With nearly 400 participants from industry, government and academia from almost 20 countries, the first International Vacuum Electronics Conference (IVEC) burst into life in Monterey CA on May 2, 3 and 4, 2000. IVEC 2000, sponsored by the IEEE Electron Devices Society (EDS), attracted the largest vacuum electronics audience in decades. While the explosive growth of electronics in the last half century has been in the area of solid state devices, vacuum devices are still widely used for displays and for high power and high frequency applications, such as satellite communications, radar and electronic countermeasures (ECM). “The response to IVEC 2000 is a clear indication of the continued vitality of vacuum electronics,” said Jim Dayton, Director of Technology for Hughes Electron Dynamics (HED), Torrance CA, who served as General Chair of IVEC 2000.
The conference commenced with a Plenary Session led by Dayton, who welcomed the participants to Monterey and introduced the members of the IEEE EDS Technical Committee on Vacuum Devices, who had organized the conference. Three speakers who focused on “The Status of the Vacuum Electronics Industry” followed this. Jon Christensen of HED, representing the US Electronic Industry Association, spoke for the United States. Takao Kageyama of NEC followed by giving an overview of the industry in Asia. Georges Faillon of Thomson Tubes Electroniques (TTE) concluded with a description of the situation in Europe. All three described an industry that is experiencing nearly flat military sales, but dynamic growth in commercial opportunities.
The next three speakers more specifically addressed “New Commercial Opportunities in Vacuum Electronics.” Ivor Brodie of SRI International spoke on what has become the most ubiquitous vacuum device today, the display tube. Brodie particularly emphasized the prospects for conventional cathode ray tube (CRT) technology to be overtaken by thin panel displays, many of which will continue to be comprised of vacuum tubes using field emission cathodes. Walter Wood of Xicom Technology described growing markets for vacuum devices in terrestrial communications both for satellite uplinks and for wireless telephony and communications systems. The final speaker on this topic, Kevin Mallon of Loral Space Systems, described how the traveling wave tube (TWT) has become the dominant amplifier for commercial space communications because of its reliability, efficiency and power handling capabilities. With the assistance of the TWT, he forecasted that with the implementation of digital radio in the near future, a traveler driving from Los Angeles to New York City could listen to the same radio station for the duration of the trip!
The final topic in the Plenary Session was a panel discussion on “Training the Next Generation,” moderated by Neville Luhmann of the University of California (UC), Davis. Panelists included Carter Armstrong of Litton Systems, Robert Barker of the Air Force Office of Scientific Research, Kwo Ray Chu of the National Tsing Hua University, Taiwan and Michael Petelin of the Institute of Applied Science, Novgorod, Russia. The panelists described successful programs merging the needs of academic institutions, industry and government to provide students with credible training and realistic career opportunities. The audience reaction to the panel discussion indicated that the hiring outlook in the vacuum electronics industry parallels its recent dynamic growth.
The highly successful IVEC is scheduled to repeat every other year in the USA, rotating to Europe and Asia in every fourth year. IVEC 2001 will be held in Noordwijk, The Netherlands, on April 2, 3 and 4 sponsored by the European Space Agency (ESA). In 2002, IVEC will return to Monterey and in 2003 it will be held in Korea. IVEC evolved from the Monterey Power Tube Conference, which had been sponsored by the US Department of Defense since 1978 and formerly had been restricted to US participants.
Vacuum electronics is a thriving and exciting field as evidenced by the technical excellence of over 170 oral and poster presentations. Several of the session technical highlights are summarized below. Selected extended articles from IVEC 2000 will be published in the January 2001 Special issue of the IEEE Transaction on Electron Devices on Vacuum Electronics.
SESSION 1 - KLYSTRONS I
This first technical session of the conference was opened by an invited paper by George Caryotakis of Stanford Linear Accelerator Center (SLAC), The Future of Klystrons, emphasizing the continuing work at SLAC to devise advanced high power klystrons for the Next Linear Collider (NLC) and other scientific applications. A new thrust is the development of cancer diagnosis and treatment by monochromatic x-rays generated with the help of NLC-like klystrons. UC, Davis is currently building a proof-of-principle device to produce these monochromatic x-rays by Compton Scattering, which results from collisions of high-energy electrons with photons. To further the art and science of klystrons, SLAC is actively pursuing development of multiple beam klystrons, which offer increased power at a lower operating voltage.
