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To produce an EIK working at THz frequencies, departure from traditional fabrication techniques is required. This paper describes the investigation and results of various fabrication techniques and their suitability for application in a VED.

A 50 watt CW 220 GHz sheet beam amplifier is under development at NRL. We report on microfabrication techniques used to construct a grating-based amplifier circuit using Ultraviolet Lithography (UV-LIGA) and Deep Reactive Ion etching (DRIE).

The development of terahertz power amplifiers presents significant new challenges as it brings into focus design, fabrication, and measurement issues that are not important factors at lower frequencies. In this paper, we describe our design approach to meet these challenges with particular emphasis on a 0.67 THz Extended-Interaction Klystron (EIK). This device is being designed to generate a peak power of ∼0.5W with gain of ∼23 dB over an instantaneous bandwidth of 15 GHz. The circuit will be driven by a 100 mA, 25kV electron beam confined in a 0.005″diameter beam tunnel with ∼1 Tesla magnetic field. This choice of beam size ensures that the same electron gun can be employed for all program development phases culminating in a 1.03 THz amplifier. A highly efficient depressed collector has also been designed to meet the efficiency requirement.

The operating characteristics of a two-cavity X-band gyroklystron experiment are reported. Beam voltages and currents up to 440 kV and 200 A, respectively, are generated in 1 mu s pulses by a thermionic magnetron injection gun. Velocity ratios ( nu /sub perpendicular to // nu /sub z/) near one in the output cavity are used to achieve peak powers of 24 MW near 9.87 GHz. The maximum saturated efficiency of more than 33% occurs at a beam voltage of 425 kV and a current of 150 A. A large signal gain in excess of 34 dB is realized by operating the input cavity just below the start oscillation threshold. Details of tube stability and the dependence of amplification on magnetic field profile, input signal parameters, and various beam quantities are presented. >

An adjustable resonance cavity was developed to measure the complex permittivity of dielectric materials. The cavity has an inner diameter of 16.400 cm and an inner height of 2.54 cm. The aluminum stationary wall holder was positioned about 10.8 cm above the top of the cavity. It was fixed into place by three 1.27-cm-diam linear shafts. By suspending from the wall holder, the movable wall moved vertically by sliding on 1.27 cm bore-closed ball bushings. By turning a 1 in.-12 nut, the movable wall could be positioned so that the cavity height equaled the height of the sample. Therefore, this enables the measurement of the permittivity of samples with heights between 0.88 and 1.91 cm and radius between 1.27 and 3.18 cm. The complex permittivity of the sample was calculated based upon the sample dimensions, central frequency of TMono modes, and Q factor of the resonance curve using an exact solution. The complex permittivity was measured at the three lowest modes, where the frequency span is 1–4 GHz.

The Vacuum Electronics Branch of the US Naval Research Laboratory (NRL) is actively engaged in research and development of key technologies for high-power MMW to upper-MMW amplifiers. This work includes the development and application of physics-based modeling and simulation tools, the design and development of high-perveance sheet electron beams and associated slow-wave and standing-wave interaction structures, research on high-current-density emitters, and the development and application of precise microfabrication techniques and thermal management schemes. An overview of these activities will be presented, including a discussion of the technological advances required to achieve order-of-magnitude increases in amplifier performance and a summary of the approaches being pursued and their status.

