokamak, it is alleged to have positive triangularity. When the curved a part of the plasma faces the middle, the plasma has negative triangularity.
Garcia-Munoz said negative triangularity should offer enhanced performance because it could possibly suppress instabilities that expel particles and energy from the plasma, stopping damage to the tokamak wall. “It’s a possible game changer with attractive fusion performance and power handling for future compact fusion reactors,” he said. “Negative triangularity has a lower level of fluctuations contained in the plasma, but it surely also has a bigger divertor area to distribute the warmth exhaust.”
The spherical shape of SMART should make it higher at confining the plasma than it could be if it were doughnut shaped. The form matters significantly when it comes to plasma confinement. That’s the reason NSTX-U, PPPL’s major fusion experiment, is not squat like another tokamaks: the rounder shape makes it easier to restrict the plasma. SMART shall be the primary spherical tokamak to completely explore the potential of a selected plasma shape referred to as negative triangularity.
PPPL’s expertise in computer codes proves essential
PPPL has an extended history of leadership in spherical tokamak research. The University of Seville fusion team first contacted PPPL to implement SMART in TRANSP, a simulation software developed and maintained by the Lab. Dozens of facilities use TRANSP, including private ventures similar to Tokamak Energy in England.
“PPPL is a world leader in lots of, many areas, including fusion simulation; TRANSP is an incredible example of their success,” said Garcia-Munoz.
Mario Podesta, formerly of PPPL, was integral to helping the University of Seville determine the configuration of the neutral beams used for heating the plasma. That work culminated in a paper published within the journal Plasma Physics and Controlled Fusion.
Stanley Kaye, director of research for NSTX-U, is now working with Diego Jose Cruz-Zabala, EUROfusion Bernard Bigot Researcher Fellow, from the SMART team, using TRANSP “to find out the shaping coil currents needed for attaining their design plasma shapes of positive triangularity and negative triangularity at different phases of operation.” The primary phase, Kaye said, will involve a “very basic” plasma. Phase two may have neutral beams heating the plasma.
Individually, other computer codes were used for assessing the soundness of future SMART plasmas by Berkery, former undergraduate intern John Labbate, who’s, now a grad student at Columbia University, and former University of Seville graduate student Jesús Domínguez-Palacios, who has now moved to an American company. A brand new paper in Nuclear Fusion by Domínguez-Palacios discusses this work.
Designing diagnostics for the long haul
The collaboration between SMART and PPPL also prolonged into and considered one of the Lab’s core areas of experience: diagnostics, that are devices with sensors to evaluate the plasma. Several such diagnostics are being designed by PPPL researchers. PPPL Physicists Manjit Kaur and Ahmed Diallo, along with Viezzer, are leading the design of the SMART’s Thomson scattering diagnostic, for instance. This diagnostic will precisely measure the plasma electron temperature and density during fusion reactions, as detailed in a brand new paper published within the journal Review of Scientific Instruments. These measurements shall be complemented with ion temperature, rotation and density measurements provided by diagnostics referred to as the charge exchange recombination spectroscopy suite developed by Alfonso Rodriguez-Gonzalez, graduate student at University of Seville, Cruz-Zabala and Viezzer.
“These diagnostics can run for a long time, so once we design the system, we keep that in mind,” said Kaur. When developing the designs, it was essential the diagnostic can handle temperature ranges SMART might achieve in the subsequent few a long time and not only the initial, low values, she said.
Kaur designed the Thomson scattering diagnostic from the beginning of the project, choosing and procuring its different subparts, including the laser she felt most closely fits the job. She was thrilled to see how well the laser tests went when Gonzalo Jimenez and Viezzer sent her photos from Spain. The test involved organising the laser on a bench and shooting it at a bit of special parchment that the researchers call “burn paper.” If the laser is designed good, the burn marks shall be circular with relatively smooth edges. “The initial laser test results were just gorgeous,” she said. “Now, we eagerly await receiving other parts to get the diagnostic up and running.”
James Clark, a PPPL research engineer whose doctoral thesis focused on Thomson scattering systems, was later brought on to work with Kaur. “I have been designing the laser path and related optics,” Clark explained. Along with working on the engineering side of the project, Clark has also helped with logistics, deciding how and when things must be delivered, installed and calibrated.
PPPL’s Head of Advanced Projects Luis Delgado-Aparicio, along with Marie Skłodowska-Curie fellow Joaquin Galdon-Quiroga and University of Seville graduate student Jesus Salas-Barcenas, are leading efforts so as to add two different kinds of diagnostics to SMART: a multi-energy, soft X-ray (ME-SXR) diagnostic and spectrometers. The ME-SXR can even measure the plasma’s electron temperature and density but using a distinct approach than the Thomson scattering system. The ME-SXR will use sets of small electronic components called diodes to measure X-rays. Combined, the Thomson scattering diagnostic and the ME-SXR will comprehensively analyze the plasma’s electron temperature and density.
By the several frequencies of sunshine contained in the tokamak, the spectrometers can provide details about impurities within the plasma, similar to oxygen, carbon and nitrogen. “We’re using off-the-shelf spectrometers and designing some tools to place them within the machine, incorporating some fiber optics,” Delgado-Aparicio said. One other recent paper published within the Review of Scientific Instruments discusses the design of this diagnostic.
PPPL Research Physicist Stefano Munaretto worked on the magnetic diagnostic system for SMART with the sector work led by University of Seville graduate student Fernando Puentes del Pozo Fernando. “The diagnostic itself is pretty easy,” said Munaretto. “It’s only a wire wound around something. Many of the work involves optimizing the sensor’s geometry by getting its size, shape and length correct, choosing where it must be situated and all of the signal conditioning and data evaluation involved after that.” The design of SMART’s magnetics is detailed in a brand new paper.
Munaretto said working on SMART has been very fulfilling, with much of the team working on the magnetic diagnostics made up of young students with little previous experience in the sector. “They’re wanting to learn, and so they work quite a bit. I definitely see a shiny future for them.”
Delgado-Aparicio agreed. “I enjoyed quite quite a bit working with Manuel Garcia-Munoz, Eleonora Viezzer and the entire other very seasoned scientists and professors on the University of Seville, but what I enjoyed most was working with the very vibrant pool of scholars they’ve there,” he said. “They’re sensible and have helped me quite a bit in understanding the challenges that we now have and find out how to move forward toward obtaining first plasmas.”
Researchers on the University of Seville have already run a test within the tokamak, displaying the pink glow of argon when heated with microwaves. This process helps prepare the tokamak’s inner partitions for a far denser plasma contained at the next pressure. While technically, that pink glow is from a plasma, it’s at such a low pressure that the researchers don’t consider it their real first tokamak plasma. Garcia-Munoz says that can likely occur in the autumn of 2024.
Support for this research comes from the DOE under contract number DE-AC02-09CH11466, European Research Council Grant Agreements 101142810 and 805162, the Euratom Research and Training Programme Grant Agreement 101052200 — EUROfusion, and the Junta de Andalucía Ayuda a Infraestructuras y Equipamiento de I+D+i IE17-5670 and Proyectos I+D+i FEDER Andalucía 2014-2020, US-15570.
