Pub Date : 2024-02-23DOI: 10.1088/1361-6595/ad28cf
R Marskar
We theoretically study the inception and propagation of positive and negative streamers in CO2. Our study is done in 3D, using a newly formulated kinetic Monte Carlo discharge model where the electrons are described as drifting and diffusing particles that adhere to the local field approximation. Our emphasis lies on electron attachment and photoionization. For negative streamers we find that dissociative attachment in the streamer channels leads to appearance of localized segments of increased electric fields, while an analogous feature is not observed for positive-polarity discharges. Positive streamers, unlike negative streamers, require free electrons ahead of them in order to propagate. In CO2, just as in air, these electrons are supplied through photoionization. However, ionizing radiation in CO2 is absorbed quite rapidly and is also weaker than in air, which has important ramifications for the emerging positive streamer morphology (radius, velocity, and fields). We perform a computational analysis which shows that positive streamers can propagate due to photoionization in CO2. Conversely, photoionization has no effect on negative streamer fronts, but plays a major role in the coupling between negative streamers and the cathode. Photoionization in CO2
{"title":"A 3D kinetic Monte Carlo study of streamer discharges in CO2","authors":"R Marskar","doi":"10.1088/1361-6595/ad28cf","DOIUrl":"https://doi.org/10.1088/1361-6595/ad28cf","url":null,"abstract":"We theoretically study the inception and propagation of positive and negative streamers in <inline-formula>\u0000<tex-math><?CDATA $mathrm{CO_{2}}$?></tex-math>\u0000<mml:math overflow=\"scroll\"><mml:mrow><mml:mi mathvariant=\"normal\">C</mml:mi><mml:msub><mml:mi mathvariant=\"normal\">O</mml:mi><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>\u0000<inline-graphic xlink:href=\"psstad28cfieqn2.gif\" xlink:type=\"simple\"></inline-graphic>\u0000</inline-formula>. Our study is done in 3D, using a newly formulated kinetic Monte Carlo discharge model where the electrons are described as drifting and diffusing particles that adhere to the local field approximation. Our emphasis lies on electron attachment and photoionization. For negative streamers we find that dissociative attachment in the streamer channels leads to appearance of localized segments of increased electric fields, while an analogous feature is not observed for positive-polarity discharges. Positive streamers, unlike negative streamers, require free electrons ahead of them in order to propagate. In <inline-formula>\u0000<tex-math><?CDATA $mathrm{CO_{2}}$?></tex-math>\u0000<mml:math overflow=\"scroll\"><mml:mrow><mml:mi mathvariant=\"normal\">C</mml:mi><mml:msub><mml:mi mathvariant=\"normal\">O</mml:mi><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>\u0000<inline-graphic xlink:href=\"psstad28cfieqn3.gif\" xlink:type=\"simple\"></inline-graphic>\u0000</inline-formula>, just as in air, these electrons are supplied through photoionization. However, ionizing radiation in <inline-formula>\u0000<tex-math><?CDATA $mathrm{CO_{2}}$?></tex-math>\u0000<mml:math overflow=\"scroll\"><mml:mrow><mml:mi mathvariant=\"normal\">C</mml:mi><mml:msub><mml:mi mathvariant=\"normal\">O</mml:mi><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>\u0000<inline-graphic xlink:href=\"psstad28cfieqn4.gif\" xlink:type=\"simple\"></inline-graphic>\u0000</inline-formula> is absorbed quite rapidly and is also weaker than in air, which has important ramifications for the emerging positive streamer morphology (radius, velocity, and fields). We perform a computational analysis which shows that positive streamers can propagate due to photoionization in <inline-formula>\u0000<tex-math><?CDATA $mathrm{CO_{2}}$?></tex-math>\u0000<mml:math overflow=\"scroll\"><mml:mrow><mml:mi mathvariant=\"normal\">C</mml:mi><mml:msub><mml:mi mathvariant=\"normal\">O</mml:mi><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>\u0000<inline-graphic xlink:href=\"psstad28cfieqn5.gif\" xlink:type=\"simple\"></inline-graphic>\u0000</inline-formula>. Conversely, photoionization has no effect on negative streamer fronts, but plays a major role in the coupling between negative streamers and the cathode. Photoionization in <inline-formula>\u0000<tex-math><?CDATA $mathrm{CO_{2}}$?></tex-math>\u0000<mml:math overflow=\"scroll\"><mml:mrow><mml:mi mathvariant=\"normal\">C</mml:mi><mml:msub><mml:mi mathvariant=\"normal\">O</mml:mi><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>\u0000<i","PeriodicalId":20192,"journal":{"name":"Plasma Sources Science and Technology","volume":"17 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-02-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140002140","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-02-16DOI: 10.1088/1361-6595/ad2491
Wei Yang
Over the past decade, extensive modeling practices on low-temperature plasmas have revealed that input data such as microscopic scattering cross-sections are crucial to output macroscopic phenomena. In Monte Carlo collision (MCC) modeling of natural and laboratory plasma, the angular scattering model is a non-trivial topic. Conforming to the pedagogical purpose of this overview, the classical and quantum theories of binary scattering, such as the commonly used Born–Bethe approximation, are first introduced. Adequate angular scattering models, which MCC simulation can handle as input, are derived based on the above theories for electron–neutral, ion–neutral, neutral–neutral, and Coulomb collisions. This tutorial does not aim to provide accurate cross-sectional data by modern approaches in quantum theory, but rather to introduce analytical angular scattering models from classical, semi-empirical, and first-order perturbation theory. The reviewed models are expected to be readily incorporated into the MCC codes, in which the scattering angle is randomly sampled through analytical inversion instead of the numerical accept–reject method. These simplified approaches are very attractive, and demonstrate in many cases the ability to achieve a striking agreement with experiments. Energy partition models on electron–neutral ionization are also discussed with insight from the binary-encounter Bethe theory. This overview is written in a tutorial style in order to serve as a guide for novices in this field, and at the same time as a comprehensive reference for practitioners of MCC modeling on plasma.
