Related Experiment Video
Updated: May 8, 2026
08:10
Building Langmuir Probes and Emissive Probes for Plasma Potential Measurements in Low Pressure, Low Temperature Plasmas
Published on: May 25, 2021
Kinetic theory of plasma sheaths surrounding electron-emitting surfaces
J P Sheehan1, N Hershkowitz, I D Kaganovich
1Engineering Physics Department, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA. sheehanj@umich.edu
Physical Review Letters
|September 3, 2013
Summary
A kinetic theory explains plasma sheath behavior around electron-emitting surfaces. Sheath potential is strongly influenced by the ratio of plasma to emitted electron temperatures, dropping to zero when they equalize.
Area of Science:
- Plasma Physics
- Surface Science
- Kinetic Theory
Background:
- Plasma sheaths form at the boundary between a plasma and a surface.
- Electron emission from surfaces can significantly alter sheath properties.
- Understanding sheath behavior is crucial for plasma-based technologies.
Purpose of the Study:
- To develop a kinetic theory for one-dimensional sheaths around electron-emitting surfaces.
- To investigate the influence of emitted electron temperature on sheath potential.
- To validate theoretical predictions with simulations and experimental measurements.
Main Methods:
- Developed a one-dimensional kinetic theory accounting for plasma electron loss and emitted electron temperature.
- Performed particle-in-cell (PIC) simulations to validate the theoretical model.
- Conducted experiments using a thermionically emitting cathode in an RF plasma afterglow.
Main Results:
- The ratio of plasma to emitted electron temperature critically affects sheath potential.
- Sheath potential approaches zero when plasma and emitted electron temperatures are comparable.
- Experimental measurements confirmed theoretical predictions, showing sheath potential collapse.
Conclusions:
- The kinetic theory accurately describes sheath behavior with electron emission.
- The temperature ratio is a key parameter governing sheath characteristics in such systems.
- The findings are relevant for low-temperature plasmas and RF plasma afterglows.
Related Concept Videos
01:30The Electrical Double Layer
In the region where two bulk phases meet, an intricate electric charge distribution arises due to charge transfer, ion adsorption, molecular orientation, and charge distortion. This complex distribution is commonly referred to as the electrical double layer.When a solid electrode interfaces with ions in an electrolyte solution, the speed of electron transfer dictates the rates of oxidation and reduction. The electrode acquires a charge through the escape of atoms into the solution as cations or...
01:19Inductively Coupled Plasma Atomic Emission Spectroscopy: Principle
Inductively coupled plasma (ICP) is the most widely used plasma source in atomic emission spectroscopy (AES), also known as Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES). The ICP source, or torch, consists of three concentric quartz tubes with argon gas flowing through them. A spark from a Tesla coil initiates the ionization of argon, generating a high-temperature plasma.
The ions and electrons produced interact with the fluctuating magnetic field created by a water-cooled...
The ions and electrons produced interact with the fluctuating magnetic field created by a water-cooled...
01:20Momentum And Radiation Pressure
An object absorbing an electromagnetic wave would experience a force in the direction of propagation of the wave. This force occurs because electromagnetic waves contain and transport momentum. The force accounts for the wave's radiation pressure exerted on the object. Maxwell's prediction was confirmed in 1903 by Nichols and Hull by precisely measuring radiation pressures with a torsion balance. The measuring instrument had mirrors suspended from a fiber kept inside a glass container. Nichols...
01:26Electric Field at the Surface of a Conductor
Consider a conductor in electrostatic equilibrium. The net electric field inside a conductor vanishes, and extra charges on the conductor reside on its outer surface, regardless of where they originate.
In the 19th century, Michael Faraday conducted the famous ice pail experiment to prove that the charges always reside on the surface of a conductor. The experimental set-up consists of a conducting uncharged container mounted on an insulating stand. The outer surface of the container is...
In the 19th century, Michael Faraday conducted the famous ice pail experiment to prove that the charges always reside on the surface of a conductor. The experimental set-up consists of a conducting uncharged container mounted on an insulating stand. The outer surface of the container is...
01:19Thomson's e/m Experiment
In a beam of charged particles created by a heated cathode, the particles move at different speeds. However, many applications need a beam with uniform particle speeds. An arrangement known as a velocity selector uses electric and magnetic fields to pick particles with a particular speed from the beam.
A particle with charge q, speed v, and mass m enters an area from the top, where the magnetic and electric fields are perpendicular both to the particle's motion and to one another. The magnetic...
A particle with charge q, speed v, and mass m enters an area from the top, where the magnetic and electric fields are perpendicular both to the particle's motion and to one another. The magnetic...
01:30Plane Electromagnetic Waves I
The existence of combined electric and magnetic fields that propagate through space as electromagnetic (EM) waves is the most significant prediction of Maxwell's equations. As Maxwell's equations hold in free space, the predicted electromagnetic waves do not require a medium for their propagation. An EM wave comprises an electric field, defined as the force per charge on a stationary charge, and a magnetic field, which is the force per charge on a moving charge.
The EM field is assumed to be a...
The EM field is assumed to be a...