The next two papers described work on high power, low frequency klystrons, primarily used for powering heavy particle (proton) accelerators. Hargreaves of Litton et al. presented progress on a prototype device yielding 2 MW of peak power at 800 MHz for a Spallation Neutron Source (SNS) for the Department of Energy. Lenci of Communications and Power Industries (CPI) et al. presented recently completed developments of four separate klystron types, ranging in frequency from 500 to 800 MHz and power levels up to 1 MW continuous wave (CW) and 2.5 MW peak, used to power accelerators for the proposed Accelerator Production of Tritium (APT), SNS, and two other Big Science programs. All four devices were designed using advanced computer codes, resulting in first-pass success. A notable feature is the capability of these klystrons to be operated at any voltage, up to the maximum, without any adjustment of the focussing magnetic field.
Wright of CPI et al. presented a paper on the first application of Multi-Stage Depressed Collector (MSDC) technology to klystron amplifiers used in satellite (and sometimes terrestrial) communications. As these amplifiers operate in the linear (unsaturated) region, MSDC technology can reduce power consumption by as much as 60%. Two klystrons were described, one at 17.3-18.4 GHz and 2.4 kW, and the other at 2.1-2.4 GHz and 7.5 kW, both with 4-stage collectors.
A paper by Scheitrum et al. of SLAC, in collaboration with CPI, described a novel high power W-band amplifier, the "klystrino." These compact, lightweight, PPM focused devices are being developed using lithographic fabrication methods (LIGA) for the ladder type cavity circuits. Each klystrino will produce 100 kW peak and 1 kW average power at 95 GHz, and four of these will be included in a single vacuum envelope.
SESSION 2 - CROSSED-FIELD DEVICES I
The session began with a current status perspective of the Crossed-Field device (CFD) industry by keynote speaker Vanzant of Naval Surface Warfare Center (NSWC). The present rate of production is constant, but a reduction in future production is expected with few new systems using these devices and the lack of an organized approach to change this trend. The second paper by Einarson of CPI described the new innovations in coolant design to increase power capability in CFDs. The vane cooling technique is being applied to the crossed field amplifier (CFA) being used in the next generation AEGIS SPY-1 radar. MacMullen of Technology Service Corp. gave an explanation of the noise structure in CFDs based on measured data and proposed a model to explain this structure. Ramacher’s (Litton Systems) paper on cold cathodes described the use of a new material (Pd/Ba) in CFD cathodes. Tests indicate this material has the potential for extremely long life without the requirement for an oxygen source. Reducing control electrode current in DC operated CFDs was the subject of Tracy’s paper from CPI. This technique will allow for simpler modulator designs for transmitters using these devices.
SESSION 3 - TWTS I
The first session on TWTs covered the full frequency range of today’s TWT applications from L-band to the development edge in W-band. The papers confirmed that tube performance parameters including output power, frequency and efficiency are still progressing at a higher rate than comparable solid state devices, therefore guaranteeing tube competitiveness far into the new millennium.
The keynote paper in this session, presented by Goebel et al. from HED, reported helix TWTs for telecommunications applications with high linearity, good intermodulation performance, and high power levels. HED developed L-band and S-band helix-TWTs with saturated power of 1600 W and 2000 W, respectively, that can compete with solid state devices with superior power and efficiency.
Fritz from CPI, spoke on a 2.25 kW X-band helix TWT of which 1700 devices were produced for US government use. The application of statistical process control in the production kept the yield above 90%.
Dibb's and Le Borgne's paper (HED) on a 120 W 43.5 to 45.5 GHz (Q-band) ground station helix TWT reported on the efficiency improvement obtained for this challenging power and frequency range with the introduction of a two stage depressed collector design. High interest was guaranteed, because a similar development was presented from TTE Velizy in the TWT II section.
Werner Gerum (TTE Ulm) presented a very interesting, new 200 W peak power 94 GHz (W-band) TWT for military radar applications. The concept uses a double comb delay line structure, which is well proven in the Ka-band frequency range and which results in a very lightweight (<1300 g), broadband and coherent microwave source at this frequency end for TWT applications.
The final paper in this session, presented by Brian Steer et al. from CPI (Canada), was on an Extended Interaction Klystron (EIK) for millimeter-wave radar and communications. This paper described the design simulation and corresponding performance results at various frequencies showing impressive figures for both bandwidth and power capability for devices from 27 GHz to 220 GHz.
SESSION 4 – KLYSTRONS II AND IOTS
The five presentations of session 4 were focused on Klystrons, Inductive output tubes (IOTs) and related devices. Boni et al. from Istituto Nazionale di Fisica Nucleare described the TTE high power 150 kW CW klystrons at 368 MHz with a very short 200 ns group delay, and 45 MW peak S-band TTE klystrons, followed by pulse compressors up to 210 MW used by the particle accelerator DAFNE in Frascati. For the same type of application, Bohlen et al. from CPI described the higher order mode IOT presenting advantages of low operational cathode voltage and small size. The first tests at 700 MHz, 31 kV confirm the predictions of the calculations at a level of 920 kW in a short pulsed regime.
