Related Experiment Video
Updated: May 14, 2026
08:19
Induction of Microstreaming by Nonspherical Bubble Oscillations in an Acoustic Levitation System
Published on: May 9, 2021
Excitation of geodesic acoustic modes by external fields
1Max Planck Institute for Plasma Physics, EURATOM Association, Boltzmannstr 2, 85748 Garching, Germany.
Physical Review Letters
|February 2, 2013
Summary
External magnetic perturbations can drive geodesic acoustic modes (GAMs) in tokamak plasmas, offering a new method to control turbulent transport. This approach is shown to be viable and efficient for generating GAMs.
Area of Science:
- Plasma physics
- Fusion energy research
- Magnetohydrodynamics
Background:
- Geodesic acoustic modes (GAMs) are crucial for turbulent transport in magnetically confined plasmas.
- Controlling GAMs is key to improving plasma confinement in fusion devices.
- Current methods for GAM generation are limited.
Purpose of the Study:
- To investigate the feasibility of driving geodesic acoustic modes (GAMs) using external magnetic perturbations.
- To assess the efficiency of this method for modifying turbulent transport in tokamak plasmas.
- To develop a theoretical framework for predicting the effectiveness of magnetic perturbations on GAMs.
Main Methods:
- Utilizing external magnetic perturbations at acoustic frequencies in the DIII-D tokamak.
- Developing an analytic method to couple dynamic equilibrium calculations with turbulence code simulations.
- Employing massively parallel, non-Boussinesq turbulence code runs.
Main Results:
- Demonstrated that external magnetic perturbations can indeed drive GAMs, despite their electrostatic nature.
- Showed this method is a viable and efficient approach for GAM generation in magnetically confined plasmas.
- Provided practical estimates for the effectiveness of the proposed method.
Conclusions:
- External magnetic perturbations offer a novel and efficient pathway to generate and control GAMs.
- This technique has the potential to significantly impact turbulent transport in fusion plasmas.
- The developed analytic and computational methods provide a robust tool for further research.
Related Concept Videos
01:03Modes of Standing Waves - I
A close look at earthquakes provides evidence for the conditions appropriate for resonance, standing waves, and constructive and destructive interference. A building may vibrate for several seconds with a driving frequency matching the building's natural frequency of vibration; this produces a resonance that results in one building collapsing while the neighboring buildings do not. Often, buildings of a certain height are devastated, while other taller buildings remain intact. This phenomenon...
01:23Induced Electric Fields
The fact that emfs are induced in circuits implies that work is being done on the conduction electrons in the wires. What can possibly be the source of this work? We know that it’s neither a battery nor a magnetic field, as a battery does not have to be present in a circuit where current is induced, and magnetic fields never do any work on moving charges. The source of the work is in fact an electric field that is induced in the wires. For example, if a stationary conductor is placed in a...
01:27Induced Electric Fields: Applications
An important distinction exists between the electric field induced by a changing magnetic field and the electrostatic field produced by a fixed charge distribution. Specifically, the induced electric field is nonconservative because it does not work in moving a charge over a closed path. In contrast, the electrostatic field is conservative and does no net work over a closed path. Hence, electric potential can be associated with the electrostatic field but not the induced field. The following...
01:14Sound Waves: Resonance
Resonance is produced depending on the boundary conditions imposed on a wave. Resonance can be produced in a string under tension with symmetrical boundary conditions (i.e., has a node at each end). A node is defined as a fixed point where the string does not move. The symmetrical boundary conditions result in some frequencies resonating and producing standing waves, while other frequencies interfere destructively. Sound waves can resonate in a hollow tube, and the frequencies of the sound...
01:28Standing Waves in a Cavity
A household microwave and lasers are examples of standing electromagnetic waves in a cavity. When two conducting metal plates are placed parallel at the nodal planes, it creates a cavity where standing waves are formed. The cavity between the two planes is analogous to a stretched string held at the points x = 0 and x = L. Here, the distance 'L' between the two planes must be an integer multiple of half of the wavelength. The wavelengths that satisfy this condition are given by:
01:04Modes of Standing Waves: II
The starting point for expressing the modes of standing waves is understanding the boundary conditions that the waves must follow. The boundary conditions are derived from the physical understanding of how the standing waves are sustained, that is, how the vibrating particles of the medium behave at the boundaries imposed on them.
For a tube open at one end and closed at the other filled with air, the modes are such that there is always an antinode at the open end and a node at the closed end.
For a tube open at one end and closed at the other filled with air, the modes are such that there is always an antinode at the open end and a node at the closed end.