Pulsed Output Power Research Articles

Experimental study on a long pulse X-band coaxial multi-beam

An X-band coaxial multi-beam relativistic klystron amplifier is designed in order to increase the output microwave power and the operating frequency of the amplifier tube. Based on the results from PIC simulation, the experiment is performed on the long pulse accelerator. In the experiment, the transmittal and bunching of electron beam are analyzed, and then the amplifier is driven by a beam of 4.2 kA at 700 kV, and an external source injects microwave power of 60 kW into an input cavity, then 670 MW microwave power of 5 Hz repeating frequency is extracted, the amplifier gain is about 40 dB, the pulse width is 89 ns, and the conversion efficiency is 23%. The experiment proves that several tens kW-level input power can drive the X-band coaxial multi-beam relativistic klystron amplifier to generate several hundred MW-level long pulse output power.

Stable seeder-injected Nd:YAG pulsed laser using a RbTiOPO4 phase modulator

A stable, single-longitudinal-mode, nanosecond-pulsed Nd:YAG laser with a laser-diode dual-end pumping arrangement is constructed. Injection seeding is performed successfully by utilizing a RbTiOPO4 crystal as the intracavity phase modulator to change the optical length of the slave cavity based on the delay-ramp-fire technique. The laser generates 9.9 mJ of pulse energy with a 16 ns pulse duration at a 400 Hz repetition rate. A near-diffraction-limit laser beam is achieved with a beam quality factor M2 of approximately 1.2. The frequency jitter is 1.5 MHz over 2 min, and the fluctuation of the output pulse power is 0.3% over 23 min.

A flat gain GaN MMIC power amplifier for X band application

A flat gain two-stage MMIC power amplifier with a 2.8 GHz bandwidth is successfully developed for X band frequency application based on a fully integrated micro-strip AlGaN/GaN HEMT technology on a semi-insulating SiC substrate. Designed with a binary-cluster matching structure integrated with RC networks and LRC networks, the developed power MMIC gets a very flat small signal gain of 15 dB with a gain ripple of 0.35 dB over 9.1–11.9 GHz at the drain bias of 20 V. These RC networks are very easy to improve the stability of used GaN HEMTs with tolerance to the MMIC technology. Inside the frequency range of 9–11.2 GHz where the measurement system calibrated, the amplifier delivers a pulsed output power of 39 dBm and an associated power added efficiency of about 20% at 28 V without saturation, as the available RF power is limited.

Ka-Band Gyrotron Traveling-Wave Tubes With the Highest Continuous-Wave and Average Power

The results of experimental investigation of two Ka-band gyrotron traveling-wave tube (gyro-TWT) amplifiers with helically corrugated waveguides are presented. The first tube produces pulsed output power of 130-160 kW within the frequency range of 33.1-35.5 GHz and is capable of operating with a 10% duty factor. Reliability of its major components in the high average power operation regime (about 10 kW) was proven in a continuous-wave (CW) experiment. The second gyro-TWT amplifier delivered CW power of up to 7.7 kW with -3-dB bandwidth of 2.6 GHz and -1-dB bandwidth of 2.1 GHz. Effective implementation of single-stage depressed collectors (to the best of our knowledge, for the first time for gyro-TWTs) enabled the electron efficiencies as high as 36% for the pulsed tube and 33% for the CW tube to be achieved at operation at the second cyclotron harmonic.

Pulsed Power Generation by Solid-State LTD

A solid-state linear transformer driver stack has been developed to demonstrate pulsed power generation and output pulse shaping. It consists of 30 modules each using 24 power metal–oxide–semiconductor field-effect transistors as switches. The output voltage of the stack is the superposition of the voltage pulse of each module no matter if the modules are switched synchronously or not. In synchronous operation, the output voltages of all modules are added up to reach an output voltage up to \(\sim 29\) kV with a maximum output current of \(\sim 240\) A. The pulsewidth is variable in the range of 50–170 ns. On the other hand, by carrying out separate switching of different modules, the output waveform can be varied by performing pulse shaping. The control signals for pulse shaping experiment are generated using an field-programmable gate array board that allows potentially automatic waveform optimization.

