Ultra-high vacuum photoelectron linear accelerator

DOEpatents

Yu, David U.L.; Luo, Yan

2013-07-16

An rf linear accelerator for producing an electron beam. The outer wall of the rf cavity of said linear accelerator being perforated to allow gas inside said rf cavity to flow to a pressure chamber surrounding said rf cavity and having means of ultra high vacuum pumping of the cathode of said rf linear accelerator. Said rf linear accelerator is used to accelerate polarized or unpolarized electrons produced by a photocathode, or to accelerate thermally heated electrons produced by a thermionic cathode, or to accelerate rf heated field emission electrons produced by a field emission cathode.

The plasma properties and electron emission characteristics of near-zero differential resistance of hollow cathode-based plasma contactors with a discharge chamber

NASA Astrophysics Data System (ADS)

Xie, Kan; Farnell, Casey C.; Williams, John D.

2014-08-01

The formation of electron emission-bias voltage (I-V) characteristics of near-zero differential resistance in the cathodic plasma contactor for bare electrodynamic tether applications, based on a hollow cathode embedded in a ring-cusp ionization stage, is studied. The existence of such an I-V regime is important to achieve low impedance performance without being affected by the space plasma properties for a cathodic plasma contactor. Experimental data on the plasma structure and properties downstream from the ionization stage are presented as functions of the xenon flow rate and the electron emission current. The electrons were emitted from the cathode to the cylindrical vacuum chamber wall (r = 0.9 m) under ≈10-5 Torr of vacuum pressure. The ring-cusp configuration selected for the plasma contactor created a 125-Gauss axial field near the cathode orifice, along with a large-volume 50-Gauss magnitude pocket in the stage. A baseline ion energy cost of ≈300 eV/ion was measured in the ionization stage when no electrons were emitted to the vacuum chamber wall. In addition, the anode fall growth limited the maximum propellant unitization to below ≈75% in the discharge loss curves for this ion stage. Detailed measurements on the plasma properties were carried out for the no-electron emission and 3 A emission conditions. The experimental data are compared with 1-D models, and the effectiveness of the model is discussed. The four key issues that played important roles in the process of building the near-zero different resistance I-V regime are: a significant amount of ionization by the emission electrons, a decrease in the number of reflected electrons in the plume, the electron-temperature increment, and low initial ion energy at the source outlet.

Investigation on the Plasma-Induced Emission Properties of Large Area Carbon Nanotube Array Cathodes with Different Morphologies

PubMed Central

2011-01-01

Large area well-aligned carbon nanotube (CNT) arrays with different morphologies were synthesized by using a chemical vapor deposition. The plasma-induced emission properties of CNT array cathodes with different morphologies were investigated. The ratio of CNT height to CNT-to-CNT distance has considerable effects on their plasma-induced emission properties. As the ratio increases, emission currents of CNT array cathodes decrease due to screening effects. Under the pulse electric field of about 6 V/μm, high-intensity electron beams of 170–180 A/cm2 were emitted from the surface plasma. The production mechanism of the high-intensity electron beams emitted from the CNT arrays was plasma-induced emission. Moreover, the distribution of the electron beams was in situ characterized by the light emission from the surface plasma. PMID:27502662

Investigation on the Plasma-Induced Emission Properties of Large Area Carbon Nanotube Array Cathodes with Different Morphologies.

PubMed

Liao, Qingliang; Qin, Zi; Zhang, Zheng; Qi, Junjie; Zhang, Yue; Huang, Yunhua; Liu, Liang

2011-12-01

Large area well-aligned carbon nanotube (CNT) arrays with different morphologies were synthesized by using a chemical vapor deposition. The plasma-induced emission properties of CNT array cathodes with different morphologies were investigated. The ratio of CNT height to CNT-to-CNT distance has considerable effects on their plasma-induced emission properties. As the ratio increases, emission currents of CNT array cathodes decrease due to screening effects. Under the pulse electric field of about 6 V/μm, high-intensity electron beams of 170-180 A/cm(2) were emitted from the surface plasma. The production mechanism of the high-intensity electron beams emitted from the CNT arrays was plasma-induced emission. Moreover, the distribution of the electron beams was in situ characterized by the light emission from the surface plasma.

Thermionic Properties of Carbon Based Nanomaterials Produced by Microhollow Cathode PECVD

NASA Technical Reports Server (NTRS)

Haase, John R.; Wolinksy, Jason J.; Bailey, Paul S.; George, Jeffrey A.; Go, David B.

2015-01-01

Thermionic emission is the process in which materials at sufficiently high temperature spontaneously emit electrons. This process occurs when electrons in a material gain sufficient thermal energy from heating to overcome the material's potential barrier, referred to as the work function. For most bulk materials very high temperatures (greater than 1500 K) are needed to produce appreciable emission. Carbon-based nanomaterials have shown significant promise as emission materials because of their low work functions, nanoscale geometry, and negative electron affinity. One method of producing these materials is through the process known as microhollow cathode PECVD. In a microhollow cathode plasma, high energy electrons oscillate at very high energies through the Pendel effect. These high energy electrons create numerous radical species and the technique has been shown to be an effective method of growing carbon based nanomaterials. In this work, we explore the thermionic emission properties of carbon based nanomaterials produced by microhollow cathode PECVD under a variety of synthesis conditions. Initial studies demonstrate measureable current at low temperatures (approximately 800 K) and work functions (approximately 3.3 eV) for these materials.

Vacuum encapsulated, high temperature diamond amplified cathode capsule and method for making same

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rao, Triveni; Walsh, Josh; Gangone, Elizabeth

2015-12-29

A vacuum encapsulated, hermetically sealed cathode capsule for generating an electron beam of secondary electrons, which generally includes a cathode element having a primary emission surface adapted to emit primary electrons, an annular insulating spacer, a diamond window element comprising a diamond material and having a secondary emission surface adapted to emit secondary electrons in response to primary electrons impinging on the diamond window element, a first high-temperature solder weld disposed between the diamond window element and the annular insulating spacer and a second high-temperature solder weld disposed between the annular insulating spacer and the cathode element. The cathode capsulemore » is formed by a high temperature weld process under vacuum such that the first solder weld forms a hermetical seal between the diamond window element and the annular insulating spacer and the second solder weld forms a hermetical seal between the annular spacer and the cathode element whereby a vacuum encapsulated chamber is formed within the capsule.« less

Vacuum encapsulated hermetically sealed diamond amplified cathode capsule and method for making same

DOEpatents

Rao, Triveni; Walsh, John; Gangone, Elizabeth

2014-12-30

A vacuum encapsulated, hermetically sealed cathode capsule for generating an electron beam of secondary electrons, which generally includes a cathode element having a primary emission surface adapted to emit primary electrons, an annular insulating spacer, a diamond window element comprising a diamond material and having a secondary emission surface adapted to emit secondary electrons in response to primary electrons impinging on the diamond window element, a first cold-weld ring disposed between the cathode element and the annular insulating spacer and a second cold-weld ring disposed between the annular insulating spacer and the diamond window element. The cathode capsule is formed by a vacuum cold-weld process such that the first cold-weld ring forms a hermetical seal between the cathode element and the annular insulating spacer and the second cold-weld ring forms a hermetical seal between the annular spacer and the diamond window element whereby a vacuum encapsulated chamber is formed within the capsule.

Extended OLED operational lifetime through phosphorescent dopant profile management

DOEpatents

Forrest, Stephen R.; Zhang, Yifan

2017-05-30

This disclosure relates, at least in part, an organic light emitting device, which in some embodiments comprises an anode; a cathode; a first emissive layer disposed between the anode and the cathode, the first emissive layer comprising an electron transporting compound and a phosphorescent emissive dopant compound; and wherein the phosphorescent emissive dopant compound has a concentration gradient, in the emissive layer, which varies from the cathode side of the first emissive layer to the anode side of the emissive layer.

Application of carbon nanoclusters in electronics

NASA Astrophysics Data System (ADS)

Krachkovskaya, T. M.; Sahadji, G. V.; Emelyanov, A. S.; Silaeva, M. V.

2018-04-01

Nanocarbon material (Ugleron and Astralens) is used for the first time for the production of metal porous cathode (MPC). It can be assumed that its implementation in the MPC matrix can change the mechanism and rate of occurrence of three-phase reactions of formation of active elements and oxygen and, thereby, improve its emission properties. The new technology of manufacturing MPC is aimed at solving the problem of increasing the durability of electro vacuum devices - more than 100,000 hours. The obtained results are intended for use in technologies for manufacturing of electron sources for electro vacuum devices used in space communication and navigation systems. In addition, they can be useful for other areas of electronics that use a metal-porous thermal cathode as sources of electron emission. There are manufactured models with the use of Ugleron and Astralens in a sponge and emission substance. A layout using Ugleron in the emission substance is tested for durability and currently has an operating time of 40,000 hours. A model with the use of Astralens and Ugleron in a sponge and emission substance respectively is tested for maximum current density. To date, it shows results comparable to the standard cathode. However, there is a suggestion that cathodes with Astralens and Ugleron have a lower evaporation rate of the active substance. There is predicted longer durability than for the standard cathode at the same emissivity.

Ultra high vacuum test setup for electron gun

NASA Astrophysics Data System (ADS)

Pandiyar, M. L.; Prasad, M.; Jain, S. K.; Kumar, R.; Hannurkar, P. R.

2008-05-01

Ultra High Vacuum (UHV) test setup for electron gun testing has been developed. The development of next generation light sources and accelerators require development of klystron as a radio frequency power source, and in turn electron gun. This UHV electron gun test setup can be used to test the electron guns ranging from high average current, quasi-continuous wave to high peak current, single pulse etc. An electron gun has been designed, fabricated, assembled and tested for insulation up to 80 kV under the programme to develop high power klystron for future accelerators. Further testing includes the electron emission parameters characterization of the cathode, as it determines the development of a reliable and efficient electron gun with high electron emission current and high life time as well. This needs a clean ultra high vacuum to study these parameters particularly at high emission current. The cathode emission current, work function and vapour pressure of cathode surface material at high temperature studies will further help in design and development of high power electron gun The UHV electron gun test setup consists of Turbo Molecular Pump (TMP), Sputter Ion Pump (SIP), pressure gauge, high voltage and cathode power supplies, current measurement device, solenoid magnet and its power supply, residual gas analyser etc. The ultimate vacuum less than 2×10-9 mbar was achieved. This paper describes the UHV test setup for electron gun testing.

Field Emission Properties of Carbon Nanotube Fibers and Sheets for a High Current Electron Source

NASA Astrophysics Data System (ADS)

Christy, Larry

Field emission (FE) properties of carbon nanotube (CNT) fibers from Rice University and the University of Cambridge have been studied for use within a high current electron source for a directed energy weapon. Upon reviewing the performance of these two prevalent CNT fibers, cathodes were designed with CNT fibers from the University of Cincinnati Nanoworld Laboratory. Cathodes composed of a single CNT fiber, an array of three CNT fibers, and a nonwoven CNT sheet were investigated for FE properties; the goal was to design a cathode with emission current in excess of 10 mA. Once the design phase was complete, the cathode samples were fabricated, characterized, and then analyzed to determine FE properties. Electrical conductivity of the CNT fibers was characterized with a 4-probe technique. FE characteristics were measured in an ultra-high vacuum chamber at Wright-Patterson Air Force Base. The arrayed CNT fiber and the enhanced nonwoven CNT sheet emitter design demonstrated the most promising FE properties. Future work will include further analysis and cathode design using this nonwoven CNT sheet material to increase peak current performance during electron emission.

Experimental Development of Low-emittance Field-emission Electron Sources

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lueangaranwong, A.; Buzzard, C.; Divan, R.

2016-10-10

Field emission electron sources are capable of extreme brightness when excited by static or time-dependent electro- magnetic fields. We are currently developing a cathode test stand operating in DC mode with possibility to trigger the emission using ultra-short (~ 100-fs) laser pulses. This contribution describes the status of an experiment to investigate field-emission using cathodes under development at NIU in collaboration with the Argonne’s Center for Nanoscale Materials.