The removal of high heat fluxes from BeO ceramic and GaN-on-SiC semiconductor dies using hierarchically branched-microchannel coolers is investigated, in order to examine the impact of the number of branching levels on performance. The microchannel coolers are made by lithography and deep reactive ion etching of single crystal silicon. The test dies contain a dc-operated resistive zone that approximates the spatially averaged heat flux that would appear in low-temperature cofired ceramic microwave circuit packages and in monolithic microwave integrated circuits. For the particular geometric constraints selected for the study (three source/exhaust channels, ∼5×5 mm2 die footprint, 200 μm deep channels in a 400 μm thick silicon wafer), the optimum performance is achieved with three hierarchical levels of branched-channel size. A heat flux of 1.5 kW/cm2 is removed from the 3.6×4.7 mm2 resistive zone of the BeO-based die, at a surface temperature of 203°C. When attached instead to a high thermal conductivity GaN-on-SiC die with a 1.2×5 mm2 resistive zone, a heat flux of 3.9 kW/cm2 is removed from the resistive zone at 198°C surface temperature. The total water flow rate is 275 ml/min in both situations. The experimental results are found to be in reasonable agreement with finite element simulations based on idealized estimates of convection coefficients within the channels. For the three-channel size configuration, an effective heat transfer coefficient in the range of 12.2–13.4 W/cm2 K (with respect to a 20°C bulk fluid temperature) is inferred to be present on the top of the microchannel cooler, based on simulations and derived values obtained from the experimental data.

The performance of four overmoded (TE011 circular), two‐cavity gyroklystron amplifier tubes operating in X band is reported. A summary of the theoretical design procedure is presented, followed by a description of the experimental setup. The stability and amplification properties of the four gyroklystron tubes are subsequently described, each being modified in sequence to improve performance. The fourth tube produced 2.0–2.7 MW pulses at 9.87 GHz for 0.5–1.0 μs, and exhibited gains of 17–19 dB and efficiencies of 5%. The results were obtained using electron beams with voltages, currents, and computed beam alphas (v⊥/vz) of 407–425 kV, 115–135 A, and 0.8–1.0, respectively. The presence of instabilities in the gun downtaper and drift tube prevented operation at the design point (500 kV, 160 A, and alpha 1.5). The effects of varying input frequency, input power, and beam parameters (voltage, current, magnetic compression) on the amplifier operation are reported. Detailed descriptions of the instabilities obs...

Experimental studies of amplification in a two-cavity X-band gyroklystron are reported. The system utilizes a thermionic magnetron injection gun at voltages up to 440 kV and currents up to 190 A in 1-μs pulses. Optimum performance is achieved by tapering the magnetic-field profile. Peak powers of 20 MW in the TE01 mode at 9.87 GHz are measured with calibrated crystals and with methanol calorimetry. Resultant efficiencies are in excess of 31% and large-signal gains surpass 26 dB. The experimental results are in good agreement with simulated results from a partially self-consistent, nonlinear, steady-state code.

The well-established procedure for producing microwave absorbers by carbon loading a porous ceramic has been modified to enhance the cleanliness of the final product and to improve the controllability of the loss tangent. The changes include soaking the ceramics in an acid bath to leach out undesirable metal oxides and a multiple-step carbonization using both carbon dioxide and hydrogen firings. These modifications allow the use of an aluminum silicate material known as Aremcolox 502-1100 as a starting material for absorbers in critical applications, such as a system with an osmium-coated dispenser cathode. The processing steps are described in detail and their relevance to the development of a high-peak power X-band gyroklystron is discussed. Representative values of the complex dielectric constants at 9.9 GHz for various carbon contents are presented. >

Computations of operating temperatures in microfabricated upper-millimeter-wave sheet beam traveling wave structures are provided. The studies include the effects of different cooling techniques and construction materials. The scaling of output power capability vs. frequency, as constrained by thermal limits, is also presented.

