Improved Concurrent Electromagnetic Particle In Cell Research Articles

Particle-in-Cell Simulations of Ten-Vane Microwave-Oven Free-Running 2.45-GHz “Cooker” Magnetron: Microwave Power Increase up to 6 kW in a Pulsed Mode (3 kW With 50% Duty Cycle)

Standard operation of a conventional microwave oven 2.45-GHz “cooker” magnetron with 4.0–4.3 kV of pulsed applied voltages at 0.17–0.19-T magnetic fields results in generation of pulsed microwave power 1.8–2.8 kW, which is recalculated to an average microwave power 0.9–1.9 kW when the “cooker” magnetron operates with 50% duty cycle while driven by a “rectified” ac voltage from the wall-plug. It has been shown in many experimental studies of “cold-start” operation of a standard ten-vane 2.45-GHz “cooker” magnetron that it readily sustains, when properly conditioned, up to ~10-kV dc and up to ~14 kV of peak-to-peak ac applied voltage with just a few microamphere cold (field emission) leakage (anode) current. The latter suggests that a standard 2.45-GHz “cooker” magnetron may successfully operate in the desired, lowest <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\pi $ </tex-math></inline-formula> -mode with much more output microwave power at even higher magnetic fields when driven by up to ~10 kV of dc or quasi-dc appropriate, synchronous applied voltage. Results of improved concurrent electromagnetic particle-in-cell (ICEPIC) simulations of magnetron operation at different magnetic fields with synchronous applied voltages show that, for example, with 8.0-kV applied voltage at 0.35-T magnetic field, the 2.45-GHz “cooker” magnetron is able to generate up to 6.0 kW of pulsed microwave power with an anode current of ~0.9 A.

Theory, simulation, and experiments on a magnetically insulated line oscillator (MILO) at 10 kA, 240 kV near Hull cutoff condition

The magnetically insulated line oscillator (MILO) is a high power microwave source that has received increased attention recently because it does not require an external magnetic field. Self-magnetic insulation typically requires operation at high currents, ∼50 kA in previous experiments (at ∼10 Ω). This paper reports the first MILO experiment operating at moderate current, less than 10 kA, at a lower voltage of 240 kV, driven by the Michigan Electron Long Beam Accelerator. The viability of this lower current operation was predicted by our recently developed theory on Brillouin flow, which also led to the rigorous derivation, for the first time, of the Buneman–Hartree condition for the cylindrical MILO using both the Brillouin flow and single particle model. The experiments show that more than 90% of shots operate at a magnetic field less than 1.3 times the Hull-cutoff magnetic field, and this magnetic field is significantly lower than the magnetic field required at the Buneman–Hartree condition. These experiments also oscillated at less current than the Hull cutoff condition on over 80% of shots, suggesting that MILOs might operate at a current lower than that expected at exactly Hull cutoff; this peculiar feature was also predicted by the theory. Particle-in-cell simulations from the improved concurrent electromagnetic particle-in-cell (ICEPIC) and CST codes are detailed, which corroborate MILO operation at lower currents than the Hull cutoff condition. The maximum efficiency achieved in these experiments is 1%, at a resonant frequency of 1 GHz. An initial comparison of the newly developed theory against prior MILO experiments is presented.

Comprehensive Particle-In-Cell Simulations of Ten-Vane Microwave Oven Free-Running 2.45 GHz “Cooker” Magnetron With ICEPIC and CST-PS Codes

Particle-in-cell (PIC) simulations of a microwave oven free-running 2.45 GHz “cooker” ten-vane magnetron operating with a “cold” explosive-emission cathode in a uniform axial magnetic field are performed with two computer codes, improved concurrent electromagnetic PIC (ICEPIC), and CST Particle Studio (CST-PS). PIC simulations are done to compare results obtained by these two codes to each other and, in such a way, identify all possible advantages and disadvantages of each code performance as a reliable tool allowing to predict all important characteristics of the magnetron operation. Results of the PIC simulations show that the range of applied voltages within which the magnetron is able to operate in the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\pi $ </tex-math></inline-formula> -mode at an external uniform axial magnetic field 0.19 T is much broader as it is predicted by the CST-PS code, from 4.00 to 4.70 kV, than as it predicted by the ICEPIC code, from 3.90 to 4.10 kV. It is also shown that while the magnetron startup time gradually decreases, as it is predicted by the ICEPIC code, from about 700 ns (3.90 kV) to about 100 ns (4.20 kV) with the applied voltage increase, it initially chaotically varies, as it is predicted by the CST-PS code, between about 1000 ns (4.03 kV) and about 300 ns (4.01 kV) and only then gradually decreases down to 10–20 ns (4.40–4.60 kV) with the applied voltage increase. Additional PIC simulation with MAGIC or VORPAL codes would be interesting to perform as well to compare the obtained with these codes simulation results with results described in this article.