Plasma-induced field emission study of carbon nanotube cathode

NASA Astrophysics Data System (ADS)

Shen, Yi; Xia, Liansheng; Zhang, Huang; Liu, Xingguang; Yang, Anmin; Shi, Jinshui; Zhang, Linwen; Liao, Qingliang; Zhang, Yue

2011-10-01

An investigation on the plasma-induced field emission (PFE) properties of a large area carbon nanotube (CNT) cathode on a 2 MeV linear induction accelerator injector is presented. Experimental results show that the cathode is able to emit intense electron beams. Intense electron beams of 14.9-127.8A/cm2 are obtained from the cathode. The CNT cathode desorbs gases from the CNTs during the PFE process. The fast cathode plasma expansion affects the diode perveance. The amount of outgassing is estimated to be 0.06-0.49Pa·L, and the ratio of outgassing and electron are roughly calculated to be within the range of 170-350 atoms per electron. The effect of the outgassing is analyzed, and the outgassing mass spectrum of the CNT cathode has been studied during the PFE. There is a significant desorption of CO2, N2(CO), and H2 gases, which plays an important role during the PFE process. All the experiments demonstrate that the outgassing plays an important role in the formation of the cathode plasma. Moreover, the characteristic turn-on time of the CNT cathode was measured to be 39 ns.

Electron emission and beam generation using ferroelectric cathodes

NASA Astrophysics Data System (ADS)

Flechtner, Donald D.

1999-06-01

In 1989, researchers at CERN published the discovery of significant electron emission (1-100 A/cm2) from Lead-Lanthanum-Zirconate- Titanate (PLZT). The publication of these results led to international interest in ferroelectric cathodes studies for use in pulsed power devices. At Cornell University in 1991, experiments with Lead-Zirconate-Titanate (PZT) compositions were begun to study the feasibility of using this ferroelectric material as a cathode in the electron gun section of High Power Traveling Wave Tube Amplifier Experiments. Current-voltage characteristics were documented for diode voltages ranging from 50-500,000 V with anode cathode gaps of.5-6 cm. A linear current-voltage relation was found for voltages less than 50 kV. For diode voltages >=200 kV, a typical Child-Langmuir V3/2 dependence was observed. Additional experiments have demonstrated repetition rates of up to 50 Hz with current densities of >=20 A/cm2. These results have been used in the ongoing design and construction of the electron gun for a 500 kV pulse modulator capable of repetitive operation at 1 Hz. The electron gun uses a PZT 55/45 (Pb(Zr.55,Ti.45 )O3) cathode to produce a <=400 A electron beam focused by a converging magnetic field. Studies of the emission process itself indicate the initial electrons are produced by field emission from the metallic grid applied to the front surface of the cathode. The field emission is induced by the application of a fast rising 1-3 kV, 150 ns pulse to the rear electrode of the 1 mm thick ferroelectric. Field emission can lead to explosive emission from microprotrusions and metal-ferroelectric-vacuum triple points forming a diffuse plasma on the surface of the sample. Under long pulse experiments (1-5 μs), plasma velocities of ~2 cm/μs were measured from gap closure rates. Results from an ion Faraday cup experiment showed ion velocities of 1-2 cm/μs. Experimental evidence indicates the electron emission is dependent on the field emission initiated by the voltage applied to rear surface of the ferroelectric; however, for current pulse durations on the order of microseconds, the surface plasma expansion into the gap can dominate current flow.

Improved materials and processes of dispenser cathodes

NASA Astrophysics Data System (ADS)

Longo, R. T.; Sundquist, W. F.; Adler, E. A.

1984-08-01

Several process variables affecting the final electron emission properties of impregnated dispenser cathodes were investigated. In particular, the influence of billet porosity, impregnant composition and purity, and osmium-ruthenium coating were studied. Work function and cathode evaporation data were used to evaluate cathode performance and to formulate a model of cathode activation and emission. Results showed that sorted tungsten powder can be reproducibly fabricated into cathode billets. Billet porosity was observed to have the least effect on cathode performance. Use of the 4:1:1 aluminate mixture resulted in lower work functions than did use of the 5:3:2 mixture. Under similar drawout conditions, the coated cathodes showed superior emission relative to uncoated cathodes. In actual Pierce gun structures under accelerated life test, the influence of impregnated sulfur is clearly shown to reduce cathode performance.

Surfing Silicon Nanofacets for Cold Cathode Electron Emission Sites.

PubMed

Basu, Tanmoy; Kumar, Mohit; Saini, Mahesh; Ghatak, Jay; Satpati, Biswarup; Som, Tapobrata

2017-11-08

Point sources exhibit low threshold electron emission due to local field enhancement at the tip. In the case of silicon, however, the realization of tip emitters has been hampered by unwanted oxidation, limiting the number of emission sites and the overall current. In contrast to this, here, we report the fascinating low threshold (∼0.67 V μm -1 ) cold cathode electron emission from silicon nanofacets (Si-NFs). The ensembles of nanofacets fabricated at different time scales, under low energy ion impacts, yield tunable field emission with a Fowler-Nordheim tunneling field in the range of 0.67-4.75 V μm -1 . The local probe surface microscopy-based tunneling current mapping in conjunction with Kelvin probe force microscopy measurements revealed that the valleys and a part of the sidewalls of the nanofacets contribute more to the field emission process. The observed lowest turn-on field is attributed to the absence of native oxide on the sidewalls of the smallest facets as well as their lowest work function. In addition, first-principle density functional theory-based simulation revealed a crystal orientation-dependent work function of Si, which corroborates well with our experimental observations. The present study demonstrates a novel way to address the origin of the cold cathode electron emission sites from Si-NFs fabricated at room temperature. In principle, the present methodology can be extended to probe the cold cathode electron emission sites from any nanostructured material.

Particle-in-cell modeling of the nanosecond field emission driven discharge in pressurized hydrogen

NASA Astrophysics Data System (ADS)

Levko, Dmitry; Yatom, Shurik; Krasik, Yakov E.

2018-02-01

The high-voltage field-emission driven nanosecond discharge in pressurized hydrogen is studied using the one-dimensional Particle-in-Cell Monte Carlo collision model. It is obtained that the main part of the field-emitted electrons becomes runaway in the thin cathode sheath. These runaway electrons propagate the entire cathode-anode gap, creating rather dense (˜1012 cm-3) seeding plasma electrons. In addition, these electrons initiate a streamer propagating through this background plasma with a speed ˜30% of the speed of light. Such a high streamer speed allows the self-acceleration mechanism of runaway electrons present between the streamer head and the anode to be realized. As a consequence, the energy of runaway electrons exceeds the cathode-anode gap voltage. In addition, the influence of the field emission switching-off time is analyzed. It is obtained that this time significantly influences the discharge dynamics.

Ab initio investigation of the surface properties of dispenser B-type and scandate thermionic emission cathodes

NASA Astrophysics Data System (ADS)

Vlahos, Vasilios; Lee, Yueh-Lin; Booske, John H.; Morgan, Dane; Turek, Ladislav; Kirshner, Mark; Kowalczyk, Richard; Wilsen, Craig

2009-05-01

Scandate cathodes (BaxScyOz on W) are important thermionic electron emission materials whose emission mechanism remains unclear. Ab initio modeling is used to investigate the surface properties of both scandate and traditional B-type (Ba-O on W) cathodes. We demonstrate that the Ba-O dipole surface structure believed to be present in active B-type cathodes is not thermodynamically stable, suggesting that a nonequilibrium steady state dominates the active cathode's surface structure. We identify a stable, low work function BaxScyOz surface structure, which may be responsible for some scandate cathode properties and demonstrate that multicomponent surface coatings can lower cathode work functions.

Facile synthesis of ZnPc nanocubes: An electron emitting material for field emission display devices

NASA Astrophysics Data System (ADS)

Samanta, M.; Ghorai, U. K.; Mukherjee, M.; Howli, P.; Chattopadhyay, K. K.

2017-05-01

A simple low temperature water chemical route for synthesizing Zinc Phthalocyanine (ZnPc) nanostructures were reported here. The as-prepared samples were well analysed by X-ray diffraction (XRD) and Field Emission Scanning Electron Microscopy (FESEM) technique. The plausible formation mechanism of cube like nanostructures was also explained here. Cold cathode emission properties of ZnPc nanocubes were studied by using an indigenously designed high vacuum system at anode to cathode distance 130 µm. The turn on field and enhancement factor is found to be 5.0 V/μm @ 1µA/cm2 and 1757 respectively. Cold cathode emission properties were further investigated theoretically by finite element method using ANSYS Maxwell simulation package. The obtained results strongly professed that ZnPc nanocubes can act as potential candidate for electron emitter for field emission display devices and many more.

Robust, easily shaped, and epoxy-free carbon-fiber-aluminum cathodes for generating high-current electron beams.

PubMed

Liu, Lie; Li, Limin; Wen, Jianchun; Wan, Hong

2009-02-01

This paper presents the construction of carbon-fiber-aluminum (CFA) cathode by squeezing casting and its applications for generating high-current electron beams to drive high-power microwave sources. The fabrication process avoided using epoxy, a volatile deteriorating the vacuum system. These cathodes had a higher hardness than conventional aluminum, facilitating machining. After surface treatment, carbon fibers became the dominator determining emission property. A multineedle CFA cathode was utilized in a triode virtual cathode oscillator (vircator), powered by a approximately 450 kV, approximately 400 ns pulse. It was found that 300-400 MW, approximately 250 ns microwave was radiated at a dominant frequency of 2.6 GHz. Further, this cathode can endure high-current-density emission without detectable degradation in performance as the pulse shot proceeded, showing the robust nature of carbon fibers as explosive emitters. Overall, this new class of cold cathodes offers a potential prospect of developing high-current electron beam sources.

Spindt cold cathode electron gun development program

NASA Technical Reports Server (NTRS)

Spindt, C. A.

1983-01-01

A thin film field emission cathode array and an electron gun based on this emitter array are summarized. Fabricating state of the art cathodes for testing at NASA and NRL, advancing the fabrication technology, developing wedge shaped emitters, and performing emission tests are covered. An anistropic dry etching process (reactive ion beam etching) developed that leads to increasing the packing density of the emitter tips to about 5 x 10 to the 6th power/square cm. Tests with small arrays of emitter tips having about 10 tips has demonstrated current densities of over 100 A/sq cm. Several times using cathodes having a packing density of 1.25 x 10 to the 6th power tips/sq cm. Indications are that the higher packing density achievable with the dry etch process may extend this capability to the 500 A/sq cm range and beyond. The wedge emitter geometry was developed and shown to produce emission. This geometry can (in principle) extend the current density capability of the cathodes beyond the 500 A/sq cm level. An emission microscope was built and tested for use with the cathodes.

Non-Self-Maintained Discharge Application for Fuel Activation

DTIC Science & Technology

2010-09-21

provision of law, no person shall be subject to any penalty for failing to comply with a collection of information if it does not display a currently ...voltage accelerating tube (1); - An injector of electrons with the thermo emission heated cathode (2); - The high-voltage rectifier (3); - A...auxiliary systems of the accelerator. The electron injector (2) is supplied by the thermo - emission cathode, allowing to generate an electron

Ecton processes in the generation of pulsed runaway electron beams in a gas discharge

NASA Astrophysics Data System (ADS)

Mesyats, G. A.

2017-09-01

As was shown earlier for pulsed discharges that occur in electric fields rising with extremely high rates (1018 V/(cm s)) during the pulse rise time, the electron current in a vacuum discharge is lower than the current of runaway electrons in an atmospheric air discharge in a 1-cm-long gap. In this paper, this is explained by that the field emission current from cathode microprotrusions in a gas discharge is enhanced due to gas ionization. This hastens the initiation of explosive electron emission, which occurs within 10-11 s at a current density of up to 1010 A/cm2. Thereafter, a first-type cathode spot starts forming. The temperature of the cathode spot decreases due to heat conduction, and the explosive emission current ceases. Thus, the runaway electron current pulse is similar in nature to the ecton phenomenon in a vacuum discharge.

High-emission cold cathode

DOEpatents

Mancebo, L.