Polymer/ceramic nanocomposites provide a means of combining the high permittivities (εr) of metal oxide nanoparticles with the solution-processability and high dielectric strength of polymeric hosts. Simple mixing of nanoparticles and polymers generally results in poor quality nanocomposites due to the agglomeration of nanoparticles and poor miscibility of nanoparticles with host materials. We have shown that surface modification of metal oxide nanoparticles with phosphonic acid-based ligands affords robust surface modification and improves the processiblity and the quality of the resulting nanocomposites. We report on the use of phosphonic-acid modified barium titanate (BaTiO3, BT) nanoparticles in dielectric nanocomposites and their applications to high-energy-density capacitors and solution-processable high permittivity gate insulators in organic field-effect transistors (OFETs). Surface modification of BT nanoparticles enabled the formation of high quality nanocomposite thin films with ferroelectric polymer hosts such as poly(vinylidene fluoride-co-hexafluoropropylene), P(VDF-HFP), with large volume fractions (up to 50 vol. %), which are potentially useful materials for electrical energy storage. Similarly, the use of phosphonic acid-modified BT nanoparticles in cross-linked poly(4-vinylphenol) (PVP) allowed to form gate insulators for OFETs. High quality nanocomposite thin films at high nanoparticle volume fractions (up to 37 vol. %) with a large capacitance density (∼50 nF/cm2) and a low leakage current (10−8 A/cm2) were obtained. Pentacene-based p-type OFETs using these nanocomposites showed a large on/off current ratio (Ion/off 104 ∼ 106). We will also present the results from a recent experimental and theoretical study where the BT nanoparticle volume fraction was systematically varied in P(VDF-HFP) host, εr = 11, to find the optimum permittivity and dielectric strength, which provided a guideline for the optimization of the volume fraction for achieving maximum energy density.

We have conducted an accelerated temperature, RF Arrhenius life test study of GaN HEMTs delivered under the DARPA Wide Bandgap Semiconductors for RF Applications (WBGS-RF) program. The transistors were embedded in a single-stage MMIC with 50 ohm input and output impedances. The HEMTs were of source-connected field-plate design with a total gate width of 1.25 mm.

Circuit designs for 91 GHz and 220-GHz sheet-beam extended-interaction klystrons (EIKs) are presented. The W-band circuit employs a relatively simple two-cavity configuration to demonstrate beam transport and high peak power RF generation, which will serve as the basis for future scaling to higher gain and frequencies. Uniform (solenoidal) magnetic focusing is employed in both cases. Simulations with MAGIC-3D indicate peak RF powers of 10.5 kW and >400 W are feasible with a 3 A, 19.5 kV beam and a 0.5 A, 16.5 kV beam at 91 GHz and 220 GHz, respectively. Proof of principle experimental demonstrations are planned.

The current research involves the synthesis of microwave-absorbing ceramic-based composites which exhibit a controllable variation in complex dielectric permittivity with respect to frequency. This study focuses on the synthesis and dielectric analysis of both porous and fully dense Al2O3-precursor-derived-SiC, as well as AlN-precursor-derived-SiC composites, obtained by applying various types of high temperature treatments to as-pyrolyzed porous composites

The complex dielectric permittivity properties of lossy ceramic materials used in vacuum electronics are presented. The studies include broadband room temperature behavior in the 0.1-18 GHz range and in W-Band (75-110 GHz). Variable temperature measurements of selected materials at 94 GHz are also presented.

The results of passing digital communications signals through a 1-D physics-based klystron model are presented and compared to the series block model. Non-linear memory effects are shown to be important at high data rates near saturation.

The complex dielectric permittivity has been measured in W-band for samples of BeO-SiC and AlN-based composites, at temperatures from 18/spl deg/C to 200/spl deg/C. Experimental techniques and results are presented.

Research on the microstructure-based modeling of composite dielectrics for capacitor applications is described. Methods for predicting the composite dielectric permittivity and internal electric field distributions within the microstructure using finite difference quasi-electrostatic modeling are described, along with methods of generating realistic model spaces of particulate microstructures. An existing algorithm for generating random, monosized spheres-in-a-dielectric matrix model spaces is modified to allow the treatment of bimodal composites in which small particles are deliberately segregated into the spaces between large particles. Such composites can have substantially higher total volumetric filling fractions of particles, leading to higher composite permittivity. The variations in permittivity with the filling fractions of bimodal inclusions are studied with the new model, with cases covering three different types of polymer matrix material. The effect of the small particle additions on the electric field statistics within the polymer matrix is also explored.

