Effects of rf magnetic field on upstream dielectric multipactor

Wang, Huihui; Liu, Dagang; Liu, Laqun; Xie, Mengjun; Meng, Lin

doi:10.1088/1361-6595/aaef0e

Cited by 20 publications

(22 citation statements)

References 26 publications

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“…Global models have been developed by many researchers to study hydrogen discharges. [27][28][29][30][31][32] A verified and validated model is required to characterize the mechanism of volume production of H − ions and to further improve the NHIS performance. Here, by verification we mean a comparison between simulation results and analytic solution, while validation is a comparison with experimental data.…”

Section: Introductionmentioning

confidence: 99%

Benchmarking and validation of global model code for negative hydrogen ion sources

et al. 2018

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Benchmarking and validation are prerequisite for using simulation codes as predictive tools. In this work, we have developed a Global Model for Negative Hydrogen Ion Source (GMNHIS) and performed benchmarking of GMNHIS against another independently developed code, Global Enhanced Vibrational Kinetic Model (GEVKM). This is the first study to present quite comprehensive benchmarking test of this kind for models of negative hydrogen ion sources (NHIS), and very good agreement has been achieved for electron temperature, vibrational distribution function (VDF) of hydrogen molecules, and H e nn − ratio. The small discrepancies in number densities of negative hydrogen ions, positive ions, as well as hydrogen atoms can be attributed to the differences in the predicted electron number density for given discharge power. Higher electron number density obtained with GMNHIS is possibly due to fewer dissociation channels accounted for in GMNHIS, leading to smaller energy loss. In addition, we validated GMNHIS against experimental data obtained in an electron cyclotron resonance (ECR) discharge used for H − production. The model qualitatively (and even quantitatively for certain conditions) reproduces the experimental H − number density. The H − number density as a function of pressure first increases at pressures below 12 mTorr, and then saturates for higher pressures. This dependence was analyzed by evaluating contributions from different reaction pathways to the creation and loss of the H − ions. The developed codes can be used for predicting the H − production, improving the performance of NHIS, and ultimately optimizing the parameters of negative ion beams for ITER.

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Section: Introductionmentioning

confidence: 99%

Benchmarking and validation of global model code for negative hydrogen ion sources

et al. 2018

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“…The number of electrons grows exponentially with time. Throughout the discussion, the growth of electrons has been modeled with an exponential growth curve, 𝑁 (𝑡) = 𝑁 0 𝑒 𝛼𝑡 , where 𝛼 is the growth rate [23]. In this case, the growth rate has been calculated to be about 0.185 nS −1 .…”

Section: Simulation Resultsmentioning

confidence: 99%

Suppression of multipacting growth in a superconducting spoke resonator by the use of higher order modes

Ghosh,

Sista

2024

J. Inst.

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Multipacting is a vacuum discharge phenomenon that constrains the performance of accelerator structures and various microwave devices significantly. The different ways to mitigate multipacting discharge have been a central research goal in Accelerator Physics & Technologies for a prolonged period. In this work, both Monte-Carlo and particle-in-cell (PIC) simulations show that the multipactor avalanche can be mitigated, by the use of Higher Order Modes (HOMs). The intuition behind the approach of using HOMs to suppress multipacting has been explained first. Then, the multipacting suppression has been demonstrated in a simple 1-D metallic gap, when it is exposed to a second carrier frequency in addition to fundamental rf mode, with the help of a Monte-Carlo simulation code. Finally, a detailed PIC simulation has been carried out using CST Microwave studio, to investigate the effect of various HOMs on the multipactor growth in a superconducting spoke cavity. It is observed that a slight excitation of some particular modes can drastically diminish the multipactor growth. Simulation has been done first without any HOMs, to calculate the growth rate and also to spot the discharge location. Next, among various HOMs (more specifically, quadrupole modes), only those have been selected, whose magnetic field locations coincide with the multipacting prone zone of the cavity. In a simulation study, the presence of these preselected quadrupole modes has been found to exhibit a substantial suppression effect on the multipacting growth of the cavity.

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“…16) In recent years, some new electron multipactor theories and suppression methods of the multipactor have been reported. [17][18][19][20][21][22][23][24] Considering both the electric and magnetic fields of TEM microwaves, a theoretical model for predicting the growth rate of window multipactor was proposed by Wang et al 17) The results of this theoretical model are in good agreement with those of electromagnetic PIC method. The Monte Carlo simulation model was developed by Iqbal et al to investigate the multipactor process on the single side caused by the microwave electric field of two carrier frequencies.…”

Section: Introductionmentioning

confidence: 89%

Comparative analysis of single-surface multipactor discharges at different microwave frequencies

Shu¹,

Zhao²

2022

Jpn. J. Appl. Phys.

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The dielectric multipactor discharge in vacuum has become one of the main factors limiting the power capacity of high-power microwave system. In this paper, the particle-in-cell method is used to study the effects of microwave frequency on the single-surface multipactor discharge under the fixed ratio of microwave field to frequency. As the microwave frequency increases, the change in the amplitude of mean electron energy and secondary electron yield is very small, but the number of electrons in a steady state increases linearly. This results in an increase in the delay time for the number of electrons to reach the steady state. The thickness of normalized electron number density decreases with the increase of microwave frequency, because the normal restoring electric field increases linearly with the microwave frequency. Finally, we confirm that the multipactor threshold increases linearly with the microwave frequency, which is consistent with the trend of the experimental results.

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Effects of rf magnetic field on upstream dielectric multipactor

Cited by 20 publications

References 26 publications

Benchmarking and validation of global model code for negative hydrogen ion sources

Benchmarking and validation of global model code for negative hydrogen ion sources

Suppression of multipacting growth in a superconducting spoke resonator by the use of higher order modes

Comparative analysis of single-surface multipactor discharges at different microwave frequencies

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