Pub Date : 2021-08-31DOI: 10.1088/2516-1067/ac1c9a
C. Ryu
The transport dynamo mechanism, which describes the magnetic field generation by diffusion flow is reviewed. In this mechanism, the cross-field transport caused by the random motion of fluid breaks the frozen-flux approximation, and the resulting cross-field diffusion that can generate the magnetic field. Turbulence can play an important role in inducing such random motion. Compared to the conventional dynamo mechanism, this transport mechanism has several special features that the field generation can occur on a very slow time scale because the mechanism is mediated by diffusion and that this mechanism is practically meaningful only when there is density inhomogeneity. Turbulence can significantly enhance cross-field diffusion far beyond collisional transport. The physical meanings of the diffusion-generated magnetic fields are discussed in detail.
{"title":"Turbulence-induced transport dynamo mechanism","authors":"C. Ryu","doi":"10.1088/2516-1067/ac1c9a","DOIUrl":"https://doi.org/10.1088/2516-1067/ac1c9a","url":null,"abstract":"The transport dynamo mechanism, which describes the magnetic field generation by diffusion flow is reviewed. In this mechanism, the cross-field transport caused by the random motion of fluid breaks the frozen-flux approximation, and the resulting cross-field diffusion that can generate the magnetic field. Turbulence can play an important role in inducing such random motion. Compared to the conventional dynamo mechanism, this transport mechanism has several special features that the field generation can occur on a very slow time scale because the mechanism is mediated by diffusion and that this mechanism is practically meaningful only when there is density inhomogeneity. Turbulence can significantly enhance cross-field diffusion far beyond collisional transport. The physical meanings of the diffusion-generated magnetic fields are discussed in detail.","PeriodicalId":36295,"journal":{"name":"Plasma Research Express","volume":" ","pages":""},"PeriodicalIF":0.0,"publicationDate":"2021-08-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47129436","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 : 2021-06-04DOI: 10.1088/2516-1067/ac0580
N. Behera, Ajai Kumar, R. K. Singh
In the present work, we report the dynamics and geometrical features of the plasma plume formed by the laser ablation of copper and graphite (carbon) targets in the presence of different transverse magnetic field. This work emphasizes on the effect of atomic mass of the plume species on the diamagnetic behaviour and geometrical aspect of the expanding plasma plume in the magnetic field. The time-resolved analysis of the simultaneously captured two directional images in orthogonal to the expansion axis is carried out for the comparative study of projected three-dimensional structure of copper and carbon plasma plume. In the presence of magnetic field, sharp differences are observed between the copper and carbon plasma plumes in terms of formation of diamagnetic cavity and structure formation. An elliptical cavity-like structure is observed in case of copper plasma plume which attains the sharp conical shape with increasing the time delay or magnetic field strength. On the other hand, splitted carbon plasma plume appears as a Y-shape structure in the presence of magnetic field where the cavity-like structure is not observed for the considered time and magnetic field. Based on the modified energy balance relation for the elliptic cylindrical geometry, we have also simulated the dynamics of the plume which is in close agreement with observed plasma expansion in diamagnetic and non-diamagnetic regions.