At the University of Maryland high power microwave source development for use in linear accelerator applications continues with the design and testing of coaxial circuits for gyroklystron amplifiers. This presentation will include experimental results from a coaxial gyroklystron that was tested on the current microwave test bed, and designs for second harmonic coaxial circuits for use in the next generation of the gyroklystron program. The authors present test results for a second harmonic coaxial circuit. Similar to previous second harmonic experiments the input cavity resonated at 9.886 GHz and the output frequency was 19.772 GHz. The coaxial insert was positioned in the input cavity and drift region. The inner conductor consisted of a tungsten rod with copper and ceramic cylinders covering its length. Two tungsten rods that bridged the space between the inner and outer conductors supported the whole assembly. The tube produced over 20 MW of output power with 17% efficiency. Beam interception by the tungsten rods resulted in minor damage. Comparisons with previous non-coaxial circuits showed that the coaxial configuration increased the parameter space over which stable operation was possible. Future experiments will feature an upgraded modulator and beam formation system capable of producing 300 MW of beammore » power. The fundamental frequency of operation is 8.568 GHz. A second harmonic coaxial gyroklystron circuit was designed for use in the new system. A scattering matrix code predicts a resonant frequency of 17.136 GHz and Q of 260 for the cavity with 95% of the outgoing microwaves in the desired TE032 mode. Efficiency studies of this second harmonic output cavity show 20% expected efficiency. Shorter second harmonic output cavity designs are also being investigated with expected efficiencies near 34%.« less

Summary form only given. Ceramic materials, including ceramic composites, are used extensively in vacuum electronic (VE) devices for windows, electrode and structure supports, and for controlling electromagnetic dispersion and losses. While many of the more common low-loss materials are well characterized, detailed dielectric studies of specialized lossy ceramics of particular importance to VE devices are much less common. Furthermore, the measurement techniques and systems commonly used with low-loss dielectrics need to be modified to provide accurate data, particularly in W-band. This paper will first present broadband (0.1-18 GHz) room temperature measurements of the microwave properties of a variety of vacuum compatible lossy ceramics, including those based on SiC or carbon imbedded in BeO and AlN ceramic matrices. The microwave properties of a family of lossy ceramics composed of pyrolytic carbon in an aluminum silicate matrix ceramic that exhibits tailored frequency response and exceptional dielectric relaxation strength will be highlighted. The impact of changes in the synthesis conditions on dielectric properties, and the correlation between microstructure and frequency response, will be explored. The observed dielectric behavior will be compared to the results of first-principles, microstructure-level simulations of composite dielectric properties. A second portion of the paper will deal with measurement techniques for accurately obtaining the W-band (75-110 GHz) dielectric properties of lossy ceramics. This will include improved WR-10 waveguide-based, room temperature measurements of ceramic composites and preliminary results of variable-temperature measurements based on a resonant cavity system

The paper presents the multiple-beam amplifier development at NRL(Naval Research Laboratory). The development comprises of two phases, the first phase focuses on the development and demonstration of multiple beam gun technology. The resulting gun is tested using three-cavity multiple beam klystron circuit. The second phase is the development of high average power compatible multiple beam amplifier with an emphasis on broad bandwidth. The paper also presents the overall approach for the electron gun development and the klystron circuit design efforts.

Summary form only given. Simulations of transmitters in communications systems typically employ a simplified series block model to describe the response of the amplifier. Such a model consists of a linear, frequency-dependent block to describe the complex frequency response, cascaded with a nonlinear, frequency-independent block to account for the saturation effects on amplitude and phase. Such models are generally adequate for modeling the behavior of digital communication signals passing through the amplifier when the data rate and the nonlinearity are not simultaneously large. Klystrons are widely used in communication applications, in particular for microwave ground links and satellite uplinks. The nearly saturated condition in klystrons is desired for high efficiency, which can exceed 70%, and the use of multiple phase-shifi-keying (m-PSK)between equal amplitude digital symbols avoids the most obvious problems with nonlinearity. However, nonlinear memory effects,which cannot be described by the series block model, can occur in klystrons operated near saturation under high data rate conditions. Such effects will lead to excessive system bit error rates unless they are properly modeled and accounted for in the system design.

