Abstract: A heaterless hollow cathode with high current discharge capability for use in electric propulsion devices is presented. The heaterless hollow cathode includes a thermionic emitter insert having a tubular shape and arranged inside a hollow cathode tube. The heaterless hollow cathode further includes a propellant feed tube that longitudinally extends from an upstream region of the hollow cathode tube into an inner volume of the insert. According to one aspect, an extension of the propellant feed tube into the inner volume of the insert is in a range from one quarter to three quarters of a total longitudinal length of the insert. The propellant feed tube is made of a refractory metal that is capable of withstanding temperatures above 2200 degrees C. with negligible evaporation. According to another aspect, the refractory metal is tantalum or tungsten.

Abstract: Systems and methods for embedding a thermal management system in an electric propulsion (EP) system is presented. According to one aspect, one or more oscillating heat pipes (OHPs) are provided within functional elements of the EP system. Each OHP includes channel segments that include a sealed working fluid. The channel segments are joined to form a continuous serpentine channel with a channel path that alternates between hot and cold regions of the EP system. According to another aspect, the functional elements of the EP system are reduced to a single monolithic structure with an embedded OHP. The single monolithic structure may be a single material or a multi material. According to yet another aspect, the functional elements are elements of a magnetic circuit of the EP system, including one or more of a backplate, an outer pole, an inner pole, or a center pole.

Abstract: Systems and methods for providing a heaterless hollow cathode for use in electric propulsion devices is presented. According to one aspect the cathode includes a thermionic emitter having a constricted upstream inlet compared to a downstream outlet of the emitter. The emitter is arranged downstream a hollow cathode tube. Constriction of the upstream inlet is provided by an inner cylindrical hollow space at an upstream region of the emitter having a diameter that is smaller compared to a diameter of an inner cylindrical hollow space at a downstream region of the emitter. A hollow transition region having a varying diameter connects the upstream region to the downstream region. According to another aspect, a ratio of the diameters of the two cylindrical hollow spaces reduces penetration of electric field, and therefore of electric discharge, into the upstream region of the emitter during operation.

Abstract: Systems and methods for providing a heaterless hollow cathode for use in electric propulsion devices is presented. According to one aspect the cathode includes a thermionic emitter having a constricted upstream inlet compared to a downstream outlet of the emitter. The emitter is arranged downstream a hollow cathode tube. Constriction of the upstream inlet is provided by an inner cylindrical hollow space at an upstream region of the emitter having a diameter that is smaller compared to a diameter of an inner cylindrical hollow space at a downstream region of the emitter. A hollow transition region having a varying diameter connects the upstream region to the downstream region. According to another aspect, a ratio of the diameters of the two cylindrical hollow spaces reduces penetration of electric field, and therefore of electric discharge, into the upstream region of the emitter during operation.

Abstract: A low-power Hall thruster gains significantly improved efficiency by a combination of features, including a single piece, h-shaped magnetic screen which enables a more efficient internal volume utilization as well as optimal magnetic shielding; an internally mounted cathode with varying diameter further decreases the footprint of the thruster; an anode with multiple baffles connected by axially oriented holes generates a highly azimuthally uniform propellant flow.

Abstract: A low-power Hall thruster gains significantly improved efficiency by a combination of features, including a single piece, h-shaped magnetic screen which enables a more efficient internal volume utilization as well as optimal magnetic shielding; an internally mounted cathode with varying diameter further decreases the footprint of the thruster; an anode with multiple baffles connected by axially oriented holes generates a highly azimuthally uniform propellant flow.

Abstract: A low-power Hall thruster gains significantly improved efficiency by a combination of features, including a single piece, h-shaped magnetic screen which enables a more efficient internal volume utilization as well as optimal magnetic shielding; an internally mounted cathode with varying diameter further decreases the footprint of the thruster; an anode with multiple baffles connected by axially oriented holes generates a highly azimuthally uniform propellant flow.

