Pub Date : 2010-06-20DOI: 10.1109/PLASMA.2010.5534412
D. Go, R. Tirumala
Summary form only given. Over the past decade, the nature of breakdown in microscale electrode gaps has begun receiving significant attention both because of the potential impact breakdown could have on MEMS devices and as the development of plasma devices trends to smaller and smaller scales. It has been shown that the traditional description of breakdown called Paschen's curve holds true for larger electrode gaps, in the range of approximately 3-15 u m, breakdown deviates significantly from this form. It is now generally accepted that electron field emission is the physical mechanism that causes this deviation to form the so-called modified Paschen's curve. While a simple mathematical formulation exists for Paschen's curve, there is no simple formulation for modified Paschen's curve. A form that includes the effect of ion-enhanced field emission has been previously suggested, but this form relies heavily on a fitting factor. In this work, the underlying physics and parameters of the fitting factor are investigated to formulate an ab initio form of the modified Paschen's curve. This formulation includes the factors of the Fowler-Nordheim equation, and an electrostatics approximation for the impact an ion approaching the cathode has on the electric field. The implications of this approximation, how well it compares to experimental data, and how it may be used for parameteric design are all discussed.
{"title":"An ab initio approximation for the modified Paschen's curve for breakdown in microscale electrode gaps","authors":"D. Go, R. Tirumala","doi":"10.1109/PLASMA.2010.5534412","DOIUrl":"https://doi.org/10.1109/PLASMA.2010.5534412","url":null,"abstract":"Summary form only given. Over the past decade, the nature of breakdown in microscale electrode gaps has begun receiving significant attention both because of the potential impact breakdown could have on MEMS devices and as the development of plasma devices trends to smaller and smaller scales. It has been shown that the traditional description of breakdown called Paschen's curve holds true for larger electrode gaps, in the range of approximately 3-15 u m, breakdown deviates significantly from this form. It is now generally accepted that electron field emission is the physical mechanism that causes this deviation to form the so-called modified Paschen's curve. While a simple mathematical formulation exists for Paschen's curve, there is no simple formulation for modified Paschen's curve. A form that includes the effect of ion-enhanced field emission has been previously suggested, but this form relies heavily on a fitting factor. In this work, the underlying physics and parameters of the fitting factor are investigated to formulate an ab initio form of the modified Paschen's curve. This formulation includes the factors of the Fowler-Nordheim equation, and an electrostatics approximation for the impact an ion approaching the cathode has on the electric field. The implications of this approximation, how well it compares to experimental data, and how it may be used for parameteric design are all discussed.","PeriodicalId":6359,"journal":{"name":"2008 IEEE 35th International Conference on Plasma Science","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2010-06-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"91396178","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 : 2010-06-20DOI: 10.1109/PLASMA.2010.5534160
T. Hemke, A. Wollny, M. Gebhardt, R. Brinkmann, T. Mussenbrock
Summary form only given. An increasing number of different microplasma sources were developed over the last years. These sources differ in the underlying application, hence different types of geometry and discharge configuration, DC or RF discharges and the used chemistry exist. The variety of applications contains - among others - the wide field of surface modifications, light sources, steriliztation and display panels.
{"title":"Numerical simulation of an rf driven micro-plasmajet at atmospheric pressure","authors":"T. Hemke, A. Wollny, M. Gebhardt, R. Brinkmann, T. Mussenbrock","doi":"10.1109/PLASMA.2010.5534160","DOIUrl":"https://doi.org/10.1109/PLASMA.2010.5534160","url":null,"abstract":"Summary form only given. An increasing number of different microplasma sources were developed over the last years. These sources differ in the underlying application, hence different types of geometry and discharge configuration, DC or RF discharges and the used chemistry exist. The variety of applications contains - among others - the wide field of surface modifications, light sources, steriliztation and display panels.","PeriodicalId":6359,"journal":{"name":"2008 IEEE 35th International Conference on Plasma Science","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2010-06-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"91398192","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 : 2010-06-20DOI: 10.1109/PLASMA.2010.5534214
N. Sule, M. Kirley, B. Novaković, J. Scharer, I. Knezevic, J. Booske
We report experiments and analysis of field emission from copper knife-edge (CKE) cathodes, both bare and coated with low work function (2.6 eV) Lanthanum hexaboride (LaB6) thin films. The bare CKE cathode exhibits evidence of space charge limited emission currents at high field strengths. The LaB6 coated cathodes exhibit a nonlinear Fowler-Nordhiem (FN) type emission. An intermediate saturation region is observed from field emission data, which is more prominent at elevated (185 C) temperature. Surprisingly, the LaB6 coated cathodes are observed to emit less current than the higher work function (> 4 eV) bare CKE cathode. A hypothesis and corresponding model including both field emission and solid state electron transport from the Cu substrate, through the LaB6 thin film, is proposed to explain the experimental observations.
