Hoyoung Song

A 3-D Analysis of a Microfabricated Ladder Slow-Wave Structure for a Millimeter-Wave Traveling-Wave Tube

The design and the analysis of a ladder slow-wave structure (SWS) operating at 50 GHz is presented. A 3-D particle-in-cell (PIC) modeling of a ladder SWS is presented for the first time. Compared with a conventional helix circuit, the ladder SWS provides wide bandwidth, high interaction impedance, and ease of manufacturing at millimeter wavelengths. A small-signal code based on Pierces theory was developed to determine the dimensions and the small-signal characteristics of the device. Cold- and hot-test simulations were performed using High Frequency Structure Simulator and VORPAL codes. VORPAL, a 3-D PIC simulator that makes use of the conformal finite-difference time-domain method, predicts a small-signal gain of 15 dB and an instantaneous bandwidth of 6% for a 68-period ladder SWS that is driven by a 22-kV and 196-mA electron beam. Dispersion characteristics, large-signal characteristics, and nonlinear-beam dynamics are investigated.

Modeling of multistage depressed collectors using a 3D conformal finite-difference time-domain particle-in-cell code

Summary form only given. The feasibility of modeling a multistage depressed collector using a conformal finite-difference time-domain particle-incell code has been studied. A feedback mechanism is implemented to provide stable time-dependent voltages for each stage of the depressed collector. An arbitrary space-time dependent spent beam distribution can be given in our time domain simulations. We demonstrate the design of a five stage depressed collector recovering a triangular spent beam distribution achieving an energy recovery efficiency of 70%. Detail modeling and code capabilities will be presented.

P4-4: Design and analysis of a microfabricated ladder type slow-wave structure for a millimeter-wave traveling-wave tube

The modeling, simulation, and analysis of a ladder type millimeter-wave traveling-wave tube (TWT) slow-wave structure (SWS) are presented. The simulation contains both cold and hot tests using VORPAL [1], a particle-in-cell (PIC) simulator that uses the conformal finite difference time domain (CFDTD) method. Beam design, dispersion, gain, and particle analysis of the ladder circuit are described.

A compact S-band 1 kW traveling-wave tube for microwave power module

A compact S-band 1 kW traveling-wave tube (TWT) is being developed for microwave power module (MPM) phased antenna array radar applications. The S-band MPM provides tenfold peak power increase compared to the currently available ones. Circuit characteristics including interaction impedance, phase velocity, power, and gain of the TWT were predicted using large signal code. The test result of the compact S-band 1 kW TWT will be presented along with design the results for individual components that include the electron gun, antennas, window, and collector.

7.4: Development of a compact and lightweight S-band traveling-wave tube for microwave power module

A compact and lightweight S-band 1 kW traveling-wave tube (TWT) is being developed for microwave power module (MPM) radar applications. The S-band MPM provides a tenfold peak power increase compared to the currently available ones. Circuit characteristics including interaction impedance, phase velocity, power, and gain of the TWT were predicted using large signal code. Design of electron gun, periodic permanent magnet, and collector is complete. The helix circuit has been fabricated and is ready to be tested.

New Reset Waveform for a Large-Sustain-Gap Structure in an Alternating Current Plasma Display Panel

A new reset waveform for a large-sustain-gap structure in an ac plasma display panel is proposed. In the driving of a large-sustain-gap structure with a conventional ramp reset waveform, we cannot avoid the condition of an address electrode being a cathode, which causes lots of trouble in stabilizing the reset discharge. To resolve these problems, a square pulse instead of the conventional rising-ramp pulse is used. In order to stabilize the strong discharge in which the address electrode becomes a cathode, a priming discharge between the address (anode) and scan (cathode) electrodes is made prior to making a strong discharge between the address (cathode) and scan (anode) electrodes. With this scheme, a minimum address voltage of 60 V when the sustain gaps are 250 and 350 mum, respectively, is obtained. However, the contrast ratio using the square reset pulse is lower than that using the conventional ramp pulse. To improve the contrast ratio, the reset waveforms in each subfield are replaced by selective erase waveforms except for the first subfield. In the case of nonselective reset waveform, the background luminance is 19.4 cd/m2, whereas the background luminance of 2.4 cd/m2 is obtained with selective reset waveform.

