Pub Date : 1994-06-06DOI: 10.1109/PLASMA.1994.589036
N. Sternberg, V. Godyak
of 2 95% for large size problems. The particle pash time achieved is 115 nsecs/particle/time step for 162 mdlion particles on 512 nodes. Comparing with the performance on a single processor Cray C90, this represents a factor of 58 speedup. The code uses a finite-difference leap frog method for field solve which is significantly more efficient than fast Fourier transforms on parallel computers. The performance of this code on the 128 node Cray T3D will also be discussed.
{"title":"Approximation Of The Bounded Plasma Model By The Plasma And The Sheath Models","authors":"N. Sternberg, V. Godyak","doi":"10.1109/PLASMA.1994.589036","DOIUrl":"https://doi.org/10.1109/PLASMA.1994.589036","url":null,"abstract":"of 2 95% for large size problems. The particle pash time achieved is 115 nsecs/particle/time step for 162 mdlion particles on 512 nodes. Comparing with the performance on a single processor Cray C90, this represents a factor of 58 speedup. The code uses a finite-difference leap frog method for field solve which is significantly more efficient than fast Fourier transforms on parallel computers. The performance of this code on the 128 node Cray T3D will also be discussed.","PeriodicalId":254741,"journal":{"name":"Proceedings of 1994 IEEE 21st International Conference on Plasma Sciences (ICOPS)","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1994-06-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"129580185","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 : 1994-06-06DOI: 10.1109/PLASMA.1994.589112
M. Fazio, W. B. Haynes, B. Carlsten, R.M. Stingfield
This paper describes the experimental development of a long pulse high current, annular beam relativistic klystron amplifier. The desired performance parameters are 1 GW output power and 1 {mu}s pulse length with an operating frequency of 1.3 GHz. the electron beam voltage and current are nominally 600 kV and 5 kA. Peak powers approaching 500 MW have been achieved in pulses of 1 {mu}s nominal baseline-to-baseline duration. The half power pulse width is 0.5 {mu}s. These pulses contain an energy of about 160 J. The rf output terminates abruptly just before the highest parts of the beam voltage and current pulses are reached. The cause of the premature termination of the rf pulse has not been definitely determined. Experimental observations indicate that the rf pulse termination could be the result of the output cavity gap voltage being too high, causing electron reflection at the gap and rf breakdown across the gap. To reduce the output gap voltage, a new output cavity has been designed with a much lower shunt impedance and a loaded Q of 4. Current experimental results and theoretical design considerations for this class of tube are discussed.
{"title":"One microsecond Pulse-width Annular Beam Relativistic Klystron Operating at 500 MW","authors":"M. Fazio, W. B. Haynes, B. Carlsten, R.M. Stingfield","doi":"10.1109/PLASMA.1994.589112","DOIUrl":"https://doi.org/10.1109/PLASMA.1994.589112","url":null,"abstract":"This paper describes the experimental development of a long pulse high current, annular beam relativistic klystron amplifier. The desired performance parameters are 1 GW output power and 1 {mu}s pulse length with an operating frequency of 1.3 GHz. the electron beam voltage and current are nominally 600 kV and 5 kA. Peak powers approaching 500 MW have been achieved in pulses of 1 {mu}s nominal baseline-to-baseline duration. The half power pulse width is 0.5 {mu}s. These pulses contain an energy of about 160 J. The rf output terminates abruptly just before the highest parts of the beam voltage and current pulses are reached. The cause of the premature termination of the rf pulse has not been definitely determined. Experimental observations indicate that the rf pulse termination could be the result of the output cavity gap voltage being too high, causing electron reflection at the gap and rf breakdown across the gap. To reduce the output gap voltage, a new output cavity has been designed with a much lower shunt impedance and a loaded Q of 4. Current experimental results and theoretical design considerations for this class of tube are discussed.","PeriodicalId":254741,"journal":{"name":"Proceedings of 1994 IEEE 21st International Conference on Plasma Sciences (ICOPS)","volume":"53 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1994-06-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"124628217","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 : 1994-06-06DOI: 10.1109/PLASMA.1994.589101
Jianou Shi, W. Ernst, D. A. Santavicca
The measurements and simulation of barium atom and ion number densities in low and high frequency fluorescent lamp are presented. Barium emitted from the electrode surface has a strong interaction with the local plasma. The distributions of number densities for barium atom and ion depend mainly on the discharge conditions, such as the temperature of the operating electrode, and the number densities and distributions of other species (e.g. argon and mercury). A Monte Carlo computer simulation for the distribution of Ba{sup +} number density is described and the results from the simulation are compared to the experiment results obtained by absorption spectroscopy. A good agreement is reached between the simulation and the experimental Ba{sup +} distribution.