{"title":"Field emission from low-work function cathode coatings","authors":"N. Sule, M. Kirley, B. Novaković, J. Scharer, I. Knezevic, J. Booske","doi":"10.1109/PLASMA.2010.5534214","DOIUrl":"https://doi.org/10.1109/PLASMA.2010.5534214","url":null,"abstract":"We report experiments and analysis of field emission from copper knife-edge (CKE) cathodes, both bare and coated with low work function (2.6 eV) Lanthanum hexaboride (LaB6) thin films. The bare CKE cathode exhibits evidence of space charge limited emission currents at high field strengths. The LaB6 coated cathodes exhibit a nonlinear Fowler-Nordhiem (FN) type emission. An intermediate saturation region is observed from field emission data, which is more prominent at elevated (185 C) temperature. Surprisingly, the LaB6 coated cathodes are observed to emit less current than the higher work function (> 4 eV) bare CKE cathode. A hypothesis and corresponding model including both field emission and solid state electron transport from the Cu substrate, through the LaB6 thin film, is proposed to explain the experimental observations.","PeriodicalId":6359,"journal":{"name":"2008 IEEE 35th International Conference on Plasma Science","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2010-06-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"91396180","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 : 2010-06-20DOI: 10.1109/PLASMA.2010.5534313
O. Yardimci, Youwen Pan
Summary form only given. Microbicidal efficacy of plasma processing has been investigated as a possible alternative to conventional sterilization/decontamination methods for heat sensitive materials by a number of researchers from academia and industry. The disparity regarding the approaches to validating microbicidal efficacy makes study comparisons difficult. This review offers guidance on recommended practices for the evaluation of the microbicidal efficacy of plasma or any other sterilizing agent or process based on international industry standards and guidance documents.
{"title":"Microbicidal efficacy evaluation using plasma: International standards and recommended practices","authors":"O. Yardimci, Youwen Pan","doi":"10.1109/PLASMA.2010.5534313","DOIUrl":"https://doi.org/10.1109/PLASMA.2010.5534313","url":null,"abstract":"Summary form only given. Microbicidal efficacy of plasma processing has been investigated as a possible alternative to conventional sterilization/decontamination methods for heat sensitive materials by a number of researchers from academia and industry. The disparity regarding the approaches to validating microbicidal efficacy makes study comparisons difficult. This review offers guidance on recommended practices for the evaluation of the microbicidal efficacy of plasma or any other sterilizing agent or process based on international industry standards and guidance documents.","PeriodicalId":6359,"journal":{"name":"2008 IEEE 35th International Conference on Plasma Science","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2010-06-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"91398243","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 : 2010-01-04DOI: 10.1109/PLASMA.2010.5534189
Zheng Li, Hao Deng, D. Levin
Summary form only given. In order to extend the capability of the Hybrid Plasma Equipment Model (HPEM)1 simulation code to increasingly lower operating pressure conditions, the direct simulation Monte Carlo (DSMC)2 method is used to improve the modeling of the heavy particle species in a hollow cathode magnetron (HCM) plasma reactor, a device used to implement the Ionized Metal Physical Vapor Deposition (IMPVD) technology.The DSMC, at the current stage, is inserted between the fluid kinetics-Poisson module (FKPM) and plasma chemistry Monte Carlo module (PCMCM) module of HPEM as an correction to the FKPM at the low-pressure condition. The DSMC module initializes a large number of simulated particles (each represents 109 real atoms) at different computation cells in the plasma reactor with positions and instantaneous velocities according to the number density, temperature, flux from the FPKM. The continuous process of particle movement and interaction is uncoupled, i. e., at each time step every particle is moved according to its velocity subjecting to the electric and magnetic fields, then, the interaction between the particles is modeled by appropriate by collision and reaction models where the heavy-heavy particle reactions are implemented by total collision energy model while the electron impact reactions are introduced by the electron impact rate coefficients and source functions. In each HPEM iteration, the time-accurate DSMC calculation will be performed for a physical time of 1 μ, same as the FKPM module, with 10,000 DSMC steps. Sampling will be performed after 9,000 steps and the number density, temperature, and flux will be obtained by averaging the sampled particles at difference cells for different species. These properties along with the electric field will be output to the PCMCM module. Detailed models and simulation results will be presented in the conference paper.