{"title":"Cavitation and charge separation in laser-produced copper and carbon plasma in transverse magnetic field","authors":"N. Behera, Ajai Kumar, R. K. Singh","doi":"10.1088/2516-1067/ac0580","DOIUrl":"https://doi.org/10.1088/2516-1067/ac0580","url":null,"abstract":"In the present work, we report the dynamics and geometrical features of the plasma plume formed by the laser ablation of copper and graphite (carbon) targets in the presence of different transverse magnetic field. This work emphasizes on the effect of atomic mass of the plume species on the diamagnetic behaviour and geometrical aspect of the expanding plasma plume in the magnetic field. The time-resolved analysis of the simultaneously captured two directional images in orthogonal to the expansion axis is carried out for the comparative study of projected three-dimensional structure of copper and carbon plasma plume. In the presence of magnetic field, sharp differences are observed between the copper and carbon plasma plumes in terms of formation of diamagnetic cavity and structure formation. An elliptical cavity-like structure is observed in case of copper plasma plume which attains the sharp conical shape with increasing the time delay or magnetic field strength. On the other hand, splitted carbon plasma plume appears as a Y-shape structure in the presence of magnetic field where the cavity-like structure is not observed for the considered time and magnetic field. Based on the modified energy balance relation for the elliptic cylindrical geometry, we have also simulated the dynamics of the plume which is in close agreement with observed plasma expansion in diamagnetic and non-diamagnetic regions.","PeriodicalId":36295,"journal":{"name":"Plasma Research Express","volume":" ","pages":""},"PeriodicalIF":0.0,"publicationDate":"2021-06-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46343195","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 : 2021-05-20DOI: 10.1088/2516-1067/ac0095
Jesse Santoso, Mingming Zhu, Dongke Zhang
The so called ‘burst mode’, a rapidly pulsed power regime for dielectric barrier discharges (DBDs) has previously been reported to greatly improve the performance of an uncooled and unpacked DBD reactor for CO2 splitting. Here we explore the interaction between a DBD in burst mode and each of active cooling and a dielectric packing material (1.0–1.2 mm glass beads) in a coaxial, metal-dielectric DBD reactor for CO2 splitting. The effect of burst mode on CO2 conversion and energy efficiency under different combinations of cooling and packing were investigated and compared with those under continuous wave mode operation. The burst mode operation showed similar CO2 conversion and energy efficiency to continuous wave mode in the unpacked and uncooled configuration under the conditions investigated in this study. However, burst mode significantly outperformed continuous wave mode in the packed and uncooled configuration. When active cooling was employed, burst mode was found to provide only minor benefit or no benefit, depending on specific energy input (SEI), compared to continuous wave mode for each the packed and unpacked configurations. Maximum conversion and energy efficiency were achieved with both packing and active cooling across all SEI examined, and performance in this configuration was found to be relatively insensitive to the power delivery mode.
{"title":"Burst mode in a cooled packed-bed dielectric barrier discharge reactor for CO2 splitting","authors":"Jesse Santoso, Mingming Zhu, Dongke Zhang","doi":"10.1088/2516-1067/ac0095","DOIUrl":"https://doi.org/10.1088/2516-1067/ac0095","url":null,"abstract":"The so called ‘burst mode’, a rapidly pulsed power regime for dielectric barrier discharges (DBDs) has previously been reported to greatly improve the performance of an uncooled and unpacked DBD reactor for CO2 splitting. Here we explore the interaction between a DBD in burst mode and each of active cooling and a dielectric packing material (1.0–1.2 mm glass beads) in a coaxial, metal-dielectric DBD reactor for CO2 splitting. The effect of burst mode on CO2 conversion and energy efficiency under different combinations of cooling and packing were investigated and compared with those under continuous wave mode operation. The burst mode operation showed similar CO2 conversion and energy efficiency to continuous wave mode in the unpacked and uncooled configuration under the conditions investigated in this study. However, burst mode significantly outperformed continuous wave mode in the packed and uncooled configuration. When active cooling was employed, burst mode was found to provide only minor benefit or no benefit, depending on specific energy input (SEI), compared to continuous wave mode for each the packed and unpacked configurations. Maximum conversion and energy efficiency were achieved with both packing and active cooling across all SEI examined, and performance in this configuration was found to be relatively insensitive to the power delivery mode.","PeriodicalId":36295,"journal":{"name":"Plasma Research Express","volume":"3 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2021-05-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41449907","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 : 2021-05-12DOI: 10.1088/2516-1067/abfc2a
H. Pauna, T. Willms, M. Aula, T. Echterhof, M. Huttula, T. Fabritius
Cyanide, among with NO x , CO2, and CO, is one of the adverse compounds that form in the ironmaking and steelmaking industry. High-temperature processes are suitable environments for cyanide formation, and cyanide can form as a result of recombination in electric arc plasma. Even though the cyanides might not survive e.g. the post-combustion process, understanding the formation mechanisms of hazardous materials in the steelmaking industry is important. In this work, the recombination of cyanide in a pilot-scale AC electric arc furnace is studied with optical emissions from the CN molecule. The results show how the optical emissions from the cyanide change in different process steps. Electric input, plasma temperature, and interaction of the arc with solid charge material were observed to have an impact on the CN signal. Additionally, equilibrium composition computation highlights how different sources of carbon change the recombination rate and that the highest recombination occurs at 6821 K.
