Pub Date : 2024-02-09DOI: 10.1088/1361-6595/ad27eb
Ruilin Cui, Tianliang Zhang, Feng He, Bocong Zheng, J. Ouyang
In this paper, multiple wave modes and transitions of argon helicon plasma excited by a half right-helical in a system without any reflection endplate are investigated experimentally and theoretically at increasing radio frequency (RF) powers and external magnetic fields. Experiments show that above a critical magnetic field strength and pressure (about 250 G and 0.3 Pa in this work), two to four distinct wave coupled modes and transitions were observed at increasing RF powers and/or magnetic fields. Theoretical analysis based on dispersion relationship show that in high magnetic field helicon wave of the lowest order of axial eigenmode is always excited firstly, then the higher order axial or radial mode, hence the plasma density increases after mode jumping. There are two mechanisms responsible for the wave mode transitions in the present system, i.e., axial and radial mode transitions owning to the change of axial and radial wavenumbers from a lower eigenmode to a higher one. Higher plasma density and magnetic field are helpful for achieving more higher-order modes of helicon waves.
本文通过实验和理论研究了氩氦等离子体在一个没有任何反射端板的系统中被半直角螺旋激发时，在射频（RF）功率和外磁场不断增加的情况下的多种波模式和转换。实验表明，在临界磁场强度和压力（本研究中约为 250 G 和 0.3 Pa）之上，随着射频功率和/或磁场的增加，可观察到两到四种不同的波耦合模式和转换。基于频散关系的理论分析表明，在高磁场中，最低阶轴向特征模式的螺旋波总是首先被激发，然后是高阶轴向或径向模式，因此模式跃迁后等离子体密度会增加。本系统中的波模转换有两种机制，即轴向和径向模式转换，导致轴向和径向波文数从较低的特征模式变为较高的特征模式。较高的等离子体密度和磁场有助于获得更多的高阶螺旋波模式。
{"title":"On the wave mode transition of argon helicon plasma","authors":"Ruilin Cui, Tianliang Zhang, Feng He, Bocong Zheng, J. Ouyang","doi":"10.1088/1361-6595/ad27eb","DOIUrl":"https://doi.org/10.1088/1361-6595/ad27eb","url":null,"abstract":"\u0000 In this paper, multiple wave modes and transitions of argon helicon plasma excited by a half right-helical in a system without any reflection endplate are investigated experimentally and theoretically at increasing radio frequency (RF) powers and external magnetic fields. Experiments show that above a critical magnetic field strength and pressure (about 250 G and 0.3 Pa in this work), two to four distinct wave coupled modes and transitions were observed at increasing RF powers and/or magnetic fields. Theoretical analysis based on dispersion relationship show that in high magnetic field helicon wave of the lowest order of axial eigenmode is always excited firstly, then the higher order axial or radial mode, hence the plasma density increases after mode jumping. There are two mechanisms responsible for the wave mode transitions in the present system, i.e., axial and radial mode transitions owning to the change of axial and radial wavenumbers from a lower eigenmode to a higher one. Higher plasma density and magnetic field are helpful for achieving more higher-order modes of helicon waves.","PeriodicalId":508056,"journal":{"name":"Plasma Sources Science and Technology","volume":" 13","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-02-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139788414","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 : 2024-02-09DOI: 10.1088/1361-6595/ad27eb
Ruilin Cui, Tianliang Zhang, Feng He, Bocong Zheng, J. Ouyang
In this paper, multiple wave modes and transitions of argon helicon plasma excited by a half right-helical in a system without any reflection endplate are investigated experimentally and theoretically at increasing radio frequency (RF) powers and external magnetic fields. Experiments show that above a critical magnetic field strength and pressure (about 250 G and 0.3 Pa in this work), two to four distinct wave coupled modes and transitions were observed at increasing RF powers and/or magnetic fields. Theoretical analysis based on dispersion relationship show that in high magnetic field helicon wave of the lowest order of axial eigenmode is always excited firstly, then the higher order axial or radial mode, hence the plasma density increases after mode jumping. There are two mechanisms responsible for the wave mode transitions in the present system, i.e., axial and radial mode transitions owning to the change of axial and radial wavenumbers from a lower eigenmode to a higher one. Higher plasma density and magnetic field are helpful for achieving more higher-order modes of helicon waves.
