Band gyro-TWT Research Articles

Investigation of Power Capacity in the Output Window for a High-Power W-Band Gyro-TWT

Investigation of Power Capacity in the Output Window for a High-Power <i>W</i>-Band Gyro-TWT

Design and Experiment of a Compact Magnetron Injection Gun for a Coil Magnet X-Band Gyro-TWT

Design and Experiment of a Compact Magnetron Injection Gun for a Coil Magnet <i>X</i>-Band Gyro-TWT

Experiment and Power Capacity Investigation of Collector in the 50-kW-Average-Power Q-Band Gyro-TWT

To further increase the average output power of the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\textit{Q}$</tex-math> </inline-formula> -band gyrotron traveling wave tube (gyro-TWT), the power capacity and stability of the collector are investigated. In this article, the characteristics of the electron collection, the modeling of the cooling system, and the suppression of stray electrons are analyzed. The dissipated power is associated with the transverse energy of the electron beam. When the gyro-TWT operates at zero drive, the collector has a maximum dissipated power density of 2 kW/cm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{\text{2}}$</tex-math> </inline-formula> for a high average power state. Thermal results indicate a maximum temperature of 381 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{\circ}$</tex-math> </inline-formula> C on the collector with an optimized cooling system. By applying a transverse magnetic field, the stray electrons can be completely intercepted by the collector. The hot experiment results indicate that the gyro-TWT (45% duty cycle), driven by a 60-kV–9.82-A electron beam, can withstand a maximum beam power of 265 kW at zero drive. Then, a pulse power of 111 kW, with an average power of 50 kW and an efficiency of 18.8% at 47 GHz, is measured stably. The simulation and experimental results demonstrate the high-power capacity and high stability of the curved collector.

A Cascaded W-Band Gyro-TWT With the Configuration of Coaxial and Circular Waveguides

To realize a high-gain wideband millimeter-wave amplification, we present and simulate a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\textit{W}$</tex-math> </inline-formula> -band gyrotron traveling wave tube (gyro-TWT) with cascaded coaxial-and circular-waveguide amplifiers. The amplifiers are operated in a coaxial and circular TE <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{\text{01}}$</tex-math> </inline-formula> mode, respectively, and driven by two 60-kV gyrating electron beams with a pitch factor of 1.2 but different beam currents of 1 and 10 A. They are designed to possess relatively low individual gains below all oscillation thresholds to maintain high stability and achieve a high total cascaded gain for the whole gyro-TWT. A coupling circuit is adopted to cascade these two sections, converting the coaxial TE <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{\text{01}}$</tex-math> </inline-formula> mode to the circular one with a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$-$</tex-math> </inline-formula> 3-dB bandwidth of 6.8 GHz (94.1–100.9 GHz). particle-in-cell (PIC) simulation shows that the designed gyro-TWT can achieve a maximum saturated output power of 239.8 kW at 100 GHz, with a gain greater than 60 dB over a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$-$</tex-math> </inline-formula> 3-dB bandwidth of 8.0 GHz (94.5–102.5 GHz).

High Average Power Investigation of Dielectric Dissipation in the W-Band Gyro-TWT

The dielectric load gyro-traveling wave tube (gyro-TWT) is a primary high-power millimeter source, and its power capacity is limited by the thermal capacity of the attenuated dielectric. The heavy outgassing was observed when the gyro-TWT operated in a long pulse duration in the experiment. The heat dissipated on the dielectric, and its distribution is analyzed. Then the thermal performance for different pulse duration is investigated. The dielectric temperature reaches 390 °C and 214 °C for the pulse duration of 2 ms and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$200 ~\mu \text{s}$ </tex-math></inline-formula> with a duty cycle of 10%, respectively. It indicates the thermal resistance of the dielectric limits the power capacity. The average power capacity in different pulse duration is evaluated. Then a high average power experiment is realized. A <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${W}$ </tex-math></inline-formula> -band gyro-TWT is operated at 60.5 kV–9.4 A, with a pulse duration of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$200 ~\mu \text{s}$ </tex-math></inline-formula> and a duty cycle of 16%. A peak power of 126.1 kW and an average power of 20.2 kW are obtained at 94 GHz.