{"title":"Low pressure semiconductor processing transport property modeling using direct simulation Monte Carlo","authors":"Zheng Li, Hao Deng, D. Levin","doi":"10.1109/PLASMA.2010.5534189","DOIUrl":"https://doi.org/10.1109/PLASMA.2010.5534189","url":null,"abstract":"Summary form only given. In order to extend the capability of the Hybrid Plasma Equipment Model (HPEM)1 simulation code to increasingly lower operating pressure conditions, the direct simulation Monte Carlo (DSMC)2 method is used to improve the modeling of the heavy particle species in a hollow cathode magnetron (HCM) plasma reactor, a device used to implement the Ionized Metal Physical Vapor Deposition (IMPVD) technology.The DSMC, at the current stage, is inserted between the fluid kinetics-Poisson module (FKPM) and plasma chemistry Monte Carlo module (PCMCM) module of HPEM as an correction to the FKPM at the low-pressure condition. The DSMC module initializes a large number of simulated particles (each represents 109 real atoms) at different computation cells in the plasma reactor with positions and instantaneous velocities according to the number density, temperature, flux from the FPKM. The continuous process of particle movement and interaction is uncoupled, i. e., at each time step every particle is moved according to its velocity subjecting to the electric and magnetic fields, then, the interaction between the particles is modeled by appropriate by collision and reaction models where the heavy-heavy particle reactions are implemented by total collision energy model while the electron impact reactions are introduced by the electron impact rate coefficients and source functions. In each HPEM iteration, the time-accurate DSMC calculation will be performed for a physical time of 1 μ, same as the FKPM module, with 10,000 DSMC steps. Sampling will be performed after 9,000 steps and the number density, temperature, and flux will be obtained by averaging the sampled particles at difference cells for different species. These properties along with the electric field will be output to the PCMCM module. Detailed models and simulation results will be presented in the conference paper.","PeriodicalId":6359,"journal":{"name":"2008 IEEE 35th International Conference on Plasma Science","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2010-01-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"91396573","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 : 2009-11-10DOI: 10.1109/ICIMW.2009.5324772
K. Sakamoto, A. Kasugai, K. Kajiwara, K. Takahashi, N. Kobayashi, Y. Oda
A 1 MW 170 GHz long pulse gyrotron is required for a power source of the electron cyclotron heating and current drive (EC H&CD) system on ITER (International Thermonuclear Experimental Reactor). In the ITER gyrotron development of JAEA (Japan Atomic Energy Agency), a stable 1 MW 170 GHz oscillation has been achieved at CW-relevant pulse duration (800 s), which is a twice of burning time of ITER plasma. The efficiency was 55% with the depressed collector with the precise optimization of the oscillation parameters in the hard self-excitation region during the oscillation. The power balance is measured calorimetrically, i.e., output power from the window is 1020 kW, power deposition to the collector is 742 kW, and a stray radiation output from the relief windows is 24 kW. Total ohmic-loss power into the inner components of the gyrotron is 63 kW. The power dissipation at the cavity agreed with the design value. The attained maximum efficiency in the long pulse mode is ~60%. The gyrotron has been working since March 2006 without major trouble, and records ~150 GJ of the output energy. The results satisfy the ITER requirement. As the frequency of 170 GHz is expected for the maximum toroidal field of 5.3 T at the plasma center of ITER, it is useful to estimate a frequency tunability of the gyrotron for the operation at lower toroidal filed. A simulation indicates that a similar performance is obtained at ~137 GHz oscillation at TE27,6 mode with the 170 GHz/TE31,8 mode oscillation. Both modes penetrate the diamond window of 1.853 mm in thickness. The triode magnetron injection gun (MIG) generates the rotational electron beam of low velocity divergence for both operation parameters. As for a fast frequency control, which will be useful for profile control in the fusion plasma, a He-free magnet with an additional super conducting sweeping coil was developed. A diameter of a room temperature bore is 240 mm, and the 7 T at the center. Using a commercially available standard DC power supplies, the magnetic field sweeping was demonstrated with a speed of 0.4 T/10 sec at 7 T.