Also regarding the IOT, McCune of Microwave Power Engineering and Yates and Li of CPI Eimac foresee important improvements attributed to the implementation of a MSDC. Efficiencies up to 70% have been measured at levels of 15 to 25 kW, and such a MSDC IOT appears to be an appropriate device especially for digital TV transmitter requirements.
Wright et al. from CPI reported on air-cooled medium power klystrons developed in Ka-band at 750 and 1500 kW output powers. A number of innovations have been introduced by CPI including the tuning system, the diamond window, and the permanent magnet circuit.
Lastly, Chen et al. from National Tsing Hua University and Chen from ERSO/ITRI demonstrated efficiency enhancement experimentally for a Ku-band extended interaction oscillator, which features a five-gap interaction cavity with a coaxial section placed between the first and second gaps. Oscillation power of 2.2 kW pulsed at 30% electronic efficiency and 41% total efficiency with a depressed collector was achieved.
SESSION 5 - CROSSED-FIELD DEVICES II
Ludeking, et al. from Mission Research Corp. (MRC) and Chan from Northeastern University presented a compelling paper which described the use of MAGIC3D (a fully three-dimensional (3D), electromagnetic particle-in-cell (PIC) code) to perform simulations on several crossed-field devices. Since magnetrons, CFAs, and amplitrons are inherently 3D in nature, this tool provides insight into the design and operation of crossed-field devices, which previously had not been obtainable.
Tracy, et al. (CPI) and Chernin (Science Applications International Corporation (SAIC)) described the authors’ improvements on the two-dimensional electromagnetic PIC code, MASK, encompassing a multi-conductor transmission line (MTL) model providing a truer anode circuit model. With incorporation of the MTL model, MASK now provides accurate spurious emission data to potentially improve the noise performance of these devices.
Mitsdarffer et al. (NSWC) and Thelen et al. (Technology Service Corp.) described phase similarity tests performed at NSWC. The AEGIS CFA successfully passed these tests of instantaneous response of phase to changes in the operating duty cycle, showing its continued vitality.
Robinson of CPI described the results of a program to improve the performance of an injection-locked magnetron used in a missile-seeker application. The author was successful in increasing the Ku-band magnetron reliability by decreasing the power density inside the device, increasing the device lifetime, and in ruggedizing the device for use in the high-vibration missile-seeker environments.
SESSION 6 – TWTS II
The second TWT session included a variety of advances in worldwide TWT development. The session began with a paper presented by Thouvenin of TTE summarizing the development of mm-wave TWTs, including a 40 W Ka-band micro-TWT and a 120 Watt, EHF-band dual stage collector TWT. Komm et al. from HED stressed the revenue implications of increased TWT efficiency for satellite operators, pinpointing collector optimization as a primary focus to increase TWT efficiency. The results from several experiments were presented showing marked improvements in TWT efficiency, up to 73.2 percent for a Ku-band TWT. Kornfeld et al. from TTE addressed the issues involved in their development of a 25 W, broadband, 60 GHz, helical, space TWT. This TWT is aimed for inter-satellite link applications. This was followed by Goebel’s (HED) presentation on long term gain stability of TWTs where he demonstrated an increase in gain over time due to physical damage of carbon attenuator material from energetic particle bombardment and/or chemical erosion. Pobedonostsev et al. from State Research and Production Corporation “Istok” discussed the performance of vacuum devices manufactured at Istok followed by a report of some new areas of vacuum devices in development, including multiple beam inductive output tubes (IOTs), hollow beam formation in X and Ka-band helix TWTs, backward wave oscillators, and multi-beam klystrons. The session was concluded by Soukhov et al. from Seoul National University with their talk on a method to measure helical TWT interaction impedance using a hairline conductive wire. This method lessens inaccuracies in the analysis due to the presence of higher order space harmonics of the helix, which are perturbed if a larger diameter dielectric-perturbing rod is used.