{"title":"A tutorial overview of the angular scattering models of electron–neutral, ion–neutral, neutral–neutral, and Coulomb collisions in Monte Carlo collision modeling on low-temperature plasma","authors":"Wei Yang","doi":"10.1088/1361-6595/ad2491","DOIUrl":"https://doi.org/10.1088/1361-6595/ad2491","url":null,"abstract":"Over the past decade, extensive modeling practices on low-temperature plasmas have revealed that input data such as microscopic scattering cross-sections are crucial to output macroscopic phenomena. In Monte Carlo collision (MCC) modeling of natural and laboratory plasma, the angular scattering model is a non-trivial topic. Conforming to the pedagogical purpose of this overview, the classical and quantum theories of binary scattering, such as the commonly used Born–Bethe approximation, are first introduced. Adequate angular scattering models, which MCC simulation can handle as input, are derived based on the above theories for electron–neutral, ion–neutral, neutral–neutral, and Coulomb collisions. This tutorial does not aim to provide accurate cross-sectional data by modern approaches in quantum theory, but rather to introduce analytical angular scattering models from classical, semi-empirical, and first-order perturbation theory. The reviewed models are expected to be readily incorporated into the MCC codes, in which the scattering angle is randomly sampled through analytical inversion instead of the numerical accept–reject method. These simplified approaches are very attractive, and demonstrate in many cases the ability to achieve a striking agreement with experiments. Energy partition models on electron–neutral ionization are also discussed with insight from the binary-encounter Bethe theory. This overview is written in a tutorial style in order to serve as a guide for novices in this field, and at the same time as a comprehensive reference for practitioners of MCC modeling on plasma.","PeriodicalId":20192,"journal":{"name":"Plasma Sources Science and Technology","volume":"8 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-02-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140008568","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-02-16DOI: 10.1088/1361-6595/ad23fa
M Sackers, O Marchuk, D Dipti, Yu Ralchenko, S Ertmer, S Brezinsek, A Kreter
Laser absorption spectroscopy provides high-resolution spectra of atomic transitions that reveal many often inaccessible features. The line shapes of krypton and xenon measured in magnetized plasmas are strongly affected by the contribution of the odd-numbered isotopes 83Kr, 129Xe and 131Xe due to their hyperfine structure, creating more challenging spectra in comparison to even-numbered ones. The lines originating from metastable levels of krypton and xenon with J = 2 (Kr I 760.4 nm) and J = 0 (Kr I 785.7 nm, Xe I 764.4 nm) were measured and analyzed in the linear plasma device PSI-2 in the field range of 22.5 mT–90 mT. Evaluating the Hamiltonian, including hyperfine and Zeeman interaction terms for these magnetic field strengths, unveils a deviation from the linear energy shift of the sublevels as a function of the magnetic field and from constant relative intensities that the weak field formulas provide. We prove that modeling the transitions in Xe using the weak field approximation, frequently used in magnetized plasma, becomes inadequate at ≈50 mT. In particular, the spectra of the 131Xe isotope show pronounced deviations from the weak field results. For krypton, however, the situation is less critical compared to xenon due to the low natural abundance of the odd-numbered isotope.