Summary form only given, as follows. Summary form only given. A five-section W-band gyrotwystron amplifier was recently constructed and demonstrated at CPI. The gyrotwystron is comprised of an input cavity, three heavily-stagger-tuned buncher cavities, and a traveling-wave output section, all operating in the TEO, mode near the fundamental cyclotron frequency. Two well-benchmarked, nonlinear simulation codes, MACY and MAGYKL, were used to design the interaction circuit. Using the design codes, an extensive theoretical optimization was performed to determine the circuit performance versus variations in circuit and beam parameters. The gyrotwystron was constructed and testing began in the Summer of 2002. The measured performance of the gyrotwystron amplifier showed a significant improvement in bandwidth over previously demonstrated W-band gyro-amplifiers. Details of the design and measured performance are presented.

Current amplifier research at the NRL Vacuum Electronics Branch emphasizes techniques to extend the bandwidth and average power capability of gyro-devices for millimeter wave radar applications. This paper discusses the implementation of a wideband, high average power compatible, TE/sub 11/ mode gyro-TWT amplifier design, with a peak output power of 90 kW and a 3 dB bandwidth of 6 GHz in the K/sub a/ band, using a specific distributed loss approach.

Summary form only given, as follows. Gyrotron traveling wave tube (gyro-TWT) amplifiers are under investigation for radar applications due to their high power and broad bandwidth capabilities in the millimeter wavelength range. The design and experimental study of a 35 GHz gyro-TWT amplifier operating in the circular TEO/sub 01/ mode at the fundamental cyclotron harmonic are presented. The interaction circuit in this experiment consisted of a new type of ceramic loading that provided controlled loading of both the TEO/sub 01/ operating mode and the backward wave oscillations to ensure stable operation. The gyro-TWT circuit consisted of a lossy, linear amplification section that employed ceramic rings spaced to provide the required absorption. The final, nonlinear stage of amplification occurred in a short conducting wall section at the end of the interaction circuit.

Summary form only given. A novel microwave processing system is being developed to study fundamental issues in the sintering of advanced ceramic materials with enhanced dielectric, thermal, optical, and mechanical properties for applications in microelectronics, biomaterials, and structural applications. The system consists of a single and dual frequency microwave furnace that operates at 2.45 and 28 GHz, an optical pyrometric temperature measuring system, and an optical, non-invasive, non-contact, extensometer for measuring sintering shrinkage and kinetics. The additional ability to process at 28 GHz provides opportunities to sinter a wider range of ceramic materials by direct coupling. An even more exciting benefit of the dual frequency system is the potential to process ceramics at two frequencies simultaneously. This capability can provide a unique way to tailor the microstructure of advanced ceramics by controlling the extent of both volumetric and surface heating. Experimental results for microwave sintering studies involving ZnO, hydroxyapatite, AlN-SiC composites and alumina composites will be presented, with an emphasis on the processing of nanograin ceramics. In particular, the role of surface modification and microwave field intensification effects will be discussed.

Summary form only given. In this paper, we present the application of this frequency-doubling technology to an existing first harmonic gyroklystron which has been under investigation at the Naval Research Laboratory. This system has been successfully operated with from 2-5 cavities. In a two cavity system, a peak power of 210 kW was achieved near 35 GHz with 37% efficiency and a gain near 24 dB. The bandwidth was approximately 0.36%. The nominal beam parameters include a voltage of 70 kV, a current of 8 A, and a perpendicular to parallel velocity ratio of about 1.35. In our experiment, we utilize the first harmonic input and gain cavities, but replace the penultimate and output cavities with ones that are designed to operate in the TE/sub 021/ mode near 70 GHz. About 140 kW of power with an efficiency near 25% is predicted via MAGYKL simulations. The complete design simulations and cold test results for this system will be presented. If viable, the experimental hot test results will also be described.