{"title":"Cyanide recombination in electric arc furnace plasma","authors":"H. Pauna, T. Willms, M. Aula, T. Echterhof, M. Huttula, T. Fabritius","doi":"10.1088/2516-1067/abfc2a","DOIUrl":"https://doi.org/10.1088/2516-1067/abfc2a","url":null,"abstract":"Cyanide, among with NO x , CO2, and CO, is one of the adverse compounds that form in the ironmaking and steelmaking industry. High-temperature processes are suitable environments for cyanide formation, and cyanide can form as a result of recombination in electric arc plasma. Even though the cyanides might not survive e.g. the post-combustion process, understanding the formation mechanisms of hazardous materials in the steelmaking industry is important. In this work, the recombination of cyanide in a pilot-scale AC electric arc furnace is studied with optical emissions from the CN molecule. The results show how the optical emissions from the cyanide change in different process steps. Electric input, plasma temperature, and interaction of the arc with solid charge material were observed to have an impact on the CN signal. Additionally, equilibrium composition computation highlights how different sources of carbon change the recombination rate and that the highest recombination occurs at 6821 K.","PeriodicalId":36295,"journal":{"name":"Plasma Research Express","volume":" ","pages":""},"PeriodicalIF":0.0,"publicationDate":"2021-05-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49298754","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 : 2021-04-28DOI: 10.1088/2516-1067/abf948
R. Niranjan, J. Joycee, R. Srivastava, N. Patel, K. Joshi
Pulsed hydrocarbon ions produced in a plasma focus device were used to irradiate different substrate materials (Si, Ti, Mo and W) and to deposit thin films of carbon material over it. High energetic and high intensity pulsed hydrocarbon ions were produced when plasma focus device was filled with 0.5 mbar of acetylene gas and operated at 2 kJ. Effects of substrate materials properties, its thermal evolution under pulsed irradiation of energetic ions and plasma streams on the deposited films have been studied. Visible Raman spectroscopic measurements confirmed that deposited films were of diamond-like-carbon. Fraction of sp3 bonded carbon in films on different substrate materials (16%, 8.7%, 13% and 18.9% on Si, Ti, Mo and W respectively) was found to be correlated to substrate materials thermal properties i.e. high fraction of sp3 bonded carbon was observed over substrate materials having high thermal conductivity. Carbon atom concentrations were measured to be different (22.46 at. %, 22.7 at. %, 10.4 at. % and 32 at. % on Si, Ti, Mo and W respectively) over different substrates. Surface morphologies of DLC were also observed to be different for different substrates. On inserting graphite at anode tip, fraction of sp3 bonded carbon in DLC coating over Si substrate increased to 19.5%.
{"title":"Study of diamond like carbon coatings formed by pulsed hydrocarbon ions irradiations over different substrate materials using plasma focus device","authors":"R. Niranjan, J. Joycee, R. Srivastava, N. Patel, K. Joshi","doi":"10.1088/2516-1067/abf948","DOIUrl":"https://doi.org/10.1088/2516-1067/abf948","url":null,"abstract":"Pulsed hydrocarbon ions produced in a plasma focus device were used to irradiate different substrate materials (Si, Ti, Mo and W) and to deposit thin films of carbon material over it. High energetic and high intensity pulsed hydrocarbon ions were produced when plasma focus device was filled with 0.5 mbar of acetylene gas and operated at 2 kJ. Effects of substrate materials properties, its thermal evolution under pulsed irradiation of energetic ions and plasma streams on the deposited films have been studied. Visible Raman spectroscopic measurements confirmed that deposited films were of diamond-like-carbon. Fraction of sp3 bonded carbon in films on different substrate materials (16%, 8.7%, 13% and 18.9% on Si, Ti, Mo and W respectively) was found to be correlated to substrate materials thermal properties i.e. high fraction of sp3 bonded carbon was observed over substrate materials having high thermal conductivity. Carbon atom concentrations were measured to be different (22.46 at. %, 22.7 at. %, 10.4 at. % and 32 at. % on Si, Ti, Mo and W respectively) over different substrates. Surface morphologies of DLC were also observed to be different for different substrates. On inserting graphite at anode tip, fraction of sp3 bonded carbon in DLC coating over Si substrate increased to 19.5%.","PeriodicalId":36295,"journal":{"name":"Plasma Research Express","volume":" ","pages":""},"PeriodicalIF":0.0,"publicationDate":"2021-04-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41465945","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 : 2021-04-28DOI: 10.1088/2516-1067/abf947
D. Testa, H. Carfantan, L. M. Perrone
A common problem in many complex physical systems is the determination of pulsation modes from irregularly sampled time-series, and there is a wealth of signal processing techniques that are being applied to post-pulse and real-time data analysis in such complex systems. The aim of this report is studying the problem of detecting in real-time spatial periodicities in the spectrum of magnetic fluctuations in tokamaks, for which optimization of the algorithm run-time is essential. The main tool used hereafter will be the SparSpec algorithm, initially devised for astrophysical purposes and already applied to the analysis of magnetic fluctuation data in various tokamaks, both currently or previously operating (JET, TCV, Alcator C-mod) and under construction (ITER, DTT). For JET, the baseline version of the SparSpec algorithm, dubbed SS-H2, already regularly runs in real-time on a 1 ms clock for detecting Toroidal Alfvén Eigenmodes using synchronously-detected magnetic perturbation. It was noted that the solution is only slowly changing in time as the background plasma typically also slowly evolves. Therefore, as a specifically real-time acceleration tool, we will focus on the use of a memory with relaxation scheme, whereby solutions obtained at previous time points are used to provide weighted input constraints for the solution at the current time point. Use of the measurement uncertainties to weight the data, the spectral window and the ensuing penalization criterion (dubbed the SS-V5ν0 algorithm) is reported in a companion work. The behaviour of the SparSpec algorithm under a variety of simulated circumstances, and one actual test case from the JET tokamak, is analysed and appropriate conditions for the convergence of the memory-penalised solutions are derived. The tuning of the input parameters is discussed based on the results of our simulations. It is found that the implementation of SparSpec using such a memory with relaxation scheme is quite a complex procedure, and only when correctly optimized the results are superior, both in terms of the speed and the accuracy of the calculations, to those obtained with the SS-H2 and SS-V5ν0 versions of the SparSpec algorithm.
{"title":"The SparSpec algorithm and the application to the detection of spatial periodicities in tokamaks: using memory with relaxation","authors":"D. Testa, H. Carfantan, L. M. Perrone","doi":"10.1088/2516-1067/abf947","DOIUrl":"https://doi.org/10.1088/2516-1067/abf947","url":null,"abstract":"A common problem in many complex physical systems is the determination of pulsation modes from irregularly sampled time-series, and there is a wealth of signal processing techniques that are being applied to post-pulse and real-time data analysis in such complex systems. The aim of this report is studying the problem of detecting in real-time spatial periodicities in the spectrum of magnetic fluctuations in tokamaks, for which optimization of the algorithm run-time is essential. The main tool used hereafter will be the SparSpec algorithm, initially devised for astrophysical purposes and already applied to the analysis of magnetic fluctuation data in various tokamaks, both currently or previously operating (JET, TCV, Alcator C-mod) and under construction (ITER, DTT). For JET, the baseline version of the SparSpec algorithm, dubbed SS-H2, already regularly runs in real-time on a 1 ms clock for detecting Toroidal Alfvén Eigenmodes using synchronously-detected magnetic perturbation. It was noted that the solution is only slowly changing in time as the background plasma typically also slowly evolves. Therefore, as a specifically real-time acceleration tool, we will focus on the use of a memory with relaxation scheme, whereby solutions obtained at previous time points are used to provide weighted input constraints for the solution at the current time point. Use of the measurement uncertainties to weight the data, the spectral window and the ensuing penalization criterion (dubbed the SS-V5ν0 algorithm) is reported in a companion work. The behaviour of the SparSpec algorithm under a variety of simulated circumstances, and one actual test case from the JET tokamak, is analysed and appropriate conditions for the convergence of the memory-penalised solutions are derived. The tuning of the input parameters is discussed based on the results of our simulations. It is found that the implementation of SparSpec using such a memory with relaxation scheme is quite a complex procedure, and only when correctly optimized the results are superior, both in terms of the speed and the accuracy of the calculations, to those obtained with the SS-H2 and SS-V5ν0 versions of the SparSpec algorithm.","PeriodicalId":36295,"journal":{"name":"Plasma Research Express","volume":" ","pages":""},"PeriodicalIF":0.0,"publicationDate":"2021-04-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49006819","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 : 2021-04-28DOI: 10.1088/2516-1067/abf946
D. Testa, H. Carfantan, L. Perrone
A common problem in many complex physical systems is the determination of pulsation modes from irregularly sampled time-series, and there is a wealth of signal processing techniques that are being applied to post-pulse and real-time data analysis in such complex systems. The aim of this report is studying the problem of detecting discrete spatial periodicities in the spectrum of magnetic fluctuations in tokamaks, for which the optimization of the algorithm performance is essential, particularly when multiple sensors are used with different measurement uncertainties, and some of the processed output signals are then used in real-time for discharge control. The main tool used hereafter will be the SparSpec algorithm, initially devised for astrophysical purposes and already applied to the analysis of magnetic fluctuations in various tokamaks. In its baseline