1974-01-29

A field-emission cathode having a multitude of field emission points for emitting a copious stream of electrons when subjected to a high field is described. The cathode is constructed by compressing a multitude of tungsten strips alternately arranged with molybdenum strips and copper ribbons or compressing alternately arranged copper plated tungsten and molybdenum strips, heating the arrangement to braze the tungsten and molybdenum strips together with the copper, machining and grinding the exposed strip edges of one side of the brazed arrangement to obtain a precisely planar surface, etching a portion of the molybdenum and copper to leave the edges of the tungsten strips protruding for electron emission, and subjecting the protruding edges of the tungsten strips to a high electric field to degas and roughen the surface to pnovide a large number of emitting points. The resulting structure is particularly useful as a cathode in a transversely excited gaseous laser where the cathode is mounted in a vacuum chamber for emitting electrons under the influence of a high electric field between the cathode and an extractor grid. The electrons pass through the extractor grid, a thin window in the wall of the laser chamber and into the laser chamber which is filled with a gaseous mixture of helium, nitrogen, and carbon dioxide. A second grid is mounted on the gaseous side of the window. The electrons pass into the laser chamber under the influence of a second electric field between the second grid and an anode in the laser chamber to raise selected gas atoms of the gaseous mixture to appropriately excited states so that a subsequent coherent light beam passing through the mixture transversely to the electron stream through windows in opposite ends of the laser chamber stimulates the excited atoms to amplify the beam. (Official Gazette)

Simulation of Non-Uniform Electron Beams in the Gyrotron Electron-Optical System

NASA Astrophysics Data System (ADS)

Louksha, O. I.; Trofimov, P. A.

2018-04-01

New calculated data on the effect of emission inhomogeneities on the quality of the electron beam, which is formed in an electron-optical system of a gyrotron, have been obtained. The calculations were based on emission current density distributions, which were measured for the different cathodes in the gyrotron of Peter the Great St. Petersburg Polytechnic University. A satisfactory agreement between the experimental and calculated data on the influence of emission nonuniformities on the velocity spread of electrons has been shown. The necessity of considering the real distribution of the emission current density over the cathode surface to determine the main parameters of the electron beam—the velocity and energy spreads of the electrons, spatial structure of the beam, and coefficient of reflection of electrons from the magnetic mirror—has been demonstrated. The maximum level of emission inhomogeneities, which are permissible for effective work of gyrotrons, has been discussed.

Design of a double-anode magnetron-injection gun for the W-band gyrotron

NASA Astrophysics Data System (ADS)

Jang, Kwang Ho; Choi, Jin Joo; So, Joon Ho

2015-07-01

A double-anode magnetron-injection gun (MIG) was designed. The MIG is for a W-band 10-kW gyrotron. Analytic equations based on adiabatic theory and angular momentum conservation were used to examine the initial design parameters such as the cathode angle, and the radius of the beam emitting surface. The MIG's performances were predicted by using an electron trajectory code, the EGUN code. The beam spread of the axial velocity, Δvz/vz, obtained from the EGUN code was observed to be 1.34% at α = 1.3. The cathode edge emission and the thermal effect were modeled. The cathode edge emission was found to have a major effect on the velocity spread. The electron beam's quality was significantly improved by affixing non-emissive cylinders to the cathode.

Parametrically Optimized Carbon Nanotube-Coated Cold Cathode Spindt Arrays

PubMed Central

Yuan, Xuesong; Cole, Matthew T.; Zhang, Yu; Wu, Jianqiang; Milne, William I.; Yan, Yang

2017-01-01

Here, we investigate, through parametrically optimized macroscale simulations, the field electron emission from arrays of carbon nanotube (CNT)-coated Spindts towards the development of an emerging class of novel vacuum electron devices. The present study builds on empirical data gleaned from our recent experimental findings on the room temperature electron emission from large area CNT electron sources. We determine the field emission current of the present microstructures directly using particle in cell (PIC) software and present a new CNT cold cathode array variant which has been geometrically optimized to provide maximal emission current density, with current densities of up to 11.5 A/cm2 at low operational electric fields of 5.0 V/μm. PMID:28336845

Current-voltage characteristics of a cathodic plasma contactor with discharge chamber for application in electrodynamic tether propulsion

NASA Astrophysics Data System (ADS)

Xie, Kan; Martinez, Rafael A.; Williams, John D.

2014-04-01

This paper focuses on the net electron-emission current as a function of bias voltage of a plasma source that is being used as the cathodic element in a bare electrodynamic tether system. An analysis is made that enables an understanding of the basic issues determining the current-voltage (C-V) behaviour. This is important for the efficiency of the electrodynamic tether and for low impedance performance without relying on the properties of space plasma for varying orbital altitudes, inclinations, day-night cycles or the position of the plasma contactor relative to the wake of the spacecraft. The cathodic plasma contactor considered has a cylindrical discharge chamber (10 cm in diameter and ˜11 cm in length) and is driven by a hollow cathode. Experiments and a 1D spherical model are both used to study the contactor's C-V curves. The experiments demonstrate how the cathodic contactor would emit electrons into space for anode voltages in the range of 25-40 V, discharge currents in the range of 1-2.5 A, and low xenon gas flows of 2-4 sccm. Plasma properties are measured and compared with (3 A) and without net electron emission. A study of the dependence of relevant parameters found that the C-V behaviour strongly depends on electron temperature, initial ion energy and ion emission current at the contactor exit. However, it depended only weakly on ambient plasma density. The error in the developed model compared with the experimental C-V curves is within 5% at low electron-emission currents (0-2 A). The external ionization processes and high ion production rate caused by the discharge chamber, which dominate the C-V behaviour at electron-emission currents over 2 A, are further highlighted and discussed.

Barium-Dispenser Thermionic Cathode

NASA Technical Reports Server (NTRS)

Wintucky, Edwin G.; Green, M.; Feinleib, M.

1989-01-01

Improved reservoir cathode serves as intense source of electrons required for high-frequency and often high-output-power, linear-beam tubes, for which long operating lifetime important consideration. High emission-current densities obtained through use of emitting surface of relatively-low effective work function and narrow work-function distribution, consisting of coat of W/Os deposited by sputtering. Lower operating temperatures and enhanced electron emission consequently possible.

Bohm velocity in the presence of a hot cathode

DOE Office of Scientific and Technical Information (OSTI.GOV)

Palacio Mizrahi, J. H.; Krasik, Ya. E.

2013-08-15

The spatial distribution of the plasma and beam electrons in a region whose extension from a hot cathode is larger than the Debye length, but smaller than the electron mean free path, is analyzed. In addition, the influence of electrons thermionically emitted from a hot cathode and the ratio of electron-to-ion mass on the Bohm velocity and on the ion and electron densities at the plasma-sheath boundary in a gas discharge are studied. It is shown that thermionic emission has the effect of increasing the Bohm velocity, and this effect is more pronounced for lighter ions. In addition, it ismore » shown that the Bohm velocity cannot be increased to more than 24% above its value when there is no electron emission.« less

Effect of secondary electron emission on subnanosecond breakdown in high-voltage pulse discharge

NASA Astrophysics Data System (ADS)

Schweigert, I. V.; Alexandrov, A. L.; Gugin, P.; Lavrukhin, M.; Bokhan, P. A.; Zakrevsky, Dm E.

2017-11-01

The subnanosecond breakdown in open discharge may be applied for producing superfast high power switches. Such fast breakdown in high-voltage pulse discharge in helium was explored both in experiment and in kinetic simulations. The kinetic model of electron avalanche development was developed using PIC-MCC technique. The model simulates motion of electrons, ions and fast helium atoms, appearing due to ions scattering. It was shown that the mechanism responsible for ultra-fast breakdown development is the electron emission from cathode. The photoemission and emission by ions or fast atoms impact is the main reason of current growth at the early stage of breakdown, but at the final stage, when the voltage on discharge gap drops, the secondary electron emission (SEE) is responsible for subnanosecond time scale of current growth. It was also found that the characteristic time of the current growth τS depends on the SEE yield of the cathode material. Three types of cathode material (titanium, SiC, and CuAlMg-alloy) were tested. It is shown that in discharge with SiC and CuAlMg-alloy cathodes (which have enhanced SEE) the current can increase with a subnanosecond characteristic time as small as τS = 0.4 ns, for the pulse voltage amplitude of 5- 12 kV..

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kandlakunta, P; Pham, R; Zhang, T

Purpose: To develop and characterize a high brightness multiple-pixel thermionic emission x-ray (MPTEX) source. Methods: Multiple-pixel x-ray sources allow for designs of novel x-ray imaging techniques, such as fixed gantry CT, digital tomosynthesis, tetrahedron beam computed tomography, etc. We are developing a high-brightness multiple-pixel thermionic emission x-ray (MPTEX) source based on oxide coated cathodes. Oxide cathode is chosen as the electron source due to its high emission current density and low operating temperature. A MPTEX prototype has been developed which may contain up to 41 micro-rectangular oxide cathodes in 4 mm pixel spacing. Electronics hardware was developed for source controlmore » and switching. The cathode emission current was evaluated and x-ray measurements were performed to estimate the focal spot size. Results: The oxide cathodes were able to produce ∼110 mA cathode current in pulse mode which corresponds to an emission current density of 0.55 A/cm{sup 2}. The maximum kVp of the MPTEX prototype currently is limited to 100 kV due to the rating of high voltage feedthrough. Preliminary x-ray measurements estimated the focal spot size as 1.5 × 1.3 mm{sup 2}. Conclusion: A MPTEX source was developed with thermionic oxide coated cathodes and preliminary source characterization was successfully performed. The MPTEX source is able to produce an array of high brightness x-ray beams with a fast switching speed.« less

Pulsed Electron Source with Grid Plasma Cathode and Longitudinal Magnetic Field for Modification of Material and Product Surfaces

NASA Astrophysics Data System (ADS)

Devyatkov, V. N.; Koval, N. N.

2018-01-01

The description and the main characteristics of the pulsed electron source "SOLO" developed on the basis of the plasma cathode with grid stabilization of the emission plasma boundary are presented. The emission plasma is generated by a low-pressure arc discharge, and that allows to form the dense low-energy electron beam with a wide range of independently adjustable parameters of beam current pulses (pulse duration of 20-250 μs, pulse repetition rate of 1-10 s-1, amplitude of beam current pulses of 20-300 A, and energy of beam electrons of 5-25 keV). The special features of generation of emission plasma by constricted low-pressure arc discharge in the grid plasma cathode partially dipped into a non-uniform magnetic field and of formation and transportation of the electron beam in a longitudinal magnetic field are considered. The application area of the electron source and technologies realized with its help are specified.

Influence of cathode geometry on electron dynamics in an ultrafast electron microscope.

PubMed

Ji, Shaozheng; Piazza, Luca; Cao, Gaolong; Park, Sang Tae; Reed, Bryan W; Masiel, Daniel J; Weissenrieder, Jonas

2017-09-01

Efforts to understand matter at ever-increasing spatial and temporal resolutions have led to the development of instruments such as the ultrafast transmission electron microscope (UEM) that can capture transient processes with combined nanometer and picosecond resolutions. However, analysis by UEM is often associated with extended acquisition times, mainly due to the limitations of the electron gun. Improvements are hampered by tradeoffs in realizing combinations of the conflicting objectives for source size, emittance, and energy and temporal dispersion. Fundamentally, the performance of the gun is a function of the cathode material, the gun and cathode geometry, and the local fields. Especially shank emission from a truncated tip cathode results in severe broadening effects and therefore such electrons must be filtered by applying a Wehnelt bias. Here we study the influence of the cathode geometry and the Wehnelt bias on the performance of a photoelectron gun in a thermionic configuration. We combine experimental analysis with finite element simulations tracing the paths of individual photoelectrons in the relevant 3D geometry. Specifically, we compare the performance of guard ring cathodes with no shank emission to conventional truncated tip geometries. We find that a guard ring cathode allows operation at minimum Wehnelt bias and improve the temporal resolution under realistic operation conditions in an UEM. At low bias, the Wehnelt exhibits stronger focus for guard ring than truncated tip cathodes. The increase in temporal spread with bias is mainly a result from a decrease in the accelerating field near the cathode surface. Furthermore, simulations reveal that the temporal dispersion is also influenced by the intrinsic angular distribution in the photoemission process and the initial energy spread. However, a smaller emission spot on the cathode is not a dominant driver for enhancing time resolution. Space charge induced temporal broadening shows a close to linear relation with the number of electrons up to at least 10 000 electrons per pulse. The Wehnelt bias will affect the energy distribution by changing the Rayleigh length, and thus the interaction time, at the crossover.