Summary form only given. At the Naval Research Laboratory gyroklystron amplifiers are being investigated as high power sources for the next generation of millimeter wave radars. A four-cavity, 35 GHz gyroklystron amplifier experiment has recently demonstrated a peak output power of 203 kW at 34.90 GHz, with a -3 dB bandwidth of 0.6%, a saturated gain of 52.5 dB and an electronic efficiency of 30%. These values were obtained in the TE01 mode with a beam voltage of 70 kV, a beam current of 9.8 A and a pulse width of 2 /spl mu/s. The nominal magnetic field for these results was 13.08 kG. Recent experimental results, along with comparisons to theory, will be presented which show that variations in magnetic field and voltage affect the trade-offs between power, bandwidth and efficiency. Future experiments will investigate gyro-devices with broader bandwidth capabilities and these design studies will be discussed.

Summary form only given. Measurements of intrinsic shot noise in a 35 GHz, three-cavity gyroklystron have been obtained over a wide range of operating parameters. The noise emissions from both the input and output cavities were measured under carrier-free (zero-drive power) conditions. The spectrum of noise emitted by the input cavity is found to have a Lorentzian shape, with the peak frequency and spectral width in good agreement with the beam loaded frequency and Q predicted by simulation codes. At the nominal operating parameters of the gyroklystron, which were 70 kV, 10 A, /spl alpha/=1.27, and a magnetic field of 13.07 kG, we find the peak temperature of the input cavity noise to be 4.4/spl times/10/sup 8/ K (6.3/spl times/10/sup -15/ W/Hz), with a FWHM of 160 MHz. The peak noise temperature was found to exhibit complex variations with respect to beam current, beam velocity ratio, and magnetic field.

Summary form only given. The design of a pyrometric non-contact temperature measurement and control system for a 3 kW 2.45 GHz microwave processing furnace is presented. Design considerations specifically relevant to implementing non-contact temperature measurement and control over the wide range of 25 to 2500/spl deg/C are discussed. The completed system, in use as a research tool for microwave processing studies, provides versatile and contiguous control of sample heating from room temperature to the process temperature, with real-time access to parameters of the power control algorithm.

The University of Maryland Gyroklystron Laboratory is developing a high peak power gyroklystron for linear supercollider application. An X-band amplifier with 30-40 MW peak power and a pulse length of 1-2 mu s is being developed as the first stage of gyroklystron research for accelerator applications. The final experimental installation, the planned beam propagation studies, and the first experimental gyroklystron circuit are described. >

The final preparations for bringing the University of Maryland's 10-GHz, 30-MW gyroklystron experiment online are discussed. The authors explain the enhanced circuit modeling and present a two-cavity design with a predicted efficiency of 33% and gain of 27 dB for the simulated beam parameters. They then describe initial operation of the modulator and electron gun and detail the experimental design of the system. >

The design of an eight‐beam, four‐cavity multiple‐beam klystron (MBK) to be operated in S‐band is presented. The design methodologies for the gun, magnetic circuit, and RF interaction circuit are described, along with a brief description of the principal computational design tools. The large‐signal code, TESLA, was used to design the interaction circuit and is shown to be in excellent agreement with the three‐dimensional particle‐in‐cell code, MAGIC 3‐D. Computational simulations indicate that the optimized design has very low beam interception, producing a peak RF power of 865 kW with a corresponding gain of 34.5 dB and an electronic efficiency of ∼60% at mid‐band (3.27 GHz).

At the University of Maryland, we are exploring the suitability of gyroklystrons for linear collider applications. In this paper we discuss the design of a two-cavity, coaxial gyroklystron that is designed to produce over 100 MW in 1 /spl mu/s pulses at the second harmonic of the cyclotron frequency. We detail modifications that will be required of our test facility, present the simulated performance of a 400 MW, 500 kV single-anode magnetron injection gun, and describe the design of the coaxial microwave circuit. >

Experimental studies of amplification and stability in a series of multi-megawatt, 19.7 GHz, second harmonic gyroklystron amplifier tubes suitable for driving future linear supercolliders are reported. Four different two-cavity gyroklystron tubes have been constructed and tested, and each one has exhibited higher power, larger efficiency, and improved stability compared to its predecessor. The latest results include the production of peak output powers in excess of 29 MW, at an efficiency of 27% and a gain of 25 dB. >

