This paper presents the electrical design of a magnetron injection gun and collector for high peak and average power TE/sub 01/ W-band gyro-amplifiers. The magnetron injection gun design employs an optimized double-anode geometry and a cathode angle of 500 to achieve superior beam optics that are relatively insensitive to electrode misalignments and field errors. A transverse relative velocity spread of 1.6% at a velocity ratio of 1.5 is obtained in simulations for a 6-A 65-kV beam. Cathode edge emission was modeled, found to produce a major effect on velocity spread, and will be eliminated by nonemissive cylinders affixed to the cathode. The collector, which also serves as the output waveguide, is designed to minimize the required collector length while avoiding excessive power loading on the collector surface. An average power density of less than 640 W/cm/sup 2/ on a 3.25-cm-diameter collector is achieved for 91-kW average beam power. Both the gun and collector are currently under construction.

Electron gun and collector design for 94-GHz gyro-amplifiers

Cold field emission (FE) cathodes are being considered as the electron sources for propellant ionization and ion beam neutralization in electric propulsion systems. Compatible field emission cathodes will enable the development of microscale electric propulsion systems. The hostile environments of propulsion systems are very demanding on the cathode performance. Advanced cold FE cathode technologies are reviewed in this article. Field emission array cathode materials and configurations were optimized using theoretical and experimental results to meet the demands of electric propulsion applications. It was determined that the FE cathode configurations and materials which are required for electric propulsion systems have not yet been fabricated. It is recommended that Mo FEA cathodes are fabricated with VECTL architectures and CLAIR structures and coated with carbide or carbon films to achieve performance and lifetime compatible with microscale electric propulsion systems. Instrument systems are much less demanding on the cathode performance; therefore the advantages of the recommended cathode configuration will also be realized for instrument systems.

A review of field emission cathode technologies for electric propulsion systems and instruments

We demonstrate the effectiveness of the Telegraphist's Equations Solution for Linear-beam Amplifiers code for simulation of a range of klystron amplifier designs. Simulation results are compared to both particle-in-cell (PIC) simulations and experimental data, with good agreement obtained in each case. Specific features and optimizations included in the model are discussed and shown to allow a significant reduction in simulation times over the general PIC approach.

Validation of the large-signal klystron Simulation code TESLA

/pdf/compatibility-of-field-emission-cathode-and-electric-2nk3k2apjy.pdf

Compatibility of field emission cathode and electric propulsion technologies.

This paper describes experimental measurements of the velocity ratio (/spl alpha/=/spl nu//sub /spl perp////spl nu//sub /spl par//) of an annular electron beam for use in a quasi-optical gyrotron (QOG). The electron gun was originally designed for 80-kV 35-A operation, and identical guns have been used in gyrotron experiments by several research groups. A pair of capacitive probes in the drift region are used to characterize the beam over a wide range of voltage (20-60 kV) and current (0-6 A) while varying the magnetic compression and the intermediate-anode voltage. At low-beam voltage, the peak measured values of /spl alpha/ are much lower than those calculated from electron trajectory simulations. The capacitive probe results indicate that electrons reflecting from the peak of the magnetic field are important, increasing the operating voltage of the gun to 50 kV greatly improves the quality of the electron beam.

Velocity ratio measurements on a 20-60 kV quasi-optical gyrotron electron beam

Summary form only given, as follows. A new 3D finite element gun and collector modeling code is under development at SAIC in collaboration with industrial partners and National Laboratories. This development program has been designed specifically to address the shortcomings of current simulation and modeling tools. In particular, although there are 3D gun codes that exist today, their ability to address fine scale features is somewhat limited in 3D due to disparate length scales of certain classes of devices. Additionally, features like advanced emission rules, including thermionic Child's law and comprehensive secondary emission models also need attention. The program specifically targets problems classes including gridded-guns, sheet-beam guns, multi-beam devices, and anisotropic collectors. The presentation provides an overview of the program objectives, the approach to be taken by the development team, and a status of the project.

A description of the new 3D electron gun and collector modeling tool: MICHELLE

Summary form only given. Northrop Grumman has designed, built and tested an 805 MHz, 2.75 MW peak power klystron in support of the Spallation Neutron Source currently under construction in Oak Ridge, Tennessee. The klystron was tested at a pulse length of 1.67 msec and a repetition rate of 60 Hz (10% duty) producing an average power of 275 kW. The electron beam was produced by a mod-anode controlled electron gun. The amplifier section consisted of a total of 6 cavities, including one cavity operating at the second harmonic. Each of the cavities, with the exception of the output cavity, incorporated tuners, allowing their resonant frequencies to be optimized. The nominal power transfer curve of the klystron is shown in the figure below. The efficiency at saturation was 55%. One of the requirements of this tube was to operate into a 1.5:1 mismatch in the output waveguide. The drive curve of the klystron, with the mismatch in the output waveguide, is also shown in the figure. In this case the efficiency was 64% at saturation. This efficiency could be realized in a future klystron by adjusting the impedance of the output cavity, if the waveguide mismatch requirement were lessened. The phase characteristic of the klystron was measured from small signal up to saturation of the klystron. The second through fifth harmonics were measured as well. Design and performance data will be presented.

https://ieeexplore.ieee.org/iel5/7990/22106/01030303.pdf

An 805 MHz high-power klystron

Describes a 805 MHz, 2.75 MW peak power klystron in support of the Spallation Neutron Source currently under construction in Oak Ridge, Tennessee. The klystron was tested at a pulse length of 1.67 msec and a repetition rate of 60 Hz (10% duty) producing an average power of 275 kW. The electron beam was produced by an anode controlled electron gun operating with a nominal cathode voltage of 107 kV and a current of 43 A. The amplifier section consisted of a total of 6 cavities, including one cavity operating at the second harmonic. Each of the cavities, with the exception of the output cavity, incorporated tuners, allowing their resonant frequencies to be optimized.

Summary form only given. The harmonic gyroklystron being designed for the DARPA High Power Millimeter Wave Amplifier Program requires a hollow, axis encircling electron beam. The design and performance of the beamstick are discussed. The gun is an advanced centerpost gun. In simulation, this design produces axial velocity spreads of less than 2% and guiding center spreads of less than 4% for a 40 kV, 4A beam with an alpha of 2. The magnetic circuit was designed to accommodate an 11 kG magnetic field, which is suitable for third harmonic gyroklystron operation at 95 GHz. Since higher cyclotron harmonics require less field, the beamstick can be used to evaluate beam performance for higher harmonic operation as well.

Beamstick for a 95 GHz harmonic gyroklystron

Summary form only given. There is currently a need for high-power, W-band amplifiers for millimeter wave radars. In response to this need, a four cavity, 94 GHz gyroklystron amplifier has been designed and constructed in a collaborative effort between the Naval Research Laboratory, Litton Electron Devices, Communications and Power Industries, and the University of Maryland. The amplifier was designed to produce 80 kW peak output power and 10 kW average output power at 20% efficiency with a bandwidth in excess of 600 MHz. The amplifier was constructed and low duty tests are underway. The gyroklystron has produced peak output powers up to 115 kW and 29% efficiency with -3 dB bandwidths exceeding 600 MHz. Experimental parametric studies and the results of upcoming high duty tests will be presented.

Demonstration of a high power W-band gyroklystron amplifier for radar applications

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A description of the new 3D electron gun and collector modeling tool: MICHELLE

An 805 MHz high-power klystron

An 805 MHz high-power klystron

Beamstick for a 95 GHz harmonic gyroklystron

Demonstration of a high power W-band gyroklystron amplifier for radar applications