激光吸收光谱提供了原子跃迁的高分辨率光谱，揭示了许多通常无法获得的特征。由于奇数同位素 83Kr、129Xe 和 131Xe 的超精细结构，在磁化等离子体中测量到的氪和氙的光谱线形状会受到它们的强烈影响，从而产生比偶数同位素更具挑战性的光谱。在 22.5 mT-90 mT 的磁场范围内，在线性等离子体装置 PSI-2 中测量和分析了源自氪和氙的 J = 2（Kr I 760.4 nm）和 J = 0（Kr I 785.7 nm，Xe I 764.4 nm）的瞬变水平线。对包括这些磁场强度下超频和泽曼相互作用项在内的哈密顿方程进行评估后发现，子级的线性能量移动与磁场的函数以及弱磁场公式提供的恒定相对强度存在偏差。我们证明，使用磁化等离子体中常用的弱磁场近似方法来模拟氙的跃迁，在 ≈50 mT 时变得不够充分。特别是，131Xe 同位素的光谱显示出与弱场结果的明显偏差。不过，对于氪来说，由于奇数同位素的天然丰度较低，情况没有氙那么严重。
{"title":"Zeeman effect of isotopes of Kr and Xe investigated at the linear plasma device PSI-2","authors":"M Sackers, O Marchuk, D Dipti, Yu Ralchenko, S Ertmer, S Brezinsek, A Kreter","doi":"10.1088/1361-6595/ad23fa","DOIUrl":"https://doi.org/10.1088/1361-6595/ad23fa","url":null,"abstract":"Laser absorption spectroscopy provides high-resolution spectra of atomic transitions that reveal many often inaccessible features. The line shapes of krypton and xenon measured in magnetized plasmas are strongly affected by the contribution of the odd-numbered isotopes <sup>83</sup>Kr, <sup>129</sup>Xe and <sup>131</sup>Xe due to their hyperfine structure, creating more challenging spectra in comparison to even-numbered ones. The lines originating from metastable levels of krypton and xenon with <italic toggle=\"yes\">J</italic> = 2 (Kr I 760.4 nm) and <italic toggle=\"yes\">J</italic> = 0 (Kr I 785.7 nm, Xe I 764.4 nm) were measured and analyzed in the linear plasma device PSI-2 in the field range of 22.5 mT–90 mT. Evaluating the Hamiltonian, including hyperfine and Zeeman interaction terms for these magnetic field strengths, unveils a deviation from the linear energy shift of the sublevels as a function of the magnetic field and from constant relative intensities that the weak field formulas provide. We prove that modeling the transitions in Xe using the weak field approximation, frequently used in magnetized plasma, becomes inadequate at ≈50 mT. In particular, the spectra of the <sup>131</sup>Xe isotope show pronounced deviations from the weak field results. For krypton, however, the situation is less critical compared to xenon due to the low natural abundance of the odd-numbered isotope.","PeriodicalId":20192,"journal":{"name":"Plasma Sources Science and Technology","volume":"5 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-02-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140002092","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
We study how external magnetic fields from 0 to 40 T influence positive streamers in atmospheric pressure air, using 3D PIC-MCC (particle-in-cell, Monte Carlo collision) simulations. When a magnetic field B is applied perpendicular to the background electric field E, the streamers deflect towards the +B and −B directions which results in a branching into two main channels. With a stronger magnetic field the angle between the branches increases, and for the 40 T case the branches grow almost parallel to the magnetic field. Due to the E×B drift of electrons we also observe a streamer deviation in the opposite −E×B direction, where the minus sign appears because positive streamers propagate opposite to the electron drift velocity. The deviation due to this E×B effect is smaller than the deviation parallel to B. In both cases of B perpendicular and parallel to E, the streamer radius decreases with the magnetic field strength. We relate our observations to the effects of electric and magnetic fields on electron transport and reaction coefficients.
我们利用三维 PIC-MCC（粒子在细胞中的蒙特卡罗碰撞）模拟，研究了 0 到 40 T 的外部磁场如何影响大气压空气中的正流线。当磁场 B 垂直于背景电场 E 时，流线会向 +B 和 -B 方向偏转，从而分成两条主通道。随着磁场强度的增大，分支之间的角度也会增大，在 40 T 的情况下，分支几乎与磁场平行。由于电子的 E×B 漂移，我们还观察到流线在相反的 -E×B 方向上的偏离，出现负号是因为正流线的传播速度与电子漂移速度相反。在垂直于 B 和平行于 E 的两种情况下，流线半径都会随着磁场强度的增加而减小。我们将观察结果与电场和磁场对电子传输和反应系数的影响联系起来。
{"title":"3D simulations of positive streamers in air in a strong external magnetic field","authors":"Zhen Wang, Anbang Sun, Saša Dujko, Ute Ebert, Jannis Teunissen","doi":"10.1088/1361-6595/ad227f","DOIUrl":"https://doi.org/10.1088/1361-6595/ad227f","url":null,"abstract":"We study how external magnetic fields from 0 to 40 T influence positive streamers in atmospheric pressure air, using 3D PIC-MCC (particle-in-cell, Monte Carlo collision) simulations. When a magnetic field <bold>\u0000<italic toggle=\"yes\">B</italic>\u0000</bold> is applied perpendicular to the background electric field <bold>\u0000<italic toggle=\"yes\">E</italic>\u0000</bold>, the streamers deflect towards the <inline-formula>\u0000<tex-math><?CDATA $+boldsymbol{B}$?