本文通过实验和理论研究了氩氦等离子体在一个没有任何反射端板的系统中被半直角螺旋激发时，在射频（RF）功率和外磁场不断增加的情况下的多种波模式和转换。实验表明，在临界磁场强度和压力（本研究中约为 250 G 和 0.3 Pa）之上，随着射频功率和/或磁场的增加，可观察到两到四种不同的波耦合模式和转换。基于频散关系的理论分析表明，在高磁场中，最低阶轴向特征模式的螺旋波总是首先被激发，然后是高阶轴向或径向模式，因此模式跃迁后等离子体密度会增加。本系统中的波模转换有两种机制，即轴向和径向模式转换，导致轴向和径向波文数从较低的特征模式变为较高的特征模式。较高的等离子体密度和磁场有助于获得更多的高阶螺旋波模式。
{"title":"On the wave mode transition of argon helicon plasma","authors":"Ruilin Cui, Tianliang Zhang, Feng He, Bocong Zheng, J. Ouyang","doi":"10.1088/1361-6595/ad27eb","DOIUrl":"https://doi.org/10.1088/1361-6595/ad27eb","url":null,"abstract":"\u0000 In this paper, multiple wave modes and transitions of argon helicon plasma excited by a half right-helical in a system without any reflection endplate are investigated experimentally and theoretically at increasing radio frequency (RF) powers and external magnetic fields. Experiments show that above a critical magnetic field strength and pressure (about 250 G and 0.3 Pa in this work), two to four distinct wave coupled modes and transitions were observed at increasing RF powers and/or magnetic fields. Theoretical analysis based on dispersion relationship show that in high magnetic field helicon wave of the lowest order of axial eigenmode is always excited firstly, then the higher order axial or radial mode, hence the plasma density increases after mode jumping. There are two mechanisms responsible for the wave mode transitions in the present system, i.e., axial and radial mode transitions owning to the change of axial and radial wavenumbers from a lower eigenmode to a higher one. Higher plasma density and magnetic field are helpful for achieving more higher-order modes of helicon waves.","PeriodicalId":508056,"journal":{"name":"Plasma Sources Science and Technology","volume":"11 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-02-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139848493","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}
Packed bed dielectric barrier discharges exhibit an improved energy efficiency and selectivity in nonthermal plasma based gas conversion. They enable the direct interaction between plasma and catalyst. In this contribution a compact coaxial DBD reactor enabling the end-on imaging of the discharge with and without packed beds is constructed and studied. The discharge morphology is correlated with electrical measurements such as V-Q plots. The studies are performed for different packed bed materials, binary gas compositions of argon and carbon dioxide, voltage amplitudes, average powers, and pressures. The analysis points outs the role of parasitic capacitances and parasitic discharges as often overlooked aspects. The introduction of the packed bed material into the coaxial barrier discharge arrangement increases the total capacitance, but the barrier of the outer glass tube mostly determines the maximum effective dielectric capacitance. The choice of the packed bed material determines the voltage threshold and the average discharge power. The investigations leads to a revision of the equivalent circuit for packed bed barrier discharge reactors, which also accounts the properties of different filling materials.
