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Vacuum Tube Amplifiers
Abstract
Vacuum electronics (VE) amplifiers and oscillators are used for military and commercial applications that require high power at high frequency and also used in scientific research areas such as high-energy particle accelerators and plasma heating for controlled thermonuclear fusion. The types of amplifiers like space-based traveling-wave tube amplifiers (TWTAs) leads to significant reduction in operating cost for many systems. Solid-state power amplifiers (SSPA) led to increase in output power and higher operating frequency. The other common tube amplifiers used in high-power transmitters include three types of devices TWT including helix and coupled-cavity types, microwave power modules (MPM), and klystrons. The technique used for improving the efficiency of TWT is collector depression that enables to convert some of the kinetic energy in the spent electron beam into the potential energy of the power supplies increases the overall efficiency of the device. The other technique used to improve the performance of both SSPAs and TWTA is predistortion linearization.
... V ACUUM electronic devices with high power and broad bandwidth have a competitive edge in various applications, such as electronic countermeasures, satellite communication, plasma diagnostics, and high resolution radars [1], [2]. Lately, the designers of microwave tubes have faced many difficult design challenges, such as reducing operating voltages and minimizing the weight and dimensions of the devices and their power supplies. ...
We present an analytical method to compute the wavenumbers and electric fields of the space-charge-wave eigenmodes supported by a two-stream electron beam, consisting of a solid inner cylindrical stream and a coaxial outer annular stream, both contained within a cylindrical metallic tunnel. We extend the analytical model developed by Ramo to the case of two streams. The method accounts for the interaction between the two streams with the presence of the beam-tunnel wall; it can be used to model the complex wavenumbers associated with the two-stream instability and the plasma frequency reduction effects in vacuum electronic amplifiers and other vacuum electronic devices.
... V ACUUMelectron devices with high power and broad bandwidth have a competitive edge in various applications, such as electronic countermeasures, satellite communication, plasma diagnostics, and high-resolution radars [1], [2]. Lately, the designers of microwave tubes have faced many difficult design challenges, such as reducing operating voltages and minimizing the weight and dimensions of the devices and their power supplies. ...
We present an analytical method to compute the wavenumbers and electric fields of the space-charge-wave eigenmodes supported by a two-stream electron beam, consisting of a solid inner cylindrical stream and a coaxial outer annular stream, both contained within a cylindrical metallic tunnel.We extend the analytical model developed by Ramo to the case of two streams. The method accounts for the interaction between the two streams with the presence of the beam-tunnel wall; it can be used to model the complex wavenumbers associated with the two-stream instability and the plasma frequency reduction effects in vacuum electronic amplifiers and other vacuum electronic devices.
... High average power at millimeter-wave frequency, which is lightweight, low voltage, compact, and broadband, is demanded in many significant applications such as electronic counter measures, radar, and communications [1]. Solid-state amplifiers are lightweight and compact, but the output power, bandwidth, and efficiency struggle to meet the requirements. ...
To increase the output power of microstrip line traveling-wave tubes, a staggered rings microstrip line (SRML) slow-wave structure (SWS) based on a U-shaped mender line (U-shaped ML) SWS and a ring-shaped microstrip line (RML) SWS has been proposed in this paper. Compared with U-shaped ML SWS and RML SWS, SRML SWS has a wider transverse width, which means SRML SWS has a larger area for beam–wave interaction. The simulation results show that SRML SWS has a wider bandwidth than U-shaped ML SWS and a lower phase velocity than RML SWS. Input/output couplers, which consist of microstrip probes and transition sections, have been designed to transmit signals from a rectangular waveguide to the SWS; the simulation results present that the designed input/output structure has good transmission characteristics. Particle-in-cell (PIC) simulation results indicate that the SRML TWT has a maximum output of 322 W at 32.5 GHz under a beam voltage of 9.7 kV and a beam current of 380 mA, and the corresponding electronic efficiency is around 8.74%. The output power is over 100 W in the frequency range of 27 GHz to 38 GHz.
... [3] The technology survived, but only in a few niche applications. [4,5,6,7] However, in the last few decades, the advancement in nanofabrication techniques have allowed for the miniaturization of vacuum free-electron devices, which have started to regain interest due to their interesting properties when shrunk to the nanoscale. [8] Nano vacuum channel (NVC) electronics promise fast switching times, and low power-delay product with robust operation in harsh environments [9]. ...
Recent advancements in nanofabrication have enabled the creation of vacuum electronic devices with nanoscale free space gaps. These nanoelectronic devices promise the benefits of cold-field emission and transport through free-space, such as high nonlinearity and relative insensitivity to temperature and ionizing radiation, all the while drastically reducing the footprint, increasing the operating bandwidth and reducing the power consumption of each device. Furthermore, planarized vacuum nanoelectronics could easily be integrated at scale similar to typical micro and nanoscale semiconductor electronics. However, the interplay between different electron emission mechanisms from these devices are not well understood, and inconsistencies with pure Fowler-Nordheim emission have been noted by others. In this work, we systematically study the current-voltage characteristics of planar vacuum nano-diodes having few-nanometer radii of curvature and free-space gaps between the emitter and collector. By investigating the current-voltage characteristics of nearly identical diodes fabricated from two different materials and under various environmental conditions, such as temperature and atmospheric pressure, we were able to clearly isolate three distinct emission regimes within a single device: Schottky, Fowler-Nordheim, and saturation. Our work will enable robust and accurate modeling of vacuum nanoelectronics which will be critical for future applications requiring high-speed and low-power electronics capable of operation in extreme conditions.