></tex-math>\u0000<mml:math overflow=\"scroll\"><mml:mo>+</mml:mo><mml:mi mathvariant=\"bold-italic\">B</mml:mi></mml:math>\u0000<inline-graphic xlink:href=\"psstad227fieqn1.gif\" xlink:type=\"simple\"></inline-graphic>\u0000</inline-formula> and <inline-formula>\u0000<tex-math><?CDATA $-boldsymbol{B}$?></tex-math>\u0000<mml:math overflow=\"scroll\"><mml:mo>−</mml:mo><mml:mi mathvariant=\"bold-italic\">B</mml:mi></mml:math>\u0000<inline-graphic xlink:href=\"psstad227fieqn2.gif\" xlink:type=\"simple\"></inline-graphic>\u0000</inline-formula> directions which results in a branching into two main channels. With a stronger magnetic field the angle between the branches increases, and for the 40 T case the branches grow almost parallel to the magnetic field. Due to the <inline-formula>\u0000<tex-math><?CDATA $boldsymbol{E}timesboldsymbol{B}$?></tex-math>\u0000<mml:math overflow=\"scroll\"><mml:mi mathvariant=\"bold-italic\">E</mml:mi><mml:mo>×</mml:mo><mml:mi mathvariant=\"bold-italic\">B</mml:mi></mml:math>\u0000<inline-graphic xlink:href=\"psstad227fieqn3.gif\" xlink:type=\"simple\"></inline-graphic>\u0000</inline-formula> drift of electrons we also observe a streamer deviation in the opposite <inline-formula>\u0000<tex-math><?CDATA $-boldsymbol{E}timesboldsymbol{B}$?></tex-math>\u0000<mml:math overflow=\"scroll\"><mml:mo>−</mml:mo><mml:mi mathvariant=\"bold-italic\">E</mml:mi><mml:mo>×</mml:mo><mml:mi mathvariant=\"bold-italic\">B</mml:mi></mml:math>\u0000<inline-graphic xlink:href=\"psstad227fieqn4.gif\" xlink:type=\"simple\"></inline-graphic>\u0000</inline-formula> direction, where the minus sign appears because positive streamers propagate opposite to the electron drift velocity. The deviation due to this <inline-formula>\u0000<tex-math><?CDATA $boldsymbol{E}timesboldsymbol{B}$?></tex-math>\u0000<mml:math overflow=\"scroll\"><mml:mi mathvariant=\"bold-italic\">E</mml:mi><mml:mo>×</mml:mo><mml:mi mathvariant=\"bold-italic\">B</mml:mi></mml:math>\u0000<inline-graphic xlink:href=\"psstad227fieqn5.gif\" xlink:type=\"simple\"></inline-graphic>\u0000</inline-formula> effect is smaller than the deviation parallel to <bold>\u0000<italic toggle=\"yes\">B</italic>\u0000</bold>. In both cases of <bold>\u0000<italic toggle=\"yes\">B</italic>\u0000</bold> perpendicular and parallel to <bold>\u0000<italic toggle=\"yes\">E</italic>\u0000</bold>, the streamer radius decreases with the magnetic field strength. We relate our observations to the effects of electric and magnetic fields on electron transport and reaction coefficients.","PeriodicalId":20192,"journal":{"name":"Plasma Sources Science and Technology","volume":"26 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-02-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139762031","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-02-05DOI: 10.1088/1361-6595/ad1fd5
A Derzsi, M Vass, R Masheyeva, B Horváth, Z Donkó, P Hartmann
Phase Resolved Optical Emission Spectroscopy (PROES) measurements combined with 1d3v Particle-in-Cell/Monte Carlo Collisions simulations are performed to investigate the excitation dynamics in low-pressure capacitively coupled plasmas (CCPs) in argon-oxygen mixtures. The system used for this study is a geometrically symmetric CCP reactor operated in a 70% Ar-30% O2 mixture at 120 Pa, applying a peak-to-peak voltage of 350 V, with a wide range of driving RF frequencies (2 MHz ⩽f⩽ 15 MHz). The measured and calculated spatio-temporal distributions of the electron impact excitation rates from the Ar ground state to the Ar 2p1 level show good qualitative agreement. The distributions show significant frequency dependence, which is generally considered to be predictive of transitions in the dominant discharge operating mode. Three frequency ranges can be distinguished, showing distinctly different excitation characteristics: (i) in the low frequency range (f⩽ 3 MHz), excitation is strong at the sheaths and weak in the bulk region; (ii) at intermediate frequencies (3.5 MHz ⩽f⩽ 5 MHz), the excitation rate in the bulk region is enhanced and shows striation formation; (iii) above 6 MHz, excitation in the bulk gradually decreases with increasing frequency. Boltzmann term analysis was performed to quantify the frequency-dependent contributions of the Ohmic and ambipolar terms to the electron power absorption.