Design and Efficiency Enhancement Studies of Periodically Dielectric Loaded W-Band Gyro-TWT Amplifier

In this article, design, simulation, and efficiency improvement of W-band gyrotron traveling wave tube (gyro-TWT) amplifier operating at fundamental TE01 mode have been presented. A triode-type magnetron injection gun (MIG) has been designed and optimized for the desired quality of electron beam with a minimum spread 2% with velocity ratio 1.12 to improve the electronic efficiency of gyro-TWT. Parasitic modes in gyro-TWT have been suppressed by employing a periodic dielectric loading in the RF interaction circuit. The simulated amplifier developed an output power of ~203 kW in fundamental TE01 mode with an electronic efficiency ~29% and power gain ~57 dB for a nonspread gyrating electron beam. To improve the overall efficiency of gyro-TWT, a single-stage depressed collector has been designed as a spent electron beam recovery system. The proposed collector has enhanced the overall efficiency of gyro-TWT to ~48%.

Analysis of Phase Characteristics of Gyrotron Traveling-Wave Tubes

The phase characteristics of gyrotron traveling-wave tubes (gyro-TWTs) for high-resolution imaging radars have been investigated. Determinant equations of output phase are classified into the cold phase and warm phase in the cases of cold-field and hot-field regions, respectively. The phase–frequency characteristics of cold phase are examined regarding single-mode and multimode operations, respectively. The time stability and the sensitivity to external parameters of warm phase are also investigated. The efficient methods to make the output phase of gyro-TWTs controllable are proposed. The measured output phase of the input coupler and output taper of a Ka -band gyro-TWT is linear with respect to the frequency, without any distortion. Moreover, the warm output phase fluctuation introduced by the RF circuit is less than ±8°.

Microwave System of Transverse Output for a High-Power ${W}$ -Band Gyro-TWT

A conceptual design and the results of concrete simulations of the output microwave system of a ${W}$ -band gyrotron traveling-wave tube (gyro-TWT) with a predicted output pulse power of more than 300 kW are presented. A distinctive feature of this system is the transverse (relative to the translational velocity of the electrons in the gyro-TWT) extraction of the output power. The designed microwave circuit includes a waveguide mode converter and a set of quasi-optical mirrors. An oversized hole in the first 45° inclined mirror enables a lossless transport of the electron beam to the collector. The ring-like distribution of microwave radiation on the mirror is formed by a profiled waveguide mode converter and provides minimal radiation diffraction loss. For the synthesis of the mode converter, particle swarm optimization (PSO) method was used. The system of external quasi-optical mirrors provides the transformation of the ring-like beam into the HE1,1 mode of a corrugated waveguide with an efficiency of more than 94% in the frequency range 92–98 GHz. The mirror profiles were synthesized using the Katsenelenbaum–Semenov iterative procedure.

Investigation on High Average Power Operations of Gyro-TWTs With Dielectric-Loaded Waveguide Circuits

Gyrotron traveling-wave tubes (gyro-TWTs) have been proved to be an attractive power source in many applications such as high-resolution radars, high-power communication systems, and electronic warfare systems. The main output indexes such as peak and average output power, interaction efficiency, and bandwidth are important for these devices. In addition, a great deal of reliability requirements such as nonstop stable operating time, operation lifetime, and environmental adaptability should be met. In this paper, detailed developing processes of gyro-TWTs in high average power operations are presented, including theoretical analyses, multiphysics simulations of key components, fabrication, and construction of the automatic hot test platform. Finally, the measured results of a Ka -band gyro-TWT for industrial applications are presented. The amplifier exhibits an excellent performance of 100-h nonstop stable operation, a 1-dB fraction bandwidth of 8%, an efficiency of more than 20%, and a peak power and an average power of more 150 and 10 kW, respectively.

