08-08-2012, 02:55 PM
STUDY OF PSEUDOSPARK DISCHARGE BASED ELECTRON BEAM AND PROPAGATION FOR TERAHERTZ SOURCE GENERATION
[attachment=30601]
Plasma (Ionized gas)
A plasma is a quasi-neutral gas of charged and neutral particles which exhibits collective behavior. Also known as fourth state of matter. Quasi-neutral means neutral enough so that one can take ni≈ ne ≈n, n is common density called plasma density but not so neutral that all the interesting electromagnetic forces vanish
Plasma consists of a collection of free-moving electrons and ions - atoms that have lost electrons. Energy is needed to strip electrons from atoms to make plasma. The energy can be of various origins: thermal, electrical, or light (ultraviolet light or intense visible light from a laser). With insufficient sustaining power, plasmas recombine into neutral gas.
The three conditions a plasma must satisfy are:
λD<< L.
ND>>1.
ωτ >1.
Terahertz Radiation
Terahertz radiation often termed as sub millimeter waves, are EM radiations with frequencies between high-frequency edge of the microwave band, 300 GHz (3×1011 Hz), and the long-wavelength edge of far-infrared light, 3000 GHz (3×1012 Hz or 3 THz)
Wavelength: 0.1 mm infrared to 1.0 mm microwave
Both wave-like characteristics (MW) and particle-like characteristics (IR).
Line of sight propagation
Non-ionizing
Can penetrate a wide variety of non-conducting materials even fog and clouds BUT not metal or water
Strongly absorbed by earth’s atmosphere, so its range is quite
short, limiting its usefulness for communications but ideal for high altitude and space communication
Applications in medical imaging, security purposes, communication, manufacturing, quality control, process managing, old art study, spectroscopy and tomography
Pseudospark discharge
It is an axially symmetric, self sustained, transient, low pressure gas discharge and takes place in a special hollow-electrode geometry of a hollow cathode/planar anode configuration using various gases such as nitrogen, argon, hydrogen and xenon
Features :
Fast voltage breakdown together with a fast current rise
Complex discharge development with different discharge phases
Oscillation of fast electrons emitted from the inner walls of the cathode cavity and accelerated into the cathode sheath
Governed by Paschen’s Law
Plasma Cathode Electron Gun
“Plasma Cathode Electron gun” means a system that provides a well-defined electron beam that is formed by extraction, concentration and acceleration of electrons from the plasma (to create a plasma one needs a discharge).
There are two main parts to the plasma cathode electron gun:
Plasma generator based on some kind of electrical discharge
[attachment=30601]
Plasma (Ionized gas)
A plasma is a quasi-neutral gas of charged and neutral particles which exhibits collective behavior. Also known as fourth state of matter. Quasi-neutral means neutral enough so that one can take ni≈ ne ≈n, n is common density called plasma density but not so neutral that all the interesting electromagnetic forces vanish
Plasma consists of a collection of free-moving electrons and ions - atoms that have lost electrons. Energy is needed to strip electrons from atoms to make plasma. The energy can be of various origins: thermal, electrical, or light (ultraviolet light or intense visible light from a laser). With insufficient sustaining power, plasmas recombine into neutral gas.
The three conditions a plasma must satisfy are:
λD<< L.
ND>>1.
ωτ >1.
Terahertz Radiation
Terahertz radiation often termed as sub millimeter waves, are EM radiations with frequencies between high-frequency edge of the microwave band, 300 GHz (3×1011 Hz), and the long-wavelength edge of far-infrared light, 3000 GHz (3×1012 Hz or 3 THz)
Wavelength: 0.1 mm infrared to 1.0 mm microwave
Both wave-like characteristics (MW) and particle-like characteristics (IR).
Line of sight propagation
Non-ionizing
Can penetrate a wide variety of non-conducting materials even fog and clouds BUT not metal or water
Strongly absorbed by earth’s atmosphere, so its range is quite
short, limiting its usefulness for communications but ideal for high altitude and space communication
Applications in medical imaging, security purposes, communication, manufacturing, quality control, process managing, old art study, spectroscopy and tomography
Pseudospark discharge
It is an axially symmetric, self sustained, transient, low pressure gas discharge and takes place in a special hollow-electrode geometry of a hollow cathode/planar anode configuration using various gases such as nitrogen, argon, hydrogen and xenon
Features :
Fast voltage breakdown together with a fast current rise
Complex discharge development with different discharge phases
Oscillation of fast electrons emitted from the inner walls of the cathode cavity and accelerated into the cathode sheath
Governed by Paschen’s Law
Plasma Cathode Electron Gun
“Plasma Cathode Electron gun” means a system that provides a well-defined electron beam that is formed by extraction, concentration and acceleration of electrons from the plasma (to create a plasma one needs a discharge).
There are two main parts to the plasma cathode electron gun:
Plasma generator based on some kind of electrical discharge