{"title":"Frequency-dependent electron power absorption mode transitions in capacitively coupled argon-oxygen plasmas","authors":"A Derzsi, M Vass, R Masheyeva, B Horváth, Z Donkó, P Hartmann","doi":"10.1088/1361-6595/ad1fd5","DOIUrl":"https://doi.org/10.1088/1361-6595/ad1fd5","url":null,"abstract":"Phase Resolved Optical Emission Spectroscopy (PROES) measurements combined with 1d3v Particle-in-Cell/Monte Carlo Collisions simulations are performed to investigate the excitation dynamics in low-pressure capacitively coupled plasmas (CCPs) in argon-oxygen mixtures. The system used for this study is a geometrically symmetric CCP reactor operated in a 70% Ar-30% O<sub>2</sub> mixture at 120 Pa, applying a peak-to-peak voltage of 350 V, with a wide range of driving RF frequencies (2 MHz <inline-formula>\u0000<tex-math><?CDATA $unicode{x2A7D} f unicode{x2A7D}$?></tex-math>\u0000<mml:math overflow=\"scroll\"><mml:mtext>⩽</mml:mtext><mml:mi>f</mml:mi><mml:mtext>⩽</mml:mtext></mml:math>\u0000<inline-graphic xlink:href=\"psstad1fd5ieqn1.gif\" xlink:type=\"simple\"></inline-graphic>\u0000</inline-formula> 15 MHz). The measured and calculated spatio-temporal distributions of the electron impact excitation rates from the Ar ground state to the Ar <inline-formula>\u0000<tex-math><?CDATA $mathrm{2p_1}$?></tex-math>\u0000<mml:math overflow=\"scroll\"><mml:mrow><mml:mn>2</mml:mn><mml:msub><mml:mi mathvariant=\"normal\">p</mml:mi><mml:mn>1</mml:mn></mml:msub></mml:mrow></mml:math>\u0000<inline-graphic xlink:href=\"psstad1fd5ieqn2.gif\" xlink:type=\"simple\"></inline-graphic>\u0000</inline-formula> level show good qualitative agreement. The distributions show significant frequency dependence, which is generally considered to be predictive of transitions in the dominant discharge operating mode. Three frequency ranges can be distinguished, showing distinctly different excitation characteristics: (i) in the low frequency range (<inline-formula>\u0000<tex-math><?CDATA $f unicode{x2A7D}$?></tex-math>\u0000<mml:math overflow=\"scroll\"><mml:mi>f</mml:mi><mml:mtext>⩽</mml:mtext></mml:math>\u0000<inline-graphic xlink:href=\"psstad1fd5ieqn3.gif\" xlink:type=\"simple\"></inline-graphic>\u0000</inline-formula> 3 MHz), excitation is strong at the sheaths and weak in the bulk region; (ii) at intermediate frequencies (3.5 MHz <inline-formula>\u0000<tex-math><?CDATA $unicode{x2A7D} f unicode{x2A7D}$?></tex-math>\u0000<mml:math overflow=\"scroll\"><mml:mtext>⩽</mml:mtext><mml:mi>f</mml:mi><mml:mtext>⩽</mml:mtext></mml:math>\u0000<inline-graphic xlink:href=\"psstad1fd5ieqn4.gif\" xlink:type=\"simple\"></inline-graphic>\u0000</inline-formula> 5 MHz), the excitation rate in the bulk region is enhanced and shows striation formation; (iii) above 6 MHz, excitation in the bulk gradually decreases with increasing frequency. Boltzmann term analysis was performed to quantify the frequency-dependent contributions of the Ohmic and ambipolar terms to the electron power absorption.","PeriodicalId":20192,"journal":{"name":"Plasma Sources Science and Technology","volume":"26 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-02-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139762038","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-01-25DOI: 10.1088/1361-6595/ad227b
A. Remigy, Belkacem Menacer, Konstantinos Kourtzanidis, Odyssea Gazeli, K. Gazeli, G. Lombardi, C. Lazzaroni
In this work, nanosecond Two-photon Absorption Laser Induced Fluorescence is used to perform spatial mappings of the absolute density of nitrogen atoms generated in a micro-hollow cathode discharge (MHCD). The MHCD is operated in the normal regime, with a DC discharge current of 1.6 mA and a plasma is ignited in a 20% Ar/ 80% N2 gas mixture. A 1-inch diameter aluminum substrate acting as a third electrode (second anode) is placed further away from the MHCD to emulate a deposition substrate. The spatial profile of the N atoms is measured in three MHCD configurations. First, we study a MHCD having the same pressure (50 mbar) on both sides of the anode/cathode electrodes and the N atoms diffuse in three dimensions from the MHCD. The recorded N atoms density profile in this case satisfies our expectations, i.e., the maximal density is found at the axis of the hole, close to the MHCD. However, when we introduce a pressure differential, thus creating a plasma jet, an unexpected N atoms distribution is measured with maximum densities away from the jet axis. This behavior cannot be simply explained by the TALIF measurements. Then, as a first simplified approach in this work, we turn our attention to the role of the gas flow pattern. Compressible gas flow simulations show a correlation between the jet width and the radial distribution of the N atoms at different axial distances from the gap. Finally, a DC positive voltage is applied to the third electrode (second anode), which ignites a Micro Cathode Sustained Discharge (MCSD). The presence of the pressure differential unveils two stable working regimes depending on the current repartition between the two anodes. The MCSD enables an homogenization of the density profile along the surface of the substrate, which is suitable for nitride deposition applications.
