Hutta, "Comparison of thermionic cathode
parameters of low index single crystal faces of LaB6, CeB6 and PrB6," Applied Surface Science, vol.
The thermionic cathode
of a vacuum diode can emit electrons with a Maxwellian distribution of initial velocities (v).
Another practical limitation of the [pi]-mode scenario in the millimeter-wave band is the short life time of the thermionic cathode
due to its high current density.
As compared to the more commonly employed thermionic cathode
approach for electron-beam formation, plasma cathode or plasma electron emitter approaches can produce greater emission current density, are capable of pulsed beam generation, can operate over a wide range of back-ground gas pressure, and are only weakly dependent on the residual vacuum conditions, among other advantages which make them attractive for applications such as electron-beam welding and powder cladding, modification of material surface properties, generation of electromagnetic raditaino, plasma chemical and radiation technologies, and more.
An alternative route is the use of hard vacuum tubes with conventional thermionic cathodes
. Since a thermionic cathode
cannot provide the current density required in a single beam.
The only wear-out mechanism in a TWT is the thermionic cathode
. Rome Lab has conducted five exploratory development programs in this area in the last decade, which led to the development of cathodes that meet the requirement of 100,000 hours of performance for space application.
A crucial technology that will enable short pulse operation will be the incorporation of a gridded thermionic cathode
electron gun to modulate the electron beam.
An experiment at the NRL will use a gridded thermionic cathode
to produce 100 percent density modulation of the electron beam, prior to extracting the microwave power using a tape helix circuit.
The VFD is basically a triode consisting of a thermionic cathode
, a control grid and a phosphor-coated anode sealed in a vacuum envelope.
As the frequency increases it becomes increasingly difficult (if not impossible) using conventional thermionic cathodes
to focus and form high current density, high quality electron beams through the small size interaction region of the THz maser.
His topics include thermionic cathodes
, basic klystrons and their operation, coupled-cavity traveling wave tubes, cross-field amplifiers, and breakdown and protection.
Researchers at FEI Co., Beaverton, OR, have developed a thermionic emitter made of cerium hexaboride ([CeB.sub.6]), as a replacement for lanthanum hexaboride ([LaB.sub.6]) thermionic cathodes
in electron microscopes and e-beam lithography systems.