Operation Characteristics of A6 Relativistic Magnetron Using Single-Stepped Cavities With Axial Extraction

We report the performance of an A6 relativistic magnetron with single-stepped cavities output. Particle-in-cell simulation shows the electronic efficiency of an A6 relativistic magnetron with an anode block made of six single-stepped cavities can be up to 78% with an output power of one gigawatt for an applied voltage of 400 kV. When the A6 relativistic magnetron with axial extraction using six single-stepped cavities is applied with a voltage of \(V \sim 400~{\rm kV}\pm 50\) kV the electronic efficiency can be as high as 60%, while the output power can be as high as 1 GW. And, when a 10-ns voltage pulse of 400 kV is applied on this magnetrons with diffraction output using single-stepped cavities, the output power pulse can be as high 1.2 GW. The results in this paper will provide a reference for choosing a cavity that is easily manufactured, so that a physical experiment is more feasible.

Pulsed Power Combining System for W-Band Traveling Wave Tube Amplifiers With a Waveguide Combiner

A W-band high power combining system was designed to enhance the transmitter power for increasing weather radar's detection ability to small cloud particles and detection distance. The high power combiner with high isolation between the input ports was designed and manufactured. The effects of amplitude and phase differences on the combining efficiency were examined. The W-band pulse power combining experiment for two home-made traveling wave tube (TWT) amplifiers were carried out with the high power combiner at the frequency range of 93.5-94.5 GHz. The output pulse power from the two TWTs are about 100 W and 120 W, respectively, with duty cycle 4%, and the combining efficiency is above 79%, with the maximum efficiency 84.6% at 94 GHz. The maximum output power of the combining system reaches 194 W at 94.3 GHz.

High-power pulse millimeter traveling-wave tubes

A line of traveling-wave tubes operating in the 8-mm wave band with an output pulse power of 0.2–6 kW, which are suitable for application in transmitters of radar stations, is designed.

Ultrabroad stimulated emission from quantum well laser

Observation of ultrabroad stimulated emission from a simplex quantum well based laser at the center wavelength of 1.06 μm is reported. With increased injection current, spectrum as broad as 38 nm and a pulsed output power of ∼50 mW have been measured. The experiments show evidence of an unexplored broad emission regime in the InGaAs/GaAs quantum well material system, which still needs theoretical modeling and further analysis.

Sub-20-ps pulses from a passively Q-switched microchip laser at 1 MHz repetition rate.

We present a 50 μm Nd3+:YVO4 microchip laser that is passively Q-switched by a semiconductor saturable absorber mirror. To reduce handling problems caused by the small crystal dimensions, the 50 μm Nd3+:YVO4 crystal is optically bonded to an undoped YVO4 crystal of a length of about 500 μm. By using a saturable absorber mirror with an effective modulation depth of >10% the system is able to deliver 16 ps pulses at a repetition rate of up to 1.0 MHz. The average laser power is 16 mW at 1064 nm. To our knowledge these are the shortest Q-switched pulses ever reported from a solid-state laser. The limits in terms of pulse width, repetition rate, output power, and system stability are discussed. Additionally, continuous-wave behavior is analyzed. Experimental data is compared with the simulation results of the coupled rate equations.

Fast-Framing Optical Imaging of Plasma Formation in Resonant Microwave Pulse Compressor

Plasma evolution in the interference switch of an $S$ -band pulse compressor operating in the frequency of 2.766 GHz, with input pulses of 200–450-kW power and duration of 2.4 $\mu{\rm s}$ , was studied experimentally and in numerical simulations. The system was filled with dry air at $2\times 10^{5}\hbox{-}3\times 10^{5}\hbox{-}{\rm Pa}$ pressure. The plasma discharge that switches the phases of the compressor operation from energy storage to release was initiated by a Surelite laser. The evolution of the light emission from the plasma was studied using fast-framing optical imaging with a 4QuikE camera. From the obtained typical size of the plasma and its velocity of expansion along the electric field, the density of the plasma was estimated, and the influence of its evolution on the power and waveform of microwave output pulses observed in the experiments was determined in simulations.