{"title":"Barium Atom and ion densities in a fluorescent lamp obtained from measurements and computer simulations","authors":"Jianou Shi, W. Ernst, D. A. Santavicca","doi":"10.1109/PLASMA.1994.589101","DOIUrl":"https://doi.org/10.1109/PLASMA.1994.589101","url":null,"abstract":"The measurements and simulation of barium atom and ion number densities in low and high frequency fluorescent lamp are presented. Barium emitted from the electrode surface has a strong interaction with the local plasma. The distributions of number densities for barium atom and ion depend mainly on the discharge conditions, such as the temperature of the operating electrode, and the number densities and distributions of other species (e.g. argon and mercury). A Monte Carlo computer simulation for the distribution of Ba{sup +} number density is described and the results from the simulation are compared to the experiment results obtained by absorption spectroscopy. A good agreement is reached between the simulation and the experimental Ba{sup +} distribution.","PeriodicalId":254741,"journal":{"name":"Proceedings of 1994 IEEE 21st International Conference on Plasma Sciences (ICOPS)","volume":"42 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1994-06-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"124837688","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 : 1994-06-06DOI: 10.1109/PLASMA.1994.589001
R. Kares
{"title":"The Role Of Potential Hills And Reflexing Electrons In The Operation Of A Plasma Opening Switch","authors":"R. Kares","doi":"10.1109/PLASMA.1994.589001","DOIUrl":"https://doi.org/10.1109/PLASMA.1994.589001","url":null,"abstract":"","PeriodicalId":254741,"journal":{"name":"Proceedings of 1994 IEEE 21st International Conference on Plasma Sciences (ICOPS)","volume":"28 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1994-06-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"127267292","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 : 1994-06-06DOI: 10.1109/PLASMA.1994.589055
D. Stoudt, M. A. Richardson, D. Demske, R. Roush, K. Eure
Recent high-power, subnanosecond-switching results of the Bistable Optically controlled Semiconductor Switch (BOSS) are presented. The process of persistent photoconductivity followed by photo-quenching have been demonstrated at megawatt power levels in copper-compensated, silicon-doped, semi-insulating gallium arsenide. These processes allow a switch to be developed that can be closed by the application of one laser pulse and opened by the application of a second laser pulse with a wavelength equal to twice that of the first laser. Switch closure is primarily achieved by elevating electrons from a deep copper center which has been diffused into the material. The opening phase is a two-step process which relies initially on the absorption of the 2-{mu}m laser causing electrons to be elevated from the valance band back into the copper center, and finally on the recombination of electrons in the conduction band with boles in the valance band. The second step requires a sufficient concentration of recombination centers (RC) in the material for opening to occur in the subnanosecond regime. These RC`s are generated in the bulk GaAs material by fast-neutron irradiation ({approximately} 1 MeV) at a fluence of about 3 {times} 10{sup 15} cm{sup {minus}2}. High-power switching results which demonstrate that the BOSS switchmore » can be opened in the subnanosecond regime are presented for the first time. Neutron-irradiated BOSS devices have been opened against a rising electric field of about 20 kV/cm (10 kV) in a time less than one nanosecond. Kilovolt electrical pulses have been generated with a FWHM of roughly 250 picoseconds.« less
{"title":"High-power Subnanosecond Operation of a stable Optically Controlled Semiconductor Switch (BOSS).","authors":"D. Stoudt, M. A. Richardson, D. Demske, R. Roush, K. Eure","doi":"10.1109/PLASMA.1994.589055","DOIUrl":"https://doi.org/10.1109/PLASMA.1994.589055","url":null,"abstract":"Recent high-power, subnanosecond-switching results of the Bistable Optically controlled Semiconductor Switch (BOSS) are presented. The process of persistent photoconductivity followed by photo-quenching have been demonstrated at megawatt power levels in copper-compensated, silicon-doped, semi-insulating gallium arsenide. These processes allow a switch to be developed that can be closed by the application of one laser pulse and opened by the application of a second laser pulse with a wavelength equal to twice that of the first laser. Switch closure is primarily achieved by elevating electrons from a deep copper center which has been diffused into the material. The opening phase is a two-step process which relies initially on the absorption of the 2-{mu}m laser causing electrons to be elevated from the valance band back into the copper center, and finally on the recombination of electrons in the conduction band with boles in the valance band. The second step requires a sufficient concentration of recombination centers (RC) in the material for opening to occur in the subnanosecond regime. These RC`s are generated in the bulk GaAs material by fast-neutron irradiation ({approximately} 1 MeV) at a fluence of about 3 {times} 10{sup 15} cm{sup {minus}2}. High-power switching results which demonstrate that the BOSS switchmore » can be opened in the subnanosecond regime are presented for the first time. Neutron-irradiated BOSS devices have been opened against a rising electric field of about 20 kV/cm (10 kV) in a time less than one nanosecond. Kilovolt electrical pulses have been generated with a FWHM of roughly 250 picoseconds.« less","PeriodicalId":254741,"journal":{"name":"Proceedings of 1994 IEEE 21st International Conference on Plasma Sciences (ICOPS)","volume":"1210 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1994-06-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"116214623","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 : 1994-06-06DOI: 10.1109/PLASMA.1994.588709
