Related Experiment Video
Updated: Jun 28, 2026
08:42
How to Ignite an Atmospheric Pressure Microwave Plasma Torch without Any Additional Igniters
Published on: April 16, 2015
Intense geodesic acousticlike modes driven by suprathermal ions in a tokamak plasma
R Nazikian1, G Y Fu, M E Austin
1Princeton Plasma Physics Laboratory, Princeton, New Jersey 08543, USA.
Physical Review Letters
|November 13, 2008
Summary
Intense oscillations in the DIII-D tokamak, driven by energetic ions, were observed. These events, linked to geodesic acoustic modes, caused significant drops in neutron emission.
Area of Science:
- Plasma physics
- Fusion energy research
- Tokamak diagnostics
Background:
- Suprathermal ions can drive plasma instabilities in fusion devices.
- Geodesic acoustic modes (GAMs) are important low-frequency modes in tokamak plasmas.
- Understanding plasma oscillations is crucial for achieving stable fusion conditions.
Purpose of the Study:
- To investigate intense axisymmetric oscillations in the DIII-D tokamak.
- To characterize the properties of these oscillations and their drivers.
- To compare experimental observations with theoretical predictions for energetic-particle-driven modes.
Main Methods:
- Experiments conducted on the DIII-D tokamak.
- Injection of suprathermal ions counter to the toroidal plasma current.
- Observation of axisymmetric oscillations using diagnostic tools.
- Analysis of mode frequency, bursting, chirping, and associated plasma parameter changes.
Main Results:
- Intense axisymmetric oscillations observed at nearly half the ideal geodesic acoustic mode frequency.
- Oscillations occurred in plasmas with comparable electron and ion temperatures and q_{min}>or=2.
- Strong bursting and frequency chirping accompanied by 10%-15% drops in neutron emission.
- Large electron density fluctuations observed without detectable electron temperature fluctuations.
- Experimental results align with theoretical predictions for energetic-particle-driven geodesic acoustic modes.
Conclusions:
- Energetic ions can drive significant plasma oscillations in tokamaks.
- The observed modes are consistent with energetic-particle-driven geodesic acoustic modes.
- These oscillations can impact fusion performance, as indicated by neutron emission drops.
Related Concept Videos
01:22Intensity Of Electromagnetic Waves
The energy transport per unit area per unit time, or the Poynting vector, gives the energy flux of an electromagnetic wave at any specific time. For a plane electromagnetic wave with E0 and B0 as the peak electric and magnetic fields and traveling along the x-axis, the time-varying energy flux can be given by the following equation:
01:28Induced Electric Dipoles
A permanent electric dipole orients itself along an external electric field. This rotation can be quantified by defining the potential energy because the external torque does work in rotating it. Then, the potential energy is minimum at the parallel configuration and maximum at the antiparallel configuration. While the former is a stable equilibrium, the latter is an unstable equilibrium.
Since the absolute value of potential energy holds no physical meaning, its zero value can be chosen as per...
Since the absolute value of potential energy holds no physical meaning, its zero value can be chosen as per...
02:45Nuclear Fusion
The process of converting very light nuclei into heavier nuclei is also accompanied by the conversion of mass into large amounts of energy, a process called fusion. The principal source of energy in the sun is a net fusion reaction in which four hydrogen nuclei fuse and ultimately produce one helium nucleus and two positrons.
A helium nucleus has a mass that is 0.7% less than that of four hydrogen nuclei; this lost mass is converted into energy during the fusion. This reaction produces about...
A helium nucleus has a mass that is 0.7% less than that of four hydrogen nuclei; this lost mass is converted into energy during the fusion. This reaction produces about...
01:28Magnetostatic Boundary Conditions
An electric field suffers a discontinuity at a surface charge. Similarly, a magnetic field is discontinuous at a surface current. The perpendicular component of a magnetic field is continuous across the interface of two magnetic mediums. In contrast, its parallel component, perpendicular to the current, is discontinuous by the amount equal to the product of the vacuum permeability and the surface current. Like the scalar potential in electrostatics, the vector potential is also continuous...
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...
01:28Standing 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: