The modulational instability development of Langmuir waves is investigated in highly collisional plasmas where the characteristic frequency Ω of the modulated perturbations is much less than νeff, the effective electron collision frequency. It is demonstrated that the modulational instability for the situation considered is mostly determined by collisional effects (differential Joule heating nonlinearity), in contrast to the well‐known modulational instability in collisionless plasmas (where ponderomotive force nonlinearity dominates). Rates and thresholds of the instability are found in various limits. The modulational instability is most effective when the angles between a pump wave vector and wave vectors of the modulational perturbations are of order unity.
{"title":"Modulational instability of Langmuir waves in dense plasmas","authors":"S. Vladimirov, S. Popel, V. Tsytovich","doi":"10.1063/1.860579","DOIUrl":"https://doi.org/10.1063/1.860579","url":null,"abstract":"The modulational instability development of Langmuir waves is investigated in highly collisional plasmas where the characteristic frequency Ω of the modulated perturbations is much less than νeff, the effective electron collision frequency. It is demonstrated that the modulational instability for the situation considered is mostly determined by collisional effects (differential Joule heating nonlinearity), in contrast to the well‐known modulational instability in collisionless plasmas (where ponderomotive force nonlinearity dominates). Rates and thresholds of the instability are found in various limits. The modulational instability is most effective when the angles between a pump wave vector and wave vectors of the modulational perturbations are of order unity.","PeriodicalId":113346,"journal":{"name":"Physics of fluids. B, Plasma physics","volume":"134 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1993-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"127405032","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}
The small signal stability of crossed‐field devices fed by a thin electron beam is analyzed. The situation differs from diocotron modes in that the interaction cavity supports slow wave eigenmodes in vacuum. The rippling of the beam causes a modification of the vacuum dispersion relation and mode profiles. The growth rate is found by equating the rate of change of the power flux with the fast scale averaged wave–particle energy exchange rate. The radio frequency (rf) power flow including the energy circulating in the anode structure is related to the wave amplitude via the interaction impedance. The singularities at resonance, the trademark of any linear theory, are avoided by following the particle guiding center (GC) orbits in reference frame with the wave synchronous. The small signal gain is found by expansion in powers of the rf amplitude. A finite linear growth results, even for symmetric particle excursions, due to the self‐field of the rippled beam. Near resonance the growth rate is independent of...
{"title":"Nonsingular linear theory for stimulated microwave emission in crossed-field devices","authors":"S. Riyopoulos","doi":"10.1063/1.860585","DOIUrl":"https://doi.org/10.1063/1.860585","url":null,"abstract":"The small signal stability of crossed‐field devices fed by a thin electron beam is analyzed. The situation differs from diocotron modes in that the interaction cavity supports slow wave eigenmodes in vacuum. The rippling of the beam causes a modification of the vacuum dispersion relation and mode profiles. The growth rate is found by equating the rate of change of the power flux with the fast scale averaged wave–particle energy exchange rate. The radio frequency (rf) power flow including the energy circulating in the anode structure is related to the wave amplitude via the interaction impedance. The singularities at resonance, the trademark of any linear theory, are avoided by following the particle guiding center (GC) orbits in reference frame with the wave synchronous. The small signal gain is found by expansion in powers of the rf amplitude. A finite linear growth results, even for symmetric particle excursions, due to the self‐field of the rippled beam. Near resonance the growth rate is independent of...","PeriodicalId":113346,"journal":{"name":"Physics of fluids. B, Plasma physics","volume":"22 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1993-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"114322884","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}
The exact Hamiltonian and the first‐order corrections to the standard drift Hamiltonian are given in magnetic coordinates for a full static electromagnetic field with magnetic surfaces. The exact Hamiltonian depends on both the field strength and the shape of the magnetic surfaces (the metric of the magnetic coordinates) while the standard drift Hamiltonian depends on the field strength only. The first‐order correction to the standard drift Hamiltonian, in gyroradius to system size, depends in a generic way on the metric of the magnetic coordinates, as does the exact Hamiltonian. The finite‐Larmor‐radius effect and the polarization drift are in the first‐order corrections.