{"title":"Progress of high power gyrotron development in JAEA","authors":"K. Sakamoto, A. Kasugai, K. Kajiwara, K. Takahashi, N. Kobayashi, Y. Oda","doi":"10.1109/ICIMW.2009.5324772","DOIUrl":"https://doi.org/10.1109/ICIMW.2009.5324772","url":null,"abstract":"A 1 MW 170 GHz long pulse gyrotron is required for a power source of the electron cyclotron heating and current drive (EC H&CD) system on ITER (International Thermonuclear Experimental Reactor). In the ITER gyrotron development of JAEA (Japan Atomic Energy Agency), a stable 1 MW 170 GHz oscillation has been achieved at CW-relevant pulse duration (800 s), which is a twice of burning time of ITER plasma. The efficiency was 55% with the depressed collector with the precise optimization of the oscillation parameters in the hard self-excitation region during the oscillation. The power balance is measured calorimetrically, i.e., output power from the window is 1020 kW, power deposition to the collector is 742 kW, and a stray radiation output from the relief windows is 24 kW. Total ohmic-loss power into the inner components of the gyrotron is 63 kW. The power dissipation at the cavity agreed with the design value. The attained maximum efficiency in the long pulse mode is ~60%. The gyrotron has been working since March 2006 without major trouble, and records ~150 GJ of the output energy. The results satisfy the ITER requirement. As the frequency of 170 GHz is expected for the maximum toroidal field of 5.3 T at the plasma center of ITER, it is useful to estimate a frequency tunability of the gyrotron for the operation at lower toroidal filed. A simulation indicates that a similar performance is obtained at ~137 GHz oscillation at TE27,6 mode with the 170 GHz/TE31,8 mode oscillation. Both modes penetrate the diamond window of 1.853 mm in thickness. The triode magnetron injection gun (MIG) generates the rotational electron beam of low velocity divergence for both operation parameters. As for a fast frequency control, which will be useful for profile control in the fusion plasma, a He-free magnet with an additional super conducting sweeping coil was developed. A diameter of a room temperature bore is 240 mm, and the 7 T at the center. Using a commercially available standard DC power supplies, the magnetic field sweeping was demonstrated with a speed of 0.4 T/10 sec at 7 T.","PeriodicalId":6359,"journal":{"name":"2008 IEEE 35th International Conference on Plasma Science","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2009-11-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"82173073","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 : 2009-06-01DOI: 10.1109/PLASMA.2009.5227469
E. Lock, S. Walton, R. Fernsler, M. Barakett
The present study investigates the polymer surface changes when the incident ion energy is increased to levels comparable to conventional, low pressure plasma discharges (20 eV). This allows for a study of polar groups incorporation, topography, and surface energy analysis over a range of ion energies not easily achieved in plasmas. The use of inert gas environments (Ar) would permit us to compare the influence of ion energy, while the addition of reactive gases (02) adds a chemical component to the studies.
