Oscillators – Beam tube – With electron bunching or velocity variation means
Reexamination Certificate
2000-05-04
2001-11-06
Grimm, Siegfried H. (Department: 2817)
Oscillators
Beam tube
With electron bunching or velocity variation means
C315S005440, C315S005460, C315S005520
Reexamination Certificate
active
06313710
ABSTRACT:
BACKGROUND OF THE INVENTION
Extended interaction structures of the prior art have several cavities of the doubly re-entrant type with electromagnetic fields strongly coupled by slots in the walls (see A. S. Gilmore, Jr., “Microwave Tubes”, Artech House, Norwood, Mass., 1986, Ch. 11, A. Staprans, E. W. McCune, and J. A. Ruetz, “High-Power Linear-Beam Tubes”, Proc. IEEE, vol. 61, pp 299-330, 1973; M. Chodorow and T. Wessel-Berg, “High-Efficiency Klystron with Distributed Interaction”, IRE Trans. Electron Devices, pp. 44-55, 1961). The electrons interact with the RF field at the interaction gap of each cavity. When the electron velocity is synchronized with the gap fields, its energy can be extracted at a multiple number of gaps. For a given total gap voltage, distributed interaction in an N-gap structure proportionally reduces the field level in the cavities as compared to that of a single gap structure, thus increasing the power handling capability by a factor up to N
2
. Tubes based on the extended interaction structure, such as the extended interaction oscillator (EIO) and extended interaction klystron (EIK), are often the choice for high average power operation, especially in the millimeter wave band. For example, EIOs are capable of kilowatt continuous wave (CW) power output in the Ku-band and hundreds of watts CW in the Ka-band. They are available, with reduced power, at much higher frequencies up to 260 GHz. Additional advantages of the extended interaction structure include a high gain-bandwidth product due to its larger resistance to quality (R/Q) value.
The extended interaction structure, on the other hand, does not by itself yield high efficiency. In linear electron tubes such as the klystron or EIK, ballistic bunching of electrons provides one of the most effective means for efficient beam-wave interaction. Conversion efficiencies in excess of 70% have been achieved in klystrons.
New applications, such as ceramic sintering and materials processing, are emerging which require moderately high power millimeter wave sources. These needs (for example, several kilowatts CW) are beyond the capability of state-of-the-art EIOs, which has motivated the development of gyrotrons for such applications. However, the gyrotron technology involves a complicated electron gun configuration and a bulky magnetic/power supply system. To fulfill the requirements of such moderate power applications, it is therefore desirable to provide a device having a greater interaction efficiency and increased power handling capability than does the EIO, but without the high cost and bulkiness of gyrotrons.
SUMMARY OF THE INVENTION
The interaction structure with integral coupling and bunching section of the present invention results in a moderately high-power source which is relatively economical and compact. The interaction structure produces backward wave oscillations in an RF structure which combines ballistic bunching and extended beam-wave interaction in a complex resonator assembly. The complex extended interaction structure includes a five gap electromagnetically-coupled cavity structure with a coaxial section inserted between the first and second cavities. The first cavity serves as a buncher cavity while the four subsequent cavities serve as energy extraction cavities. In the coaxial section, beam and wave propagate in separate channels. The field in the buncher cavity is coupled to the four subsequent energy extraction cavities through the wave channel between the inner and outer conductors of the coaxial section, while the electron beam drifts along a cylindrical channel cut through the inner conductor of the coaxial section. As compared to a conventional extended interaction structure, the complex extended interaction structure of the present invention provides a drift channel (cutoff to the wave) to allow ballistic bunching of electrons. Since the buncher cavity is strongly coupled to the energy extraction cavities, the first gap exerts a large modulating voltage on the electrons, sufficient to produce a tightly bunched electron beam upon entrance into the energy extraction cavities.
To realize the advantages outlined above, the interaction structure for producing electromagnetic radiation having an integral coupling and bunching section, comprises a first cavity for electromagnetically interacting with an electron beam; a second cavity having a second gap for electromagnetically interacting with the electron beam; an inner conductor and an outer conductor forming the integral coupling and bunching section; a wave channel passing between the inner and outer conductors of the integral coupling and bunching section, the wave channel for electromagnetically coupling the first and second cavities through coupling slots in walls of the first and second cavities; and a beam bunching channel passing through the inner conductor of the integral coupling and bunching section, the radius of the beam bunching channel smaller than a cutoff radius to provide a region essentially free of electromagnetic fields within the beam bunching channel, the beam bunching channel having a length for providing ballistic bunching of the electron beam between the first and second cavities.
Also, to realize the advantages outlined above, the method for generating electromagnetic radiation using an oscillator based on an interaction structure having an integral coupling and bunching section, comprises the steps of generating an electron beam; modulating the velocity of the electron beam by passing the electron beam across a first gap of a first cavity so that the electron beam interacts electromagnetically with the first cavity; ballistically bunching the electron beam by passing the electron beam through an integral coupling and bunching section having an inner conductor and an outer conductor, the electron beam passing through a beam bunching channel passing through the inner conductor, the radius of the beam bunching channel smaller than a cutoff radius to provide a region essentially free of electromagnetic fields within the beam bunching channel, the beam bunching channel having a length for providing ballistic bunching of the electron beam; driving a gap voltage across a second gap of a second cavity by passing the electron beam through the second cavity so that the electron beam interacts electromagnetically with the second cavity; and providing feedback between the first and second cavities by electromagnetically coupling the first and second cavities through coupling slots in walls of the first and second cavities, the coupling slots connected by a wave channel passing between the inner and outer conductors.
To further realize the advantages outlined above, an oscillator based on an interaction structure having an integral coupling and bunching section producing backward wave oscillations comprises: an electron beam generated by an electron gun; A first doubly re-entrant cavity having a gap disposed so that the electron beam passes across the gap, the gap having a gap voltage which modulates the electron beam; a cascade of electromagnetically coupled doubly re-entrant energy extraction cavities having gaps disposed so that the electron beam passes across the gaps and transfers energy from the electron beam to the electromagnetic fields in the cascade of electromagnetically coupled doubly re-entrant energy extraction cavities; a coaxial waveguide section having an inner conductor and an outer conductor forming the integral coupling and bunching section; a wave channel passing between the inner and outer conductors of the coaxial waveguide section, the wave channel electromagnetically coupling the first doubly re-entrant cavity with the cascade of electromagnetically coupled doubly re-entrant energy extraction cavities through coupling slots in walls of the cavities and providing feedback from the cascade of electromagnetically coupled doubly re-entrant energy cavities to the first doubly re-entrant cavity; a tuner installed in the coaxial waveguide, the tuner having a portion adjustably extending into the wave c
Chen Han Y.
Chen Li-ming
Chu Kwo R.
Guo Hezhong
Tsai Yi C.
Bobys Marc
Grimm Siegfried H.
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