Investigation on a High Power, Low Impedance, and Long Pulse Generator Based on Magnetic Switches

Magnetic switches could improve the stability, reliability, repetition rate, and life of pulsed power systems, based on which, a high power, low impedance, and long pulse generator has been investigated numerically and experimentally. The generator accomplishes the power compression and the pulse forming at a relatively low voltage level, consisting of a core-type pulse transformer, a two-stage magnetic compression unit, a low impedance pulse forming network, and magnetic type main switches. A full circuit model was developed using PSPICE software to analyze key factors that influence output characteristics of the generator. Key subsystems were manufactured and experimental research was carried out on the whole system. Preliminary results achieved with a dummy load of 2.5 Ω show that the output pulse power is about 2.0 GW and the pulsewidth is about 170 ns, which are in reasonable agreement with the numerical analysis.

A solid-state generator with pulsed excitation of the oscillating circuit

A solid-state high-frequency damping oscillation pulse generator based on a pulsed excitation circuit is designed. The frequency of high-frequency oscillations reaches units of megahertz with a pulse repetition rate in the continuous mode of up to 1 kHz. The frequency of output pulses determines the power consumption from the supply mains that does not exceed 700 W. In this case, the peak power of output pulses reaches hundreds of kilowatts with a generator efficiency of up to 65%, if the optimal resistive load is used. The main area of the generator application is the generation of low-temperature atmospheric-pressure plasma.

Design of the RF Circuit for a Coaxial Cavity High-Power Multiple-Beam Klystron

This paper presents the design methodology and detailed design of the interaction circuit for use in an L-band 10-MW MBK, which operating in the fundamental mode at a center frequency of 1.3 GHz. Coaxial cavities are adopted to give adequate space for the use of multiple large cathodes, which has a low cathode loading and thereby facilitate a long lifetime. The emphasis for the present design is on efficiency and high-peak output power. The initial design was carried out using the large signal code KLY. To calculate the beam-wave interaction characters conveniently with cavities present, we developed a 2-D single-beam equivalent design methodology, in which the multitunnel coaxial cavities are replaced by the conventional single-tunnel cylindrical cavities with transformed RF parameters. The 3-D PIC simulations with actual coaxial cavity geometries are carried out at last to check on the large signal and the 2-D PIC simulations. The 3-D simulation results indicate that the equivalent design methodology is effective. The final RF circuit consists of six coaxial cavities including a second-harmonic cavity to reduce the device length. The circuit has a predicted gain of 50 dB at a peak pulsed output power of 10.4 MW with a corresponding electronic efficiency of more than 68%. The design and test results of the output system with two windows are also presented.

Characterization of High Power Microwave Radiation by an Axially Extracted Vircator

Characterization results of high-power microwave radiation, from an axial vircator driven by pulsed electron beam accelerator AMBICA-600 are reported in this paper. We present a study on variation in pulsed microwave power output and dominant frequency by discretely varying anode-cathode (A-C) gap. While keeping the cathode diameter fixed at 40 mm, for the A-C gap distance in the range 5-9 mm, dominant frequencies have been measured to be lying in the range 4.7-9.8 GHz. The trend of a subsequent increase in the dominant frequency at lower A-C gap distances (and vice versa) revealed that center frequency is mainly governed by the longitudinal size of the potential well. The highest microwave power of ~ 14 MW for ~ 75-ns pulse duration was obtained at A-C gap of 7 mm having the dominant frequency in C-band at ~ 6.9 GHz. The beam-to-microwave power conversion efficiency of ~ 1.2% has been demonstrated in our experiments. On the basis of power distribution pattern obtained by the gas breakdown technique, the dominant mode of emission is believed to be transverse magnetic mode. Relative analysis of frequency spectrums obtained for various A-C gap distances evidenced experimental recognition of optimum A-C spacing as a generation of narrowband distinct frequency peak of large magnitude with minimal mode hopping.