{"title":"Electrical characterization and imaging of discharge morphology in a small-scale packed bed dielectric barrier discharge","authors":"Rezvan Hosseini Rad, Volker Brüser, Ronny Brandenburg","doi":"10.1088/1361-6595/ad27ed","DOIUrl":"https://doi.org/10.1088/1361-6595/ad27ed","url":null,"abstract":"\u0000 Packed bed dielectric barrier discharges exhibit an improved energy efficiency and selectivity in nonthermal plasma based gas conversion. They enable the direct interaction between plasma and catalyst. In this contribution a compact coaxial DBD reactor enabling the end-on imaging of the discharge with and without packed beds is constructed and studied. The discharge morphology is correlated with electrical measurements such as V-Q plots. The studies are performed for different packed bed materials, binary gas compositions of argon and carbon dioxide, voltage amplitudes, average powers, and pressures. The analysis points outs the role of parasitic capacitances and parasitic discharges as often overlooked aspects. The introduction of the packed bed material into the coaxial barrier discharge arrangement increases the total capacitance, but the barrier of the outer glass tube mostly determines the maximum effective dielectric capacitance. The choice of the packed bed material determines the voltage threshold and the average discharge power. The investigations leads to a revision of the equivalent circuit for packed bed barrier discharge reactors, which also accounts the properties of different filling materials.","PeriodicalId":508056,"journal":{"name":"Plasma Sources Science and Technology","volume":" 8","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-02-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139788584","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 : 2024-02-09DOI: 10.1088/1361-6595/ad27ec
Indhu Suresh, Priti Priti, R. Srivastava, R. Gangwar
Calculation of electron impact excitation cross sections for singly charged Ga ions plays a crucial role in plasma modeling, facilitating the comprehension of plasma behavior, characteristics, and dynamics in diverse domains, such as astrophysics, fusion research, the semiconductor industry, etc. In the available literature, there is a notable scarcity of, or even a complete absence of, these cross sections. Hence, in the present work, electron impact excitation cross sections are calculated for the transitions from the fine structure resolved energy levels of the configurations 4s2 and 4s4p to the fine structure resolved energy levels of the configurations 4s4p, 4s5s, 4p2 and 4s4d of the singly charged Ga ion (Ga+) using the relativistic distorted wave approximation theory with the target states represented by multi configurational Dirac Fock wavefunctions. The cross sections are calculated for projectile electron energy varying from threshold to 500 eV. Furthermore, the electron impact excitation rate coefficients for all the transitions under investigation are also calculated for electron temperatures ranging from 0.5 to 5 eV. In addition, analytic fitting of the rate coefficients is also performed, providing a practical resource for directly utilizing in plasma modeling applications.
计算单带电镓离子的电子碰撞激发截面在等离子体建模中起着至关重要的作用，有助于理解天体物理学、核聚变研究、半导体工业等不同领域的等离子体行为、特征和动力学。在现有的文献中，这些横截面明显很少，甚至完全没有。因此，在本研究中，我们利用相对论扭曲波近似理论计算了单电荷镓离子（Ga+）从4s2和4s4p构型的精细结构分辨能级到4s4p、4s5s、4p2和4s4d构型的精细结构分辨能级的电子碰撞激发截面，目标态由多构型狄拉克-福克波函数表示。计算了从阈值到 500 eV 的射弹电子能量的截面。此外，还计算了电子温度在 0.5 至 5 eV 之间时所有研究转变的电子撞击激发率系数。此外，还对速率系数进行了分析拟合，为直接用于等离子体建模应用提供了实用资源。
{"title":"Fine structure resolved excitation cross sections of singly ionized Ga for the modeling and diagnostics of Ga plasmas","authors":"Indhu Suresh, Priti Priti, R. Srivastava, R. Gangwar","doi":"10.1088/1361-6595/ad27ec","DOIUrl":"https://doi.org/10.1088/1361-6595/ad27ec","url":null,"abstract":"\u0000 Calculation of electron impact excitation cross sections for singly charged Ga ions plays a crucial role in plasma modeling, facilitating the comprehension of plasma behavior, characteristics, and dynamics in diverse domains, such as astrophysics, fusion research, the semiconductor industry, etc. In the available literature, there is a notable scarcity of, or even a complete absence of, these cross sections. Hence, in the present work, electron impact excitation cross sections are calculated for the transitions from the fine structure resolved energy levels of the configurations 4s2 and 4s4p to the fine structure resolved energy levels of the configurations 4s4p, 4s5s, 4p2 and 4s4d of the singly charged Ga ion (Ga+) using the relativistic distorted wave approximation theory with the target states represented by multi configurational Dirac Fock wavefunctions. The cross sections are calculated for projectile electron energy varying from threshold to 500 eV. Furthermore, the electron impact excitation rate coefficients for all the transitions under investigation are also calculated for electron temperatures ranging from 0.5 to 5 eV. In addition, analytic fitting of the rate coefficients is also performed, providing a practical resource for directly utilizing in plasma modeling applications.","PeriodicalId":508056,"journal":{"name":"Plasma Sources Science and Technology","volume":" 35","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-02-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139790318","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 : 2024-02-07DOI: 10.1088/1361-6595/ad270e
