Related Experiment Video
Updated: Sep 22, 2025
08:10
Building Langmuir Probes and Emissive Probes for Plasma Potential Measurements in Low Pressure, Low Temperature Plasmas
Published on: May 25, 2021
4.5K
First-Principles Density Limit Scaling in Tokamaks Based on Edge Turbulent Transport and Implications for ITER
M Giacomin1, A Pau1, P Ricci1
1Ecole Polytechnique Fédérale de Lausanne (EPFL), Swiss Plasma Center (SPC), CH-1015 Lausanne, Switzerland.
Physical Review Letters
|May 20, 2022
Summary
A new scaling law reveals that increased turbulent transport with plasma collisionality limits maximum tokamak density. This finding predicts a larger safety margin for ITER compared to the Greenwald scaling, especially during confinement transitions.
Area of Science:
- Plasma Physics
- Fusion Energy Research
- Turbulent Transport
Background:
- Achieving high plasma density is crucial for efficient fusion energy production in tokamaks.
- Existing empirical scaling laws, like the Greenwald limit, provide benchmarks but may not capture underlying physical mechanisms.
- Understanding the factors limiting plasma density is essential for designing future fusion reactors like ITER.
Purpose of the Study:
- To develop a first-principles scaling law for the tokamak density limit based on turbulent transport.
- To investigate the role of plasma collisionality and heating power in setting the maximum achievable density.
- To compare the predictions of the new scaling law with the empirical Greenwald scaling for ITER.
Main Methods:
- Developed a first-principles scaling law derived from turbulent transport considerations.
- Compiled and analyzed a multimachine database of density limit discharges from ASDEX Upgrade, JET, and TCV tokamaks.
- Compared the new scaling law's predictions against the established Greenwald empirical scaling.
Main Results:
- The study demonstrates that the increase in boundary turbulent transport with plasma collisionality dictates the maximum attainable density in tokamaks.
- The derived scaling law exhibits a strong dependence on heating power.
- Predictions for ITER indicate a significantly larger safety margin than the Greenwald scaling, particularly in scenarios involving high-to-low confinement transitions.
Conclusions:
- Turbulent transport, influenced by plasma collisionality, is identified as the fundamental physical mechanism limiting tokamak density.
- The new first-principles scaling law offers a more robust prediction of density limits, especially under transient conditions.
- This research has important implications for optimizing the operational window and enhancing the safety margin of future fusion devices like ITER.
Related Concept Videos
01:24Reynolds Transport Theorem
1.4K
The Reynolds transport theorem provides a framework to relate the time rate of change of an extensive property within a system to that in a control volume, which is crucial for analyzing fluid dynamics. Extensive properties, such as mass, velocity, acceleration, temperature, and momentum, can be expressed in terms of the mass of a fluid portion. These properties are called extensive because they depend on the system's size, while intensive properties are their corresponding values per unit...
1.4K
01:24Turbulent Flow
299
Turbulent flow is characterized by unpredictable fluctuations in velocity and pressure, which result in a chaotic fluid movement distinct from the orderly patterns of laminar flow. While laminar flow is governed by smooth, parallel layers with minimal mixing, turbulent flow exhibits highly irregular, three-dimensional patterns. This behavior arises due to instabilities in the fluid's velocity profile, and amplifies as the flow velocity increases. Minor disturbances, known as turbulent...
299
01:17Steady, Laminar Flow Between Parallel Plates
385
Understanding steady, laminar flow between parallel plates is essential for analyzing and designing flow in narrow rectangular channels, commonly found in various water conveyance and drainage systems. The Navier-Stokes equations govern fluid motion and are generally challenging to solve due to their nonlinearity. However, simplifications are possible in certain cases, like the steady laminar flow between parallel plates. For this scenario, we assume steady, incompressible, laminar flow.
385
01:25Boundary Conditions for Current Density
977
Current density becomes discontinuous across an interface of materials with different electrical conductivities. The normal component of the current density is continuous across the boundary.
977
01:16Conservation of Mass in Finite Cotrol Volume
1.4K
The principle of conservation of mass is a fundamental law in fluid mechanics and is applied using the continuity equation. We apply the concept to a finite control volume to derive the continuity equation.
A system is defined as a collection of unchanging contents, and the conservation of mass states that a system's mass is constant.
A system is defined as a collection of unchanging contents, and the conservation of mass states that a system's mass is constant.
1.4K
01:09The Buckingham Pi Theorem
985
The Buckingham Pi theorem provides a structured method to simplify fluid dynamics problems by reducing complex systems of variables to dimensionless terms.
985