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"A two-dimensional conditional averaging method for velocity estimation immune to the barber pole effect" by J. M. Losada and O. E. Garcia

Plasmas, often referred to as the fourth state of matter, are crucial for understanding everything from the behavior of stars to the development of fusion energy. In fusion reactors, such as tokamaks, plasma dynamics in the outermost layer - known as the scrape-off layer (SOL) - play a critical role in determining how heat and particles exhaust. These dynamics are dominated by "blobs," which are filament-like structures that transport particles and energy across magnetic fields. Accurately measuring the velocity of these blobs is essential for improving fusion reactor designs and ensuring stable, efficient operation.

However, measuring blob velocities from imaging data is not straightforward. A common challenge is the "barber pole effect," which occurs when elongated structures move at an angle to their symmetry axis. This effect can distort velocity measurements, leading to inaccurate results. Traditional methods, such as time-delay estimation, often fail to account for this distortion, especially when working with low-resolution imaging data typical of plasma diagnostics.

In this study, researchers from UiT The Arctic University of Norway have developed a novel method to overcome this challenge. Their approach, based on two-dimensional conditional averaging, provides a robust way to estimate blob velocities even in the presence of the barber pole effect. By focusing on the average behavior of large-amplitude structures, the method isolates the true motion of blobs from other noise and distortions in the data.

Key highlights of the study are as follows: (i) Barber pole effect resolved: The two-dimensional conditional averaging method accurately estimates blob velocities regardless of their tilt angle, a scenario where traditional methods often fail. (ii) Validation with synthetic data: The researchers tested their method using computer-generated datasets that mimic real plasma conditions. These tests demonstrated that the conditional averaging method consistently outperforms time-delay estimation techniques. (iii) Two tracking techniques: The study explores two ways to track blob positions - subgrid maximum tracking and contouring. Both approaches work well, but contouring is found to be slightly more accurate and robust. (iv) Broad applicability: While designed for coarse-grained imaging diagnostics like gas puff imaging and beam emission spectroscopy, the method could be adapted for other fields where tracking moving structures in noisy data is required.

Accurate velocity measurements are critical for understanding how blobs contribute to cross-field transport at the boundary of magnetically confined plasmas. This, in turn, affects the design of fusion reactors, as engineers aim to minimize heat and particle losses while maintaining stable plasma confinement. The conditional averaging method provides a new tool for researchers to study plasma turbulence and transport with greater precision, paving the way for advancements in fusion energy research.

The next step is to apply this method to real experimental data from fusion devices like tokamaks. If successful, it could significantly enhance our understanding of plasma behavior and help optimize the performance of future fusion reactors. Beyond fusion, the technique could also find applications in other scientific fields that rely on imaging data to study moving structures, such as fluid dynamics and atmospheric science.

This work, funded by the Trond Mohn Foundation and the Tromsø Research Foundation, represents a significant step forward in plasma physics and highlights the importance of innovative data analysis techniques in tackling complex scientific challenges.

This work has been accepted for publication in Physics of Plasmas. A link to the publication will be provided as soon as it is published online.

New simulations reveal universal patterns in turbulent plasma at the edge of fusion reactors

Researchers at UiT The Arctic University of Norway have used advanced computer simulations to uncover new insights into the turbulent behavior of plasma at the boundary of magnetically confined fusion devices. Their findings shed light on how plasma particles escape along magnetic field lines and how this process shapes the violent, burst-like fluctuations that strike reactor walls — a key challenge for future fusion power plants.

In fusion reactors, plasma is confined by strong magnetic fields, but at the outer edge, known as the scrape-off layer, the plasma becomes highly turbulent. Instead of flowing smoothly, it forms filament-like “blobs” that move rapidly outward and deliver heat and particles to material surfaces. Understanding this turbulent region is essential for predicting wall damage and improving reactor designs.

Using long-duration numerical simulations, the researchers systematically varied how quickly particles are lost along magnetic field lines, a quantity closely related to the length of the magnetic connection between the plasma and reactor surfaces. They found that stronger particle losses lead to steeper plasma density profiles, smaller turbulent structures, and more intense, intermittent bursts of plasma. In other words, when plasma can escape more easily along magnetic field lines, the turbulence becomes sharper and more extreme.

Despite these changes, the statistical behavior of the fluctuations remained remarkably consistent. The large bursts of plasma followed simple and universal mathematical patterns, with their sizes and timing described by well-known probability distributions. The turbulence could be accurately modeled as a sequence of random, uncorrelated pulses, much like raindrops hitting a surface. This unexpected simplicity suggests that even complex plasma turbulence follows robust and predictable statistical rules.

The results also showed that turbulent transport spreads plasma much farther than would be expected from ordinary diffusion alone, flattening the overall plasma profile compared to what would occur without collective motion. This highlights the dominant role of blob-like structures in carrying particles across magnetic field lines.

These findings are highly relevant for the design of future fusion reactors, including advanced divertor concepts that aim to control how plasma interacts with material surfaces. By linking magnetic connection length to both plasma profiles and fluctuation properties, the study provides valuable guidance for engineering strategies that seek to reduce heat loads and extend material lifetimes.

Beyond their immediate implications for fusion technology, the simulations establish a powerful new framework for validating more complex turbulence models. The statistical methods used in this work can serve as a benchmark for next-generation plasma simulation tools, helping researchers build more reliable predictions of plasma behavior at the reactor boundary.

The study demonstrates that beneath the apparent chaos of edge plasma turbulence lies a set of universal patterns — a discovery that brings scientists one step closer to controlling one of the most challenging regions in fusion energy research.