Influence of cathode geometry on electron dynamics in an ultrafast electron microscope

PubMed Central

Ji, Shaozheng; Piazza, Luca; Cao, Gaolong; Park, Sang Tae; Reed, Bryan W.; Masiel, Daniel J.; Weissenrieder, Jonas

2017-01-01

Efforts to understand matter at ever-increasing spatial and temporal resolutions have led to the development of instruments such as the ultrafast transmission electron microscope (UEM) that can capture transient processes with combined nanometer and picosecond resolutions. However, analysis by UEM is often associated with extended acquisition times, mainly due to the limitations of the electron gun. Improvements are hampered by tradeoffs in realizing combinations of the conflicting objectives for source size, emittance, and energy and temporal dispersion. Fundamentally, the performance of the gun is a function of the cathode material, the gun and cathode geometry, and the local fields. Especially shank emission from a truncated tip cathode results in severe broadening effects and therefore such electrons must be filtered by applying a Wehnelt bias. Here we study the influence of the cathode geometry and the Wehnelt bias on the performance of a photoelectron gun in a thermionic configuration. We combine experimental analysis with finite element simulations tracing the paths of individual photoelectrons in the relevant 3D geometry. Specifically, we compare the performance of guard ring cathodes with no shank emission to conventional truncated tip geometries. We find that a guard ring cathode allows operation at minimum Wehnelt bias and improve the temporal resolution under realistic operation conditions in an UEM. At low bias, the Wehnelt exhibits stronger focus for guard ring than truncated tip cathodes. The increase in temporal spread with bias is mainly a result from a decrease in the accelerating field near the cathode surface. Furthermore, simulations reveal that the temporal dispersion is also influenced by the intrinsic angular distribution in the photoemission process and the initial energy spread. However, a smaller emission spot on the cathode is not a dominant driver for enhancing time resolution. Space charge induced temporal broadening shows a close to linear relation with the number of electrons up to at least 10 000 electrons per pulse. The Wehnelt bias will affect the energy distribution by changing the Rayleigh length, and thus the interaction time, at the crossover. PMID:28781982

Correlation of emission capability and longevity of dispenser cathodes with characteristics of tungsten powders

NASA Astrophysics Data System (ADS)

Melnikova, Irina P.; Vorozheikin, Victor G.; Usanov, Dmitry A.

2003-06-01

The intercorrelation of tungsten powder properties, such as grain size, distribution and morphology, and porous matrix parameters with electron emission capability and longevity of Ba dispenser cathodes are investigated for three different grain morphologies. Best results of tungsten cathode life were found for isoaxis polyhedron morphology in combination with certain powder and matrix parameters.

Magnetically insulated coaxial vacuum diode with partial space-charge-limited explosive emission from edge-type cathode

NASA Astrophysics Data System (ADS)

Belomyttsev, S. Ya.; Rostov, V. V.; Romanchenko, I. V.; Shunailov, S. A.; Kolomiets, M. D.; Mesyats, G. A.; Sharypov, K. A.; Shpak, V. G.; Ulmaskulov, M. R.; Yalandin, M. I.

2016-01-01

The vacuum current associated with any type of electron emission for arbitrary configuration of the diode depends on the combination of the applied electric field and vacuum space charge (VSC) field created by the current. Such fundamental statement should give very close links between the diode current and the normalized cathode field θ which has been introduced by Forbes in 2008 for planar diodes as a reduction in the cathode surface field: θ = field-with/field-without VSC. This article reports the universal approximation of the type of cos(πθ/2) that is the ratio of the actual current and the fully space-charge-limited current. Also, the theoretical treatment and the experimental method of determination of the dynamic emissive characteristics of the macroscopic explosive emission from edge-type cathodes in the coaxial diode are developed. The experimental results obtained with a picosecond time reference between the cathode voltage and the onset of the high-current electron beam exhibit a good coincidence with the theoretical predictions. The presented methods enable the analysis of a real-time-resolved dynamics associated with the dense, magnetized electron beam formation, acceleration and drift motion, including kinematic effects and the phase-stable excitation of high-power microwave oscillators.

Magnetically insulated coaxial vacuum diode with partial space-charge-limited explosive emission from edge-type cathode

DOE Office of Scientific and Technical Information (OSTI.GOV)

Belomyttsev, S. Ya.; Rostov, V. V.; Romanchenko, I. V.

2016-01-14

The vacuum current associated with any type of electron emission for arbitrary configuration of the diode depends on the combination of the applied electric field and vacuum space charge (VSC) field created by the current. Such fundamental statement should give very close links between the diode current and the normalized cathode field θ which has been introduced by Forbes in 2008 for planar diodes as a reduction in the cathode surface field: θ = field-with/field-without VSC. This article reports the universal approximation of the type of cos(πθ/2) that is the ratio of the actual current and the fully space-charge-limited current. Also, themore » theoretical treatment and the experimental method of determination of the dynamic emissive characteristics of the macroscopic explosive emission from edge-type cathodes in the coaxial diode are developed. The experimental results obtained with a picosecond time reference between the cathode voltage and the onset of the high-current electron beam exhibit a good coincidence with the theoretical predictions. The presented methods enable the analysis of a real-time-resolved dynamics associated with the dense, magnetized electron beam formation, acceleration and drift motion, including kinematic effects and the phase-stable excitation of high-power microwave oscillators.« less

Emission and evaporation properties of 75 at.% Re-25 at.% W mixed matrix impregnated cathode

NASA Astrophysics Data System (ADS)

Lai, Chen; Wang, Jinshu; Zhou, Fan; Liu, Wei; den Engelsen, Daniel; Miao, Naihua

2018-01-01

We present a comprehensive study on the phase, emission performance, surface composition, chemical states and evaporation properties of a 75 at.% Re-25 at.% W (75Re) mixed matrix impregnated cathode by several modern analyzers, including XRD, electron emission test device, in situ AES, XPS and Quartz Crystal Oscillation Instrument (QCOI). On the basis of experimental results, the adsorption energy and charge transfer of the Ba-O dipole adsorbed on cathode surface was investigated by the first-principles density functional theory calculations. The in situ AES analyses indicate that the atomic ratio of Ba:O of the active emission layer on the cathode surface converged to 3:2 for a conventional Ba-W cathode and to about 3:1 for the 75Re cathode. Due to the larger adsorption energy of Ba and Ba-O on 75Re cathode surface, the total evaporation rate of Ba and BaO in the 75Re cathode is much lower than that for the Ba-W cathode, which is agreed favorably with the experimental evaporation data. Our characterizations and calculations suggest that rhenium in the matrix of impregnated cathodes improves the stability of Ba-O dipole on the cathode surface and enhances the emission capability substantially.

Development of multi-pixel x-ray source using oxide-coated cathodes.

PubMed

Kandlakunta, Praneeth; Pham, Richard; Khan, Rao; Zhang, Tiezhi

2017-07-07

Multiple pixel x-ray sources facilitate new designs of imaging modalities that may result in faster imaging speed, improved image quality, and more compact geometry. We are developing a high-brightness multiple-pixel thermionic emission x-ray (MPTEX) source based on oxide-coated cathodes. Oxide cathodes have high emission efficiency and, thereby, produce high emission current density at low temperature when compared to traditional tungsten filaments. Indirectly heated micro-rectangular oxide cathodes were developed using carbonates, which were converted to semiconductor oxides of barium, strontium, and calcium after activation. Each cathode produces a focal spot on an elongated fixed anode. The x-ray beam ON and OFF control is performed by source-switching electronics, which supplies bias voltage to the cathode emitters. In this paper, we report the initial performance of the oxide-coated cathodes and the MPTEX source.

Influence of emission threshold of explosive emission cathodes on current waveform in foilless diodes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wu, P.; Liu, G. Z.; Science and Technology on High Power Microwave Laboratory, Northwest Institute of Nuclear Technology, Xi'an 710024

The emission threshold of explosive emission cathodes (EECs) is an important factor for beam quality. It can affect the explosive emission delay time, the plasma expansion process on the cathode surface, and even the current amplitude when the current is not fully space-charge-limited. This paper researches the influence of the emission threshold of an annular EEC on the current waveform in a foilless diode when the current is measured by a Rogowski coil. The particle-in-cell simulation which is performed under some tolerable and necessary simplifications shows that the long explosive emission delay time of high-threshold cathodes may leave an apparentmore » peak of displacement current on the rise edge of the current waveform, and this will occur only when the electron emission starts after this peak. The experimental researches, which are performed under a diode voltage of 1 MV and a repetitive frequency of 20 Hz, demonstrate that the graphite cathode has a lower emission threshold and a longer lifetime than the stainless steel cathode according to the variation of the peak of displacement current on the rise edge of the current waveform.« less

Hollow cathode plasma coupling study, 1986

NASA Technical Reports Server (NTRS)

Wilbur, Paul J.

1986-01-01

The electron collection and emission characteristics of a simple hollow cathode contactor, an extended anode hollow cathode contactor supplied by JSC, and a ring cusp magnetic field contactor are presented and the effects of discharge power and argon or xenon expellant flowrate on these characteristics are examined. All of the contactors are shown to exhibit good electron emission performance over a wide range of discharge power and expellant type and flowrate. Good electron performance is shown to be more difficult to achieve. Results suggest that the extended anode and ring cusp contactors should perform satisfactorily to electron emission currents beyond 1000 mA and electron collection currents beyond 500 mA. All contactors performed better on xenon than argon. A general theory of plasma contactor operation in both the electron collection and electron emission modes, which describes the current-limiting effects of space-charge phenomena is given. This current-limiting and collecting phenomenon is shown to be a function of driving potential differences and emitting and collecting surface radius ratio for the case of a spherical geometry. Discharge power did not appear to influence the electron collection current substantially in the experiments so it is suggested in light of the model that the contactors are generally not limited by their ion production capabilities under conditions at which they were tested.

An ultrafast electron microscope gun driven by two-photon photoemission from a nanotip cathode

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bormann, Reiner; Strauch, Stefanie; Schäfer, Sascha, E-mail: schaefer@ph4.physik.uni-goettingen.de

We experimentally and numerically investigate the performance of an advanced ultrafast electron source, based on two-photon photoemission from a tungsten needle cathode incorporated in an electron microscope gun geometry. Emission properties are characterized as a function of the electrostatic gun settings, and operating conditions leading to laser-triggered electron beams of very low emittance (below 20 nm mrad) are identified. The results highlight the excellent suitability of optically driven nano-cathodes for the further development of ultrafast transmission electron microscopy.

Electron beam dynamics in an ultrafast transmission electron microscope with Wehnelt electrode.

PubMed

Bücker, K; Picher, M; Crégut, O; LaGrange, T; Reed, B W; Park, S T; Masiel, D J; Banhart, F

2016-12-01

High temporal resolution transmission electron microscopy techniques have shown significant progress in recent years. Using photoelectron pulses induced by ultrashort laser pulses on the cathode, these methods can probe ultrafast materials processes and have revealed numerous dynamic phenomena at the nanoscale. Most recently, the technique has been implemented in standard thermionic electron microscopes that provide a flexible platform for studying material's dynamics over a wide range of spatial and temporal scales. In this study, the electron pulses in such an ultrafast transmission electron microscope are characterized in detail. The microscope is based on a thermionic gun with a Wehnelt electrode and is operated in a stroboscopic photoelectron mode. It is shown that the Wehnelt bias has a decisive influence on the temporal and energy spread of the picosecond electron pulses. Depending on the shape of the cathode and the cathode-Wehnelt distance, different emission patterns with different pulse parameters are obtained. The energy spread of the pulses is determined by space charge and Boersch effects, given by the number of electrons in a pulse. However, filtering effects due to the chromatic aberrations of the Wehnelt electrode allow the extraction of pulses with narrow energy spreads. The temporal spread is governed by electron trajectories of different length and in different electrostatic potentials. High temporal resolution is obtained by excluding shank emission from the cathode and aberration-induced halos in the emission pattern. By varying the cathode-Wehnelt gap, the Wehnelt bias, and the number of photoelectrons in a pulse, tradeoffs between energy and temporal resolution as well as beam intensity can be made as needed for experiments. Based on the characterization of the electron pulses, the optimal conditions for the operation of ultrafast TEMs with thermionic gun assembly are elaborated. Copyright © 2016 Elsevier B.V. All rights reserved.