SESSION 7 CATHODES
At the heart of all vacuum electron devices is the source of electrons, the cathode, that makes it possible for the device to exist. This session described the substantial work being done to meet the severe demands put on the cathode as electron devices have become more sophisticated. The first paper by Longo of HED reported on refinements to his model for predicting the lifetime of dispenser cathodes, which are used extensively in microwave power tubes due to their low temperature of operation, high current density, ability to be machined to the precise shape required for electron guns and their long lives. Jensen et al. from Naval Research Laboratory (NRL) and Lau from the University of Michigan reported on an ambitious attempt to quantitatively model migration of barium to the emitting surface and its subsequent removal by evaporation and ion sputtering in dispenser cathodes - important in estimating the current/noise limits for use of these cathodes in radar systems. Next, Miyamoto and his colleagues from New Japan Radio Co. reported on a novel dispenser cathode that was developed especially for the advanced CRT’s required for high definition television. They showed substantially increased emission at a given temperature for samples with a five-micron layer of tungsten over those with zero thickness (standard cathode) and those with 20 microns. The fourth paper presented by Sewell of LAB-6 (co-authored by Katsap et al from Lucent Technologies) reported on the development of a cathode meeting the requirements of an electron beam lithography tool known as SCALPEL.
Wintucky of NASA Glenn Research Center (GRC) reported on progress in the field of cavity (as opposed to impregnated) dispenser cathodes, where the reagents that produce the free barium are situated in a cavity behind a porous tungsten plug (rather than within the pores), thus separating the variables between producing the barium and controlling its arrival rate at the cathode surface. Finally, Espinosa of Microwave Power Technology and Busta of Sarnoff Corp. described cold cathodes that emit electrons by quantum mechanical tunneling under the action of strong electric fields. The cathode is successfully being used in an X-ray tube where it shows advantages in terms of savings in cost associated with the filament supply of a conventional thermionic cathode device.
SESSION 8 - CODE DEVELOPMENT I
The clear indication from Session 8 is that 3D simulations for TWTs are ready for the main-stream. NRL was involved in five of the six presented papers in this session, so the focus, summarized by Levush (NRL), Antonsen (University of Maryland) and Mondelli et al. (SAIC) in the keynote paper, was on NRL's code development. This included a 3D gun/collector code, MICHELLE, a helix TWT large signal code, CHRISTINE, and a periodic permanent magnetic stack design code, LesPPM. Several example simulations from each code were shown. MICHELLE is finite-element based and is designed with complex gun geometries in mind. It uses a novel particle pushing scheme that tracks particles separately through each mesh element. Initial results from Christine 3D agree nicely with measured TWT body current under saturated drive conditions. LesPPM, which is driven by Microsoft Excel, has an easy-to-use graphical interface, and, at a slight expense of accuracy, calculates the magnetic field (even off-axis) very rapidly (seconds on a PC). Wilson from NASA GRC presented the last paper on optimizing the performance of a coupled-cavity TWT. He showed impressive agreement with measured data as well as a design improvement that significantly increased the TWT efficiency at the band edges (8% bandwidth).
SESSION 9 - VACUUM MICROELECTRONICS
The Vacuum Microelectronics session at IVEC 2000 included papers on micromachined field emission cathodes and their applications. The session keynote, by Whaley and his colleagues at Northrop Grumman, reported on their successful collaboration with Capp Spindt from SRI to generate RF power from a TWT with a field emission cathode. This exciting work demonstrated a TWT producing 55 Watts of RF power at 4.5 GHz with a beam current of 91.4 mA from a Spindt field emitter array. Their experimental data is in an elite class with the previous NEC work, showing vacuum microelectronics to be a viable cathode technology for microwave power tubes.
Galdetskiy of Istok in Russia presented theory and simulation data on a proposed field emission gun with current stabilization utilizing a dual anode configuration. Makhov from Litton Systems in Williamsport presented a 70 kW, X-band magnetron with a cold cathode designed for industrial applications. Milanovic et al. of the UC, Berkeley presented data on a novel field emission structure discovered as a side effect of a deep silicon etch process. Chenggang Xie et al. from the Motorola Flat Panel Display Division presented theory and simulation data on the sensitivity to the dimensions of the tip and gate electrode on the output current from a field emitter array. Jie Li et al. from Advanced Vision Technologies presented a microfabricated structure that is useful for testing the field emission characteristics of planar films.