We report the operating characteristics of a sequence of two-cavity second harmonic K-band gyroklystrons. The TE/sub 011/ input cavity is driven near 9.88 GHz. The first four tubes utilized smooth transition output cavities which resonate at twice the drive frequency in the TE/sub 021/ mode. Peak powers in excess of 30 MW were achieved with efficiencies greater than 28% and large signal gains of 27 dB. The results of an abrupt transition complex TE/sub 01/, TE/sub 02/ mixed mode output cavity are also discussed, as well as the prospect of placing a coaxial insert into the highest power tube. >

Summary form only given. One of the most critical technical issues associated with the microwave processing of ceramics is understanding the propagation of electromagnetic waves within the physical structure and the interaction mechanisms of the fields with the materials that make up the green body. These factors directly determine the types of components and possible new materials that can be effectively and uniquely processed. The physical size scales of interest for this problem span a very large range. On the macroscopic level one is dealing with the overall part shape, and the principle concern is modeling the energy deposition distribution and thermal flow inside a complex shaped part under very high heating rates. The goals of such procedures are to optimize the absorption of energy and simultaneously minimize thermal gradients. Methods and examples of this large-scale modeling, using finite difference EM codes and time-dependent thermal codes, will be described. However, during the vast majority of the sintering cycle, the ceramic is porous and the dielectric properties (which determine the behavior of microwaves within the structure, including the power absorption) are quite different from those of a fully dense body.

Summary form only given. A test bed for implementation of first harmonic and second harmonic coaxial gyroklystrons is nearing its completion stages. This presentation includes the details of each major component's construction status as well as any relevant physical parameters. Designs of a fundamental frequency (8.568 GHz) and second-harmonic (17.136 GHz) microwave circuit have already been accomplished after selection among various two and three cavity designs. Predicted efficiencies near 40% for both these circuits using a large signal code have made them acceptable candidates for high power testing on the new test bed. The first harmonic circuit consists only of an input and output cavity while the second harmonic system has an additional buncher cavity situated between the input and output cavity to boost gain and efficiency up to 49 dB and 41% respectively. Cold testing of the constructed cavity parts are performed to verify their resonant frequency and Q with those predicted from our scattering matrix codes. These microwave circuits are ultimately studied using a 320 MW electron beam from the newly designed and constructed magnetron injection gun (MIG). Cold test results of the first harmonic output cavity indicate that its resonant frequency and Q are 8.568 GHz/spl plusmn/2 MHz and 134/spl plusmn/6 respectively. Because the input cavity's Q derives mostly from lossy properties introduced via ceramics, the required Q of 52 as dictated by the large signal codes are obtained purely from empirical methods during cold testing. The measured resonant frequency and Q of the input and buncher cavities along with descriptions and schematics of all these coaxial circuit cold test setups are presented.

We present a summary of the results achieved with our 30 MW gyro-amplifier test facility during the past several years. Twenty-one different tube configurations have been tested in 5 major categories: fundamental, second harmonic, and third harmonic gyroklystrons, as well as fundamental and second harmonic gyrotwystrons. We also present designs of experiments with fundamental and second harmonic coaxial gyroklystrons which are expected to produce output powers near 100 MW at 8.568 and 17.136 GHz, respectively, in the near future. >

The authors are working to develop high-power gyroklystron amplifiers with properties suitable for driving future electron-positron colliders. Initial experiments have involved a sequence of six different two-cavity configurations, operating in the TE/sub 01/ mode near 9.85 GHz. Each design was modified in accordance with its predecessor's performance to either improve tube stability or enhance amplifier operation (or both). The energy is derived from a rotating beam in 300-440 kV, 100-200 A, 1- mu s pulses. With perpendicular-to-parallel velocity ratios near one, the studies have culminated in peak powers approaching 24 MW, with efficiencies and large-signal gains of 33% and 34 dB, respectively. The experimental setup is described, and amplifier performance of the most recent configuration is discussed. >

