Odd Erik Garcia  –  Professor

Audun Theodorsen  –  Associate Professor

Jan Petter Hansen  –  Professor

Laszlo Pal Csernai  –  Professor Emeritus

Martin Møller Greve  –  Associate Professor

Anders Henry Nielsen  –  Adjunct Professor

Juan Manuel Losada  –  Postdoctoral Fellow

Gregor Decristoforo  –  Senior Engineer

Olga Paikina  –  Doctoral Research Fellow

Synne Brynjulfsen  –  Doctoral Research Fellow

Rolf Annar Berg Nilsen  –  Doctoral Research Fellow

Johannes Mørkrid  –  Doctoral Research Fellow

New publication from the FUSENOW center

"Multimachine analysis of intermittent fluctuations in the scrape-off layer of magnetically confined fusion plasmas" by S. Ahmed et al.

Fusion energy holds the promise of providing a nearly limitless, clean, and sustainable energy source. To achieve this, scientists are working to develop fusion reactors that can confine extremely hot plasma—a state of matter where atoms are stripped of their electrons—using powerful magnetic fields. However, controlling plasma is a significant challenge, as it exhibits turbulent behavior that can lead to energy losses and damage to reactor walls. A new study published in Plasma Physics and Controlled Fusion sheds light on these turbulent fluctuations in the outer regions of plasma, known as the scrape-off layer (SOL), across six different fusion devices.

In fusion reactors, the SOL is the boundary region where plasma interacts with the reactor walls. This region is characterized by bursts of plasma filaments, often called "blobs," which carry particles and heat outward. These blobs can erode reactor walls and reduce the efficiency of the fusion process. Understanding the behavior of these fluctuations is crucial for designing future reactors, such as ITER and SPARC, to minimize damage and improve performance.

The study analyzed plasma fluctuations in six tokamaks—Alcator C-Mod, DIII-D, TCV, KSTAR, MAST, and MAST-U—using data from specialized probes inserted into the SOL. These devices represent a range of sizes, shapes, and magnetic field strengths, providing a comprehensive dataset for comparison. The researchers applied a statistical model, known as a filtered Poisson process, to describe the fluctuations as a series of random pulses. This model allowed them to extract key parameters, such as the duration of each pulse, the time between pulses, and the amplitude of the fluctuations.

The key findings include the following:

1. Density matters: The study found that as the core plasma density increases, the fluctuations in the SOL become more intermittent, with larger and less frequent bursts. This trend was particularly pronounced for the Alcator C-Mod device, where the amplitude of the fluctuations increased sharply as the plasma density approached a critical limit.

2. Impact of magnetic fields: Stronger magnetic fields were associated with shorter fluctuation durations and less intermittent behavior. This suggests that higher magnetic fields, like those planned for future reactors, could help stabilize the plasma.

3. Differences between devices: The study revealed differences in fluctuation behavior between conventional tokamaks (e.g., DIII-D and TCV) and spherical tokamaks (e.g., MAST and MAST-U). Spherical tokamaks exhibited longer fluctuation durations and waiting times, indicating a distinct behavior in their SOL.

4. Engineering implications: The findings suggest that future reactors with strong magnetic fields and high plasma currents, such as ITER and SPARC, may experience less intermittent fluctuations in the SOL. This could reduce the risk of wall damage and improve reactor performance.

By comparing data from multiple fusion devices, this study provides valuable insights into the universal properties of plasma fluctuations and how they depend on key parameters like particle density, magnetic field strength, and reactor geometry. These findings will help scientists refine their models of plasma behavior and design more robust fusion reactors.

As we move closer to realizing fusion energy, understanding and controlling plasma turbulence will be critical. This research represents an important step toward making fusion a practical and reliable energy source for the future.

The manuscript is published as an open access paper by Plasma Physics and Controlled Fusion.