{"title":"Polystyrene and PMMA surface modification by electron beam generated plasma in argon and oxygen - effect of increased ion energy on polymer surface characteristics","authors":"E. Lock, S. Walton, R. Fernsler, M. Barakett","doi":"10.1109/PLASMA.2009.5227469","DOIUrl":"https://doi.org/10.1109/PLASMA.2009.5227469","url":null,"abstract":"The present study investigates the polymer surface changes when the incident ion energy is increased to levels comparable to conventional, low pressure plasma discharges (20 eV). This allows for a study of polar groups incorporation, topography, and surface energy analysis over a range of ion energies not easily achieved in plasmas. The use of inert gas environments (Ar) would permit us to compare the influence of ion energy, while the addition of reactive gases (02) adds a chemical component to the studies.","PeriodicalId":6359,"journal":{"name":"2008 IEEE 35th International Conference on Plasma Science","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2009-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"91395236","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 : 2009-06-01DOI: 10.1109/PLASMA.2009.5227758
D. Abe, F. Wood, B. Levush, D. Pershing, E. Wright, K. Nguyen, R. Myers, E. Eisen
Summary form only given. We present recent progress on the development of an 18-beam multiple-beam klystron (MBK). The principal performance goals for this device include a peak rf output power of > 500 kW, an instantaneous bandwidth of 13% (1- dB), and high duty operation up to 2.5%. The detailed designs of the 18-beam electron gun and 7-cavity circuit are described in [K.T. Nguyen et. al., 2005] and [K.T. Nguyen et al., 2009], respectively. Experimental measurements of the resonant frequencies and Q's of the individual cavities comprising the circuit will be compared with 3D electromagnetics simulations using HFSS (Ansoft Corp.) and Analyst (STAAR). Final assembly of the gun and circuit is planned for April 2009 with hot-testing of the device to follow immediately. We will present comparisons of the experimentally measured voltage-current characteristics of the electron gun with 3D particle simulations using MICHELLE [J.J. Petillo, 2002], and, as available, results of high power rf performance tests.
{"title":"Recent progress on the development of a multiple-beam klystron with 13% bandwidth","authors":"D. Abe, F. Wood, B. Levush, D. Pershing, E. Wright, K. Nguyen, R. Myers, E. Eisen","doi":"10.1109/PLASMA.2009.5227758","DOIUrl":"https://doi.org/10.1109/PLASMA.2009.5227758","url":null,"abstract":"Summary form only given. We present recent progress on the development of an 18-beam multiple-beam klystron (MBK). The principal performance goals for this device include a peak rf output power of > 500 kW, an instantaneous bandwidth of 13% (1- dB), and high duty operation up to 2.5%. The detailed designs of the 18-beam electron gun and 7-cavity circuit are described in [K.T. Nguyen et. al., 2005] and [K.T. Nguyen et al., 2009], respectively. Experimental measurements of the resonant frequencies and Q's of the individual cavities comprising the circuit will be compared with 3D electromagnetics simulations using HFSS (Ansoft Corp.) and Analyst (STAAR). Final assembly of the gun and circuit is planned for April 2009 with hot-testing of the device to follow immediately. We will present comparisons of the experimentally measured voltage-current characteristics of the electron gun with 3D particle simulations using MICHELLE [J.J. Petillo, 2002], and, as available, results of high power rf performance tests.","PeriodicalId":6359,"journal":{"name":"2008 IEEE 35th International Conference on Plasma Science","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2009-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"91395690","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 : 2009-06-01DOI: 10.1109/PLASMA.2009.5227631
I. Alexeff, T. Anderson
We have developed a steerable plasma microwave mirror based on our previous work on the reflection of microwaves on a plasma slab. We have discovered that for plasma densities above microwave cutoff, the phase of the reflection varies continuously from a voltage antinode at the plasma surface when the plasma density just reaches microwave cutoff, to a voltage node at the plasma surface when the plasma density is much larger than that required for microwave cutoff. An analogy to the reflection at the end of a coaxial cable is that the first case corresponds to an open line (displacement and conduction currents equal and opposite), and the second case corresponds to a shorted line (conduction current much greater than displacement current). The operating plasma mirror as presently designed comprises a surface of plasma tubes. By programming the plasma density in the various tubes, the reflected microwaves experience a varying phase shift from tube to tube and the reflected beam is steered in analogy to the way an emitted microwave beam is steered by a phased transmission antenna array. The time required for reconfiguring the beam direction corresponds to the time required for plasma modification-in this case, a few milliseconds.