Abstract: A low-power Hall thruster gains significantly improved efficiency by a combination of features, including a single piece, h-shaped magnetic screen which enables a more efficient internal volume utilization as well as optimal magnetic shielding; an internally mounted cathode with varying diameter further decreases the footprint of the thruster; an anode with multiple baffles connected by axially oriented holes generates a highly azimuthally uniform propellant flow.

Abstract: Magnetically shielded miniature Hall thrusters are disclosed that use a unique magnetic field topology that prevents the magnetic field lines from intersecting the discharge channel walls in the acceleration region of the thruster. Instead, the lines of force originating from both the inner and outer pole pieces curve around the downstream edges of the discharge channel and follow the channel walls towards the anode. This unique field topology results in low electron temperature at the discharge channel walls while eliminating strong electric field components that would otherwise lead to high erosion rates and power deposition from ion acceleration into the channel walls.

Abstract: An apparatus and method for achieving an efficient central cathode in a Hall effect thruster is disclosed. A hollow insert disposed inside the end of a hollow conductive cathode comprises a rare-earth element and energized to emit electrons from an inner surface. The cathode employs an end opening having an area at least as large as the internal cross sectional area of the rare earth insert to enhance throughput from the cathode end. In addition, the cathode employs a high aspect ratio geometry based on the cathode length to width which mitigates heat transfer from the end. A gas flow through the cathode and insert may be impinged by the emitted electrons to yield a plasma. One or more optional auxiliary gas feeds may also be employed between the cathode and keeper wall and external to the keeper near the outlet.

Abstract: An apparatus and method for achieving an efficient central cathode in a Hall effect thruster is disclosed. A hollow insert disposed inside the end of a hollow conductive cathode comprises a rare-earth element and energized to emit electrons from an inner surface. The cathode employs an end opening having an area at least as large as the internal cross sectional area of the rare earth insert to enhance throughput from the cathode end. In addition, the cathode employs a high aspect ratio geometry based on the cathode length to width which mitigates heat transfer from the end. A gas flow through the cathode and insert may be impinged by the emitted electrons to yield a plasma. One or more optional auxiliary gas feeds may also be employed between the cathode and keeper wall and external to the keeper near the outlet.

Abstract: A protection circuit (30) for a Traveling Wave Tube having multiple tone operation. The protection circuit (30) is a dual sensor (52, 54) arrangement. One sensor (52) is an operational amplifier circuit (56) having a short time constant and a high threshold current. The first sensor (52) provides protection against short time scale faults. The second sensor (54) is an operational amplifier circuit (58) having a time constant higher than the first sensor (52) and a lower current threshold than the first sensor (52) to provide protection against long time scale events. The two sensors (52 and 54) are logically “OR”ed with each other and eliminate spurious shutdowns and circuit damage.

Abstract: A collector for collecting an electron beam in a traveling wave tube is disclosed. The collector has an input end for receiving the electron beam from the traveling wave tube. The collector also has a plurality of stages biased at given voltages and arranged along a common collector axis and positioned at a different axial position with respect to the input end. A stage is biased more negatively with a voltage than a successive stage positioned axially farther from the input end to generate an electrostatic focusing lens for focusing the electron beam toward successive stages thereby increasing the collection efficiency of the collector.

Abstract: A traveling wave tube apparatus and method is disclosed. The traveling wave tube includes a slow wave structure such as a helix member. The helix member has an input end for receiving a microwave input signal having a selected power level and an output end for supplying a microwave output signal having a given power level. A microwave source is connected to the input end of the helix member for applying the microwave input signal to the helix member. An electron gun assembly is adjacent the input end of the helix member and has a cathode for injecting electrons as an electron beam through the helix member. A collector assembly is adjacent the output end of the helix member and has at least four collector electrodes for collecting the electrons in the electron beam. The power level of the microwave input signal is selected such that the given power level of the microwave output signal is at least 3 dB lower than the power level of the microwave output signal at saturation.