Hollow cathodes for arcjet thrusters

NASA Technical Reports Server (NTRS)

Luebben, Craig R.; Wilbur, Paul J.

1987-01-01

In an attempt to prevent exterior spot emission, hollow cathode bodies and orifice plates were constructed from boron nitride which is an electrical insulator, but the orifice plates melted and/or eroded at high interelectrode pressures. The most suitable hollow cathodes tested included a refractory metal orifice plate in a boron nitride body, with the insert insulated electrically from the orifice plate. In addition, the hollow cathode interior was evacuated to assure a low pressure at the insert surface, thus promoting diffuse electron emission. At high interelectrode pressures, the electrons tended to flow through the orifice plate rather than through the orifice, which could result in overheating of the orifice plate. Using a carefully aligned centerline anode, electron flow through the orifice could be sustained at interelectrode pressures up to 500 torr - but the current flow path still occasionally jumped from the orifice to the orifice plate. Based on these tests, it appears that a hollow cathode would operate most effectively at pressures in the arcjet regime with a refractory, chemically stable, and electrically insulating cathode body and orifice plate.

Subnanosecond breakdown development in high-voltage pulse discharge: Effect of secondary electron emission

NASA Astrophysics Data System (ADS)

Alexandrov, A. L.; Schweigert, I. V.; Zakrevskiy, Dm. E.; Bokhan, P. A.; Gugin, P.; Lavrukhin, M.

2017-10-01

A subnanosecond breakdown in high-voltage pulse discharge may be a key tool for superfast commutation of high power devices. The breakdown in high-voltage open discharge at mid-high pressure in helium was studied in experiment and in kinetic simulations. The kinetic model of electron avalanche development was constructed, based on PIC-MCC simulations, including dynamics of electrons, ions and fast helium atoms, produced by ions scattering. Special attention was paid to electron emission processes from cathode, such as: photoemission by Doppler-shifted resonant photons, produced in excitation processes involving fast atoms; electron emission by ions and fast atoms bombardment of cathode; the secondary electron emission (SEE) by hot electrons from bulk plasma. The simulations show that the fast atoms accumulation is the main reason of emission growth at the early stage of breakdown, but at the final stage, when the voltage on plasma gap diminishes, namely the SEE is responsible for subnanosecond rate of current growth. It was shown that the characteristic time of the current growth can be controlled by the SEE yield. The influence of SEE yield for three types of cathode material (titanium, SiC, and CuAlMg-alloy) was tested. By changing the pulse voltage amplitude and gas pressure, the area of existence of subnanosecond breakdown is identified. It is shown that in discharge with SiC and CuAlMg-alloy cathodes (which have enhanced SEE) the current can increase with a subnanosecond characteristic time value as small as τs = 0.4 ns, for the pulse voltage amplitude of 5÷12 kV. An increase of gas pressure from 15 Torr to 30 Torr essentially decreases the time of of current front growth, whereas the pulse voltage variation weakly affects the results.

Electron Field Emission Properties of Textured Platinum Surfaces

NASA Technical Reports Server (NTRS)

Sovey, James S.

2002-01-01

During ground tests of electric microthrusters and space tests of electrodynamic tethers the electron emitters must successfully operate at environmental pressures possibly as high as 1x10(exp -4) Pa. High partial pressures of oxygen, nitrogen, and water vapor are expected in such environments. A textured platinum surface was used in this work for field emission cathode assessments because platinum does not form oxide films at low temperatures. Although a reproducible cathode conditioning process did not evolve from this work, some short term tests for periods of 1 to 4 hours showed no degradation of emission current at an electric field of 8 V/mm and background pressures of about 1x10(exp -6) Pa. Increases of background pressure by air flow to about 3x10(exp -4) Pa yield a hostile environment for the textured platinum field emission cathode.

Non-Uniform Cathode Emission Studies of a MIG Gun

NASA Astrophysics Data System (ADS)

Marchewka, C. D.; Shapiro, M. A.; Sirigiri, J. R.; Temkin, R. J.

2004-11-01

We present the initial results of the modeling of the effect of emission non-uniformity in 96 kV, 40 A Magnetron Injection Gun (MIG) of a 1.5 MW 110 GHz gyrotron using a 3D gun simulation code. The azimuthal emission nonuniformity can lead to increased mode competition and an overall decreased efficiency of the device [1]. The electron beam is modeled from the cathode to a downstream position where the velocity spread saturates using the AMAZE 3D suite of codes. After bench marking the results of the 3D code with 2D codes such as TRAK2D and EGUN, the emitter was modified to simulate asymmetric emission from the cathode to gain an understanding into the effects of inhomogeneous beam current density on the velocity spread and pitch factor of the electron beam. [1] G. S. Nusinovich, A.N. Vlasov, M. Botton, T. M. Antonsen, Jr., S. Cauffman, K. Felch, ``Effect of the azimuthal inhomogeneity of electron emission on gyrotron operation,'' Phys. Plasmas, vol. 8, no. 7, pp. 3473-3479, 2001

A Robust High Current Density Electron Gun

NASA Astrophysics Data System (ADS)

Mako, F.; Peter, W.; Shiloh, J.; Len, L. K.

1996-11-01

Proof-of-principle experiments are proposed to validate a new concept for a robust, high-current density Pierce electron gun (RPG) for use in klystrons and high brightness electron sources for accelerators. This rugged, long-life electron gun avoids the difficulties associated with plasma cathodes, thermionic emitters, and field emission cathodes. The RPG concept employs the emission of secondary electrons in a transmission mode as opposed to the conventional mode of reflection, i.e., electrons exit from the back face of a thin negative electron affinity (NEA) material, and in the same direction as the incident beam. Current amplification through one stage of a NEA material could be over 50 times. The amplification is accomplished in one or more stages consisting of one primary emitter and one or more secondary emitters. The primary emitter is a low current density robust emitter (e.g., thoriated tungsten). The secondary emitters are thin NEA electrodes which emit secondary electrons in the same direction as the incident beam. Specific application is targeted for a klystron gun to be used by SLAC with a cold cathode at 30-40 amps/cm^2 output from the secondary emission stage, a ~2 μs pulse length, and ~200 pulses/second.

Efficient polymer light-emitting diode with air-stable aluminum cathode

NASA Astrophysics Data System (ADS)

Abbaszadeh, D.; Wetzelaer, G. A. H.; Doumon, N. Y.; Blom, P. W. M.

2016-03-01

The fast degradation of polymer light-emitting diodes (PLEDs) in ambient conditions is primarily due to the oxidation of highly reactive metals, such as barium or calcium, which are used as cathode materials. Here, we report the fabrication of PLEDs using an air-stable partially oxidized aluminum (AlOx) cathode. Usually, the high work function of aluminum (4.2 eV) imposes a high barrier for injecting electrons into the lowest unoccupied molecular orbital (LUMO) of the emissive polymer (2.9 eV below the vacuum level). By partially oxidizing aluminum, its work function is decreased, but not sufficiently low for efficient electron injection. Efficient injection is obtained by inserting an electron transport layer of poly[(9,9-di-n-octylfluorenyl-2,7-diyl)-alt-(benzo[2,1,3]thiadiazol-4,8-diyl)] (F8BT), which has its LUMO at 3.3 eV below vacuum, between the AlOx cathode and the emissive polymer. The intermediate F8BT layer not only serves as a hole-blocking layer but also provides an energetic staircase for electron injection from AlOx into the emissive layer. PLEDs with an AlOx cathode and F8BT interlayer exhibit a doubling of the efficiency as compared to conventional Ba/Al PLEDs, and still operate even after being kept in ambient atmosphere for one month without encapsulation.

Simulations of Gaussian electron guns for RHIC electron lens

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pikin, A.

Simulations of two versions of the electron gun for RHIC electron lens are presented. The electron guns have to generate an electron beam with Gaussian radial profile of the electron beam density. To achieve the Gaussian electron emission profile on the cathode we used a combination of the gun electrodes and shaping of the cathode surface. Dependence of electron gun performance parameters on the geometry of electrodes and the margins for electrodes positioning are presented.

A first-principles model for orificed hollow cathode operation

NASA Technical Reports Server (NTRS)

Salhi, A.; Turchi, P. J.

1992-01-01

A theoretical model describing orificed hollow cathode discharge is presented. The approach adopted is based on a purely analytical formulation founded on first principles. The present model predicts the emission surface temperature and plasma properties such as electron temperature, number densities and plasma potential. In general, good agreements between theory and experiment are obtained. Comparison of the results with the available related experimental data shows a maximum difference of 10 percent in emission surface temperature, 20 percent in electron temperature and 35 percent in plasma potential. In case of the variation of the electron number density with the discharge current a maximum discrepancy of 36 percent is obtained. However, in the case of the variation with the cathode internal pressure, the predicted electron number density is higher than the experimental data by a maximum factor of 2.

Plasma characteristics in the discharge region of a 20 A emission current hollow cathode

NASA Astrophysics Data System (ADS)

Mingming, SUN; Tianping, ZHANG; Xiaodong, WEN; Weilong, GUO; Jiayao, SONG

2018-02-01

Numerical calculation and fluid simulation methods were used to obtain the plasma characteristics in the discharge region of the LIPS-300 ion thruster’s 20 A emission current hollow cathode and to verify the structural design of the emitter. The results of the two methods indicated that the highest plasma density and electron temperature, which improved significantly in the orifice region, were located in the discharge region of the hollow cathode. The magnitude of plasma density was about 1021 m-3 in the emitter and orifice regions, as obtained by numerical calculations, but decreased exponentially in the plume region with the distance from the orifice exit. Meanwhile, compared to the emitter region, the electron temperature and current improved by about 36% in the orifice region. The hollow cathode performance test results were in good agreement with the numerical calculation results, which proved that that the structural design of the emitter and the orifice met the requirements of a 20 A emission current. The numerical calculation method can be used to estimate plasma characteristics in the preliminary design stage of hollow cathodes.

Fundamental Materials Studies for Advanced High Power Microwave and Terahertz Vacuum Electronic Radiation Sources

DTIC Science & Technology

2014-12-10

AFRL-OSR-VA-TR-2014-0359 Fundamental Materials Studies for Advanced High Power Microwave and Terahertz John Booske UNIVERSITY OF WISCONSIN SYSTEM...12-2014 Final Technical Performance Report October 1, 2011 - September 30, 2014 Fundamental Materials Studies for Advanced High Power Microwave and...emission-barrier scandate cathodes and identify related, alternative cathode materials systems for advanced vacuum electronic cathodes for high power THz

A Fully-Sealed Carbon-Nanotube Cold-Cathode Terahertz Gyrotron

PubMed Central

Yuan, Xuesong; Zhu, Weiwei; Zhang, Yu; Xu, Ningsheng; Yan, Yang; Wu, Jianqiang; Shen, Yan; Chen, Jun; She, Juncong; Deng, Shaozhi

2016-01-01

Gigahertz to terahertz radiation sources based on cold-cathode vacuum electron technology are pursued, because its unique characteristics of instant switch-on and power saving are important to military and space applications. Gigahertz gyrotron was reported using carbon nanotube (CNT) cold-cathode. It is reported here in first time that a fully-sealed CNT cold-cathode 0.22 THz-gyrotron is realized, typically with output power of 500 mW. To achieve this, we have studied mechanisms responsible for CNTs growth on curved shape metal surface, field emission from the sidewall of a CNT, and crystallized interface junction between CNT and substrate material. We have obtained uniform growth of CNTs on and direct growth from cone-cylinder stainless-steel electrode surface, and field emission from both tips and sidewalls of CNTs. It is essential for the success of a CNT terahertz gyrotron to have such high quality, high emitting performance CNTs. Also, we have developed a magnetic injection electron gun using CNT cold-cathode to exploit the advantages of such a conventional gun design, so that a large area emitting surface is utilized to deliver large current for electron beam. The results indicate that higher output power and higher radiation frequency terahertz gyrotron may be made using CNT cold-cathode electron gun. PMID:27609247

A Fully-Sealed Carbon-Nanotube Cold-Cathode Terahertz Gyrotron.