A. Srivastava, J. Asmussen
{"title":"Measurements Of The Impressed Electric Field Inside A Coaxial Ecr Plasma Source","authors":"A. Srivastava, J. Asmussen","doi":"10.1109/PLASMA.1994.588709","DOIUrl":"https://doi.org/10.1109/PLASMA.1994.588709","url":null,"abstract":"","PeriodicalId":254741,"journal":{"name":"Proceedings of 1994 IEEE 21st International Conference on Plasma Sciences (ICOPS)","volume":"144 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1994-06-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"116443072","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 : 1994-06-06DOI: 10.1109/PLASMA.1994.588816
S. Nikitin, A. Ponomarenko
{"title":"Exploding Plasma In Dipole Magnetic Field","authors":"S. Nikitin, A. Ponomarenko","doi":"10.1109/PLASMA.1994.588816","DOIUrl":"https://doi.org/10.1109/PLASMA.1994.588816","url":null,"abstract":"","PeriodicalId":254741,"journal":{"name":"Proceedings of 1994 IEEE 21st International Conference on Plasma Sciences (ICOPS)","volume":"10 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1994-06-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125517085","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 : 1994-06-06DOI: 10.1109/PLASMA.1994.589071
J. E. Beers
High power microwave tubes require well focussed high energy electron beams High frequencies cause the r-f interaction with the beam to concentrate in the outer edge of the beam making the center relatively unimportant The Magnetron Injection Gun (MIG) uses a truncated cone for a cathode and an axial magnetic field to concentrate the electron current in an annulus eliminating the current in the center of the beam High power microwave tubes used for r f plasma generation, and for accelerators require these high current relativistic beams A theoretical study of Relativistic MIG's has been carried out using PBGUNS', a digital program for the Poisson simulation of particle beams The simulations show that there are two types of guns that need to be considered those with cathodes that are short axially compared with their mean radius from the axis and those whose length are comparable to or longer than the mean radius Short cathodes are dominated by the axial end conditions which need to be close to the Pierce angle (67 5 degrees) but are little effected by the shape of the accelerating electrode The longer cathodes are critically dependent on both the end conditions and the accelerating electrode One or two transition regions are needed, one to transporl the beam to its final diameter and a second to turn it axially in such a way that it does not ripple excessively before it reaches the front of the cathode, but can be relieved by reducing the magnetic field so that the electrons rise well above the cathode Longer cathodes can also be stabilized by using larger cone angles Cone half angles of less than 15 degrees tend to be more unstable The longer the cathode and the higher the current the greater the difficulty in forming a transportable, compressed beam Several examples will be presented
{"title":"Computer Simulations Of Relativistic Mlg's With Magnetically Compressed Beams For High Power Microwave Tubes","authors":"J. E. Beers","doi":"10.1109/PLASMA.1994.589071","DOIUrl":"https://doi.org/10.1109/PLASMA.1994.589071","url":null,"abstract":"High power microwave tubes require well focussed high energy electron beams High frequencies cause the r-f interaction with the beam to concentrate in the outer edge of the beam making the center relatively unimportant The Magnetron Injection Gun (MIG) uses a truncated cone for a cathode and an axial magnetic field to concentrate the electron current in an annulus eliminating the current in the center of the beam High power microwave tubes used for r f plasma generation, and for accelerators require these high current relativistic beams A theoretical study of Relativistic MIG's has been carried out using PBGUNS', a digital program for the Poisson simulation of particle beams The simulations show that there are two types of guns that need to be considered those with cathodes that are short axially compared with their mean radius from the axis and those whose length are comparable to or longer than the mean radius Short cathodes are dominated by the axial end conditions which need to be close to the Pierce angle (67 5 degrees) but are little effected by the shape of the accelerating electrode The longer cathodes are critically dependent on both the end conditions and the accelerating electrode One or two transition regions are needed, one to transporl the beam to its final diameter and a second to turn it axially in such a way that it does not ripple excessively before it reaches the front of the cathode, but can be relieved by reducing the magnetic field so that the electrons rise well above the cathode Longer cathodes can also be stabilized by using larger cone angles Cone half angles of less than 15 degrees tend to be more unstable The longer the cathode and the higher the current the greater the difficulty in forming a transportable, compressed beam Several examples will be presented","PeriodicalId":254741,"journal":{"name":"Proceedings of 1994 IEEE 21st International Conference on Plasma Sciences (ICOPS)","volume":"149 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1994-06-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"124159606","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 : 1994-06-06DOI: 10.1109/PLASMA.1994.589048