Propagation Characteristics of Confocal Waveguides Based on Spheroidal Functions for a ${W}$ -Band Gyro-TWT

The propagation characteristics of a confocal waveguide are related to the radial spheroidal function, which is extremely complicated. A quadratic polynomial fitting (QPF) expression derived from numerical results by interpolation was successfully applied to the development of confocal gyrotrons. However, the QPF expression is valid only for a moderate spheroidal parameter. As a result, it cannot work well for confocal gyrotron travelling-wave tube (gyro-TWT) applications since the Fresnel parameter may be small for stable operations. For the first time, an efficient algorithm is developed to accurately calculate the spheroidal functions. Based on it, the MATLAB code with high accuracy and efficiency is developed to analyze the propagation characteristics of confocal waveguide. The calculated results and the QPF results are compared for different mirror apertures, and then demonstrated by high frequency structure simulator (HFSS). The calculated results show good agreement with the HFSS results for different mirror apertures while the QPF solution agrees with the HFSS results only for large apertures. The code is valid for arbitrary mirror apertures for both the confocal gyrotron and gyro-TWT applications.

Design and Experimental Study of a High-Gain W-Band Gyro-TWT With Nonuniform Periodic Dielectric Loaded Waveguide

Gyrotron traveling wave tubes (gyro-TWTs) are of considerable interest for high-power millimeter and submillimeter radiation sources. The analytical design and experiment of a <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">W</i> -band gyro-TWT loaded with nonuniform periodic lossy dielectric rings is presented in this paper. The gyro-TWT is operating in the circular TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">01</sub> mode at the fundamental cyclotron harmonic, and driven by a 60 kV, 8-A gyrating electron beam with velocity ratio 1.2. Hot test results were: 1) maximum peak output power 112 kW; 2) 69.7-dB saturated gain; and 3) 23.3% efficiency at 93.5 GHz. The measured bandwidth with peak power greater than 90 kW is about 4 GHz in the range of 93–97 GHz. The hot test results show excellent agreement with the theoretical prediction. The potential backward wave oscillations involving the spurious modes TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> , TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">21</sub> , and TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">02</sub> are effectively suppressed by the nonuniformly loaded periodic lossy dielectric rings. The <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">W</i> -band gyro-TWT is zero-drive stable at the operating points. It demonstrates that a nonuniform loaded lossy dielectric structure is excellent for suppressing potential spurious oscillations.

Experimental Study of a Ka Band Gyro-TWT with the Mode-Selective Circuits

The design and experimental study of a Ka-band gyrotron-travelling-wave tube (gyro-TWT) amplifier operating in the circular TE01 mode at fundamental cyclotron harmonic are presented. A mode-selective technique was adopted in the interaction circuit of the gyro-TWT to suppress spurious modes TE11 and TE21. A saturated peak power of 86 kW was obtained with saturated gain of 33 dB , an efficiency of 21.3%, in operating voltage 62 kV, electron current 6.5 A and -3 dB bandwidth of 2 GHz (~6%) .

Effects of beam velocity spread on two-stage tapered gyro-TWT amplifier

The recent successful operation of a two-stage K/sub a/-band gyro-TWT amplifier at the Naval Research Laboratory has demonstrated its viability as a source of broadband high-power millimeter waves. However, it has been observed experimentally that sharp gain reductions occur at certain frequencies. In this paper, an analytical theory is presented which describes the effect of electron beam quality on the device's instantaneous bandwidth. It is shown that these observed gain dips are due to electron phase-mixing, resulting from finite beam velocity spreads, in the frequency-dependent sever. In addition, the theory demonstrates that the velocity-spread induced dips can be shifted or reduced by adjusting the magnetic field profile, circuit length, and beam axial velocity, consistent with experimental observations.