Wan Dong, Yifan Zhang, Julian Schulze, Yuan-Hong Song
Instabilities in capacitively coupled Ar/CF4 plasma discharges driven by dual frequency sources are investigated using a one-dimensional fluid/electron Monte Carlo (MC) hybrid model. Periodic oscillations of the electron density and temperature on the timescale of multiple low frequency periods are observed. As the electron density increases, an intense oscillation of the electron temperature within each high frequency period is initiated. This causes a fluctuation of the electron density and results in a discharge instability. This phenomenon is consistent with the discharge behavior observed in scenarios with single-frequency (SF) sources, as reported by Dong et al. [PSST 31 (2022) 025006]. However, unlike the single-frequency case, plasma parameters such as the electron density, electric field, electron power absorption and ionization rate exhibit not only periodic fluctuations but also a spatial asymmetry under the influence of the dual-frequency source. This spatial asymmetry leads to a non-uniform distribution of the electron density between the electrodes, which is related to a spatially asymmetric electric field, electron heating, and ionization around a region of minimum electron density (inside the bulk). This region of minimum electron density is shifted back and forth through the entire plasma bulk from one electrode to the other within multiple low frequency period. The above phenomena are related to superposition effect between the instabilities and the dual-frequency source. Moreover, the time averaged electric field influences the spatio-temporal evolution of ion fluxes. The ion fluxes at the electrodes, which play an important role in etching processes, are affected by both the high and low frequency components of the driving voltage waveform as well as the observed instabilities. As the high frequency increases, the electronegativity and electron temperature are reduced and the electron density increases, resulting in a gradual disappearance of the instabilities.
{"title":"Hybrid simulation of instabilities in capacitively coupled RF CF4/Ar plasmas driven by a dual frequency source","authors":"Wan Dong, Yifan Zhang, Julian Schulze, Yuan-Hong Song","doi":"10.1088/1361-6595/ad270e","DOIUrl":"https://doi.org/10.1088/1361-6595/ad270e","url":null,"abstract":"\u0000 Instabilities in capacitively coupled Ar/CF4 plasma discharges driven by dual frequency sources are investigated using a one-dimensional fluid/electron Monte Carlo (MC) hybrid model. Periodic oscillations of the electron density and temperature on the timescale of multiple low frequency periods are observed. As the electron density increases, an intense oscillation of the electron temperature within each high frequency period is initiated. This causes a fluctuation of the electron density and results in a discharge instability. This phenomenon is consistent with the discharge behavior observed in scenarios with single-frequency (SF) sources, as reported by Dong et al. [PSST 31 (2022) 025006]. However, unlike the single-frequency case, plasma parameters such as the electron density, electric field, electron power absorption and ionization rate exhibit not only periodic fluctuations but also a spatial asymmetry under the influence of the dual-frequency source. This spatial asymmetry leads to a non-uniform distribution of the electron density between the electrodes, which is related to a spatially asymmetric electric field, electron heating, and ionization around a region of minimum electron density (inside the bulk). This region of minimum electron density is shifted back and forth through the entire plasma bulk from one electrode to the other within multiple low frequency period. The above phenomena are related to superposition effect between the instabilities and the dual-frequency source. Moreover, the time averaged electric field influences the spatio-temporal evolution of ion fluxes. The ion fluxes at the electrodes, which play an important role in etching processes, are affected by both the high and low frequency components of the driving voltage waveform as well as the observed instabilities. As the high frequency increases, the electronegativity and electron temperature are reduced and the electron density increases, resulting in a gradual disappearance of the instabilities.","PeriodicalId":508056,"journal":{"name":"Plasma Sources Science and Technology","volume":"68 3","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-02-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139794909","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 : 2024-02-07DOI: 10.1088/1361-6595/ad270f