The publication is available online in the journal Physics of Plasmas.

In this study, researchers investigated the behavior of plasma in the boundary region of the Alcator C-Mod tokamak, a compact, high-field fusion reactor. Using advanced diagnostic tools, they focused on the "scrape-off layer" (SOL), the outermost region of the plasma where particles and heat escape and interact with the reactor walls. This region is critical because it determines how much heat and particle flux the reactor walls must endure, which directly impacts the longevity and safety of fusion devices.

The team observed the movement of "blobs"—coherent structures of plasma that carry particles and heat radially outward. These blobs are like turbulent bursts that can deposit significant energy onto the reactor walls in short, localized pulses. By analyzing data from specialized probes and imaging systems, the researchers discovered that as the core plasma density increases, these blobs become faster, larger, and more dominant throughout the SOL. This leads to a "flattening" of the plasma density profile, meaning the plasma spreads further out toward the walls.

To explain these observations, the researchers used a stochastic model, which treats the plasma fluctuations as a superposition of random, uncorrelated pulses. The model successfully predicted key features of the plasma behavior, including the density profile and the statistical properties of the fluctuations. Importantly, the study showed that the e-folding length of the plasma density profile (a measure of how quickly the density decreases with distance) is directly linked to the velocity of the blobs and the time it takes particles to escape along magnetic field lines.

These findings have significant implications for the design of future fusion reactors. As fusion devices operate at higher densities to achieve better performance, the increased blob activity and flattened profiles could lead to more intense interactions with reactor walls. Understanding and predicting these effects will help engineers design materials and structures that can withstand the harsh conditions at the plasma edge, bringing us closer to realizing the dream of fusion energy.

This research highlights the importance of studying plasma turbulence and edge dynamics in fusion devices. By combining advanced diagnostics with theoretical modeling, the team has provided valuable insights into the complex behavior of plasma at the boundary, paving the way for more robust and efficient fusion reactors in the future.

The publication is available online in the journal Nuclear Fusion.

The leaders of the FUSENOW center has just published a popular science article in Norwegian at forskning.no, descrbing developments in the field of fusion power, activities in Norway and the FUSENOW center.

At the Department of Physics and Technology, University of Bergen, there is a vacancy for a postdoctoral research position within experimental quantum technologies for laser fusion experiments within the NAPLIFE collaboration. The position is for a fixed term of 3 years and is financed by the ongoing Fusion Research Center Norway (FUSENOW) supported by the Trond
Mohn Research Foundation.

The project aims to design, develop and characterize nano-fabricated targets for use in laser fusion experiments, to increase, and improve the target ignition and utilization. In addition to developing and fabricating the targets, a part of the project will be to build a test setup for target characterization at UiB. The most promising targets fabricated will be brought to the ELI-ALPs European laser-infrastructure at Szeged, Hungary, for characterization.

The postdoctoral position involves tasks such as designing, manufacturing and testing the laser fusion targets. The work will include simulation, experimental work, characterization and data analysis. The modelling and analysing of experimental results will be done in collaboration with the local and international NAPLIFE team. The candidate is expected to take an active part in the target design and the continuous development based on experimental results. The candidate will have the chance to take an active role in the development of the research and steer the target development together with the PI.

At UiB the candidate will have access to several lab-facilities with modern fabrication and characterization equipment. The work will be carried out in an active research environment as a member of Nanophysics group.

We encourage applicants that meet the requirements, with a strong motivation for experimental challenges and good ideas to apply.

The position is announced at Jobbnorge.

Four researchers from UiT The Arctic University of Norway and FUSENOW participated at the 29th EU-US Transport Task Force Workshop 2025, arranged in Budapest. The research center presented advances in statistical and computational description of the transport at the boundary of fusion devices through poster presentations and an oral contribution. The goal of the international Transport Task Force is to develop a physics-based understanding of particle, momentum and heat transport in magnetically confined fusion plasmas. This understanding should be of sufficient depth that it allows the development of predictive models of plasma transport that can be validated against experiment, and then used to simulate the future performance of burning plasmas and aid the design and optimization of next-step fusion energy reactors. The contributions at the workshop will be published in a special issue of the journal Plasma Physics and Controlled Fusion.

On August 18, 2025, Johannes Eiriksønn Mørkrid was employed as a PhD fellow in the FUSENOW center at UiT The Arctic University of Norway. Mørkrid has his Bachelor studies in physics from NTNU and a master degree from UiT. The title of his doctoral thesis porject is "Numerical simulations of turbulence at the boundary of magnetically confined fusion plasmas". He will use mathematical modelling and high performance computations to investigate the turbulence-driven transport of particle and heat at the boundary of magnetically confined plasmas. Specifically, he will develop a simulation code in the programming language Julia to solve a set of coupled partial differential equations to simulate turbulent motions and fluctuation-induced transport of particle and heat in the scrape-off layer in fusion plasmas.

First ever research center on fusion energy established in Norway

Durinig the annual celebration of the Tromsø Science Foundation, it was announced that the Trond Mohn Research Foundation will fund the research center Fusion research center Norway (FUSENOW) as a thematic initiative. This is the first fusion reseach center ever to be established in Norway, working to realize clean power from fusion of Hydrogen isotopes. The funding from the research foundation is MNOK 20, with an equal amount matched by UiT The Arctic University of Norway and the University of Bergen. The project comprises both magnetic confinement fusion (at UiT) and laser fusion (at UiB).