Secondary electron emission serves as the foundation for a broad range of vacuum electronic devices and instrumentation, from particle detectors and multipliers to high-power amplifiers. While secondary yields of at least 3–4 are required in practical applications, the emitter stability can be compromised by surface dynamics during operation. As a result, the range of practical emitter materials is limited. The development of new emitter materials with high yield and robust operation would advance the state-of-the-art and enable new device concepts and applications. In this Perspective article, I first present an analysis of the secondary emission process, with an emphasis on the influence of material properties. From this analysis, ultra-wide bandgap (UWBG) semiconductors and oxides emerge as superior emitter candidates owing to exceptional surface and transport properties that enable a very high yield of low-energy electrons with narrow energy spread. Importantly, exciting advances are being made in the development of promising UWBG semiconductors such as diamond, cubic boron nitride (c-BN), and aluminum nitride (AlN), as well as UWBG oxides with improved conductivity and crystallinity. These advances are enabled by epitaxial growth techniques that provide control over the electronic properties critical to secondary electron emission, while advanced theoretical tools provide guidance to optimize these properties. Presently, H-terminated diamond offers the greatest opportunity because of its thermally stable negative electron affinity (NEA). In fact, an electron amplifier under development exploits the high yield from this NEA surface, while more robust NEA diamond surfaces are demonstrated with potential for high yields in a range of device applications. Although c-BN and AlN are less mature, they provide opportunities to design novel heterostructures that can enhance the yield further.
A frequency-tunable gyrotron with multiband radiation has been designed, manufactured, and investigated experimentally. The frequency tuning scheme utilizing transverse modes switching and axial mode transition is employed to obtain multiband radiation. Three modes TE
$_{\text{02}}$
, TE
$_{\text{43}}$
, and TE
$_{\text{24}}$
are excited successively with the increase of the magnetic field. The main operating frequency of these modes are 140, 250, and 263 GHz, respectively. Experimental results indicate that a certain frequency-tuning range can be obtained at each frequency band by means of exciting a series of high-order axial modes.
To improve the performance of a pencil beam electron gun for terahertz traveling wave tubes (TWT), a support vector regression (SVR) method combined with a goal attainment algorithm, which is used to optimize its structural parameters considering the periodic permanent magnetic (PPM) focusing system, is proposed in this article. Moreover, a parameter correction method to reduce the impact of the thermal expansion on the electron gun is proposed. An electron gun for 0.22-THz TWT gun is developed, in which a 30-mA/23.8-kV electron beam emitted by a curved barium–tungsten cathode with a beam loading of 4 A/cm
<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup>
is achieved with the optimized parameters. To the high current density for THz beam–wave interaction, the area compression ratio of electron beam is used in beam tunnel and reaches 144. The experimental results are very similar to the simulation results, which indicate that the methods would be beneficial to the development of TWT.
A U-shaped microstrip meander-line (MML) with an additional conformal dielectric substrate layer (CMML) is investigated for application in
${W}$
-band traveling-wave tubes (TWTs). The interaction impedance of such slow wave structure (SWS) is at least 29% higher than that of typical N-shaped and U-shaped MML circuits with the same dimensions. Furthermore, the conformal substrate layer probably results in less energy concentration in the dielectric substrate to reduce attenuation and also reduces the chance of electron striking and accumulation on the substrate. In addition, a customized waveguide housing with input–output coupler is optimized for the relatively wider substrate width to house the SWSs and facilitate measurements. The particle-in-cell (PIC) simulation results predict that it potentially could provide maximum saturated output power 31.4 W and 21.9 dB gain at 96 GHz, with a 3-dB bandwidth of 92–98 GHz when the operating voltage is 6550 V and beam current is 100 mA, respectively. If the thickness of conformal quartz layer increases to
$30 ~\mu \text{m}$
, the maximum output power can reach over 80 W. The measured S-parameters of the proposed entire 20-period structure match the simulated one well. The measured
${S}_{21}$
is better than −5.3 dB in the frequency range of 88–102 GHz. Attenuation is about 5.9–7.7 dB/cm in the
${W}$
-band, which is better than the measured results reported before.