在这项工作中，我们利用纳秒双光子吸收激光诱导荧光对微型空心阴极放电（MHCD）中产生的氮原子绝对密度进行空间映射。微空心阴极放电在正常状态下运行，直流放电电流为 1.6 mA，在 20% Ar/80% N2 混合气体中点燃等离子体。直径为 1 英寸的铝基板作为第三电极（第二阳极）放置在离 MHCD 较远的地方，以模拟沉积基板。我们在三种 MHCD 配置中测量了 N 原子的空间分布。首先，我们研究了阳极/阴极电极两侧具有相同压力（50 毫巴）的 MHCD，N 原子从 MHCD 向三维扩散。在这种情况下记录到的 N 原子密度曲线符合我们的预期，即最大密度出现在靠近 MHCD 的孔轴线处。然而，当我们引入压差，从而产生等离子体射流时，测得的 N 原子密度分布却出乎意料地远离射流轴线。TALIF 测量无法简单地解释这种现象。然后，作为这项工作的第一种简化方法，我们将注意力转向气体流动模式的作用。可压缩气体流动模拟显示，在距离间隙不同的轴向距离上，射流宽度与 N 原子的径向分布之间存在相关性。最后，在第三个电极（第二个阳极）上施加直流正电压，点燃微阴极持续放电（MCSD）。压差的存在揭示了两种稳定的工作状态，这取决于两个阳极之间的电流分配。微阴极持续放电（MCSD）可使基底表面的密度分布均匀化，适用于氮化物沉积应用。
{"title":"Absolute atomic nitrogen density spatial mapping in three MHCD configurations","authors":"A. Remigy, Belkacem Menacer, Konstantinos Kourtzanidis, Odyssea Gazeli, K. Gazeli, G. Lombardi, C. Lazzaroni","doi":"10.1088/1361-6595/ad227b","DOIUrl":"https://doi.org/10.1088/1361-6595/ad227b","url":null,"abstract":"\u0000 In this work, nanosecond Two-photon Absorption Laser Induced Fluorescence is used to perform spatial mappings of the absolute density of nitrogen atoms generated in a micro-hollow cathode discharge (MHCD). The MHCD is operated in the normal regime, with a DC discharge current of 1.6 mA and a plasma is ignited in a 20% Ar/ 80% N2 gas mixture. A 1-inch diameter aluminum substrate acting as a third electrode (second anode) is placed further away from the MHCD to emulate a deposition substrate. The spatial profile of the N atoms is measured in three MHCD configurations. First, we study a MHCD having the same pressure (50 mbar) on both sides of the anode/cathode electrodes and the N atoms diffuse in three dimensions from the MHCD. The recorded N atoms density profile in this case satisfies our expectations, i.e., the maximal density is found at the axis of the hole, close to the MHCD. However, when we introduce a pressure differential, thus creating a plasma jet, an unexpected N atoms distribution is measured with maximum densities away from the jet axis. This behavior cannot be simply explained by the TALIF measurements. Then, as a first simplified approach in this work, we turn our attention to the role of the gas flow pattern. Compressible gas flow simulations show a correlation between the jet width and the radial distribution of the N atoms at different axial distances from the gap. Finally, a DC positive voltage is applied to the third electrode (second anode), which ignites a Micro Cathode Sustained Discharge (MCSD). The presence of the pressure differential unveils two stable working regimes depending on the current repartition between the two anodes. The MCSD enables an homogenization of the density profile along the surface of the substrate, which is suitable for nitride deposition applications.","PeriodicalId":20192,"journal":{"name":"Plasma Sources Science and Technology","volume":"121 6","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-01-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139596480","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-01-25DOI: 10.1088/1361-6595/ad227c
A. Marín-Cebrián, E. Bello-Benítez, A. Domínguez-Vázquez, E. Ahedo
A 2D axial-radial particle-in-cell (PIC) model of a Hall thruster discharge has been developed to analyze (mainly) the fluid equations satisfied by the azimuthally-averaged slow dynamics of electrons. Their weak collisionality together with a strong interaction with the thruster walls lead to a non-Maxwellian velocity distribution function (VDF). Consequently, the resulting macroscopic response differs from a conventional collisional fluid. First, the gyrotropic (diagonal) part of the pressure tensor is anisotropic. Second, its gyroviscous part, although small, is relevant in the azimuthal momentum balance, where the dominant contributions are orders of magnitude lower than in the axial momentum balance. Third, the heat flux vector does not satisfy simple laws, although convective and conductive behaviors can be identified for the parallel and perpendicular components, respectively. And fourth, the electron wall interaction parameters can differ largely from the classical sheath theory, based on near Maxwellian VDF. Furthermore, these effects behave differently in the near-anode and near-exit regions of the channel. Still, the profiles of basic plasma magnitudes agree well with those of 1D axial fluid models. To facilitate the interpretation of the plasma response, a quasiplanar geometry, a purely-radial magnetic field, and a simple empirical model of cross-field transport were used; but realistic configurations and a more elaborated anomalous diffusion formulation can be incorporated. Computational time was controlled by using an augmented vacuum permittivity and a stationary depletion law for neutrals.