version, dubbed SS-H2, the SparSpec algorithm runs in currently or previously operating tokamaks (JET, TCV and Alcator C-mod), and is foreseen to be deployed for data analysis in tokamak under construction (ITER, DTT). For JET, SS-H2 regularly runs also in real-time on a 1ms clock for detecting Alfvén Eigenmodes using synchronously-measured magnetic perturbations. On JET and TCV, it was noted that often a reduced set of sensors had to be used as the measurement uncertainties were not the same for all available sensors, somewhat deteriorating the overall performance of the algorithm. Hence, as part of a major update of the SparSpec algorithm, specifically intended for accelerating the real-time performance, use of the measurement uncertainties to weight the data, the spectral window and the ensuing penalization criterion was introduced. The behaviour of this new version of the SparSpec algorithm under a variety of simulated circumstances is analysed. It is found that the implementation of SparSpec using such error weighting produces superior results to those obtained with SS-H2, both in terms of the speed and the accuracy of the calculations. A test on actual data from the JET tokamak also shows a clear improvement in the performance of the algorithm.
{"title":"The SparSpec algorithm and the application to the detection of spatial periodicities in tokamaks: error weighting the penalization criterion to improve the performance of the algorithm","authors":"D. Testa, H. Carfantan, L. Perrone","doi":"10.1088/2516-1067/abf946","DOIUrl":"https://doi.org/10.1088/2516-1067/abf946","url":null,"abstract":"A common problem in many complex physical systems is the determination of pulsation modes from irregularly sampled time-series, and there is a wealth of signal processing techniques that are being applied to post-pulse and real-time data analysis in such complex systems. The aim of this report is studying the problem of detecting discrete spatial periodicities in the spectrum of magnetic fluctuations in tokamaks, for which the optimization of the algorithm performance is essential, particularly when multiple sensors are used with different measurement uncertainties, and some of the processed output signals are then used in real-time for discharge control. The main tool used hereafter will be the SparSpec algorithm, initially devised for astrophysical purposes and already applied to the analysis of magnetic fluctuations in various tokamaks. In its baseline version, dubbed SS-H2, the SparSpec algorithm runs in currently or previously operating tokamaks (JET, TCV and Alcator C-mod), and is foreseen to be deployed for data analysis in tokamak under construction (ITER, DTT). For JET, SS-H2 regularly runs also in real-time on a 1ms clock for detecting Alfvén Eigenmodes using synchronously-measured magnetic perturbations. On JET and TCV, it was noted that often a reduced set of sensors had to be used as the measurement uncertainties were not the same for all available sensors, somewhat deteriorating the overall performance of the algorithm. Hence, as part of a major update of the SparSpec algorithm, specifically intended for accelerating the real-time performance, use of the measurement uncertainties to weight the data, the spectral window and the ensuing penalization criterion was introduced. The behaviour of this new version of the SparSpec algorithm under a variety of simulated circumstances is analysed. It is found that the implementation of SparSpec using such error weighting produces superior results to those obtained with SS-H2, both in terms of the speed and the accuracy of the calculations. A test on actual data from the JET tokamak also shows a clear improvement in the performance of the algorithm.","PeriodicalId":36295,"journal":{"name":"Plasma Research Express","volume":" ","pages":""},"PeriodicalIF":0.0,"publicationDate":"2021-04-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42723462","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 : 2021-04-22DOI: 10.1088/2516-1067/abf73f
H. Y. Kim, M. Gołkowski, V. Harid
Enhanced post-pulse electric field reversals of Ar, Xe, and XeAr mixture gases in capacitively coupled nanosecond discharges are investigated with Particle-In-Cell simulations in the context of maximizing electron density. The electric field reversal occurs at the falling edge of the voltage pulse and induces electron oscillatory movement in the plasma bulk region. The amplitude of field reversals is affected by driven voltage and the ratio of bulk length to gap distance. Exploiting the field reversal with a so called Plasma frequency dependent Square Wave (PSW) in an optimal gas mixture leads to the highest electron density. Specifically, for a 250 V PSW XeAr mixture case, the electron density is 2.2 times higher compared to a 1 kV DC pure Xe case even if the driven voltage is 4 times less than DC voltage. In 250 V PSW cases, XeAr mixture plasma has 1.2 times higher average electron density and 1.2 times electron temperature in the sheath region than a pure Xe plasma. With a narrower bulk region, the XeAr plasma has an enhanced field reversal and this leads to higher and faster growing electron density and electron temperature than a Xe plasma. For applications using Xe plasmas, XeAr mixture plasmas with PSW can be exploited for high electron density and temperature at reduced costs.
