Plasma physics is a field at the forefront of both fundamental science and applied research, with implications for nuclear fusion, space exploration, and advanced materials. At the Institut Jean Lamour (IJL) in Nancy, France, the SPEKTRE device plays a pivotal role in advancing our understanding of magnetized plasmas in a cylindrical configuration. This sophisticated experimental setup enables scientists to study plasma dynamics, instabilities, and interactions under controlled conditions, contributing invaluable insights that support progress toward fusion energy and other plasma applications.

Integral to SPEKTRE’s research is a suite of advanced modeling techniques that help interpret experimental results and predict plasma behavior.

SPEKTRE is a cylindrical magnetized plasma device. Its characteristics are described in [F Brochard, et al., 49th EPS Conference on Plasma Physics (2023)]:

https://hal.science/hal-04171543/
SPEKTRE (Sheaths, Plasma Edge & Kinetic Turbulence Radiofrequency Experiment) is a research platform in plasma physics and nuclear fusion, currently under construction in Nancy. SPEKTRE is the result of a cooperation within a research agreement between the University of Lorraine and the IPP Garching. It will produce a plasma 40 cm in diameter and 6 m long, under a maximum magnetic field of 0.5 Tesla generated by 13 large flat coils of the former W7-AS stellarator. SPEKTRE can be seen as a step beyond the IShTAR device [1], of which it integrates several components such as the helicon source chamber. SPEKTRE aims at studying the physics of RF sheaths and ICRF heating thanks to an antenna currently being designed that will be coupled to a 100 kW RF generator. Such long plasma column will also allow to study the physics of instabilities and turbulent transport, in particular of impurities, and to conduct targeted studies on plasma-wall interactions. SPEKTRE aims at being widely open to the whole plasma physics community. Finally, the device will host a liquid metal test bench in the framework of a collaboration with the company Renaissance Fusion, in order to study the interactions between plasma and a flowing lithium wall, in conditions similar to those of fusion edge plasmas.

An introduction video was produced in 2021

Key Research Objectives

The main research objectives form the acronym SPEKTRE: Sheaths, Plasma Edge & Kinetic Turbulence Radio-frequency Experiment

Plasma Stability and Instabilities

A major focus of the research on SPEKTRE is on understanding plasma instabilities, which arise when plasmas are exposed to magnetic fields. Such instabilities are central to many fusion-related phenomena, where plasma confinement is critical to sustaining reactions. By carefully controlling the magnetic field and observing plasma behavior, researchers can observe how instabilities form, evolve, and possibly stabilize under various parameters.

Plasma Turbulence

Turbulence is a fundamental phenomenon that greatly influences the transport of heat and particles in magnetized plasmas. SPEKTRE enables detailed investigations into the turbulent dynamics of plasmas and the mechanisms that drive them. The insights gained from SPEKTRE's experiments can inform the development of confinement strategies that minimize turbulence, optimizing the efficiency of magnetic confinement fusion devices.

Plasma-Wall Interactions

Plasma-wall interactions influence particle and energy loss from the plasma, as well as potential degradation of wall materials. Understanding plasma-wall dynamics helps researchers mitigate erosion, impurity generation, and understand the formation of plasma sheaths. Through controlled experiments, SPEKTRE allows scientists to study these effects under various conditions, providing valuable insights into the selection and optimization of materials that can withstand extreme plasma environments.

Radio Frequency Heating

Research on radio frequency (RF) heating is another important focus for SPEKTRE, as RF waves are commonly used to heat plasma to the high temperatures required for fusion reactions. By investigating how RF energy is absorbed and distributed within the plasma, researchers can gain a better understanding of the efficiency and dynamics of different heating techniques. SPEKTRE's experiments in RF heating explore the interactions between RF waves and plasma particles, as well as potential challenges like wave damping and mode conversion.

Modeling Efforts: Enhancing Our Understanding of Plasma Dynamics

To maximize the insights obtained from the SPEKTRE experiments, scientists at the Institut Jean Lamour collaborate on sophisticated modeling efforts. These models play a crucial role in analyzing experimental data, verifying theories, and making predictions about plasma behavior under varied conditions. Some of the key modeling techniques applied to SPEKTRE data include:

1. Fluid Models

In fluid models, plasma is treated as a continuous medium, where equations based on mass, momentum, and energy conservation are solved to describe plasma dynamics. Fluid models are particularly useful in cases where the macroscopic behavior of plasma is of interest, as they can capture large-scale instabilities and turbulence within the magnetic confinement.

2. Kinetic Models

When the behavior of individual particles and their distribution functions become essential, kinetic models are employed. These models use the Boltzmann or Vlasov equations to describe the evolution of particle distributions within the plasma. In SPEKTRE, kinetic modeling is often used to study the formation of plasma sheaths and boundary layers, where particle behavior is highly non-uniform.

3. Hybrid Models

Hybrid models combine fluid and kinetic approaches, providing a flexible framework to study plasmas in regimes where fluid descriptions are insufficient, but full kinetic modeling may be computationally impractical. These models are used in SPEKTRE experiments to explore the complex interactions between different plasma regions.

4. Magnetohydrodynamic (MHD) Models

MHD models describe the motion of plasmas as electrically conducting fluids, taking magnetic field effects into account. In SPEKTRE, MHD models are applied to study how magnetic fields influence plasma instabilities and wave propagation. This modeling approach is highly effective in analyzing plasma confinement and the stability of magnetized configurations.

5. Computational Plasma Simulations

To further support experimental findings, large-scale computational simulations are used. By employing particle-in-cell (PIC) and Vlasov simulations, scientists can simulate particle dynamics, wave-particle interactions, and non-linear behaviors that are often challenging to capture experimentally. These simulations enable researchers to test theoretical hypotheses under controlled virtual conditions, providing insights that guide and complement physical experiments on the SPEKTRE device.

Collaborative Efforts and Applications

The research conducted on SPEKTRE is part of a broader collaborative effort within the plasma physics community. Insights gained from SPEKTRE are shared with other research institutions, supporting applications that extend beyond fusion, such as space physics, materials processing, and environmental applications. The combination of experimental data from SPEKTRE with advanced modeling techniques is helping to push the boundaries of plasma physics, offering a more comprehensive understanding of complex plasma behaviors.

SPEKTRE stands as a testament to the Institut Jean Lamour’s commitment to advancing plasma physics through both experimental and theoretical approaches. By combining state-of-the-art diagnostics with cutting-edge modeling, researchers at IJL are uncovering the intricacies of plasma behavior in magnetized environments. The discoveries made through SPEKTRE’s research and modeling efforts contribute to the fundamental understanding of plasma physics and foster innovations that bring us closer to the reality of sustainable fusion energy and other technological advancements.

SPEKTRE and its modeling initiatives illustrate the powerful synergy between experiment and simulation, proving essential for tackling the challenges of modern plasma research. As these efforts continue, the SPEKTRE device remains a vital resource in the quest to harness the potential of plasma in scientific and industrial applications.