{"title":"The exact and drift Hamiltonian in a toroidal magnetic field","authors":"Qun Yao, A. Boozer","doi":"10.1063/1.860608","DOIUrl":"https://doi.org/10.1063/1.860608","url":null,"abstract":"The exact Hamiltonian and the first‐order corrections to the standard drift Hamiltonian are given in magnetic coordinates for a full static electromagnetic field with magnetic surfaces. The exact Hamiltonian depends on both the field strength and the shape of the magnetic surfaces (the metric of the magnetic coordinates) while the standard drift Hamiltonian depends on the field strength only. The first‐order correction to the standard drift Hamiltonian, in gyroradius to system size, depends in a generic way on the metric of the magnetic coordinates, as does the exact Hamiltonian. The finite‐Larmor‐radius effect and the polarization drift are in the first‐order corrections.","PeriodicalId":113346,"journal":{"name":"Physics of fluids. B, Plasma physics","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1993-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125528925","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}
Comparative observations of the Vacuum Spark discharge are presented under differing electrical drive conditions but identical geometrical conditions. A 1.5 Ω 120 nsec, coaxial line is used to provide maximum currents to 90 kA. The line may be operated in the usual switched mode to give a rectangular voltage and current wave form, or in the Hybrid mode, in which case the voltage builds slowly until breakdown occurs. In both modes of operation the value of dI/dt is about 1×1012 A/sec. A Nd:YAG is focused onto either electrode to initiate the discharge. With the laser focused onto the anode a low‐density plasma accompanied by intense electron beams is formed. With the laser focused on the cathode a much higher plasma density is observed in the gap, with the formation of a dense tight pinch close to the cathode, in which hot spots form at peak current. The Hybrid mode is favored for its reproducible behavior.
{"title":"Observations of a vacuum spark under different driver conditions of the applied voltage","authors":"H. Chuaqui, M. Favre, L. Soto, E. Wyndham","doi":"10.1063/1.860590","DOIUrl":"https://doi.org/10.1063/1.860590","url":null,"abstract":"Comparative observations of the Vacuum Spark discharge are presented under differing electrical drive conditions but identical geometrical conditions. A 1.5 Ω 120 nsec, coaxial line is used to provide maximum currents to 90 kA. The line may be operated in the usual switched mode to give a rectangular voltage and current wave form, or in the Hybrid mode, in which case the voltage builds slowly until breakdown occurs. In both modes of operation the value of dI/dt is about 1×1012 A/sec. A Nd:YAG is focused onto either electrode to initiate the discharge. With the laser focused onto the anode a low‐density plasma accompanied by intense electron beams is formed. With the laser focused on the cathode a much higher plasma density is observed in the gap, with the formation of a dense tight pinch close to the cathode, in which hot spots form at peak current. The Hybrid mode is favored for its reproducible behavior.","PeriodicalId":113346,"journal":{"name":"Physics of fluids. B, Plasma physics","volume":"9 2","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1993-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"120898525","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}
A sheared slab magnetic field model B=B0[ẑ+(x/Ls)ŷ], with inhomogeneous flows in the ŷ and ẑ directions, is used to perform a fully kinetic stability analysis of the ion temperature gradient (ITG) and dissipative trapped electron (DTE) modes. The concomitant quasilinear stress components that couple to the local perpendicular (y component) and parallel (z component) momentum transport are also calculated and the anomalous perpendicular and parallel viscous stresses obtained. A breakdown of the ITG‐induced viscous stresses are generally observed at moderate values of the sheared perpendicular flow. Even in the absence of external momentum sources, ion diamagnetic effects can generate an inhomogeneous radial electric field which gives rise to a sheared perpendicular flow which can sustain a sheared parallel flow. The effect of the perpendicular stress component in the momentum balance equations is generally small while the parallel stress component, which is primarily determined by the perpendicular flow sh...