Theoretical and simulation study of 0.14 THz fundamental mode multi-beam folded waveguide traveling wave tube

To improve the current and output power of the THz traveling wave tube (TWT), a fundamental mode multi-beam folded waveguide (FMMBFW) TWT scheme is proposed. Firstly, an equivalent circuit model FMMBFW for calculating the high-frequency characteristic is established and compared with numerical simulation. Secondly, the transmission characteristic of 60 periods FMMBFW is analyzed. Finally, the beam-wave interaction characteristic of 0.14 THz FMMBFW TWT is completed by numerical simulation and theoretical calculation. When the DC current is 12 mA and the applied voltage is 15.75 kV, the 3 dB bandwidth of 0.14 THz FMMBFW TWT is 25 GHz (128-153 GHz), the maximum gain is 33.61 dB and the maximum output power is 23 W. When the DC current is 30 mA and the voltage is 15.75 kV, the maximum gain is 38 dB and the maximum pulse output power is 63.1 W at 0.14 THz. Compared with the fundamental single-beam folded waveguide (FW) TWT under the same working condition, the 3 dB bandwidth is doubled, its output power is raised by a factor of 9.66 and the interaction efficiency is increased by 3.22 times. Based on the same gain, the length of FMMBFW TWT is just 52.6 mm while the length of single beam FW-TWT is 78.2 mm. The proposed method can increase effectively the current of FMMBFW TWT; and the interaction gain, efficiency, 3 dB bandwidth, output power can be improved. When the gain is the same, a shorted and compact FMMBFW TWT can be constucuted.

Investigation and suppression of pulse shortening problem caused by non-working mode self-excitation in an S-band long pulse relativistic klystron amplifier

We have investigated the pulse shortening problem of relativistic klystron amplifier. It is shown that non-working mode self-excitation is an important cause of pulse shortening. Theoretical and numerical analyses show the mechanism of non-working mode self-excitation caused by the coupling between cavities. By the use of radio frequency absorbers, the problem of non-working mode self-excitation can be solved. In the experiment, the RF output power is 920 MW, the output power pulse width of the device can be increased from 77 ns to 137 ns.

Pulse Power Nanosecond-Range DSRD-Based Generators for Electric Discharge Technologies

New design of power nanosecond-range generators for electric discharge in gases is described. These generators are based on semiconductor opening switches-Drift Step Recovery Diodes (DSRD). The main advantages of DSRD are very short switching-off time (<;3 ns), high commutated power (>500 kW for single DSRD with 2 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> of semiconductor structure), and high reliability of high voltage stacks consisting of many connected in series DSRD. The experimental results of DSRDbased generator application for ozone production and waste gas cleaning are presented. The main parameters of the generators: output pulse voltage up to 36 kV, pulse rise time <;4 ns, pulse repetition rate up to 3.5 kHz, output pulse power >4.5 MW.

S-Band 300 W Output SiC MESFET

High power internally-matched 4H-SiC MESFET with a total gate width of 4×27mm was demonstrated. The double p-type buffer layers were used for preventing electrons from entering the buffer and reaching the substrate traps. The peak of the electric field in the edge of the gate is restrained by the double recess gate structure, which is advantageous to the high break down voltage. A thermal oxide layer was grown and subsequently etched to remove etch-induced damage. The ohmic contact resistivity of 2 ×10-6Ω•cm2 was achieved. The pulsed output power, gain and drain efficiency of the internally-matched 4x27mm SiC MESFET measured at 2GHz were 300W, 9.2dB, and 24.8%, respectively.

Optically pumped quantum-dot Cd(Zn)Se/ZnSe laser and microchip converter for yellow – green spectral region

The room temperature laser generation in the yellow – green () spectral range has been demonstrated under optical pumping by a pulsed nitrogen laser of quantum dot heterostructures. The maximum achieved laser wavelength was as high as at a laser cavity length of . High values of both the output pulsed power (up to ) and the external differential quantum efficiency () were obtained at a cavity length of . Both a high quality of the laser heterostructure and a low lasing threshold () make it possible to use a pulsed InGaN laser diode as a pump source. A laser microchip converter based on this heterostructure has demonstrated a maximum output pulse power of at . The microchip converter was placed in a standard TO-18 ( in diameter) laser diode package.