在最大化电子密度的情况下，利用粒子-电池模拟研究了Ar, Xe和XeAr混合气体在电容耦合纳秒放电中增强的脉冲后电场逆转。电场反转发生在电压脉冲的下降沿，引起等离子体体区电子振荡运动。磁场反转的幅值受驱动电压和体长与间隙距离之比的影响。利用所谓的等离子体频率相关方波(PSW)在最佳气体混合物中的场反转导致最高的电子密度。具体来说，对于250 V PSW XeAr混合情况，即使驱动电压比直流电压低4倍，电子密度也比1 kV直流纯Xe情况高2.2倍。在250 V PSW条件下，XeAr混合等离子体的平均电子密度是纯Xe等离子体的1.2倍，鞘区电子温度是纯Xe等离子体的1.2倍。由于XeAr等离子体的体区较窄，其场反转增强，导致电子密度和电子温度的增长比Xe等离子体更高更快。对于使用Xe等离子体的应用，XeAr混合等离子体与PSW可以以更低的成本获得更高的电子密度和温度。
{"title":"Rapid ionization of Xe/Ar mixtures in nanosecond discharges exploiting post-pulse field reversals","authors":"H. Y. Kim, M. Gołkowski, V. Harid","doi":"10.1088/2516-1067/abf73f","DOIUrl":"https://doi.org/10.1088/2516-1067/abf73f","url":null,"abstract":"Enhanced post-pulse electric field reversals of Ar, Xe, and XeAr mixture gases in capacitively coupled nanosecond discharges are investigated with Particle-In-Cell simulations in the context of maximizing electron density. The electric field reversal occurs at the falling edge of the voltage pulse and induces electron oscillatory movement in the plasma bulk region. The amplitude of field reversals is affected by driven voltage and the ratio of bulk length to gap distance. Exploiting the field reversal with a so called Plasma frequency dependent Square Wave (PSW) in an optimal gas mixture leads to the highest electron density. Specifically, for a 250 V PSW XeAr mixture case, the electron density is 2.2 times higher compared to a 1 kV DC pure Xe case even if the driven voltage is 4 times less than DC voltage. In 250 V PSW cases, XeAr mixture plasma has 1.2 times higher average electron density and 1.2 times electron temperature in the sheath region than a pure Xe plasma. With a narrower bulk region, the XeAr plasma has an enhanced field reversal and this leads to higher and faster growing electron density and electron temperature than a Xe plasma. For applications using Xe plasmas, XeAr mixture plasmas with PSW can be exploited for high electron density and temperature at reduced costs.","PeriodicalId":36295,"journal":{"name":"Plasma Research Express","volume":" ","pages":""},"PeriodicalIF":0.0,"publicationDate":"2021-04-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46023887","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 : 2021-04-20DOI: 10.1088/2516-1067/abf6af
Dinkar Mishra, P. Sharma, Saumya Singh, Bhupesh Kumar, P. Jha
This paper presents an analytical and simulation study of terahertz (THz) radiation generation using short, circularly polarized laser pulses propagating in plasma embedded in arbitrarily oriented magnetic field. Perturbation technique is used to obtain generated electric and magnetic wakefields within and behind the laser pulse. Coupling of components of the obliquely applied magnetic field with transverse and axial plasma electron velocities leads to the generation of linearly as well as elliptically polarized transverse electromagnetic radiation oscillating at THz frequency, under appropriate conditions. The amplitude of these fields and ellipticity of the elliptically polarized THz radiation can be varied with the help of the obliqueness of the external magnetic field. Analytical results are validated using VSim PIC simulation code.