{"title":"Anomalous momentum transport from drift wave turbulence","authors":"R. Dominguez, G. Staebler","doi":"10.1063/1.860610","DOIUrl":"https://doi.org/10.1063/1.860610","url":null,"abstract":"A sheared slab magnetic field model B=B0[ẑ+(x/Ls)ŷ], with inhomogeneous flows in the ŷ and ẑ directions, is used to perform a fully kinetic stability analysis of the ion temperature gradient (ITG) and dissipative trapped electron (DTE) modes. The concomitant quasilinear stress components that couple to the local perpendicular (y component) and parallel (z component) momentum transport are also calculated and the anomalous perpendicular and parallel viscous stresses obtained. A breakdown of the ITG‐induced viscous stresses are generally observed at moderate values of the sheared perpendicular flow. Even in the absence of external momentum sources, ion diamagnetic effects can generate an inhomogeneous radial electric field which gives rise to a sheared perpendicular flow which can sustain a sheared parallel flow. The effect of the perpendicular stress component in the momentum balance equations is generally small while the parallel stress component, which is primarily determined by the perpendicular flow sh...","PeriodicalId":113346,"journal":{"name":"Physics of fluids. B, Plasma physics","volume":"15 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1993-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"124948651","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}
The stability of toroidicity‐induced Alfven eigenmodes (TAE) is investigated in general tokamak equilibria with finite aspect ratio and finite plasma beta. The finite orbit width of the hot particles and the collisional damping of the trapped electrons are included. For the trapped hot particles, the finite orbit width is found to be stabilizing. For the circulating hot particles, the finite orbit width effect is stabilizing for larger values of vh/vA (≳1) and destabilizing for smaller values of vh/vA (<1), where vh is the hot particle speed and vA is the Alfven speed. The collisional damping of the trapped electrons is found to have a much weaker dependence on the collision frequency than the previous analytic results. The contribution of the curvature term to the trapped electron collisional damping is negligible compared to that of the parallel electric field term for typical parameters. The calculated critical hot particle beta values for the TAE instability are consistent with the experimental measur...
{"title":"Stability of the toroidicity‐induced Alfvén eigenmode in axisymmetric toroidal equilibria","authors":"G. Fu, C. Cheng, K. Wong","doi":"10.1063/1.860572","DOIUrl":"https://doi.org/10.1063/1.860572","url":null,"abstract":"The stability of toroidicity‐induced Alfven eigenmodes (TAE) is investigated in general tokamak equilibria with finite aspect ratio and finite plasma beta. The finite orbit width of the hot particles and the collisional damping of the trapped electrons are included. For the trapped hot particles, the finite orbit width is found to be stabilizing. For the circulating hot particles, the finite orbit width effect is stabilizing for larger values of vh/vA (≳1) and destabilizing for smaller values of vh/vA (<1), where vh is the hot particle speed and vA is the Alfven speed. The collisional damping of the trapped electrons is found to have a much weaker dependence on the collision frequency than the previous analytic results. The contribution of the curvature term to the trapped electron collisional damping is negligible compared to that of the parallel electric field term for typical parameters. The calculated critical hot particle beta values for the TAE instability are consistent with the experimental measur...","PeriodicalId":113346,"journal":{"name":"Physics of fluids. B, Plasma physics","volume":"57 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1993-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"123829221","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}
Toroidal drift mode features and stability are studied, using a fluid description, for a plasma with two ion species: impurity and main ions. Impurity and main ion temperature gradient (ITG) modes dominate for larger temperature gradients, ηi≳1, while dissipative trapped electron (DTE) and impurity‐induced modes are present also for ηi<1. Simple analytical expressions for the stability thresholds are derived from conditions given by the impurity and main ion fluids.
{"title":"Toroidal drift mode stability in a contaminated plasma","authors":"A. Jarmén, M. Fröjdh","doi":"10.1063/1.860621","DOIUrl":"https://doi.org/10.1063/1.860621","url":null,"abstract":"Toroidal drift mode features and stability are studied, using a fluid description, for a plasma with two ion species: impurity and main ions. Impurity and main ion temperature gradient (ITG) modes dominate for larger temperature gradients, ηi≳1, while dissipative trapped electron (DTE) and impurity‐induced modes are present also for ηi<1. Simple analytical expressions for the stability thresholds are derived from conditions given by the impurity and main ion fluids.","PeriodicalId":113346,"journal":{"name":"Physics of fluids. B, Plasma physics","volume":"12 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1993-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"128627753","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}
A compact formula for fully relativistic Thomson scattering spectrum including depolarization term is presented. By rational approximation, an analytic formula with high accuracy (relative error<0.1% at 100 keV) is obtained, which is applicable to a wide range of plasmas.