PubMed

Yuan, Xuesong; Zhu, Weiwei; Zhang, Yu; Xu, Ningsheng; Yan, Yang; Wu, Jianqiang; Shen, Yan; Chen, Jun; She, Juncong; Deng, Shaozhi

2016-09-09

Gigahertz to terahertz radiation sources based on cold-cathode vacuum electron technology are pursued, because its unique characteristics of instant switch-on and power saving are important to military and space applications. Gigahertz gyrotron was reported using carbon nanotube (CNT) cold-cathode. It is reported here in first time that a fully-sealed CNT cold-cathode 0.22 THz-gyrotron is realized, typically with output power of 500 mW. To achieve this, we have studied mechanisms responsible for CNTs growth on curved shape metal surface, field emission from the sidewall of a CNT, and crystallized interface junction between CNT and substrate material. We have obtained uniform growth of CNTs on and direct growth from cone-cylinder stainless-steel electrode surface, and field emission from both tips and sidewalls of CNTs. It is essential for the success of a CNT terahertz gyrotron to have such high quality, high emitting performance CNTs. Also, we have developed a magnetic injection electron gun using CNT cold-cathode to exploit the advantages of such a conventional gun design, so that a large area emitting surface is utilized to deliver large current for electron beam. The results indicate that higher output power and higher radiation frequency terahertz gyrotron may be made using CNT cold-cathode electron gun.

A New Electron Source for Laboratory Simulation of the Space Environment

NASA Technical Reports Server (NTRS)

Krause, Linda Habash; Everding, Daniel; Bonner, Mathew; Swan, Brian

2012-01-01

We have developed a new collimated electron source called the Photoelectron Beam Generator (PEBG) for laboratory and spaceflight applications. This technology is needed to replace traditional cathodes because of serious fundamental weaknesses with the present state of the art. Filament cathodes suffer from numerous practical problems, even if expertly designed, including the dependence of electron emission on filament temperature, short lifetimes (approx 100 hours), and relatively high power (approx 10s of W). Other types of cathodes have solved some of these problems, but they are plagued with other difficult problems, such as the Spindt cathode's extreme sensitivity to molecular oxygen. None to date have been able to meet the demand of long lifetime, robust packaging, and precision energy and flux control. This new cathode design avoids many common pitfalls of traditional cathodes. Specifically, there are no fragile parts, no sensitivity to oxygen, no intrinsic emission dependencies on device temperature, and no vacuum requirements for protecting the source from contamination or damage. Recent advances in high-brightness Light Emitting Diodes (LEDs) have provided the key enabling technology for this new electron source. The LEDs are used to photoeject electrons off a target material of a low work-function, and these photoelectrons are subsequently focused into a laminar beam using electrostatic lenses. The PEBG works by illuminating a target material and steering photoelectrons into a laminar beam using electrostatic lenses

Microplasma device architectures with various diamond nanostructures

NASA Astrophysics Data System (ADS)

Kunuku, Srinivasu; Jothiramalingam Sankaran, Kamatchi; Leou, Keh-Chyang; Lin, I.-Nan

2017-02-01

Diamond nanostructures (DNSs) were fabricated from three different morphological diamonds, microcrystalline diamond (MCD), nanocrystalline diamond (NCD), and ultrananocrystalline diamond (UNCD) films, using a reactive ion etching method. The plasma illumination (PI) behavior of microplasma devices using the DNSs and the diamond films as cathode were investigated. The Paschen curve approach revealed that the secondary electron emission coefficient (γ value) of diamond materials is similar irrespective of the microstructure (MCD, NCD, and UNCD) and geometry of the materials (DNSs and diamond films). The diamond materials show markedly larger γ-coefficient than conventional metallic cathode materials such as Mo that resulted in markedly better PI behavior for the corresponding microplasma devices. Moreover, the PI behavior, i.e. the voltage dependence of plasma current density (J pl-V), plasma density (n e-V), and the robustness of the devices, varied markedly with the microstructure and geometry of the cathode materials that was closely correlated to the electron field emission (EFE) properties of the cathode materials. The UNCD nanopillars, possessing good EFE properties, resulted in superior PI behavior, whereas the MCD diamond films with insufficient EFE properties led to inferior PI behavior. Consequently, enhancement of plasma characteristics is the collective effects of EFE behavior and secondary electron emission characteristics of diamond-based cathode materials.

Suppression of shunting current in a magnetically insulated coaxial vacuum diode

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yalandin, M. I.; Sharypov, K. A.; Shpak, V. G.

2015-06-08

Real-time investigations of the dynamics of explosive electron emission from a high-voltage cathode holder made of nonmagnetic stainless steel in a magnetically insulated coaxial vacuum diode have been performed. It has been shown that aging the cathode with several tens of voltage pulses at a field of 1–2 MV/cm provides a stray emission delay ranging from hundreds of picoseconds to a nanosecond or more. In addition, the magnetic field must be configured so that the magnetic lines would not cross the vacuum gap between the diode case and the cathode holder in the region behind the emitting edge of themore » cathode. These efforts provide conditions for stable emission of the working beam from a graphite cathode with a sharp emitting edge.« less

ION SOURCE FOR CALUTRONS

DOEpatents

Tolmie, J.R.

1958-09-16

An improvement is presented in ion sources of the type employed in calutron devices. The described ion source has for its inventive contribution the incorporation of a plate-like cathode having the general configuration of a polygon including a given number of apices. When a polyphase source of current has a phase connected to each of the apices, the cathode is heated and rendered electron emissive. This particular cathode configuration is of sturdy construction and provides unuform emission over a considerable area.

Preparation and surface characteristics of Re3W matrix scandate cathode: An experimental and theoretical study

NASA Astrophysics Data System (ADS)

Lai, Chen; Wang, Jinshu; Zhou, Fan; Liu, Wei; Hu, Peng; Wang, Changhao; Wang, Ruzhi; Miao, Naihua

2018-05-01

The Scandia doped thermionic cathodes have received great attention owing to their high electron emission density in past two decades. Here, Scandia doped Re3W matrix scandate (RS) cathodes are fabricated by using Sc2O3 doped Re3W powders that prepared by spray drying method. The micromorphology, surface composition and chemical states of RS cathode are investigated with various modern technologies. It reveals that the reduction temperature of RS powders is dramatically increased by Sc2O3. On the surface of RS cathode, a certain amount of Sc2O3 nanoparticles and barium salt submicron particles are observed. According to the in situ Auger electron spectroscopy analysis, the concentration ratio of Ba:Sc:O is determined to be 2.9:1.1:2.7. The X-ray photoelectron spectroscopy data indicates that low oxidation state of Sc is clearly observed in scandate cathodes. The high atomic ratio of Ba on RS cathode surface is suggested due to the high adsorption of Re3W to Ba. Moreover, RS cathode shows better adsorption to Sc by comparison with conventional tungsten matrix scandate cathode. For RS cathode, the main depletion of Sc is suggested to -OSc desorbing from RS cathode surface. RS cathode is expected to be an impressive thermionic cathode with good emission properties and ion anti-bombarding insensitivity.

RF Photoelectric injectors using needle cathodes

NASA Astrophysics Data System (ADS)

Lewellen, J. W.; Brau, C. A.

2003-07-01

Photocathode RF guns, in various configurations, are the injectors of choice for both current and future applications requiring high-brightness electron beams. Many of these applications, such as single-pass free-electron lasers, require beams with high brilliance but not necessarily high charge per bunch. Field-enhanced photoelectric emission has demonstrated electron-beam current density as high as 10 10 A/m 2, with a quantum efficiency in the UV that approaches 10% at fields on the order of 10 10 V/m. Thus, the use of even a blunt needle holds promise for increasing cathode quantum efficiency without sacrificing robustness. We present an initial study on the use of needle cathodes in photoinjectors to enhance beam brightness while reducing beam charge. Benefits include lower drive-laser power requirements, easier multibunch operation, lower emittance, and lower beam degradation due to charge-dependent effects in the postinjector accelerator. These benefits result from a combination of a smaller cathode emission area, greatly enhanced RF field strength at the cathode, and the charge scaling of detrimental postinjector linac effects, e.g., transverse wakefields and CSR.

Study of a contracted glow in low-frequency plasma-jet discharges operating with argon

DOE Office of Scientific and Technical Information (OSTI.GOV)

Minotti, F.; Giuliani, L.; Xaubet, M.

2015-11-15

In this work, we present an experimental and theoretical study of a low frequency, atmospheric plasma-jet discharge in argon. The discharge has the characteristics of a contracted glow with a current channel of submillimeter diameter and a relatively high voltage cathode layer. In order to interpret the measurements, we consider the separate modeling of each region of the discharge: main channel and cathode layer, which must then be properly matched together. The main current channel was modeled, extending a previous work, as similar to an arc in which joule heating is balanced by lateral heat conduction, without thermal equilibrium betweenmore » electrons and heavy species. The cathode layer model, on the other hand, includes the emission of secondary electrons by ion impact and by additional mechanisms, of which we considered emission due to collision of atoms excited at metastable levels, and field-enhanced thermionic emission (Schottky effect). The comparison of model and experiment indicates that the discharge can be effectively sustained in its contracted form by the secondary electrons emitted by collision of excited argon atoms, whereas thermionic emission is by far insufficient to provide the necessary electrons.« less

High-current electron gun with a planar magnetron integrated with an explosive-emission cathode

NASA Astrophysics Data System (ADS)

Kiziridi, P. P.; Ozur, G. E.

2017-05-01

A new high-current electron gun with plasma anode and explosive-emission cathode integrated with planar pulsed powered magnetron is described. Five hundred twelve copper wires 1 mm in diameter and 15 mm in height serve as emitters. These emitters are installed on stainless steel disc (substrate) with 3-mm distance between them. Magnetron discharge plasma provides increased ion density on the periphery of plasma anode formed by high-current Penning discharge ignited within several milliseconds after starting of the magnetron discharge. The increased on the periphery ion density improves the uniformity of high-current electron beam produced in such an electron gun.

Chemically synthesized boron carbon oxynitride as a new cold cathode material

NASA Astrophysics Data System (ADS)

Banerjee, Diptonil; Maity, Supratim; Chattopadhyay, K. K.

2015-11-01

Synthesis of boron carbon oxynitride (BCNO) nanosheets at different temperature from amorphous to crystalline regime has been reported. The synthesis was done by a simple molten salt process using sodium borohydride and urea as precursors. Transmission electron microscopic study confirms the formation of sheet-like structure of the as-synthesized material. The performances of the as-synthesized BCNO nanosheets as cold cathode materials have been studied for the first time in the high vacuum electron field emission set up. It has been seen that the material gives considerable field emission current with turn on field as low as 2.95 V/μm with good stability and thus a new cold cathode material can be postulated.

Secondary electron emission and glow discharge properties of 12CaO·7Al2O3 electride for fluorescent lamp applications.

PubMed

Watanabe, Satoru; Watanabe, Toshinari; Ito, Kazuhiro; Miyakawa, Naomichi; Ito, Setsuro; Hosono, Hideo; Mikoshiba, Shigeo

2011-06-01

12CaO·7Al 2 O 3 electride, a sub-nanoporous compound having a work function of 2.4 eV, was examined as a candidate cathode material in fluorescent lamps. The electron emission yield was higher and the discharge voltage was lower for 12CaO·7Al 2 O 3 than for existing cathode materials such as Ni, Mo or W; therefore, the energy consumption of the fluorescent lamps can be improved using 12CaO·7Al 2 O 3 cathodes. Prototype glow-discharge lamps using 12CaO·7Al 2 O 3 were constructed and exhibited reasonable durability.

