Patent Application
20080012657
The foregoing and other objects, features and advantages of the invention, as well as the invention itself, will be more fully understood from the following illustrative description, when read together with the accompanying drawings which are not necessarily to scale.
The electron gun 104 includes a cathode 128 and an anode 132. In operation, an electric potential is applied between the cathode 128 and the anode 132. The cathode 128 generates and emits a beam of electrons 152 in response to the applied electric potential. In one embodiment, a potential of greater than several thousand volts is generally applied between the cathode 128 and the anode 132 to generate the beam of electrons. To generate the beam of electrons, the cathode 128 is set at a large negative voltage relative to the anode 132. In some embodiments, a heater (not shown) is used to heat the cathode 128 to initiate and/or maintain a flow of electrons emitted from the cathode 128 to produce the beam of electrons.
The slow-wave structure 108 is located adjacent the electron gun 104 such that the electron beam passes through a passage 136 in the slow-wave structure 108. The slow-wave structure 108 generally includes a helical structure or a coupled cavity circuit. In operation, a microwave signal is introduced to the slow-wave structure via the input port 116 of the slow-wave structure 108. The microwave signal propagates along the slow-wave structure 108 at an axial velocity that is substantially less than the speed of light. The axial velocity is a function of the electrical and geometrical properties of the slow-wave structure 108. The ratio of the axial velocity to the free-space velocity is often referred to as the velocity factor of the slow-wave structure 108.
The velocity factor of the slow-wave structure 108 and the electrical potential between the cathode 128 and the anode 132 are chosen so that the electric fields of the microwave signal interact with the beam of electrons in the slow-wave structure 108. The interaction between the microwave signal and the beam of electrons results in velocity modulation of the beam of electrons and energy is transferred from the beam of electrons to the microwave signal, thereby amplifying the microwave signal while slowing the velocity of the electrons in the beam of electrons. The amplified microwave signal exits the output port 120 of the slow-wave structure 108. The electrons in the beam of electrons that pass through the passage 136 of the slow-wave structure 108 are collected by the collector electrode 112 of the collector 110. The collector 110 is maintained at a negative DC voltage, for example, −11 kV in one embodiment. A collector high voltage power supply 140 provides the DC voltage to the collector 110 via an ion trap power supply 144. Alternative DC voltage magnitudes can be applied to the collector 110.
By way of example, the microwave signal initially travels close to the speed of light and must be slowed down to the speed of the beam of electrons which travel at about 10% to about 50% of the speed of light. In a slow-wave structure 128 incorporating a helix structure, the microwave signal travels along the generally circular/spiral path of the helix. The beam of electrons travels a distance of about one pitch of the helical structure which is a smaller distance than one revolution of the circular path of the helical structure. In this manner, the speed of the microwave signal is reduced to approximately the speed of the beam of electrons so energy can be transferred from the beam of electrons to the microwave signal while they interact with each other.
A coupled cavity circuit (or structure) may, alternatively, be used in the slow-wave structure 108. In a coupled cavity circuit, the microwave signal travels along the inner surfaces of the cavities of the circuit while the beam of electrons passes through openings between adjacent cavities. The microwave signal travels over a larger distance than the beam of electrons, thereby slowing the microwave signal relative to the beam of electrons.
In some embodiments, the traveling-wave tube system 100 includes a plurality of collector electrodes, each at a different electric potential relative to the body (e.g., housing) of the traveling-wave tube 124 to collect electrons of different electric potential levels. In some embodiments, the traveling-wave tube system 100 incorporates a vacuum ion pump to collect ions generated.
The traveling-wave tube system 100 also includes a high voltage power supply 156 that provides the electrical potential between the cathode 128 and the anode 132 of the traveling-wave tube 124. The high voltage power supply 156 maintains the cathode 128 at a large, negative electrical potential (e.g., about −20 kV). In some embodiments, the high voltage power supply 156 maintains the cathode 128 at an electric potential between about −10 kV and about −50 kV.
A high voltage potential (e.g., −20 kV) is applied to the cathode 128 by the power supply 156 and a low voltage (e.g., 0 V or ground) is applied to the anode 132 (which is electrically isolated from the cathode 128). The potential difference between the cathode 128 and the anode 132 generates the beam of electrons 152 that flows from the cathode 128, through the slow-wave structure 108, and terminates at the collector electrode 112, as described herein previously. The electrons from the beam of electrons 152 that terminate at the collector electrode 112 generate a flow of current that is provided by the collector 110 to the ion trap power supply 144.
The flow of the collector current through the ion trap power supply 144 generates an electrical voltage of about +200V on the isolated anode 132 which provides the ion trap that prevents positive ions from traveling to the cathode 128. The +200 volt electrical potential applied to the anode 132 repels ions generated in the slow-wave structure 108 from the anode 132. The ions are positively charged molecules formed by the interaction of the beam of electrons 152 with residual gas molecules located in the slow-wave structure 108. Because the anode 132 is maintained at a positive voltage (e.g., +200 volts in one embodiment) and the ions are positively charged, the anode 132 acts as an electrical barrier that prevents the ions from traveling towards the cathode 128 (which has a large negative electrical voltage potential relative to the positively charged ions).
In some embodiments, different components of the system may be incorporated together in, for example, a single housing or enclosure. For example, the collector high voltage power supply 140 and the high voltage power supply 156 may be incorporated into a single electronics enclosure.
The current produced by the electrons that impact the collector electrode 112 flows through the ion trap power supply circuit 300. The DC voltage on the collector electrode 112 is provided by the high voltage power supply 140 (e.g., −11 kV applied by the collector high voltage power supply 140 via the ion trap power supply 144). In some embodiments of the invention, alternative voltage levels can be applied to the anode 132 if the voltage is sufficient to repel the positive ions generated. For example, in some embodiments, a voltage level between about 50 volts and about 400 volts can be applied to the anode 132.
In one embodiment of the invention, the current of the collector electrode 112 flows through zener diodes in the ion trap power supply circuit via a collector connection (e.g., the collector connection 308 of
Alternative ion trap power supply circuits and circuit topologies can be implemented in alternative embodiments of the invention in which current flow from the collector is provided to a power supply to generate the desired DC bus voltage (e.g., +200 volts) that is provide to the anode of the system to create the ion trap.
Variations, modifications, and other implementations of what is described herein will occur to those of ordinary skill in the art without departing from the spirit and the scope of the invention as claimed. Accordingly, the invention is to be defined not by the preceding illustrative description but instead by the spirit and scope of the following claims.