SESSION 10 – CODE DEVELOPMENT II
Session 10 included five presentations on state-of-the-art software for microwave tube design. COCA, presented by Coco et al. from University of Catania in Italy and Emma (ESA/ESTEC) is a finite-element package for simulation of multi-element depressed collectors in three dimensions. Secondary electrons are included in the model, which has shown good agreement with experimental data. The CTLSS code, presented by Cooke et al. from NRL and Shtokhamer et al. from SAIC, is an integrated cold test and large signal simulation suite. The cold-test simulation capabilities of the code were presented for a variety of different microwave structures. Vlasov (SAIC), Antonsen (University of Maryland) and Nguyen (KN Research) developed the code MAGY to model the non-linear interaction between electromagnetic fields in an axi-symmetric structure and a gyrating electron beam. The presentation demonstrated the ability of the code to model problems where the microwave structure is lossy. Ives et al. from Calabazas Creek Research and Cendes (Ansoft) detailed BOA, a finite element charged particle analysis program, which is integrated into the Ansoft Corporation’s Maxwell 2D suite. This code has an impressive adaptive meshing capability which enables the total number of elements to be greatly reduced without loss of accuracy. The final presentation was a demonstration of the capabilities of the 3D PIC code developed at Culham Science Centre in England by Eastwood et al. The presentation showed how complex structures could be modeled by blocks of mesh joined by ‘glue patches’. The capabilities of the code were demonstrated by a variety of examples, which included dynamic displays of the particle motion and the electromagnetic fields. Together these presentations showed significant advances in the computer modeling of the complex structures used in microwave tubes.
SESSION 11 – CODE APLLICATIONS
The Code Applications session included several reports on the exciting advances made in the area of computational modeling of electron devices. The first talk was an invited paper by Benton et al., given by Menninger of HED, summarizing the computational design procedures at Hughes and corresponding first-pass design success. Carter, from Lancaster University, presented a comparison of the methods used to experimentally and computationally calculate helical TWT interaction impedance. This was followed by Kory from Analex Corporation/ NASA GRC, who presented the effects of azimuthally asymmetric characteristics of TWT periodic permanent magnet (PPM) focusing, such as C-magnets, shunts and magnet misalignment. The TWT performance was particularly affected with the inclusion of C-magnets. Musyoki et al. of NEC Corp. presented the development of a TWT potential depressed collector code incorporating secondary electron yield using an empirical formula and the emitted secondary electrons according to a cosine spatial distribution. The session was concluded with a talk by Dionne from Raytheon (co-authored by Petillo from SAIC) also discussing secondary electron emission modeling for depressed collectors using the code, MICHELLE. The secondary emission mode separates the emission problem into two macroparticle species: true secondary electrons and rediffused, or backscattered, primary electrons; both are assigned empirically, based on discrete angular and energy distributions, dependent upon the incident energy and angle of incidence.
SESSION 12 – GYRO-AMPLIFIERS I
The two Gyro-Amplifier sessions at IVEC detailed advances in gyro-amplifier devices. These devices are, in principle, capable of producing high power in the millimeter wave band that far exceeds that achievable by slow-wave, linear beam devices such as the TWT or klystron. The session was kicked off by a keynote talk by Danly of NRL where he summarized past and present activities in the gyro-amplifier field, exciting opportunities afforded by new concepts, and a disparate collection of applications including radar and electron spin resonance excitation in conjunction with NMR imaging techniques. Calame et al. discussed noise measurements in a Ka-band gyro-klystron amplifier performed at NRL. Results from a systematic study of the gyro-amplifier phase noise as a function of magnetic field were presented, and measured and theoretical predictions of shot noise as a function of beam current were presented and discussed. Garven (Omega-P Inc.) et al. presented the experimental results for a four cavity, Ka-band gyro-klystron amplifier operating in the TE 011 cylindrical mode at the fundamental cyclotron frequency. A peak output power of 208 kW at 34.9 GHz, with a 3 dB bandwidth of 178 MHz, electronic efficiency of 30% and saturated gain of 53 dB was obtained with a 72 kV, 9.6 A electron beam. The work being done at the University of Maryland on harmonic coaxial-klystrons for accelerators was presented by Lawson et al. The experimental results of a three cavity, second harmonic coaxial gyro-klystron tube were presented, expected to produce 80 MW of peak power at 17.14 GHz in 1 ms pulses. Nguyen (NK Research) et al. presented the design of a high average power compatible Ka-band gyro-TWT employing the circular TE11 mode, operating in the fundamental cyclotron harmonic.