Secondary electron emission and glow discharge properties of 12CaO·7Al2O3 electride for fluorescent lamp applications

PubMed Central

Watanabe, Satoru; Watanabe, Toshinari; Ito, Kazuhiro; Miyakawa, Naomichi; Ito, Setsuro; Hosono, Hideo; Mikoshiba, Shigeo

2011-01-01

12CaO·7Al2O3 electride, a sub-nanoporous compound having a work function of 2.4 eV, was examined as a candidate cathode material in fluorescent lamps. The electron emission yield was higher and the discharge voltage was lower for 12CaO·7Al2O3 than for existing cathode materials such as Ni, Mo or W; therefore, the energy consumption of the fluorescent lamps can be improved using 12CaO·7Al2O3 cathodes. Prototype glow-discharge lamps using 12CaO·7Al2O3 were constructed and exhibited reasonable durability. PMID:27877401

Detailed Modeling of Physical Processes in Electron Sources for Accelerator Applications

NASA Astrophysics Data System (ADS)

Chubenko, Oksana; Afanasev, Andrei

2017-01-01

At present, electron sources are essential in a wide range of applications - from common technical use to exploring the nature of matter. Depending on the application requirements, different methods and materials are used to generate electrons. State-of-the-art accelerator applications set a number of often-conflicting requirements for electron sources (e.g., quantum efficiency vs. polarization, current density vs. lifetime, etc). Development of advanced electron sources includes modeling and design of cathodes, material growth, fabrication of cathodes, and cathode testing. The detailed simulation and modeling of physical processes is required in order to shed light on the exact mechanisms of electron emission and to develop new-generation electron sources with optimized efficiency. The purpose of the present work is to study physical processes in advanced electron sources and develop scientific tools, which could be used to predict electron emission from novel nano-structured materials. In particular, the area of interest includes bulk/superlattice gallium arsenide (bulk/SL GaAs) photo-emitters and nitrogen-incorporated ultrananocrystalline diamond ((N)UNCD) photo/field-emitters. Work supported by The George Washington University and Euclid TechLabs LLC.

Efficient polymer light-emitting diode with air-stable aluminum cathode

DOE Office of Scientific and Technical Information (OSTI.GOV)

Abbaszadeh, D.; Dutch Polymer Institute, P.O. Box 902, 5600 AX Eindhoven; Wetzelaer, G. A. H.

2016-03-07

The fast degradation of polymer light-emitting diodes (PLEDs) in ambient conditions is primarily due to the oxidation of highly reactive metals, such as barium or calcium, which are used as cathode materials. Here, we report the fabrication of PLEDs using an air-stable partially oxidized aluminum (AlO{sub x}) cathode. Usually, the high work function of aluminum (4.2 eV) imposes a high barrier for injecting electrons into the lowest unoccupied molecular orbital (LUMO) of the emissive polymer (2.9 eV below the vacuum level). By partially oxidizing aluminum, its work function is decreased, but not sufficiently low for efficient electron injection. Efficient injection is obtainedmore » by inserting an electron transport layer of poly[(9,9-di-n-octylfluorenyl-2,7-diyl)-alt-(benzo[2,1,3] thiadiazol-4,8-diyl)] (F8BT), which has its LUMO at 3.3 eV below vacuum, between the AlO{sub x} cathode and the emissive polymer. The intermediate F8BT layer not only serves as a hole-blocking layer but also provides an energetic staircase for electron injection from AlO{sub x} into the emissive layer. PLEDs with an AlO{sub x} cathode and F8BT interlayer exhibit a doubling of the efficiency as compared to conventional Ba/Al PLEDs, and still operate even after being kept in ambient atmosphere for one month without encapsulation.« less

Investigations and Applications of Field- and Photo-emitted Electron Beams from a Radio Frequency Gun

DOE Office of Scientific and Technical Information (OSTI.GOV)

Panuganti, SriHarsha

Production of quality electron bunches using e cient ways of generation is a crucial aspect of accelerator technology. Radio frequency electron guns are widely used to generate and rapidly accelerate electron beams to relativistic energies. In the current work, we primarily study the charge generation processes of photoemission and eld emission inside an RF gun installed at Fermilab's High Brightness Electron Source Laboratory (HBESL). Speci cally, we study and characterize second-order nonlinear photoemission from a Cesium Telluride (Cs 2Te) semiconductor photocathode, and eld emission from carbon based cathodes including diamond eld emission array (DFEA) and carbon nanotube (CNT) cathodes locatedmore » in the RF gun's cavity. Finally, we discuss the application experiments conducted at the facility to produce soft x-rays via inverse Compton scattering (ICS), and to generate uniformly lled ellipsoidal bunches and temporally shaped electron beams from the Cs 2Te photocathode.« less

Electronic structure of BaO/W cathode surfaces

NASA Technical Reports Server (NTRS)

Muller, Wolfgang

1989-01-01

The local electronic structure of the emissive layer of barium dispenser thermionic cathodes is investigated theoretically using the relativistic scattered-wave approach. The interaction of Ba and O with W, Os, and W-Os alloy surfaces is studied with atomic clusters modeling different absorption environments representative of B- and M-type cathodes. Ba is found to be strongly oxidized, while O and the metal substrate are in a reduced chemical state. The presence of O enhances the surface dipole and Ba binding energy relative to Ba on W. Model results for W-Os alloy substrates show only relatively small changes in Ba and O for identical geometries, but very large charge redistributions inside the substrate, which are attributed to the electronegativity difference between Os and W. If Os is present in the surface layer, the charge transfer from Ba to the substrate and the Ba binding energy increase relative to W. Explanations are offered for the improved electron emission from alloy surfaces and the different emission enhancement for different alloy substrates.

Effects of nanoscale vacuum gap on photon-enhanced thermionic emission devices

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Yuan; Liao, Tianjun; Zhang, Yanchao

2016-01-28

A new model of the photon-enhanced thermionic emission (PETE) device with a nanoscale vacuum gap is established by introducing the quantum tunneling effect and the image force correction. Analytic expressions for both the thermionic emission and tunneling currents are derived. The electron concentration and the temperature of the cathode are determined by the particle conservation and energy balance equations. The effects of the operating voltage on the maximum potential barrier, cathode temperature, electron concentration and equilibrium electron concentration of the conduction band, and efficiency of the PETE device are discussed in detail for different given values of the vacuum gapmore » length. The influence of the band gap of the cathode and flux concentration on the efficiency is further analyzed. The maximum efficiency of the PETE and the corresponding optimum values of the band gap and the operating voltage are determined. The results obtained here show that the efficiency of the PETE device can be significantly improved by employing a nanoscale vacuum gap.« less

Surface chemical analysis and ab initio investigations of CsI coated C fiber cathodes for high power microwave sources

NASA Astrophysics Data System (ADS)

Vlahos, Vasilios; Morgan, Dane; LaCour, Matthew; Golby, Ken; Shiffler, Don; Booske, John H.

2010-02-01

CsI coated C fiber cathodes are promising electron emitters utilized in field emission applications. Ab initio calculations, in conjunction with experimental investigations on CsI-spray coated C fiber cathodes, were performed in order to better understand the origin of the low turn-on E-field obtained, as compared to uncoated C fibers. One possible mechanism for lowering the turn-on E-field is surface dipole layers reducing the work function. Ab initio modeling revealed that surface monolayers of Cs, CsI, Cs2O, and CsO are all capable of producing low work function C fiber cathodes (1 eV<Φ<1.5 eV), yielding a reduction in the turn-on E-field by as much as ten times, when compared to the bare fiber. Although a CsI-containing aqueous solution is spray deposited on the C fiber surface, energy dispersive x-ray spectroscopy and scanning auger microscopy measurements show coabsorption of Cs and I into the fiber interior and Cs and O on the fiber surface, with no surface I. It is therefore proposed that a cesium oxide (CsxOy) surface coating is responsible, at least in part, for the low turn E-field and superior emission characteristics of this type of fiber cathode. This CsxOy layer could be formed during preconditioning heating. CsxOy surface layers cannot only lower the fiber work function by the formation of surface dipoles (if they are thin enough) but may also enhance surface emission through their ability to emit secondary electrons due to a process of grazing electron impact. These multiple electron emission processes may explain the reported 10-100 fold reduction in the turn-on E-field of coated C fibers.

Phosphorescent organic light emitting diodes with high efficiency and brightness

DOEpatents

Forrest, Stephen R; Zhang, Yifan

2015-11-12

An organic light emitting device including a) an anode; b) a cathode; and c) an emissive layer disposed between the anode and the cathode, the emissive layer comprising an organic host compound and a phosphorescent compound exhibiting a Stokes Shift overlap greater than 0.3 eV. The organic light emitting device may further include a hole transport layer disposed between the emissive layer and the anode; and an electron transport layer disposed between the emissive layer and the cathode. In some embodiments, the phosphorescent compound exhibits a phosphorescent lifetime of less than 10 .mu.s. In some embodiments, the concentration of the phosphorescent compound ranges from 0.5 wt. % to 10 wt. %.

The Experimental Study of Novel Pseudospark Hollow Cathode Plasma Electron Gun

NASA Astrophysics Data System (ADS)

Gu, Xiaowei; Meng, Lin; Sun, Yiqin; Yu, Xinhua

2008-11-01

The high-power microwave devices with plasma-filled have unique properties. One of the major problems associated with plasma-filled microwave sources is that ions from the plasma drift toward the gun regions of the tube. This bombardment is particularly dangerous for the gun, where high-energy ion impacts can damage the cathode surface and degrade its electron emission capabilities. One of the techniques investigated to mitigate this issue is to replace the material cathode with plasma cathode. Now, we study the novel electron gun (E-gun) that can be suitable for high power microwave device applications, adopting two forms of discharge channel, 1: a single hole channel, the structure can produce a solid electron beam; 2: porous holes channel, the structure can generate multiple electronic injection which is similar to the annular electron beam.

Noise characteristics of a plasma relativistic microwave amplifier

DOE Office of Scientific and Technical Information (OSTI.GOV)

Strelkov, P. S., E-mail: strelkov@fpl.gpi.ru; Ivanov, I. E.; Shumeiko, D. V.

2016-07-15

Reasons for the occurrence of microwave noise at the output of a plasma relativistic amplifier have been analyzed. It is found that, in the absence of an input signal, the emission spectrum of the plasma relativistic microwave amplifier is similar to that of an electron beam in vacuum. It is concluded that microwave noise at the output of the amplifier appears as a result of amplification of the intrinsic noise of the electron beam. The emission characteristics of a relativistic electron beam formed in a magnetically insulated diode with an explosive emission cathode in vacuum have been studied experimentally formore » the first time. An important point is that, in this case, there is no virtual cathode in the drift space.« less

Nano-scale investigations of electric-dipole-layer enhanced field and thermionic emission from high current density cathodes

NASA Astrophysics Data System (ADS)

Vlahos, Vasilios

Cesium iodide coated graphitic fibers and scandate cathodes are two important electron emission technologies. The coated fibers are utilized as field emitters for high power microwave sources. The scandate cathodes are promising thermionic cathode materials for pulsed power vacuum electron devices. This work attempts to understand the fundamental physical and chemical relationships between the atomic structure of the emitting cathode surfaces and the superior emission characteristics of these cathodes. Ab initio computational modeling in conjunction with experimental investigations was performed on coated fiber cathodes to understand the origin of their very low turn on electric field, which can be reduced by as much as ten-fold compared to uncoated fibers. Copious amounts of cesium and oxygen were found co-localized on the fiber, but no iodine was detected on the surface. Additional ab initio studies confirmed that cesium oxide dimers could lower the work function significantly. Surface cesium oxide dipoles are therefore proposed as the source of the observed reduction in the turn on electric field. It is also proposed that emission may be further enhanced by secondary electrons from cesium oxide during operation. Thermal conditioning of the coated cathode may be a mechanism by which surface cesium iodide is converted into cesium oxide, promoting the depletion of iodine by formation of volatile gas. Ab initio modeling was also utilized to investigate the stability and work functions of scandate structures. The work demonstrated that monolayer barium-scandium-oxygen surface structures on tungsten can dramatically lower the work function of the underlying tungsten substrate from 4.6 eV down to 1.16 eV, by the formation of multiple surface dipoles. On the basis of this work, we conclude that high temperature kinetics force conventional dispenser cathodes (barium-oxygen monolayers on tungsten) to operate in a non-equilibrium compositional steady state with higher than optimal work functions of ˜2 eV. We hypothesize that scandium enables the barium-oxygen surface monolayer kinetics to access a more thermodynamically stable phase with reported work functions as low as ˜1.3 eV.