{"title":"Non-Maxwellian electron effects on the macroscopic response of a Hall thruster discharge from an axial-radial kinetic model","authors":"A. Marín-Cebrián, E. Bello-Benítez, A. Domínguez-Vázquez, E. Ahedo","doi":"10.1088/1361-6595/ad227c","DOIUrl":"https://doi.org/10.1088/1361-6595/ad227c","url":null,"abstract":"\u0000 A 2D axial-radial particle-in-cell (PIC) model of a Hall thruster discharge has been developed to analyze (mainly) the fluid equations satisfied by the azimuthally-averaged slow dynamics of electrons. Their weak collisionality together with a strong interaction with the thruster walls lead to a non-Maxwellian velocity distribution function (VDF). Consequently, the resulting macroscopic response differs from a conventional collisional fluid. First, the gyrotropic (diagonal) part of the pressure tensor is anisotropic. Second, its gyroviscous part, although small, is relevant in the azimuthal momentum balance, where the dominant contributions are orders of magnitude lower than in the axial momentum balance. Third, the heat flux vector does not satisfy simple laws, although convective and conductive behaviors can be identified for the parallel and perpendicular components, respectively. And fourth, the electron wall interaction parameters can differ largely from the classical sheath theory, based on near Maxwellian VDF. Furthermore, these effects behave differently in the near-anode and near-exit regions of the channel. Still, the profiles of basic plasma magnitudes agree well with those of 1D axial fluid models. To facilitate the interpretation of the plasma response, a quasiplanar geometry, a purely-radial magnetic field, and a simple empirical model of cross-field transport were used; but realistic configurations and a more elaborated anomalous diffusion formulation can be incorporated. Computational time was controlled by using an augmented vacuum permittivity and a stationary depletion law for neutrals.","PeriodicalId":20192,"journal":{"name":"Plasma Sources Science and Technology","volume":"58 36","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-01-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139598484","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-01-25DOI: 10.1088/1361-6595/ad227d
C. Pavan, Santosh J. Shanbhogue, D. Weibel, Felipe Gomez del Campo, Ahmed Ghoniem, C. Guerra-Garcia
When using nanosecond repetitively pulsed discharges to actuate on dynamic combustion instabilities, the environment the discharge is created in is unsteady and changing on the timescale of the combustion processes. As a result, individual discharge pulses are triggered in a background gas that evolves at the timescale of combustion dynamics, and pulse-to-pulse variations may be observed during the instability cycle. Prior work has studied nanosecond pulsed discharges in pin-to-ring configurations used to control instabilities in lean-operating swirl-stabilized combustors, and observed variable discharge behaviour. The focus of this work is on characterizing how the pulse-to-pulse discharge morphology, energy deposition, and actuation authority, evolve during the combustion instability cycle. This has important implications for designing effective plasma-assisted combustion control schemes. The discharge is observed in two distinct modes, a streamer corona and a nanosecond spark, with the occurrence of each regime directly linked to the phase of the combustor instability. Variation of pulse repetition frequency affects the total fraction of pulses in each mode, while variation of voltage affects the onset of the nanosecond spark mode. The transitions are described in terms of ratios of the relevant combustion and plasma timescales and the implications of this coupled interaction on the design of an effective control scheme is discussed.