SESSION 13 - LOSSY DIELECTRICS
This session focused on new developments in advanced dielectric materials having high thermal conductivity and specific microwave properties. These materials are used in high power coupled cavity TWTs, klystrons and gyrotron devices. The first paper by Tousey of CPI described the cooperative efforts of CPI, Litton and Hughes to develop and qualify a Beryllia-Silicon Carbide composite material produced by CBL Ceramics, Ltd, Wales, U.K. The CBL BeO-SiC material has successfully demonstrated excellent physical and vacuum properties and good RF characteristics in both resonant loss button and sever termination configurations. Mikijelj of Ceradyne Inc. reported on the evaluation of several AlN based lossy ceramic composite materials as possible replacements for the toxic BeO-SiC ceramics. The Ceradyne 137-CB material has comparable dielectric constant and loss tangent to the BeO-SiC material over the frequency range of 1 to 10 GHz, and thermal conductivity greater than the BeO-SiC material at temperatures above 200 C. The work of Sienna Technologies to develop their AlN doped and composite materials was described by Savrun along with Abe of NRL. The AlN composites have the same loss tangent from 9 to 12 GHz and comparable thermal conductivity as the BeO-SiC material, and the doped AlN material has a similar dielectric constant and a higher thermal conductivity than BeO-SiC. Calame et al. and Wood presented the work at NRL and DynCorp Inc. to measure the complex dielectric permittivity of lossy ceramics from 27 to 40 GHz over a temperature range of –185 to +250 C, giving a description of the apparatus, measurement techniques, GUI-based codes, and preliminary measurement results on commercial AlN-20% SiC lossy ceramic composites. Finally, Carmel et al. from the University of Maryland discussed their work focusing on microwave processing of AlN and AlN-SiC ceramic composites and material characterization to understand the links between microstructure, composition and processing history and the resultant material properties. Microwave processing techniques suitable for AlN and AlN-SiC materials were described.
SESSION 14 - SWITCHES AND POWER SUPPLIES
The first paper written by Phelps and Cardwell of HED introduced a new family of lightweight, high efficiency power processors to power traveling wave tubes for space applications. The second paper authored by Delporte et al. of Alcatel ETCA in Belgium, gave details about an ESA qualified, light weight, high efficiency power processor used to power space borne traveling wave tubes. Then, Gaudreau, et al. from Diversified Technologies Inc. described a multi-MW solid state switch that is capable of switching hundreds of amperes at thousands of volts. This switch has applications in processing power for very large vacuum devices. The next paper described multipactor effects, and the possible damage to hardware caused by multipaction on spacecraft. D. Raboso from ESA/ESTEC, in the Netherlands, presented the paper and offered suggested research into this problem. The last paper, authored by True et al. of Litton Electron Devices, described a pair of multi-MW vacuum switches called the Hobetron and the Hobetron-plus. These switches are also capable of switching hundreds of amps at thousands of volts.
SESSION 15 - GYRO-AMPLIFIERS II
The second of the IVEC gyro-amplifier sessions began with a keynote talk on the development of high average power, W-band gyro-amplifiers for radar applications by Blank et al. (CPI), along with participants from NRL, KN Research, Mission Research Corp., SAIC, Litton and the University of Maryland. Experimental results from a 10 kW average power, W-band, gyro-klystron amplifier were presented. Rodgers et al. from the University of Maryland discussed their studies on a millimeter wave, harmonic frequency-doubling gyro-TWT. They have demonstrated 100-200 kW peak power at the second harmonic of the electron cyclotron frequency, centered at 33 GHz with a bandwidth of 3% and gain of 20 dB. One of the goals of this work is to investigate whether harmonic frequency-multiplying gyro-amplifiers can produce radiation with better phase coherence than in fundamental devices. Sirigiri et al. from Massachusetts Institute of Technology (MIT) reported on a novel quasi-optical, W-band gyro-TWT design, embodying quasi-optical components for the input coupler, interaction structure and a novel sever. Bratman et al. (Russian Academy of Sciences) presented their experimental results on a broadband gyro-TWT based on a new microwave system formed from a cylindrical waveguide with a helical corrugation of the inner surface. Read et al. concluded the session with a description of a 1 kW, 360 GHz gyro-klystron being developed at Physical Sciences, Inc. to provide radiation for an instrument for pulse and CW Electron Paramagnetic Resonance (EPR) spectroscopy.
SESSION 16 - ADVANCED TECHNOLOGY
The first paper by Rosenau and his colleagues at UC, Davis presented experimental data from two quantum barrier varactor based frequency tripler grid arrays and a Schottky varactor based frequency doubler grid arrays, all of which employ spatial power combining techniques. Chen et al. from MIT presented theoretical, computational, and experimental analyses of a 17 GHz cavity consisting of an array of metallic cylinders. An analysis of a method used to measure the attenuation due to lossy material applied to support rods in helix traveling wave tubes was then given by Lally of Teledyne Electronic Technologies, Mountain View and Christeson of Teledyne in Rancho Cordova. Ives et al. (Calabazas Creek Research), Lawson (University of Maryland) and Shapiro (MIT) reported on various computer codes used to design mode converters, waveguide bends, and other devices in overmoded waveguides, and compared the computer predictions with measured data from the actual devices. Lastly, the effects of machining and cleaning on the initiation of DC breakdown for electrodes built of different grades of stainless steel were discussed by Dolak from CPI, Palo Alto.
