The electrons enter a "drift tube" in which faster electrons overtake the slower ones, creating the bunches, after which the electrons pass through another resonant cavity from which the output power is taken. Since the velocity sorting process takes time, the drift tube must often be several feet long. In comparison, in the TWT the acceleration is caused by the interactions with the helix along the entire length of the tube. This allows the TWT to have a very low noise output, a major advantage of the design. More usefully, this process is much less sensitive to the physical arrangement of the tube, which allows the TWT to operate over a wider variety of frequencies.
TWT's are generally at an advantage when low noise and frequency variability are useful. Helix TWTs are limited in peak RF power by the current handling and therefore thickness of the helix wire. As power level increases, the wire can overheat and cause the helix geometry to warp. Wire thickness can be increased to improve matters, but if the wire is too thick it becomes impossible to obtain the required helix pitch for proper operation. Typically helix TWTs achieve less than 2.
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The coupled-cavity TWT overcomes this limit by replacing the helix with a series of coupled cavities arranged axially along the beam. This structure provides a helical waveguide , and hence amplification can occur via velocity modulation. Helical waveguides have very nonlinear dispersion and thus are only narrowband but wider than klystron. Operation is similar to that of a klystron , except that coupled-cavity TWTs are designed with attenuation between the slow-wave structure instead of a drift tube. The slow-wave structure gives the TWT its wide bandwidth.
A free electron laser allows higher frequencies. It is used to produce high-power radio frequency signals. A TWTA consists of a traveling-wave tube coupled with its protection circuits as in klystron and regulated power supply electronic power conditioner EPC , which may be supplied and integrated by a different manufacturer. The main difference between most power supplies and those for vacuum tubes is that efficient vacuum tubes have depressed collectors to recycle kinetic energy of the electrons, so the secondary winding of the power supply needs up to 6 taps of which the helix voltage needs precise regulation.
His original patent, "Device for and Method of Controlling High Frequency Currents", was filed in and granted in These configuration changes resulted in much greater wave amplification than Haeff's design as they relied on the physical principles of velocity modulation and electron bunching. Pierce ,  and Lester M. Field at Bell Labs. Note that Kompfner's US patent, granted in , does cite Haeff's previous work.
TWTAs are commonly used as amplifiers in satellite transponders , where the input signal is very weak and the output needs to be high power. A TWTA whose output drives an antenna is a type of transmitter. TWTA transmitters are used extensively in radar , particularly in airborne fire-control radar systems, and in electronic warfare and self-protection systems.
The circuit that drives the control grid is usually referred to as a grid modulator. From Wikipedia, the free encyclopedia. Infrared Millim.
Terahertz Waves , 33 2 , pp. Nonlinear self-consistent theory of superheterodyne and parametric electron laser.
Electron Tubes Electronic Tube Design Klystrons Thermionic Cathode - E Beam, Inc
Terahertz Waves , 14 3 , pp. Nonlinear self-consistent theory of two-stream superheterodyne free electron lasers. Terahertz Waves , 15 1 , pp. On the theory of a plasma-beam superheterodyne free electron laser with H -ubitron pumping. Telecommunications and Radio Engineering , 69 20 , pp.
EEC234A – Physics and Technology of Microwave Vacuum Electron Beam Devices I
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The effect of beam and plasma parameters on the four modes of plasma-loaded traveling-wave tube with tape helix. Nonlinear theory of a free electron laser with a helical wiggler and an axial guide magnetic field. ST Accel. These cookies allow you to explore OverDrive services and use our core features. Without these cookies, we can't provide services to you.
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