Zhan Shu, N. Popov, S. Starikovskaia
The paper presents a calibration of the ratio of two-photon absorption cross sections, $sigma^{(2)}_{Xe}/ sigma^{(2)}_O$, necessary for the absolute O-atom density measurements by two-photon absorption laser-induced fluorescence (TALIF) technique. To calibrate the ratio of the cross-sections, a special discharge with 100% dissociation of molecular oxygen, and so with a known “reference” density of O-atom [O]$_{ref}$=2$cdot$[O$_2$] was suggested. This is a nanosecond capillary discharge in N$_2$: O$_2$ mixtures with a few percent of oxygen at a reduced electric field of a few hundred of Td and specific deposited energy of about 1 eV/molecule. Voltage at the electrodes, electrical current in the plasma, longitudinal electric field and energy delivered to the gas were measured with 0.2~ns synchronisation. Additionally, radial distribution of emission of excited nitrogen molecules and gas temperature in the discharge and afterglow were obtained experimentally. Detailed 1D kinetic modeling was suggested to confirm complete O$_2$ dissociation and to analyse the main reactions. By comparing the data measured by TALIF technique with the ``reference'' density of oxygen atoms [O]$_{ref}$, the ratio of the two-photon absorption cross-sections $sigma^{(2)}_{Xe}/ sigma^{(2)}_O$ was determined.
{"title":"Absolute calibration of the ratio of Xe/O two-photon absorption cross-sections for O-TALIF applications","authors":"Zhan Shu, N. Popov, S. Starikovskaia","doi":"10.1088/1361-6595/ad270f","DOIUrl":"https://doi.org/10.1088/1361-6595/ad270f","url":null,"abstract":"\u0000 The paper presents a calibration of the ratio of two-photon absorption cross sections, $sigma^{(2)}_{Xe}/ sigma^{(2)}_O$, necessary for the absolute O-atom density measurements by two-photon absorption laser-induced fluorescence (TALIF) technique. To calibrate the ratio of the cross-sections, a special discharge with 100% dissociation of molecular oxygen, and so with a known “reference” density of O-atom [O]$_{ref}$=2$cdot$[O$_2$] was suggested. This is a nanosecond capillary discharge in N$_2$: O$_2$ mixtures with a few percent of oxygen at a reduced electric field of a few hundred of Td and specific deposited energy of about 1 eV/molecule. Voltage at the electrodes, electrical current in the plasma, longitudinal electric field and energy delivered to the gas were measured with 0.2~ns synchronisation. Additionally, radial distribution of emission of excited nitrogen molecules and gas temperature in the discharge and afterglow were obtained experimentally. Detailed 1D kinetic modeling was suggested to confirm complete O$_2$ dissociation and to analyse the main reactions. By comparing the data measured by TALIF technique with the ``reference'' density of oxygen atoms [O]$_{ref}$, the ratio of the two-photon absorption cross-sections $sigma^{(2)}_{Xe}/ sigma^{(2)}_O$ was determined.","PeriodicalId":508056,"journal":{"name":"Plasma Sources Science and Technology","volume":"40 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-02-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139857951","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 : 2024-02-07DOI: 10.1088/1361-6595/ad270e
Wan Dong, Yifan Zhang, Julian Schulze, Yuan-Hong Song
Instabilities in capacitively coupled Ar/CF4 plasma discharges driven by dual frequency sources are investigated using a one-dimensional fluid/electron Monte Carlo (MC) hybrid model. Periodic oscillations of the electron density and temperature on the timescale of multiple low frequency periods are observed. As the electron density increases, an intense oscillation of the electron temperature within each high frequency period is initiated. This causes a fluctuation of the electron density and results in a discharge instability. This phenomenon is consistent with the discharge behavior observed in scenarios with single-frequency (SF) sources, as reported by Dong et al. [PSST 31 (2022) 025006]. However, unlike the single-frequency case, plasma parameters such as the electron density, electric field, electron power absorption and ionization rate exhibit not only periodic fluctuations but also a spatial asymmetry under the influence of the dual-frequency source. This spatial asymmetry leads to a non-uniform distribution of the electron density between the electrodes, which is related to a spatially asymmetric