Full 3-D Simulation and Optimization of Gigawatt Class C-Band 20% Efficient Coaxial Vircator

An investigation of several configurations of a gigawatt class coaxial triode vircator is presented. To maximize averaged power output efficiency, several device dimensions are optimized. Simulations of the source were carried out using a full 3-D simulation code called improved concurrent electromagnetic particle in cell (ICEPIC). The optimization method used was a gradient-free method called asynchronous parallel pattern search. The optimization was run until convergence; until efficiency would no longer increase. The converged optimization resulted in a device that has 2.08 GW of output power with a steady-state efficiency of 20%. The device's output power is almost pure in the TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">01</sub> mode. The operating frequency is approximately 4.43 GHz, a frequency band previously unexplored for gigawatt class vircators. Additionally presented is a configuration designed to mitigate explosive emission on undesirable surfaces along the cathode. The configuration successfully keeps nonemission surface E-fields below 300 kV/cm. It maintains multigigawatt output power at 1.86 GW and has an operating frequency of 4.43 GHz.

Design and Simulation of a T-Vane Relativistic Inverted Magnetron

A design for a high-power relativistic inverted magnetron oscillator (IMO) is presented and modeled numerically using the massively parallel electromagnetic particle-in-cell code, improved concurrent electromagnetic particle in cell (ICEPIC). The inverted magnetron presented here is designed to operate in the $L$ -band for magnetic fields ranging from 0.07 to 0.1 T with voltages ranging from ~250 to 480 kV. Simulations in that voltage/magnetic field range demonstrate that the inverted magnetron is capable of fast startup, $\pi $ -mode dominance with little-to-no mode competition, as well as high output power, exceeding 2.5 GW at the high end of voltages examined. End-loss current, a common source of energy loss in relativistic magnetrons, is not present for this IMO design. The IMO radiates RF energy axially through the use of a novel dual-ring radiator that excites the TM01 mode in the downstream waveguide. This approach yields nominal RF output power efficiencies near 20%. ICEPIC simulations predict that the above features combined with the IMO’s stable, robust, and reliable performance in the desired mode over a large voltage range yield a class of high-power microwave source notable for its inverted geometry and T-vane slow-wave structure.

ICEPIC Simulation of a Strapped Nonrelativistic High-Power UHF Magnetron With a Transparent Cathode Operating in the Explosive Electron Emission Mode

The operation of a high-power nonrelativistic strapped ultra-high-frequency (UHF) multicavity magnetron with transparent cathode is simulated using the Improved Concurrent Electromagnetic Particle-in-Cell (ICEPIC) code. Results of the simulations are compared with simulations of the same magnetron with a solid cylindrical cathode. Both cathodes are explosive-emission electron sources that operate in the space-charge-limited mode of the electron extraction from the cathode. Simulations are part of an effort searching for methods and technologies that enable an increase of output microwave power of strapped nonrelativistic high-power UHF magnetrons by replacing thermionic direct-heated cathodes with a non-thermionic-emission cathode. Results of the simulations show that the anode current Ia and the output power Pout of the magnetron with the transparent cathode are higher than Ia and Pout of the same magnetron with a solid cathode. At the same time, the electronic efficiency ηe of the magnetron with the transparent cathode is less, and the startup time ts is shorter than ηe and ts of the magnetron with the solid cathode.

Full-Scale Three-Dimensional Electromagnetic Simulations of a Terahertz Folded-Waveguide Traveling-Wave Tube Using ICEPIC

This paper discusses simulation and modeling of the slow wave structure of a folded-waveguide terahertz traveling wave tube (TWT) using the Improved Concurrent Electromagnetic Particle In Cell (ICEPIC) software. This is the first time ICEPIC has been used for simulation of a TWT amplifier. Cold test simulations compare favorably with analytical models; at 368 GHz, the on-axis interaction impedance is 7.8 Ω. Hot test (beam included) ICEPIC simulations were used to determine the effects of space charge on the gain calculations. At 368 GHz, the normalized beam plasma frequency from ICEPIC simulations is Ωp = 0.56. Analysis of our ICEPIC simulations at 368 GHz indicates a normalized beam plasma frequency 75% larger than an analytical model we improvised from a sheath helix model taken from the literature. The hot test ICEPIC simulations at 368 GHz for a 64 periods long slow wave structure and a 10 mA, 25 kV electron beam produce small signal gain of 27 dB. The small-signal fractional 3-dB bandwidth of the TWT is 2.9%. The saturated fractional 3-dB bandwidth is 3.2%. Large signal simulations indicate that the saturated power at 368 GHz is 39.4 dBm and the saturated gain is 21.8 dB. A snapshot of a cross section of the electron beam shows bunching in space and a corresponding modulation in the velocity of the electron beam.

