The possibility of generating clean energy from fusion has been a significant motivation for the study of plasma physics. The journey from early plasma confinement experiments to a fusion power plant has been arduous and more difficult than initially thought. Every new experiment and success revealed new challenges and mysteries. In addition to the engineering challenges of constructing new confinement devices, fusion plasmas have proven to be deeply complex and fascinating, with decades of groundbreaking research around the world. This has brought the field to the cusp of a foundational goal: net energy production. The SPARC tokamak is on track to be the first device to achieve this goal, demonstrating a fusion gain (the ratio of the fusion power generated in the plasma to the externally applied heating power required to sustain the plasma temperature) greater than two.

The design of SPARC is built on the knowledge collected through decades of plasma physics research. Projections of SPARC’s fusion gain and power utilize data that has been collected on tokamaks around the world and is based on the same methodology that has been used to design ITER, the large, internationally-funded tokamak under construction in France. This physics basis is sound and does not rely on large extrapolations from demonstrated results to predict the performance of SPARC. In fact, there are numerous “wind-tunnel” examples of plasmas from the JET tokamak that match the SPARC baseline in nearly all dimensionless parameters that have been demonstrated to govern plasma confinement.

On the other hand, the generation of fusion power is governed by nuclear physics, which depends on absolute temperature and density, not dimensionless plasma parameters. Since SPARC is being built at a higher magnetic field, it will operate at higher absolute performance and is projected to surpass the fusion gain and power achieved in previous tokamaks, including JET, while remaining in well explored plasma confinement regimes. Because of this, SPARC has the potential to explore the exciting new regime of dominantly self-heated burning plasmas, which will be key in informing power plant designs. The articles about SPARC in this Journal of Plasma Physics collection validate SPARC’s path to high performing plasmas and a fusion gain greater than two.

SPARC is being designed jointly by Commonwealth Fusion Systems, a private company based in Massachusetts, USA, and the Massachusetts Institute of Technology along with collaborators around the world. It is the next step on the path to a fusion power plant, demonstrating the governing physics of fusion and that the high magnetic fields enabled by new high temperature superconductors allow for compact, economically-competitive fusion devices. Following SPARC’s operation, CFS and its collaborators plan to move rapidly to the construction of a fusion power plant based on the ARC concept. A successful fusion power plant will be a testament to the tireless work of plasma physicists and engineers around the world, lead to new frontiers of plasma physics research, and begin a new era of clean energy generation.

Read the Introduction to the SPARC special issue: ‘Status of the SPARC Physics Basis’ by Martin Greenwald

All seven articles in the Journal of Plasma Physics Special Issue: Status of the SPARC Physics Basis are open access and can be found at www.cambridge.org/plasma/sparc