{"title":"Dynamic Response of Nanosecond Repetitively Pulsed Discharges to Combustion Dynamics: Regime Transitions Driven by Flame Oscillations","authors":"C. Pavan, Santosh J. Shanbhogue, D. Weibel, Felipe Gomez del Campo, Ahmed Ghoniem, C. Guerra-Garcia","doi":"10.1088/1361-6595/ad227d","DOIUrl":"https://doi.org/10.1088/1361-6595/ad227d","url":null,"abstract":"\u0000 When using nanosecond repetitively pulsed discharges to actuate on dynamic combustion instabilities, the environment the discharge is created in is unsteady and changing on the timescale of the combustion processes. As a result, individual discharge pulses are triggered in a background gas that evolves at the timescale of combustion dynamics, and pulse-to-pulse variations may be observed during the instability cycle. Prior work has studied nanosecond pulsed discharges in pin-to-ring configurations used to control instabilities in lean-operating swirl-stabilized combustors, and observed variable discharge behaviour. The focus of this work is on characterizing how the pulse-to-pulse discharge morphology, energy deposition, and actuation authority, evolve during the combustion instability cycle. This has important implications for designing effective plasma-assisted combustion control schemes. The discharge is observed in two distinct modes, a streamer corona and a nanosecond spark, with the occurrence of each regime directly linked to the phase of the combustor instability. Variation of pulse repetition frequency affects the total fraction of pulses in each mode, while variation of voltage affects the onset of the nanosecond spark mode. The transitions are described in terms of ratios of the relevant combustion and plasma timescales and the implications of this coupled interaction on the design of an effective control scheme is discussed.","PeriodicalId":20192,"journal":{"name":"Plasma Sources Science and Technology","volume":"8 8","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-01-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139595851","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-01-25DOI: 10.1088/1361-6595/ad227e
Kimika Fushimi, Naoki Shirai, Koichi Sasaki
Atmospheric-pressure discharges generated in air are expected to be electronegative, but experiments that examine negative ion densities are limited to date. In this work, we measured the temporal variation of the negative ion density in a streamer discharge generated in air. We adopted cavity ringdown spectroscopy, where negative ions were detected via weak optical absorption caused by laser photodetachment. The temporal variation of the absolute negative ion density was deduced by the transient analysis of the ringdown curve. Negative ions were detected after the disappearance of the discharge voltage and current. The negative ion density started the increase at 0.4 μs after the initiation of the discharge. The increase means the enhancement of the electron attachment frequency in the late phase of the secondary streamer with electron cooling. The survival of electrons until 0.4 μs is understood by the steep decrease in the cross section of dissociative recombination with the electron energy. The maximum negative ion density was observed at 1 μs, and it was around the noise level at 1.5 μs. The rapid decay is consistent with the destruction of negative ions by mutual neutralization with positive ions.
{"title":"Detection of negative ions in streamer discharge in air by transient cavity ringdown spectroscopy","authors":"Kimika Fushimi, Naoki Shirai, Koichi Sasaki","doi":"10.1088/1361-6595/ad227e","DOIUrl":"https://doi.org/10.1088/1361-6595/ad227e","url":null,"abstract":"\u0000 Atmospheric-pressure discharges generated in air are expected to be electronegative, but experiments that examine negative ion densities are limited to date. In this work, we measured the temporal variation of the negative ion density in a streamer discharge generated in air. We adopted cavity ringdown spectroscopy, where negative ions were detected via weak optical absorption caused by laser photodetachment. The temporal variation of the absolute negative ion density was deduced by the transient analysis of the ringdown curve. Negative ions were detected after the disappearance of the discharge voltage and current. The negative ion density started the increase at 0.4 μs after the initiation of the discharge. The increase means the enhancement of the electron attachment frequency in the late phase of the secondary streamer with electron cooling. The survival of electrons until 0.4 μs is understood by the steep decrease in the cross section of dissociative recombination with the electron energy. The maximum negative ion density was observed at 1 μs, and it was around the noise level at 1.5 μs. The rapid decay is consistent with the destruction of negative ions by mutual neutralization with positive ions.","PeriodicalId":20192,"journal":{"name":"Plasma Sources Science and Technology","volume":"99 7","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-01-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139596772","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-01-22DOI: 10.1088/1361-6595/ad2116
Malong Fu, Haitao Wang, Z. Hou
The conventional two-beam interferometry adopts only one expression about plasma density and thickness because only fringe shift is recognized from the recorded fringes. Therefore, the prior hypotheses that the plasma is thickness-uniform or circular symmetry have to be introduced to separate them, which limits the applied range and accuracy of the conventional method. This paper found that the laser beam will be deflected if the thickness changes, leading the recorded fringes to be defocused. As a result, a new expression relying on recognizing the defocus parameter of the recorded fringes is derived, and a pointwise separation algorithm to separate density and thickness is proposed based on the two expressions. Compared to the conventional algorithms, the new algorithm requires no hypotheses and thus has a wider applied range.
{"title":"A pointwise separation algorithm to separate plasma density and thickness in two-beam interferometry","authors":"Malong Fu, Haitao Wang, Z. Hou","doi":"10.1088/1361-6595/ad2116","DOIUrl":"https://doi.org/10.1088/1361-6595/ad2116","url":null,"abstract":"\u0000 The conventional two-beam interferometry adopts only one expression about plasma density and thickness because only fringe shift is recognized from the recorded fringes. Therefore, the prior hypotheses that the plasma is thickness-uniform or circular symmetry have to be introduced to separate them, which limits the applied range and accuracy of the conventional method. This paper found that the laser beam will be deflected if the thickness changes, leading the recorded fringes to be defocused. As a result, a new expression relying on recognizing the defocus parameter of the recorded fringes is derived, and a pointwise separation algorithm to separate density and thickness is proposed based on the two expressions. Compared to the conventional algorithms, the new algorithm requires no hypotheses and thus has a wider applied range.","PeriodicalId":20192,"journal":{"name":"Plasma Sources Science and Technology","volume":"31 2","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-01-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139609092","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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