SESSION 17 - NOISE I AND INTERMODULATION
Session 17 provided valuable information on present efforts to understand and reduce noise and intermodulation products in microwave tubes. In the first paper, Tighe of HED presented information on disturbances in the output power and phase of traveling wave tubes caused by transient ion generation. Two types of such low-frequency TWT “jitter” called periodic and random jitter, were discussed and techniques effective in eliminating these problems were presented. Thorington of HED followed this talk with a presentation on computer simulations of the ion trapping and detrapping mechanisms associated with “jitter” in TWTs. Thorington was able to show ion accumulation and radial detrapping consistent with the low-frequency jitter observed in many microwave tubes. Thelen presented a sensitivity study on “Efforts to Reduce CWI TWT Noise and Body Current.” He showed that the phase jitter amplitude could be dramatically reduced by the optimization of tube parameters such as magnetic field strength. Manheimer of NRL presented results from a coupled 2D fluid electron and 1D ion particle code on ion-generated noise in microwave tubes. A video presentation shown by Manheimer and Freund of the time dependence of the trapping and detrapping of ions predicted by this code was very effective in illustrating some of the underlying mechanisms of this effect. Finally, Safier of NRL presented simulations of Noise-Power Ratio using the Large-Signal Code CHRISTINE. This very interesting talk demonstrated that noise power ratio in traveling wave tubes could be accurately predicted with reasonable running times by CHRISTINE using the injection of only 16 tones.
SESSION 18 - GYRO-OSCILLATOR I
The gyrotron oscillator has now been widely used for electron cyclotron resonance heating of fusion plasmas following two decades of intensive research and development. An overview of its inception to fruition as the most powerful millimeter-wave source in long-pulse and CW operation was presented by George from the Department of Energy. This invited talk was followed by presentations of the latest progress in Russia (by Denisov et al of GYCOM, Ltd., Institue of Apllied Physics) and the U.S. (by Felch et al. from CPI, Palo Alto and by Kreischer et al. from MIT and Cauffman et al. from CPI, Palo Alto). Power levels up to 1 MW in the frequency range of 110-170 GHz are operational in long-pulse and CW modes, while 1.5 MW versions are being developed. Experimental results of an alternative source, the Dutch Free Electron Maser, were reported on by M. Caplan of Lawrence Livermore National Laboratory, Verhoeven et al. of Institute of Plasma Physics “Rijnhuizen” and Bratman et al. of Institute of Applied Physics.
SESSION 19 - HIGH POWER AND NOVEL DEVICES
The first paper by Eastwood et al. from Culham Science Centre presented results from studies of a 15 and 30-Ohm tapered magnetically insulated line oscillator (MILO), which uses novel tapered slow-wave structures, diode layout and axial power extraction. Their tapered MILO designs, obtained using a combination of computational modeling and experiment, show superior performance compared to other tubes in terms of peak power, energy per pulse and efficiencies at powers of over 1 GW and frequencies close to 1 GHz. Eastwood and Arter also demonstrated Culham’s progress in the accurate modeling of high power relativistic magnetrons using a 3D PIC code, as well as their progress towards producing novel designs meeting operational requirements, while minimizing hardware requirements. Chernyavsky of the Institute of High Current Electronics and Pikunov of Moscow State University reported on the ongoing intensive investigations to improve the characteristics and expand applications of the relativistic backward wave oscillator (RBWO). Animation of electromagnetic fields in an open resonator RBWO was included. Smakhtin et al. from Moscow State Aviation Institute (Technical University) discussed an alternative method to generate microwave radiation in the millimeter and sub-millimeter wavelength ranges – the direct conversion of plasma stream energy to monochromatic microwave radiation through a deceleration of the plasma stream in a transverse magnetic field. Lastly, Savvin of Moscow State University described new types of high quality vacuum microwave devices based on transverse grouping of homogeneous (non-bunched) electron beams in circularly polarized electromagnetic fields from slow-wave structures and resonant cavities.