FUSENOW participates at the 27th PSI conference

"Two-point model connecting near- and far-SOL" by A. Theodorsen and O. E. Garcia

Researchers at UiT The Arctic University of Norway are advancing our understanding of plasma behavior in fusion devices by developing innovative models of the scrape-off layer (SOL)—the region where plasma interacts with the walls of a fusion reactor. This work, presented at the PSI 2026 conference, extends the classical "two-point model" into a more comprehensive "two-box model" that accounts for both the near-SOL and far-SOL regions.

The team investigates how particles and heat are transported radially outward in the SOL, focusing on the role of filamentary structures, or "blobs," that carry energy and particles to the reactor walls. By incorporating factors like anomalous transport, collisionality, and recycling effects, the model provides new insights into how plasma behaves under different conditions.

Key findings include:

• The far-SOL is primarily sheath-limited, meaning its behavior is dominated by interactions with the reactor walls.

• Higher collisionality reduces the perpendicular heat flux to the walls, which has implications for managing heat loads in fusion devices.

• The relationship between density and temperature in the near-SOL aligns with experimental scaling laws, offering validation for the model.

This research contributes to the broader goal of optimizing plasma confinement and minimizing material damage in fusion reactors, bringing us closer to achieving sustainable nuclear fusion as a clean energy source.

This work was presented as a poster at the PSI conference and will be written up for publication in the journal Nuclear Materials and Energy.

New publication from the FUSENOW center

"Velocity scaling regimes for blob-like filaments in the Alcator C-Mod scrape-off layer" by O. E. Garcia et al.

 In the quest for clean and sustainable energy, nuclear fusion holds immense promise. Fusion reactors, like tokamaks, aim to replicate the processes powering the Sun by confining extremely hot plasma using magnetic fields. However, controlling the plasma near the reactor walls remains a significant challenge. This region, known as the scrape-off layer (SOL), is turbulent and filled with "blobs"—localized structures of high-density plasma that move radially outward. These blobs can carry heat and particles to the reactor walls, potentially causing damage and reducing the reactor's efficiency. Understanding how these blobs behave is crucial for designing future fusion reactors.

In this study, researchers from the FUSENOW center analyzed the size and velocity of plasma blobs in the SOL of the Alcator C-Mod tokamak, a high-field fusion device at MIT. Using advanced imaging techniques and diagnostic tools, they investigated how these blobs change with increasing plasma density in the reactor core. The findings provide new insights into the dynamics of these structures and their implications for plasma-wall interactions.

The key findings are as follows: (i) Blob size and velocity Increase with density: The study revealed that as the core plasma density increases, the average size and velocity of the blobs in the SOL also increase. This behavior is linked to changes in the plasma's collisionality—a measure of how often particles in the plasma collide with each other. (ii) Transition between velocity regimes: At low plasma densities, the blobs behave as "sheath-connected" structures, meaning their motion is influenced by interactions with the reactor walls. At higher densities, the blobs enter a "resistive" regime, where their motion is dominated by collisions within the plasma itself. This transition leads to faster blob velocities and more flattened plasma density profiles in the SOL. (iii)
Implications for future reactors: The study's results suggest that in next-generation fusion devices like SPARC, which will operate at higher magnetic fields and plasma densities, blobs will behave similarly to those in Alcator C-Mod. The researchers estimate that SPARC's blobs will have sizes of about 4–5 millimeters and velocities of 300–600 meters per second. These insights are critical for designing diagnostics and mitigating heat loads on reactor walls.

Why does this matter? Plasma blobs play a central role in determining how particles and heat are transported to the walls of a fusion reactor. If not properly managed, this transport can lead to excessive heat loads, material erosion, and impurity generation, all of which can limit the reactor's performance and lifespan. By understanding the behavior of blobs, scientists can develop strategies to control them, optimize plasma confinement, and improve the overall efficiency of fusion reactors.

This study also highlights the universality of blob dynamics across different fusion devices, providing a foundation for predicting and managing plasma behavior in future reactors. As fusion research progresses toward devices like SPARC and ITER, these findings will help pave the way for achieving practical and sustainable fusion energy.

The manuscript is published as an open access paper by Plasma Physics and Controlled Fusion.