Numerical Simulations of a Relativistic Inverted Magnetron

A new design for an inverted magnetron is presented and modeled both analytically, using a single particle smooth bore relativistic approach, and numerically, using a massively parallel electromagnetic particle-in-cell code, Improved Concurrent Electromagnetic Particle-In-Cell (ICEPIC) code. Analysis and simulation confirm that the inverted magnetron design presented here is capable of oscillating in the π mode at axial magnetic fields of the order of ~0.1 T. ICEPIC simulations demonstrate that the inverted magnetron is capable of fast start-up, mitigation of mode competition, π-mode dominance, and high output power, of the order of 1 GW in some cases. Moreover, these performance features spanned over a variety of magnetic fields and input voltages. In simulations, the inverted magnetron design presented here demonstrated that end-loss current, a common source of energy leakage in relativistic magnetrons, has been eliminated as a source of energy loss. However, radio frequency output power efficiencies only remained comparable with standard relativistic designs. This was due to poor energy exchange between the particle and field. Thus, a refinement of the slow wave structure may be necessary.

Particle-in-Cell (PIC) Simulation of CW Industrial Heating Magnetron

Modern CW industrial heating magnetrons are capable for producing as high as 300 kW of continuous-wave microwave power at frequencies around 900 MHz and are sold commercially [Wynn et al., 2004]. However, to utilize these magnetrons in some specific research and scientific applications being of interest for the Air Force, the necessary adaptation and redesign are required. It means that the detailed knowledge of principles of their operation and full understanding of how the changes of the design parameters affect their operational characteristics are necessary. We have developed and tested computer model of a 10-vane highpower strapped magnetron, which geometrical dimensions and design parameters are close to those of the California Tube Laboratory’s commercially produced CWM-75/100L tube. The computer model is built by using the 3-D Improved Concurrent Electromagnetic Particle-in-Cell (ICEPIC) code. Simulations of the strapped magnetron operation are performed and the following operational characteristics are obtained during the simulation: frequency and mode of magnetron oscillations, output microwave power and efficiency of magnetron operation, anode current and anode-cathode voltage dynamics. The developed computer model of a non-relativistic high-power strapped magnetron may be used by the industrial magnetron community for designing following generations of the CW industrial heating high-power magnetrons.

Magnetic priming effects on noise, startup, and mode competition in magnetrons

Azimuthally varying axial magnetic fields have been utilized to perform "magnetic priming" of magnetrons for rapid startup, low noise, and mode control. An overview of the latest magnetic priming experimental and simulation results are presented in this paper. Magnetic priming experiments in dc-operating microwave oven magnetrons show sideband elimination, even with the cathode heater turned off. Simulations using three three-dimensional (3-D) improved concurrent electromagnetic particle-in-cell (ICEPIC) codes with two different computational algorithms recover the oven magnetron experimental results obtained with magnetic priming including fast mode growth, rapid spoke formation, and the tendency toward lower noise operation. A new, axially symmetric, azimuthally varying magnetic field geometry for oven magnetrons is explored and preliminary results are reported. Simulations using two-dimensional (2-D) MAGIC code for the University of Michigan/Titan relativistic magnetron show that the oscillation startup time can be dramatically decreased (almost by a factor of 3) and mode competition can be suppressed with magnetic priming.

3-D ICEPIC simulations of the relativistic klystron oscillator

Improved concurrent electromagnetic particle-in-cell (ICEPIC), developed at the US Air Force Research Laboratory, is a three-dimensional (3-D) particle-in-cell (PIC) code specifically designed for parallel high-performance computing resources. ICEPIC simulates collisionless plasma physics phenomena on a Cartesian grid. ICEPIC has several novel features that allow efficient use of parallel architectures, including automated partitioning, dynamic load balancing, and an advanced parallel PIC algorithm. Even though ICEPIC is still in development, it has successfully simulated real-world high-power microwave (HPM) experimental devices, such as the magnetically insulated line oscillator (MILO) and the relativistic klystron oscillator (RKO), and the results from recent RKO simulations will be presented.