Abstract: A traveling wave tube and method of operation is disclosed. The traveling wave tube includes a slow wave structure such as a helix member provided with input and output ends and located within a tube member. An electron gun assembly is adjacent the input end for injecting electrons as an electron beam along an axial path through the helix member. A magnetic focusing device generates a magnetic field having a given strength to confine the beam to the axial path. The given strength of the magnetic field is sufficient to confine the beam only when the power level of the microwave input signal is selected such that the given power level of the microwave output signal is at least 6 dB lower than the power level of the microwave output signal at saturation. Boron Nitride (BN) supporting rods are engaged between the tube and helix members for supporting and transferring heat away from the helix member.

Abstract: A cold-cathode, crossed field switch has a magnet system which generates a magnetic field that is radially-oriented about a switch axis and a planar electrode system which generates an axially-oriented electric field. These structures facilitate a switch whose capacitance, inductance and fabrication costs are all reduced from that of conventional cold-cathode, crossed-field switches. Magnets of the magnet system are arranged in two concentric annular rings with their north and south poles aligned either axially or radially. The planar electrode system includes a cathode, a source grid, a control grid and an anode which are arranged in a substantially parallel relationship.

Abstract: The invention is directed to the reduction of an electron beam transport problem during microwave generation in plasma-assisted microwave sources. A small, e.g., <200 gauss, secondary magnetic field is positioned in association with a slow-wave structure (SWS) of the sources to reduce the radial divergence of electron bunches in the sources' electron beams. The secondary magnetic field exerts radial forces on diverging electrons to supplement radial forces of a primary magnetic field and radial forces of an electrostatic field. The primary magnetic field is generated by electron movement in the electron beam and the electrostatic field is generated by ions which are created as the electron beam transits an ionizable gas in the plasma-assisted source. The addition of the secondary magnetic field can be implemented with a coil that is positioned to direct at least a portion of its magnetic field through a passage of the SWS.

Abstract: Microwave amplifiers are disclosed having a hollow helix slow-wave structure coupled directly to input and output waveguides. This helix-waveguide coupling structure couples the TEM mode of the helix to the TE10 mode of the rectangular waveguides and also defines ports communicating with the helix interior. Heating of the helix during high-power operation can be removed by cooling liquid pumped through the helix via these ports. The helix is surrounded by a cylindrical housing containing a low-pressure ionizable gas which forms a plasma channel that focuses the electron beam without the need for surrounding magnetic structures. A plasma cathode electron gun is arranged to inject an electron beam through the helix. Backflowing ions from the housing are harmlessly absorbed into the face of the plasma cathode. The microwave amplifier is converted to a backward wave oscillator by coupling a load to one of the waveguides.

Abstract: A microwave switch selectively directs a microwave signal along first and second signal paths. The switch includes a microwave transmission member, a microwave chamber formed by the transmission member for containing an ionizable gas, input and output ports formed by the transmission member to communicate with the microwave chamber and a triggered plasma generator which is configured to generate, in response to a voltage trigger signal, a trigger electron density N.sub.t in the gas. The microwave signal increases the trigger electron density N.sub.t to a reflective electron density N.sub.r. Consequently, the microwave signal is reflected along a first path from the input port when the trigger electron density N.sub.t is present and is directed along a second path to the output port when the trigger electron density N.sub.t is absent. A plurality of these microwave switches is arranged to form a tunable microwave short.

Abstract: Apparatus for coating substrates 31, 31", . . . in a vacuum chamber 2 including a substrate carrier 30 disposed therein and a device 29 for generating a first plasma cloud 28 and, further, including magnets 26, 27 directing the plasma cloud 28 onto the surface of the substrates 31, 31" . . . wherein this device for generating the plasma cloud 28 has an election emitter 11 and a downstream tubular anode 38, the anode has an inlet 10 for the process gas to ignite the plasma and, further, the device is provided with magnets 4, 7 for directing and guiding the plasma through the anode tube 38 into the process chamber 43 and including a device for generating atoms, molecules or clusters of the materials for producing a layer on the substrates 31, 31", . . . , preferably an electron beam evaporator 37 from which the evaporated or sputtered material 33 can be directly applied onto the substrates 31, 31" . . . .