Three-dimensional simple conformal symplectic particle-in-cell methods for simulations of high power microwave devices

2020

Self Cite

To increase the generation efficiency of the terahertz wave in the Y band, the idea of dual-reflector is introduced in the relativistic surface wave oscillator (SWo) with large oversized structures. the dual-reflector and the slow-wave structure (SWS) construct a resonator where the field strength of tM 01 mode inside is intensively enhanced and then the efficiency is increased. The pre-modulation on electron beam caused by the reflector is also helpful in improving the output power. Meanwhile, the reflector can reduce the loss of negatively going electrons. Through the particle-in-cell (PIC) simulations, the optimized structure is tested to be stable and little power is transmitting back to the diode area. The output power reaches 138 MW in the perfectly electrical conductivity condition and the frequency is 337.7 GHz with a pure spectrum. The device's efficiency is increased from 10.7% to 16.2%, compared with the device without any reflectors. The performance of device with lossy material is also focused on. In the situation of copper device, the output power is about 41 MW under the same input conditions and the corresponding efficiency is about 4.8%. In recent years, the terahertz wave has shown great potential in the applications of remote high-resolution imaging, remote detection of radioactive material, deep space research and communications, plasma diagnostic in nuclear fusion, materials research, biomedical diagnostics, high data rate communications, basic biological spectroscopy, chemical spectroscopy, and so on 1-8. The prospect of terahertz technology has attracted many researchers to devote to developing the high power terahertz generators, especially the vacuum electronic devices (VEDs) 9-13. And the slow wave devices are an important class of the VEDs. Based on the interaction between the intense electron beam and the slow-wave structure (SWS), the backward wave oscillator (BWO) becomes a remarkable kind of slow wave device with good performance in high output power and compact structure 14,15. In a BWO, the electrons are in synchronism with −1 st spatial harmonic wave. When a slow wave device operates near the upper edge of the transmission band, it becomes a surface wave oscillator (SWO) whose operation point is close to π point. In an SWO, the fundamental wave slows down to the electron velocity 16. The Q-factor in the SWO is relatively large due to the large reflection and small group velocity, and then the start current is usually lowered in this case 17,18. What's more, the large coupling impedance in the SWO is significant in obtaining high interaction efficiency. Besides, use of the surface wave is valid in achieving mode selection in the overmoded structure as well. Thus, the SWO attracts more and more attention in generating millimeter and terahertz waves. However, their structural dimensions decrease rapidly as the working frequency goes up, causing many crucial problems that must be solved, such as the internal breakdown, limitation of the power capacity, and difficulties in manufacturi...

Section: Particle Simulation Resultsmentioning

confidence: 99%

Relativistic Surface Wave Oscillator in Y-Band with Large Oversized Structures Modulated by Dual Reflectors

2020

Self Cite

“…To optimize other structural parameters of the proposed SWO and figure out its operation mode, the simulations are performed by using a fully electromagnetic PIC code UNIPIC-3D 37 , in which the relativistic Newton-Lorentz force equation and Maxwell’s equations are solved on conformal meshes, and the distribution loss on the device wall is included 38 , 39 . After dozens of computation cycles, the main dimensions of the structure of our device are obtained as follows: thickness of electron beam 0.3 mm, radius of collimator 2.9 mm, inner radius of SWS 3 mm, and period number of SWS 27.…”

Section: Pic Simulationsmentioning

confidence: 99%

A megawatt-level surface wave oscillator in Y-band with large oversized structure driven by annular relativistic electron beam

et al. 2018

Self Cite

High power vacuum electronic devices of millimeter wave to terahertz regime are attracting extensive interests due to their potential applications in science and technologies. In this paper, the design and experimental results of a powerful compact oversized surface wave oscillator (SWO) in Y-band are presented. The cylindrical slow wave structure (SWS) with rectangular corrugations and large diameter about 6.8 times the radiation wavelength is proposed to support the surface wave interacting with annular relativistic electron beam. By choosing appropriate beam parameters, the beam-wave interaction takes place near the π-point of TM01 mode dispersion curve, giving high coupling impedance and temporal growth rate compared with higher TM0n modes. The fundamental mode operation of the device is verified by the particle-in-cell (PIC) simulation results, which also indicate its capability of tens of megawatts power output in the Y-band. Finally, a compact experimental setup is completed to validate our design. Measurement results show that a terahertz pulse with frequency in the range of 0.319–0.349 THz, duration of about 2 ns and radiation power of about 2.1 MW has been generated.

“…To validate the physical design of the BWO, its working characteristics is simulated by using a three dimensional fully electromagnetic particle-in-cell (PIC) code UNIPIC-3D 29 , 30 , in which the relativistic Newton-Lorentz force equation and Maxwell’s equations are solved on conformal meshes, and the distributing loss on the device wall is included 31 . The cross section of the sheet electron beam with the voltage of 5.0 kV and current of 150 mA is 2.5 mm × 0.14 mm.…”

Section: Physical Design Of the Planar Bwomentioning

confidence: 99%

Continuous-wave Y-band planar BWO with wide tunable bandwidth

et al. 2018

Self Cite

A high performance continuous-wave (CW) backward wave oscillator (BWO) with planar slow wave structure (SWS) and sheet electron beam in Y-band is presented in this paper. The mode selection is discussed by studying the dispersion curve of SWSs, distributions of the electric field, and particle-in-cell simulation results, showing that the designed BWO operates in the fundamental mode TM11. The planar SWSs are fabricated by using the UV-LIGA technology with the processing error less than 0.003 mm. The electron gun can provide the 2.5 mm × 0.14 mm sheet electron beam with maximum current density of 57 A/cm2 at the CW mode. Experimental results show that the developed BWO can operate in the fundamental mode TM11 and generate the state-of-art output power of 182 mW at the frequency of 0.3426 THz with a large frequency tuning range from 0.318 THz to 0.359 THz.