{"title":"Generation of terahertz radiation by short laser pulses propagating in obliquely magnetized plasma","authors":"Dinkar Mishra, P. Sharma, Saumya Singh, Bhupesh Kumar, P. Jha","doi":"10.1088/2516-1067/abf6af","DOIUrl":"https://doi.org/10.1088/2516-1067/abf6af","url":null,"abstract":"This paper presents an analytical and simulation study of terahertz (THz) radiation generation using short, circularly polarized laser pulses propagating in plasma embedded in arbitrarily oriented magnetic field. Perturbation technique is used to obtain generated electric and magnetic wakefields within and behind the laser pulse. Coupling of components of the obliquely applied magnetic field with transverse and axial plasma electron velocities leads to the generation of linearly as well as elliptically polarized transverse electromagnetic radiation oscillating at THz frequency, under appropriate conditions. The amplitude of these fields and ellipticity of the elliptically polarized THz radiation can be varied with the help of the obliqueness of the external magnetic field. Analytical results are validated using VSim PIC simulation code.","PeriodicalId":36295,"journal":{"name":"Plasma Research Express","volume":" ","pages":""},"PeriodicalIF":0.0,"publicationDate":"2021-04-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46352988","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 : 2021-04-20DOI: 10.1088/2516-1067/abf6b0
R. Xiao, Youyou Gui, Guangshuai Zhang, Yanchao Shi, Huida Wang, Kun Chen
Microwave breakdown has always been a huge challenge to the development of high-power microwave (HPM) sources. Some unique breakdown phenomena in a novel and powerful overmoded relativistic backward wave oscillator (RBWO) operating at low magnetic field are demonstrated. Three different breakdown mechanisms are utilized to explain these phenomena through detailed electromagnetic field calculation and particle-in-cell demonstration and effective methods are applied or suggested to mitigate the breakdown. The breakdown in the slow wave structure (SWS) mainly results from bombardment by the main electron beam under the intense radial electric field. Increasing the span between the main electron beam and the SWS or applying a coaxial extraction structure operating at coaxial TM01 mode might decrease the radial electric field and lessen the bombardment. The breakdown in the internal reflector originates with the field-induced emission in the inner ring under the intense axial electric field of the TM01 and TM02 mode and the subsequent electron-triggered emission in the outer ring. Removing the central part or constructing a complex reflector surface can suppress the emission. The breakdown in the slot retained for the Rogowski coil results from low pressure gas discharge initiated by microwave leakage from the RBWO into the diode region. Pasting microwave absorbing material into the coaxial diode region helps to obtain normal beam current waveforms measured by the Rogowski coil.
{"title":"Microwave breakdown in an overmoded relativistic backward wave oscillator operating at low magnetic field","authors":"R. Xiao, Youyou Gui, Guangshuai Zhang, Yanchao Shi, Huida Wang, Kun Chen","doi":"10.1088/2516-1067/abf6b0","DOIUrl":"https://doi.org/10.1088/2516-1067/abf6b0","url":null,"abstract":"Microwave breakdown has always been a huge challenge to the development of high-power microwave (HPM) sources. Some unique breakdown phenomena in a novel and powerful overmoded relativistic backward wave oscillator (RBWO) operating at low magnetic field are demonstrated. Three different breakdown mechanisms are utilized to explain these phenomena through detailed electromagnetic field calculation and particle-in-cell demonstration and effective methods are applied or suggested to mitigate the breakdown. The breakdown in the slow wave structure (SWS) mainly results from bombardment by the main electron beam under the intense radial electric field. Increasing the span between the main electron beam and the SWS or applying a coaxial extraction structure operating at coaxial TM01 mode might decrease the radial electric field and lessen the bombardment. The breakdown in the internal reflector originates with the field-induced emission in the inner ring under the intense axial electric field of the TM01 and TM02 mode and the subsequent electron-triggered emission in the outer ring. Removing the central part or constructing a complex reflector surface can suppress the emission. The breakdown in the slot retained for the Rogowski coil results from low pressure gas discharge initiated by microwave leakage from the RBWO into the diode region. Pasting microwave absorbing material into the coaxial diode region helps to obtain normal beam current waveforms measured by the Rogowski coil.","PeriodicalId":36295,"journal":{"name":"Plasma Research Express","volume":" ","pages":""},"PeriodicalIF":0.0,"publicationDate":"2021-04-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43204467","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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