SESSION 20 - NOISE II, ELECTRON GUNS AND MAGNETS
This session embodied impelling discussions from computational methods to predict intermodulation distortion in TWTs to the development of new magnetic materials for high temperature applications. Abe et al. from NRL, Ngô (MRC), Chernin (SAIC) and Antonsen (University of Maryland) compared two-tone intermodulation experiments with the 1D helix interaction code CHRISTINE and an empirical model. Using CHRISTINE, better agreement was achieved compared to experiment in terms of third order intermodulation products (IM3) versus that obtained using the empirical formula. Datta (Microwave Tube Research & Development Centre) and Basu (Banaras Hindu University) addressed IM3 distortion, reporting on their simple and fast Eulerian analysis of IM3 distortion in a TWT and its control by harmonic injection. Mako et al. from FM Technologies, Inc. described micro-pulse electron gun (MPG) technology, the objective being the development of novel electron guns producing self-bunched, high-current density beams with cold emission, long life and non-contamination. Cold-cathode self-bunching was demonstrated at several operating frequencies. Katsap et al. from Lucent Technologies, Sewell from LAB-6, Rouse from Munro’s Electron Beam Software and Read from University of Manchester discussed the unusual specifications of the SCALPEL E-beam lithography tool and using a grid-controlled gun as an alternative electron beam source. The session concluded with a paper by Walmer et al. from Electron Energy Corp. describing a new class of Sm2TM17 type of permanent magnetic materials to meet the needs of applications at high temperatures (≥ 400° C). Results were presented from investigations on the thermal stability of this class of magnets.
SESSION 21 - GYRO-OSCILLATORS II
The second session on gyro-oscillators began with an invited talk by Magne et al. describing the collaboration between Association Euratom-CEA, Association Euratom-Confédération Suisse and TTE to develop a high power, quasi-CW, gyrotron working at 118 GHz for plasma heating and current drive for Electron Cyclotron Resonance interaction. One prototype and three series devices have already been manufactured and accepted. In the talk by Koppenburg et al., the need for fast frequency-tunable gyrotrons for controlling instabilities in large fusion reactors was described. To address this need, a 1 MW frequency-step-tunable gyrotron that operates between 114 and 166 GHz is under development at the Association Euratom-FZK, where the frequency change is performed by a slow variation of the magnetic field by modification of the current in the superconducting coils. Bykov discussed gyrotrons and gyrotron systems for several applications in technology, being developed at the Institute of Applied Physics (Russia), who pioneered in the development of a 10 kW, 30 GHz, CW gyrotron system specifically designed for research into mm-wave processing of materials. Wagner et al. from CPI described the need to excite a high order gyrotron cavity mode at low powers in order to cold test the performance of quasi-optical mode converters of gyrotrons. To generate such modes, they focused on a quasi-optical solution where a free space Gaussian beam is directly coupled to the higher order gyrotron mode through a translucent cavity wall. The contrast between linear and saturated behavior in the gyrotron backward wave oscillator was studied using a numerical approach by Chen of National Center for High-Performance Computing and Chu et al. from National Tsing Hua University. Evolution from the linear to the nonlinear state as well as its effect on efficiency and power scaling with respect to the interaction length was presented and physically interpreted. Lastly, Petelin, also from the Institute of Applied Physics, gave an in depth discussion of mode selection in high power microwave sources.
SESSION 22 - MICROWAVE POWER MODULES
Microwave power modules integrate the solid state driver, TWT and power supply resulting in a device with decreased mass and power consumption compared to conventional TWT amplifiers. The MPM session at IVEC 2000 began with a description of the work in this area at Officine Galileo Spazio B.U. Nebuloni et al. summarized the main design aspects and performance presenting results for Ku and Ka-band MPMs for space applications. Until now, the MPM concept was utilized mainly in the military market. Significant progress has been made at CPI (Palo Alto) over the last decade in mini helix TWT MPMs and helix millimeter wave TWTs. Scott described CPI's history in building over 10,000 mini TWT's and their current work on millimeter wave power modules, describing the latter as a “A marriage made in heaven.” In addition to their large number of wideband MPM type vacuum devices for military applications, Watkins described the work being done at Litton Systems Inc. in the area of decoy operation. The challenges and successes in developing this device were presented showing impressive results. Ballagh, also from Litton, discussed their full line of existing, recently developed and future MPMs operating in 2 to 8 GHz, 6 to 18 GHz, 18 to 40 GHz, X, Ku and Ka-bands. Applications include military and commercial applications as well as UAV data links and satellite communications uplinks. Stolz et al. from Northrop Grumman Corp. focused on advances in manufacturing MPMs, stressing the importance of lean, flexible manufacturing methods to reduce acquisition costs. The program underway at Northrop is targeted to reduce the production cost of helix TWTs by 30-40 percent. Lastly, Kennedy et al. from Litton talked about the miniature, low voltage, vacuum power booster TWT for a Q-band millimeter wave power module. Experimental results were presented and ongoing work in device modeling and simulation was described.