K. Riemann
{"title":"Theory Of The Plasma-sheath Transition And The Bohm Criterion","authors":"K. Riemann","doi":"10.1109/PLASMA.1994.589048","DOIUrl":"https://doi.org/10.1109/PLASMA.1994.589048","url":null,"abstract":"","PeriodicalId":254741,"journal":{"name":"Proceedings of 1994 IEEE 21st International Conference on Plasma Sciences (ICOPS)","volume":"42 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1994-06-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"126763010","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 : 1994-06-06DOI: 10.1109/PLASMA.1994.588913
W. Zhang, C. Xiao, L. Zhang, A. Hirose
Liniiter biasiiig experiments has been carried out on the STOR-51 tokaiiiak. The liiniter consists of eight stainless steel scgiiieiits in a sandwich structure with equal number of segments on hotli sides of a ceramic base. In the experiments reported here, all four segments on one side are connected togct1ic.r to form a limiter and can be biased either positively (1120 lr, 25 A) or nega.tively (-380 V, -40 A) with respect to tlie tokamak chamber. The segments on the other side are used to measure the plasma floating potential and its fluctuations ( V J ) in the scrape-off-layer (SOL). A movable Langmuir probe at the outer board measures those quantities in both SOL and at the edge (./a < 1) regions. It has been found that floating potential fluctuations in the SOL region depend mainly on the polarity of the limiter potential, not the potential gradient. The potential fluctuations in the SOL were strongly suppressed with a positive limiter potential and enhanced dramatically with a negative limiter potential, despite observations that the potential profile was steeper in the SOL region during negative biasing. The behaviour of Vf may be related to the interchange-flute instability with dissipation caused by fluctuating currents flowing through the Langmuir sheath potential near the surface of the limiter'. At the plasma edge the suppression of the fluctuations is always accompanied by a steeper potential profile, which indicates that the rotational shear layer may be the cause for fluctuation suppression inthat region. Despite different behaviours of Vf during the positive and negative bias, improved confinement has been observed for both bias polarities. The improved confinement is characterized by significant density increase (100% for positive bias and 80% for negative bias) and sudden drop in H, radiation level.
{"title":"Limiter Biasing Experiments On The Stor-m Tokamak","authors":"W. Zhang, C. Xiao, L. Zhang, A. Hirose","doi":"10.1109/PLASMA.1994.588913","DOIUrl":"https://doi.org/10.1109/PLASMA.1994.588913","url":null,"abstract":"Liniiter biasiiig experiments has been carried out on the STOR-51 tokaiiiak. The liiniter consists of eight stainless steel scgiiieiits in a sandwich structure with equal number of segments on hotli sides of a ceramic base. In the experiments reported here, all four segments on one side are connected togct1ic.r to form a limiter and can be biased either positively (1120 lr, 25 A) or nega.tively (-380 V, -40 A) with respect to tlie tokamak chamber. The segments on the other side are used to measure the plasma floating potential and its fluctuations ( V J ) in the scrape-off-layer (SOL). A movable Langmuir probe at the outer board measures those quantities in both SOL and at the edge (./a < 1) regions. It has been found that floating potential fluctuations in the SOL region depend mainly on the polarity of the limiter potential, not the potential gradient. The potential fluctuations in the SOL were strongly suppressed with a positive limiter potential and enhanced dramatically with a negative limiter potential, despite observations that the potential profile was steeper in the SOL region during negative biasing. The behaviour of Vf may be related to the interchange-flute instability with dissipation caused by fluctuating currents flowing through the Langmuir sheath potential near the surface of the limiter'. At the plasma edge the suppression of the fluctuations is always accompanied by a steeper potential profile, which indicates that the rotational shear layer may be the cause for fluctuation suppression inthat region. Despite different behaviours of Vf during the positive and negative bias, improved confinement has been observed for both bias polarities. The improved confinement is characterized by significant density increase (100% for positive bias and 80% for negative bias) and sudden drop in H, radiation level.","PeriodicalId":254741,"journal":{"name":"Proceedings of 1994 IEEE 21st International Conference on Plasma Sciences (ICOPS)","volume":"251 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1994-06-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"132677733","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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