electric field, electron heating, and ionization around a region of minimum electron density (inside the bulk). This region of minimum electron density is shifted back and forth through the entire plasma bulk from one electrode to the other within multiple low frequency period. The above phenomena are related to superposition effect between the instabilities and the dual-frequency source. Moreover, the time averaged electric field influences the spatio-temporal evolution of ion fluxes. The ion fluxes at the electrodes, which play an important role in etching processes, are affected by both the high and low frequency components of the driving voltage waveform as well as the observed instabilities. As the high frequency increases, the electronegativity and electron temperature are reduced and the electron density increases, resulting in a gradual disappearance of the instabilities.
{"title":"Hybrid simulation of instabilities in capacitively coupled RF CF4/Ar plasmas driven by a dual frequency source","authors":"Wan Dong, Yifan Zhang, Julian Schulze, Yuan-Hong Song","doi":"10.1088/1361-6595/ad270e","DOIUrl":"https://doi.org/10.1088/1361-6595/ad270e","url":null,"abstract":"\u0000 Instabilities in capacitively coupled Ar/CF4 plasma discharges driven by dual frequency sources are investigated using a one-dimensional fluid/electron Monte Carlo (MC) hybrid model. Periodic oscillations of the electron density and temperature on the timescale of multiple low frequency periods are observed. As the electron density increases, an intense oscillation of the electron temperature within each high frequency period is initiated. This causes a fluctuation of the electron density and results in a discharge instability. This phenomenon is consistent with the discharge behavior observed in scenarios with single-frequency (SF) sources, as reported by Dong et al. [PSST 31 (2022) 025006]. However, unlike the single-frequency case, plasma parameters such as the electron density, electric field, electron power absorption and ionization rate exhibit not only periodic fluctuations but also a spatial asymmetry under the influence of the dual-frequency source. This spatial asymmetry leads to a non-uniform distribution of the electron density between the electrodes, which is related to a spatially asymmetric electric field, electron heating, and ionization around a region of minimum electron density (inside the bulk). This region of minimum electron density is shifted back and forth through the entire plasma bulk from one electrode to the other within multiple low frequency period. The above phenomena are related to superposition effect between the instabilities and the dual-frequency source. Moreover, the time averaged electric field influences the spatio-temporal evolution of ion fluxes. The ion fluxes at the electrodes, which play an important role in etching processes, are affected by both the high and low frequency components of the driving voltage waveform as well as the observed instabilities. As the high frequency increases, the electronegativity and electron temperature are reduced and the electron density increases, resulting in a gradual disappearance of the instabilities.","PeriodicalId":508056,"journal":{"name":"Plasma Sources Science and Technology","volume":"16 3","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-02-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139854928","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 : 2024-02-07DOI: 10.1088/1361-6595/ad270f
Zhan Shu, N. Popov, S. Starikovskaia
The paper presents a calibration of the ratio of two-photon absorption cross sections, $sigma^{(2)}_{Xe}/ sigma^{(2)}_O$, necessary for the absolute O-atom density measurements by two-photon absorption laser-induced fluorescence (TALIF) technique. To calibrate the ratio of the cross-sections, a special discharge with 100% dissociation of molecular oxygen, and so with a known “reference” density of O-atom [O]$_{ref}$=2$cdot$[O$_2$] was suggested. This is a nanosecond capillary discharge in N$_2$: O$_2$ mixtures with a few percent of oxygen at a reduced electric field of a few hundred of Td and specific deposited energy of about 1 eV/molecule. Voltage at the electrodes, electrical current in the plasma, longitudinal electric field and energy delivered to the gas were measured with 0.2~ns synchronisation. Additionally, radial distribution of emission of excited nitrogen molecules and gas temperature in the discharge and afterglow were obtained experimentally. Detailed 1D kinetic modeling was suggested to confirm complete O$_2$ dissociation and to analyse the main reactions. By comparing the data measured by TALIF technique with the ``reference'' density of oxygen atoms [O]$_{ref}$, the ratio of the two-photon absorption cross-sections $sigma^{(2)}_{Xe}/ sigma^{(2)}_O$ was determined.