{"title":"A steerable plasma microwave mirror","authors":"I. Alexeff, T. Anderson","doi":"10.1109/PLASMA.2009.5227631","DOIUrl":"https://doi.org/10.1109/PLASMA.2009.5227631","url":null,"abstract":"We have developed a steerable plasma microwave mirror based on our previous work on the reflection of microwaves on a plasma slab. We have discovered that for plasma densities above microwave cutoff, the phase of the reflection varies continuously from a voltage antinode at the plasma surface when the plasma density just reaches microwave cutoff, to a voltage node at the plasma surface when the plasma density is much larger than that required for microwave cutoff. An analogy to the reflection at the end of a coaxial cable is that the first case corresponds to an open line (displacement and conduction currents equal and opposite), and the second case corresponds to a shorted line (conduction current much greater than displacement current). The operating plasma mirror as presently designed comprises a surface of plasma tubes. By programming the plasma density in the various tubes, the reflected microwaves experience a varying phase shift from tube to tube and the reflected beam is steered in analogy to the way an emitted microwave beam is steered by a phased transmission antenna array. The time required for reconfiguring the beam direction corresponds to the time required for plasma modification-in this case, a few milliseconds.","PeriodicalId":6359,"journal":{"name":"2008 IEEE 35th International Conference on Plasma Science","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2009-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"89380349","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 : 2008-08-08DOI: 10.1109/PLASMA.2008.4591078
A. Esaulov, V. Kantsyrev, A. Safronova, K. Williamson, I. Shrestha, G. Osborne, R. Mcbride, P. Knapp, D. Chalenski, J. Greenly, D. Hammer
Summary form only given. Wire array implosions with different current pulse rise times have been studied on the 1 MA COBRA facility at Cornell University. The flexibility of the COBRA generator allowed switching between the short (100 ns) and long (220 ns) current pulse rise time to study the implosion of nested wire array loads in these two regimes. The load design and optimization was performed by simulations with the novel wire ablation dynamics model (WADM) code, which extended the original wire dynamics model by including the dynamics of wire ablation and precursor plasma formation on the array axis. As compared to the short current pulse, the longer current rise time allows increasing the array mass. By switching between the different pulse shapes the implosion dynamics of nested arrays made from the same wires, but with different wire numbers, have been compared. While the time of the wire core ablation is directly proportional of the array mass, the implosion time is proportional to the square root of the array mass. WADM simulations demonstrate that the implosion dynamics of the arrays with higher mass is more ablation dominated. If the process of core ablation is long enough, it causes the delay of the array implosion versus the predictions by a 0D model that does not account for ablation. Another factor that affects the result of the trade between the ablation and implosion time scales is the form of the current pulse, which can be very different from the classical sin2 shape. This factor was self-consistently taken into account in the WADM simulations. The prediction of the array implosion times by the WADM are in a very good agreement with the recent experiments on the COBRA generator.
{"title":"Wire array load design and optimization for short (100 ns) and long (220 ns) current rise time on the 1 MA cobra generator","authors":"A. Esaulov, V. Kantsyrev, A. Safronova, K. Williamson, I. Shrestha, G. Osborne, R. Mcbride, P. Knapp, D. Chalenski, J. Greenly, D. Hammer","doi":"10.1109/PLASMA.2008.4591078","DOIUrl":"https://doi.org/10.1109/PLASMA.2008.4591078","url":null,"abstract":"Summary form only given. Wire array implosions with different current pulse rise times have been studied on the 1 MA COBRA facility at Cornell University. The flexibility of the COBRA generator allowed switching between the short (100 ns) and long (220 ns) current pulse rise time to study the implosion of nested wire array loads in these two regimes. The load design and optimization was performed by simulations with the novel wire ablation dynamics model (WADM) code, which extended the original wire dynamics model by including the dynamics of wire ablation and precursor plasma formation on the array axis. As compared to the short current pulse, the longer current rise time allows increasing the array mass. By switching between the different pulse shapes the implosion dynamics of nested arrays made from the same wires, but with different wire numbers, have been compared. While the time of the wire core ablation is directly proportional of the array mass, the implosion time is proportional to the square root of the array mass. WADM simulations demonstrate that the implosion dynamics of the arrays with higher mass is more ablation dominated. If the process of core ablation is long enough, it causes the delay of the array implosion versus the predictions by a 0D model that does not account for ablation. Another factor that affects the result of the trade between the ablation and implosion time scales is the form of the current pulse, which can be very different from the classical sin2 shape. This factor was self-consistently taken into account in the WADM simulations. The prediction of the array implosion times by the WADM are in a very good agreement with the recent experiments on the COBRA generator.","PeriodicalId":6359,"journal":{"name":"2008 IEEE 35th International Conference on Plasma Science","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2008-08-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"88019654","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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