Recent advancements in nanofabrication have enabled the creation of vacuum electronic devices with nanoscale free-space gaps. These nanoelectronic devices promise the benefits of cold-field emission and transport through free space, such as high nonlinearity and relative insensitivity to temperature and ionizing radiation, all while drastically reducing the footprint, increasing the operating bandwidth, and reducing the power consumption of each device. Furthermore, planarized vacuum nanoelectronics could easily be integrated at scale similar to typical microscale and nanoscale semiconductor electronics. However, the interplay between different electron emission mechanisms from these devices is not well understood, and inconsistencies with pure Fowler–Nordheim (FN) emission have been noted by others. In this work, we systematically study the current–voltage characteristics of planar vacuum nanodevices having few-nanometer radii of curvature and free-space gaps between the emitter and the collector. By investigating the current–voltage characteristics of nearly identical devices fabricated from two different materials and under various environmental conditions, such as temperature and atmospheric pressure, we are able to clearly isolate three distinct emission regimes within a single device: Schottky, FN, and saturation. Our work will enable robust and accurate modeling of vacuum nanoelectronics, which will be critical for future applications requiring high-speed and low-power electronics capable of operation in extreme conditions.
In this article, a terahertz traveling-wave tube (TWT) with two identical folded double-ridge groove waveguides (DRGWs) operated in parallel is presented. Driven by a sheet electron beam in each DRGW TWT allows a higher beam current, and hence higher output power can be achieved. A magic T based on DRGW is designed as the input and output power couplers for this novel TWT. The performance of the magic T is optimized using Chebyshev impedance transforming structures. The simulated reflection and transmission coefficients of the whole tube with magic T in the operating frequency range of 330–350 GHz are less than −20 and −75 dB, respectively. In addition, a particle in cell (PIC) simulation of the beam–wave interactions involving the two sheet electron beams predicted an output power of 160 W at 340 GHz with a 3-dB bandwidth of 11 GHz when a beam of 27.68 keV in energy and 0.25 A in total current is used.
This presentation describes the extended interaction klystron technology and presents improvements and design modifications in order to extend operational frequency into the sub-millimeter region
W‐band source research at Los Alamos is focused on developing a high peak and average power, wideband traveling‐wave tube, based on the interaction of a sheet electron beam with a planar slow‐wave structure. We report on progress on the formation and transport of high‐aspect ratio sheet beams, the rf structure
design, a low‐power gain demonstration experiment, and future advanced concepts including use of a photonic band gap
structure as the slow‐wave structure.
The design and construction of a 100 kW peak power, 2% duty, PCM focused, W-band sheet beam klystron is discussed. The elliptical cross section beam is produced by a new electron gun design using a cylindrical cathode and a racetrack shaped focus electrode. The multi-gap cavities produce acceptable values of R/Q and are designed to produce a uniform electric field over the width of the 12:1 aspect ratio beam. The prototype cavities are produced using normal machining, however, LIGA will be used to fabricate the cavities in production versions.
This paper reports on progress on a high‐power mm‐wave source concept being pursued at Los Alamos. The concept is based on passing a high‐brightness, sheet electron beam through a slow‐wave structure created from a vane‐loaded waveguide. Component development was conducted with at 10‐kV experiment, and design work and fabrication work has been conducted for a demonstration experiment with a 120‐kV, 20‐A sheet electron beam operating at 95 GHz. © 2003 American Institute of Physics
A comprehensive study of microwave vacuum electronic devices and their
current and future applications While both vacuum and solid-state
electronics continue to evolve and provide unique solutions, emerging
commercial and military applications that call for higher power and
higher frequencies to accommodate massive volumes of transmitted data
are the natural domain of vacuum electronics technology. Modern
Microwave and Millimeter-Wave Power Electronics provides systems
designers, engineers, and researchers-especially those with primarily
solid-state training-with a thoroughly up-to-date survey of the rich
field of microwave vacuum electronic device (MVED) technology. This book
familiarizes the R&D and academic communities with the capabilities
and limitations of MVED and highlights the exciting scientific
breakthroughs of the past decade that are dramatically increasing the
compactness, efficiency, cost-effectiveness, and reliability of this
entire class of devices. This comprehensive text explores a wide range
of topics: * Traveling-wave tubes, which form the backbone of satellite
and airborne communications, as well as of military electronic
countermeasures systems * Microfabricated MVEDs and advanced electron
beam sources * Klystrons, gyro-amplifiers, and crossed-field devices *
"Virtual prototyping" of MVEDs via advanced 3-D computational models *
High-Power Microwave (HPM) sources * Next-generation microwave
structures and circuits * How to achieve linear amplification * Advanced
materials technologies for MVEDs * A Web site appendix providing a
step-by-step walk-through of a typical MVED design process Concluding
with an in-depth examination of emerging applications and future
possibilities for MVEDs, Modern Microwave and Millimeter-Wave Power
Electronics ensures that systems designers and engineers understand and
utilize the significant potential of this mature, yet continually
developing technology. SPECIAL NOTE: All of the editors' royalties
realized from the sale of this book will fund the future research and
publication activities of graduate students in the vacuum electronics
field.
The extracted field emission current can be used to controllably heat microfabricated cold field emission cathode tips. The heating can be sufficient to smooth and recrystallize the tip surface by surface self-diffusion, and at least partially clean the surface of contaminants by thermal desorption. Self-heating not only allows for the achievement and maintenance of stable emission characteristics, but can be used to make the current-voltage characteristics of microfabricated field emitter tips nearly identical to one another. The resulting improvement in emission uniformity will allow for more reliable array operation at increased electron emission current densities. © 2003 American Vacuum Society.