{"title":"Absolute calibration of the ratio of Xe/O two-photon absorption cross-sections for O-TALIF applications","authors":"Zhan Shu, N. Popov, S. Starikovskaia","doi":"10.1088/1361-6595/ad270f","DOIUrl":"https://doi.org/10.1088/1361-6595/ad270f","url":null,"abstract":"\u0000 The paper presents a calibration of the ratio of two-photon absorption cross sections, $sigma^{(2)}_{Xe}/ sigma^{(2)}_O$, necessary for the absolute O-atom density measurements by two-photon absorption laser-induced fluorescence (TALIF) technique. To calibrate the ratio of the cross-sections, a special discharge with 100% dissociation of molecular oxygen, and so with a known “reference” density of O-atom [O]$_{ref}$=2$cdot$[O$_2$] was suggested. This is a nanosecond capillary discharge in N$_2$: O$_2$ mixtures with a few percent of oxygen at a reduced electric field of a few hundred of Td and specific deposited energy of about 1 eV/molecule. Voltage at the electrodes, electrical current in the plasma, longitudinal electric field and energy delivered to the gas were measured with 0.2~ns synchronisation. Additionally, radial distribution of emission of excited nitrogen molecules and gas temperature in the discharge and afterglow were obtained experimentally. Detailed 1D kinetic modeling was suggested to confirm complete O$_2$ dissociation and to analyse the main reactions. By comparing the data measured by TALIF technique with the ``reference'' density of oxygen atoms [O]$_{ref}$, the ratio of the two-photon absorption cross-sections $sigma^{(2)}_{Xe}/ sigma^{(2)}_O$ was determined.","PeriodicalId":508056,"journal":{"name":"Plasma Sources Science and Technology","volume":"48 25","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-02-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139798099","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 : 2024-02-02DOI: 10.1088/1361-6595/ad257f
De-Hua Shi, Xiao-Kun Wang, Yong-Xin Liu, Zoltán Donkó, Julian Schulze, You-Nian Wang
The ignition process of a pulse modulated capacitively coupled argon discharge driven simultaneously by two different radio frequency voltages (12.5 MHz (high frequency, HF) and 2.5 MHz (low frequwncy, LF)) is investigated by multifold experimental diagnostics and particle in cell / Monte Carlo collision (PIC/MCC) simulations. In particular, (i) the effects of the low frequency voltage amplitude measured at the end of the pulse-on period, V L,end, on the spatiotemporal distribution of the electron impact excitation rate determined by phase resolved optical emission spectroscopy, and (ii) the electrical parameters acquired by analyzing the measured waveforms of the plasma current and voltage, are studied. Computed spatiotemporal distributions of the electron impact excitation rate and electrical parameters show a good qualitative agreement with the experimental results. Generally, the HF and LF electrical parameters (amplitudes and relative phase of the voltage and the current) change with time in a similar manner during the ignition process for each V L,end. However, various scenarios of the breakdown mechanism are found as a function of V L,end. At low values of V L,end, the “RF-avalanche” mode dominates the electron multiplication process. By increasing V L,end, the ionization caused by the volume electrons is suppressed and the electron loss at the electrodes is enhanced, leading to a delayed ignition. At higher values of V L,end, the avalanche ionization is significantly enhanced by ion-induced secondary electron emission at the electrodes.