Summary form only given. A TE/sub 01/ gyroklystron experiment in the 9.7-10.0 GHz range is discussed. The target microwave power of 30 MW is to be derived from the interaction of a 500 kV, 160-A beam with a two-cavity circuit. The first tube was tested in spring 1990 and was plagued by a multitude of spurious oscillations. The most damaging oscillations included 'whole tube' modes and modes in the beam tunnel between the electron gun and the input cavity. Limited amplification studies were performed at 175 kV and produced only tens of kilowatts at nearly zero gain. The second tube featured additional beam tunnel loss and a new drift tube configuration, and was tested in summer 1990. Enhanced stability allowed amplification studies up to 350 kV, which resulted in output powers in excess of 1.5 MW with gains of 16 dB and efficiencies of approximately 5%. A spurious mode near 9.85 GHz existing in the output waveguide adjacent to the final cavity severely limited the available magnetic field range. A third tube, with a redesigned output waveguide, will undergo testing by September 1, 1990. >

Summary form only given. There is currently a need for high-power, W-band amplifiers for millimeter-wave radars. To meet this need, a 94-GHz gyroklystron has been designed by a collaboration of the Naval Research Laboratory (NRL), Litton Electron Devices, Communication and Power Industries (CPI), and the University of Maryland. A four cavity gyroklystron capable of delivering 10 kW of average power is currently under construction at Litton and CPI. This amplifier is predicted to produce in excess of 80 kW peak power at 20% efficiency with a bandwidth of 740 MHz and 41 dB of gain. It will utilize a magnetron injection gun designed to produce a 65-kV, 6 ampere electron beam with very low velocity spread (dv/spl circ//v/spl circ/=1.8%) at a velocity ratio (v/spl circ//v/spl par/) of 1.5. Low-duty, proof-of-principle, experiments have been done at NRL8 producing 60 kW peak power with a 3-dB bandwidth of 640 MHz, 25% efficiency, and greater than 27 dB saturated gain. The experimental results obtained are in good agreement with code predictions. The same codes have been used in designing the high average power gyroklystron to be described. This gyroklystron is scheduled for testing in 1998. Available results will be discussed.

Summary form only given. Accurate temperature measurements and uniform processing of a material with microwaves can be difficult with thermocouples that perturb the electromagnetic field. Arcing and field intensification is particularly a problem with low loss materials that do not couple well. Optical pyrometers offer a non-invasive alternative, but are generally restricted to surface temperature measurements and are usually non-linear over the temperature range of interest. Improved accuracy over the entire range of interest is possible with an integrated approach using a PC to calibrate the pyrometer against a thermocouple reference. A pyrometer-retrofitted microwave processing system that can measure and control from 40/spl deg/C to 1600/spl deg/C is presented.

Summary form only given. Experimental studies of a three-cavity gyroklystron amplifier employing stagger-tuning have been completed. Each cavity operates in the TE/sub 011/ cylindrical mode. Drive power is directed into a passive TE/sub 411/ coaxial resonator which surrounds the TE/sub 011/ input cavity. Power is coupled to the circular-electric mode inside the inner cavity by four axial slots placed every 90 degrees in azimuth. The cold-test resonant frequency is 34.89 GHz and the Q is 188 (primarily diffractive due to the coupling slots). The intermediate (buncher) cavity employs an annular ring of lossy ceramic against the upstream endwall to provide the desired cold-test Q of 194 and a resonant frequency of 34.62 GHz. The downstream end of the output cavity employs an outward radial step and a nonlinear uptaper to achieve a cold-test Q of 175 and a resonant frequency of 34.83 GHz. The drift tubes between cavities are loaded with lossy ceramic rings to suppress instabilities.

Potential applications for millimeter wave radar include high resolution imaging, precision tracking and cloud physics studies. For most of the applications in the millimeter wave band the relatively high atmospheric absorption necessitates the use of high power sources. In addition, many of the applications call for extended instantaneous bandwidth. Recent investigations at Naval Research Laboratory have been focused on enhancement of the power-bandwidth product in millimeter wave gyro-amplifiers. Both gyroklystron and gyrotwystron type circuits have been investigated to achieve this goal.