{"title":"Analytic formula for fully relativistic Thomson scattering spectrum","authors":"O. Naito, H. Yoshida, T. Matoba","doi":"10.1063/1.860593","DOIUrl":"https://doi.org/10.1063/1.860593","url":null,"abstract":"A compact formula for fully relativistic Thomson scattering spectrum including depolarization term is presented. By rational approximation, an analytic formula with high accuracy (relative error<0.1% at 100 keV) is obtained, which is applicable to a wide range of plasmas.","PeriodicalId":113346,"journal":{"name":"Physics of fluids. B, Plasma physics","volume":"24 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1993-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"132000523","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}
A new scheme of feedback suppression of the radiative condensation instability in the tokamak edge plasma is presented. The physics basis of this scheme is the modulation of the parallel electron thermal flux at the instability frequency via a feedback circuit. The latter consists of a temperature sensor, amplifiers, phase shifters, and a suitable form of insulated segmented poloidal limiter sections used as suppressors. The necessary feedback power is the order of a kilowatt for small tokamaks and a few megawatts for large reactor‐type machines.
{"title":"Feedback suppression of the radiative condensation instability","authors":"A. Sen","doi":"10.1063/1.860618","DOIUrl":"https://doi.org/10.1063/1.860618","url":null,"abstract":"A new scheme of feedback suppression of the radiative condensation instability in the tokamak edge plasma is presented. The physics basis of this scheme is the modulation of the parallel electron thermal flux at the instability frequency via a feedback circuit. The latter consists of a temperature sensor, amplifiers, phase shifters, and a suitable form of insulated segmented poloidal limiter sections used as suppressors. The necessary feedback power is the order of a kilowatt for small tokamaks and a few megawatts for large reactor‐type machines.","PeriodicalId":113346,"journal":{"name":"Physics of fluids. B, Plasma physics","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1993-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"122983746","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}
Y. Tsui, R. Fedosejevs, A. Offenberger, R. Rankin, C. Capjack
A calculation of the charge state distribution of the asymptotic evolution of a plasma produced by an ultraviolet laser has been carried out by coupling the results of a detailed two‐dimensional hydrodynamic simulation of the creation and heating of the plasma to a simpler one‐dimensional hydrodynamic code. The latter incorporates time‐dependent ionization and recombination physics and is used to model the subsequent expansion and cooling of the plasma. The simulation results are compared to experimental charge state distributions obtained by using a single shot electrodynamic charge analyzer. The sensitivity of the results to the rate coefficients used for the recombination calculations was tested and the calculated distributions were found to be most sensitive to the values of the three‐body recombination rate and the amount of heat returned to the plasma. Reasonable agreement was found between the measured and calculated charge state distributions.
{"title":"Numerical simulations of charge state distribution from a KrF laser-produced plasma","authors":"Y. Tsui, R. Fedosejevs, A. Offenberger, R. Rankin, C. Capjack","doi":"10.1063/1.860580","DOIUrl":"https://doi.org/10.1063/1.860580","url":null,"abstract":"A calculation of the charge state distribution of the asymptotic evolution of a plasma produced by an ultraviolet laser has been carried out by coupling the results of a detailed two‐dimensional hydrodynamic simulation of the creation and heating of the plasma to a simpler one‐dimensional hydrodynamic code. The latter incorporates time‐dependent ionization and recombination physics and is used to model the subsequent expansion and cooling of the plasma. The simulation results are compared to experimental charge state distributions obtained by using a single shot electrodynamic charge analyzer. The sensitivity of the results to the rate coefficients used for the recombination calculations was tested and the calculated distributions were found to be most sensitive to the values of the three‐body recombination rate and the amount of heat returned to the plasma. Reasonable agreement was found between the measured and calculated charge state distributions.","PeriodicalId":113346,"journal":{"name":"Physics of fluids. B, Plasma physics","volume":"1 18 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1993-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"127981892","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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