通过多重实验诊断和粒子池/蒙特卡罗碰撞（PIC/MCC）模拟，研究了由两种不同射频电压（12.5 MHz（高频）和 2.5 MHz（低频））同时驱动的脉冲调制电容耦合氩放电的点火过程。特别是，研究了(i) 脉冲接通期结束时测量的低频电压振幅 V L,end，对相位分辨光学发射光谱测定的电子撞击激发率时空分布的影响，以及(ii) 通过分析测量的等离子体电流和电压波形获得的电参数。计算得出的电子撞击激发率和电气参数的时空分布与实验结果在质量上有很好的一致性。一般来说，在点火过程中，每个 V L 端的高频和低频电参数（电压和电流的幅值和相对相位）随时间的变化情况相似。然而，随着 V L 端值的变化，击穿机制也会出现不同的情况。在 V L 端值较低时，"射频雪崩 "模式在电子倍增过程中占主导地位。增大 V L,end，体积电子引起的电离被抑制，电极上的电子损耗增加，从而导致延迟点火。当 V L,end 值较高时，雪崩电离因电极上的离子诱导二次电子发射而显著增强。
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Pub Date : 2024-02-02DOI: 10.1088/1361-6595/ad257f
De-Hua Shi, Xiao-Kun Wang, Yong-Xin Liu, Zoltán Donkó, Julian Schulze, You-Nian Wang
The ignition process of a pulse modulated capacitively coupled argon discharge driven simultaneously by two different radio frequency voltages (12.5 MHz (high frequency, HF) and 2.5 MHz (low frequwncy, LF)) is investigated by multifold experimental diagnostics and particle in cell / Monte Carlo collision (PIC/MCC) simulations. In particular, (i) the effects of the low frequency voltage amplitude measured at the end of the pulse-on period, V L,end, on the spatiotemporal distribution of the electron impact excitation rate determined by phase resolved optical emission spectroscopy, and (ii) the electrical parameters acquired by analyzing the measured waveforms of the plasma current and voltage, are studied. Computed spatiotemporal distributions of the electron impact excitation rate and electrical parameters show a good qualitative agreement with the experimental results. Generally, the HF and LF electrical parameters (amplitudes and relative phase of the voltage and the current) change with time in a similar manner during the ignition process for each V L,end. However, various scenarios of the breakdown mechanism are found as a function of V L,end. At low values of V L,end, the “RF-avalanche” mode dominates the electron multiplication process. By increasing V L,end, the ionization caused by the volume electrons is suppressed and the electron loss at the electrodes is enhanced, leading to a delayed ignition. At higher values of V L,end, the avalanche ionization is significantly enhanced by ion-induced secondary electron emission at the electrodes.
通过多重实验诊断和粒子池/蒙特卡罗碰撞（PIC/MCC）模拟，研究了由两种不同射频电压（12.5 MHz（高频）和 2.5 MHz（低频））同时驱动的脉冲调制电容耦合氩放电的点火过程。特别是，研究了(i) 脉冲接通期结束时测量的低频电压振幅 V L,end，对相位分辨光学发射光谱测定的电子撞击激发率时空分布的影响，以及(ii) 通过分析测量的等离子体电流和电压波形获得的电参数。计算得出的电子撞击激发率和电气参数的时空分布与实验结果在质量上有很好的一致性。一般来说，在点火过程中，每个 V L 端的高频和低频电参数（电压和电流的幅值和相对相位）随时间的变化情况相似。然而，随着 V L 端值的变化，击穿机制也会出现不同的情况。在 V L 端值较低时，"射频雪崩 "模式在电子倍增过程中占主导地位。增大 V L,end，体积电子引起的电离被抑制，电极上的电子损耗增加，从而导致延迟点火。当 V L,end 值较高时，雪崩电离因电极上的离子诱导二次电子发射而显著增强。
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