Optimizing operation of a 220 GHz folded waveguide traveling wave tube using a 3-D EM PIC simulation

The designs of a 220 GHz folded waveguide traveling wave tube (FWTWT) have been reviewed and studied systematically via 3-D electromagnetic particle-in-cell (EM PIC) simulations. 3-D Cold test simulations using both the CFDTD and FEM methods have been carried out and compared with each other as basis for the hot test simulations. The hot test simulation results show that the gain-bandwidth features at 220 GHz are achievable while carefully avoiding beam interceptions. It is found that that the interaction characteristics are very sensitive to the operating beam parameters. The confinement of the electron beam with a beam filling factor of 50%, 60%, and 70% has been studied and the required focusing magnetic field is found to be 1.2, 1.4, and 1.8 times of the Brillouin field, respectively, to ensure no interception with the walls during operation. A variety of operating voltages have been simulated to optimize the operation of the FWTWT. The best case reaches 25 dB and centers at 220 GHz, supporting the required bandwidth from 210 GHz to 230 GHz for an input power of 100 mW. An optimized operating configuration was determined using 3-D EM PIC simulations.

Carbon dioxide dissociation using TM 011 cavity mode atmospheric microwave plasma

Summary form only given. Carbon dioxide (CO2) is the primary greenhouse gas that is responsible for global warming. It accounts for 84% of all US greenhouse gas emitted mainly due to fossil fuel combustion. One way to mitigate the environmental effects due to CO2 is to dissociate it into Carbon monoxide (CO) and Oxygen (O) using atmospheric microwave plasma. Advantages of atmospheric microwave plasma include reduction in the capital cost of equipment and elimination of constraints imposed by vacuum compatibility, generation of highly active species, and electrodeless power coupling. In this paper, we present an atmospheric microwave plasma system based on a TM011 cavity mode for CO2 dissociation. Analytical calculations, modeling, and design of the system will be described.

Calculation of start-oscillationcurrent for lossy gyro-TWT using linear TWT parameter conversions

Summary form only given. The start-oscillation-current of a gyro-TWT determines the stable operating current level of the device. The amplifier is susceptible for oscillations when the operating current level is higher than the start-oscillation current. There are several ways of calculating the start-oscillation current, including using the linear theory of a gyro-TWT. In this paper, we present a simple way of determining the start oscillation current of lossy gyro-TWT. The linear TWT parameters that include the effects of synchronism, loss, and gain, were converted to gyro-TWT parameters to calculate the start oscillation-current. The dependence on magnetic field, loss, and beam alpha was investigated. Calculations were carried out for a Ka-band gyro-TWT for both operating and competing modes. Comparison with linear theory will be presented.

A new class of S-band microwave poewr module for phased antenna array radar applications

Summary form only given. A new class of microwave power module (MPM) is being developed for phased antenna array applications. The MPM consists of a compact S-band 1 kW traveling-wave tube (TWT), a solid-state pre-amplifier, and a power supply. The proposed S-band MPM provides tenfold peak power increase compared to state-of-the art S-band MPMs. The TWT amplifier is driven by a 6 kV, 0.9 A electron beam. A depressed collector which was designed by using a 3-D conformal finite-difference time-domain particle-in-cell code,VORPAL [1], was employed to maximize the efficiency. The compact and lightweight S-band TWT is short in length (circuit length is six inches) and weighs only 700 g. The preliminary hot test result of the TWT showed 900 W peak power in S-band. The design, fabrication, and characterization of each components that consist the MPM will be discussed. The cold and hot test results will be presented.