Spatial and temporal dynamics of a pulsed spark microplasma used for aerosol analysis

NASA Astrophysics Data System (ADS)

Zheng, Lina; Kulkarni, Pramod; Diwakar, Prasoon

2018-06-01

The spatial and temporal dynamics of a pulsed, electrical spark microplasma used for spectrochemical analysis of aerosols was investigated. The spark discharge was generated by applying a high voltage pulse between a coaxial anode and cathode. Aerosol particles of black carbon were collected on the cathode for 2 min, following which the pulsed microplasma was introduced, leading to ablation and atomization of the collected particles. The space- and time-resolved emission spectra showed that the atomic emission signal from the carbon species originated from the region close to the cathode surface during the early evolution of the microplasma. The C I and C II atomic emission reached peak intensities at 11 and 6 μs delay time, respectively. Peak emission intensities occurred between 0.5-1.3 mm above the cathode surface. The average excitation temperature and the electron number density of the spark microplasma were estimated to be 23,000 K, and 1.6 × 1017 cm-3, respectively. The effects of pulse energy on the excitation temperature and electron density were also investigated. The results provide insights into the dynamics of the pulsed spark microplasma and are helpful in optimizing elemental analysis of aerosols using this technique.

A phenomenological model for orificed hollow cathodes. Ph.D. Thesis, 1 Dec. 1981 - 1 Dec. 1982; [electrostatic thruster

NASA Technical Reports Server (NTRS)

Siegfried, D. E.

1982-01-01

A quartz hollow tube cathode was used to determine the operating conditions within a mercury orificed hollow cathode. Insert temperature profiles, cathode current distributions, plasma properties profile, and internal pressure-mass flow rate results are summarized and used in a phenomenological model which qualitatively describes electron emission and plasma production processes taking place within the cathode. By defining an idealized ion production region within which most of the plasma processes are concentrated, this model is expressed analytically as a simple set of equations which relate cathode dimensions and specifiable operating conditions, such as mass flow rate and discharge current, to such important parameters as emission surface temperature and internal plasma properties. Key aspects of the model are examined.

Negative space charge effects in photon-enhanced thermionic emission solar converters

DOE Office of Scientific and Technical Information (OSTI.GOV)

Segev, G.; Weisman, D.; Rosenwaks, Y.

2015-07-06

In thermionic energy converters, electrons in the gap between electrodes form a negative space charge and inhibit the emission of additional electrons, causing a significant reduction in conversion efficiency. However, in Photon Enhanced Thermionic Emission (PETE) solar energy converters, electrons that are reflected by the electric field in the gap return to the cathode with energy above the conduction band minimum. These electrons first occupy the conduction band from which they can be reemitted. This form of electron recycling makes PETE converters less susceptible to negative space charge loss. While the negative space charge effect was studied extensively in thermionicmore » converters, modeling its effect in PETE converters does not account for important issues such as this form of electron recycling, nor the cathode thermal energy balance. Here, we investigate the space charge effect in PETE solar converters accounting for electron recycling, with full coupling of the cathode and gap models, and addressing conservation of both electric and thermal energy. The analysis shows that the negative space charge loss is lower than previously reported, allowing somewhat larger gaps compared to previous predictions. For a converter with a specific gap, there is an optimal solar flux concentration. The optimal solar flux concentration, the cathode temperature, and the efficiency all increase with smaller gaps. For example, for a gap of 3 μm the maximum efficiency is 38% and the optimal flux concentration is 628, while for a gap of 5 μm the maximum efficiency is 31% and optimal flux concentration is 163.« less

Field emission electron source

DOEpatents

Zettl, Alexander Karlwalter; Cohen, Marvin Lou

2000-01-01

A novel field emitter material, field emission electron source, and commercially feasible fabrication method is described. The inventive field emission electron source produces reliable electron currents of up to 400 mA/cm.sup.2 at 200 volts. The emitter is robust and the current it produces is not sensitive to variability of vacuum or the distance between the emitter tip and the cathode. The novel emitter has a sharp turn-on near 100 volts.

Operation of a gated field emitter using an individual carbon nanofiber cathode

NASA Astrophysics Data System (ADS)

Guillorn, M. A.; Melechko, A. V.; Merkulov, V. I.; Ellis, E. D.; Britton, C. L.; Simpson, M. L.; Lowndes, D. H.; Baylor, L. R.

2001-11-01

We report on the operation of an integrated gated cathode device using a single vertically aligned carbon nanofiber as the field emission element. This device is capable of operation in a moderate vacuum for extended periods of time without experiencing a degradation of performance. Less than 1% of the total emitted current is collected by the gate electrode, indicating that the emitted electron beam is highly collimated. As a consequence, this device is ideal for applications that require well-focused electron emission from a microscale structure.

Extremely-efficient, miniaturized, long-lived alpha-voltaic power source using liquid gallium

NASA Technical Reports Server (NTRS)

Snyder, G. Jeffrey (Inventor); Patel, Jagdishbhai (Inventor); Fleurial, Jean-Pierre (Inventor)

2004-01-01

A power source converts .alpha.-particle energy to electricity for use in electrical systems. Liquid gallium or other liquid medium is subjected to .alpha.-particle emissions. Electrons are freed by collision from neutral gallium atoms to provide gallium ions. The electrons migrate to a cathode while the gallium ions migrate to an anode. A current and/or voltage difference then arises between the cathode and anode because of the work function difference of the cathode and anode. Gallium atoms are regenerated by the receiving of electrons from the anode enabling the generation of additional electrons from additional .alpha.-particle collisions.

In Situ observation of dark current emission in a high gradient rf photocathode gun

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shao, Jiahang; Shi, Jiaru; Antipov, Sergey P.

Undesirable electron field emission (also known as dark current) in high gradient rf photocathode guns deteriorates the quality of the photoemission current and limits the operational gradient. To improve the understanding of dark current emission, a high-resolution (~100 μm) dark current imaging experiment has been performed in an L-band photocathode gun operating at ~100 MV/m of surface gradient. Scattered strong emission areas with high current have been observed on the cathode. The field enhancement factor β of selected regions on the cathode has been measured. Finally, the postexaminations with scanning electron microscopy and white light interferometry reveal the origins ofmore » ~75% strong emission areas overlap with the spots where rf breakdown has occurred.« less

In Situ observation of dark current emission in a high gradient rf photocathode gun

DOE PAGES

Shao, Jiahang; Shi, Jiaru; Antipov, Sergey P.; ...

2016-08-15

Undesirable electron field emission (also known as dark current) in high gradient rf photocathode guns deteriorates the quality of the photoemission current and limits the operational gradient. To improve the understanding of dark current emission, a high-resolution (~100 μm) dark current imaging experiment has been performed in an L-band photocathode gun operating at ~100 MV/m of surface gradient. Scattered strong emission areas with high current have been observed on the cathode. The field enhancement factor β of selected regions on the cathode has been measured. Finally, the postexaminations with scanning electron microscopy and white light interferometry reveal the origins ofmore » ~75% strong emission areas overlap with the spots where rf breakdown has occurred.« less

Process For Patterning Dispenser-Cathode Surfaces

NASA Technical Reports Server (NTRS)

Garner, Charles E.; Deininger, William D.

1989-01-01

Several microfabrication techniques combined into process cutting slots 100 micrometer long and 1 to 5 micrometer wide into tungsten dispenser cathodes for traveling-wave tubes. Patterned photoresist serves as mask for etching underlying aluminum. Chemically-assisted ion-beam etching with chlorine removes exposed parts of aluminum layer. Etching with fluorine or chlorine trifluoride removes tungsten not masked by aluminum layer. Slots enable more-uniform low-work function coating dispensed to electron-emitting surface. Emission of electrons therefore becomes more uniform over cathode surface.

Observations of a mode transition in a hydrogen hollow cathode discharge using phase resolved optical emission spectroscopy

NASA Astrophysics Data System (ADS)

Dixon, Sam; Charles, Christine; Dedrick, James; Gans, Timo; O'Connell, Deborah; Boswell, Rod

2014-07-01

Two distinct operational modes are observed in a radio frequency (rf) low pressure hydrogen hollow cathode discharge. The mode transition is characterised by a change in total light emission and differing expansion structures. An intensified CCD camera is used to make phase resolved images of Balmer α emission from the discharge. The low emission mode is consistent with a typical γ discharge, and appears to be driven by secondary electrons ejected from the cathode surface. The bright mode displays characteristics common to an inductive discharge, including increased optical emission, power factor, and temperature of the H2 gas. The bright mode precipitates the formation of a stationary shock in the expansion, observed as a dark region adjacent to the source-chamber interface.

Transition in discharge plasma of Hall thruster type in presence of secondary electron emissive surface

NASA Astrophysics Data System (ADS)

Schweigert, I. V.; Yadrenkin, M. A.; Fomichev, V. P.

2017-11-01

Modification of the sheath structure near the emissive plate placed in magnetized DC discharge plasma of Hall thruster type was studied in the experiment and in kinetic simulations. The plate is made from Al2O3 which has enhanced secondary electron emission yield. The energetic electrons emitted by heated cathode provide the volume ionization and the secondary electron emission from the plate. An increase of the electron beam energy leads to an increase of the secondary electron generation, which initiates the transition in sheath structure over the emissive plate.

Arrays of Bundles of Carbon Nanotubes as Field Emitters

NASA Technical Reports Server (NTRS)

Manohara, Harish; Bronkowski, Michael

2007-01-01

Experiments have shown that with suitable choices of critical dimensions, planar arrays of bundles of carbon nanotubes (see figure) can serve as high-current-density field emitter (cold-cathode) electron sources. Whereas some hot-cathode electron sources must be operated at supply potentials of thousands of volts, these cold-cathode sources generate comparable current densities when operated at tens of volts. Consequently, arrays of bundles of carbon nanotubes might prove useful as cold-cathode sources in miniature, lightweight electron-beam devices (e.g., nanoklystrons) soon to be developed. Prior to the experiments, all reported efforts to develop carbon-nanotube-based field-emission sources had yielded low current densities from a few hundred microamperes to a few hundred milliamperes per square centimeter. An electrostatic screening effect, in which taller nanotubes screen the shorter ones from participating in field emission, was conjectured to be what restricts the emission of electrons to such low levels. It was further conjectured that the screening effect could be reduced and thus emission levels increased by increasing the spacing between nanotubes to at least by a factor of one to two times the height of the nanotubes. While this change might increase the emission from individual nanotubes, it would decrease the number of nanotubes per unit area and thereby reduce the total possible emission current. Therefore, to maximize the area-averaged current density, it would be necessary to find an optimum combination of nanotube spacing and nanotube height. The present concept of using an array of bundles of nanotubes arises partly from the concept of optimizing the spacing and height of field emitters. It also arises partly from the idea that single nanotubes may have short lifetimes as field emitters, whereas bundles of nanotubes could afford redundancy so that the loss of a single nanotube would not significantly reduce the overall field emission.

Amorphous-diamond electron emitter

DOEpatents

Falabella, Steven

2001-01-01

An electron emitter comprising a textured silicon wafer overcoated with a thin (200 .ANG.) layer of nitrogen-doped, amorphous-diamond (a:D-N), which lowers the field below 20 volts/micrometer have been demonstrated using this emitter compared to uncoated or diamond coated emitters wherein the emission is at fields of nearly 60 volts/micrometer. The silicon/nitrogen-doped, amorphous-diamond (Si/a:D-N) emitter may be produced by overcoating a textured silicon wafer with amorphous-diamond (a:D) in a nitrogen atmosphere using a filtered cathodic-arc system. The enhanced performance of the Si/a:D-N emitter lowers the voltages required to the point where field-emission displays are practical. Thus, this emitter can be used, for example, in flat-panel emission displays (FEDs), and cold-cathode vacuum electronics.

Development program on a cold cathode electron gun

NASA Technical Reports Server (NTRS)

Spindt, C. A.

1979-01-01

A prototype electron gun with a field emitter cathode capable of producing 95 mA in a 1/4 mm diameter beam at 12 kV was produced. Achievement of this goal required supporting studies in cathode fabrication, cathode performance, gun design, cathode mounting and gun fabrication. A series of empirical investigations advanced fabrication technology: More stable emitters were produced and multiple cone failure caused by chain reaction discharges were reduced. The cathode is capable of producing well over 95 mA, but a substantial collector development effort was required to demonstrate emission levels in the 100 mA region. Space charge problems made these levels difficult to achieve. Recommendations are made for future process and materials investigation. Electron gun designs were modeled and tested. A pair of two-electrode gun structures were fabricated and tested; one gun was delivered to NASA. Cathodes were pretested up to 100 mA at SRI and delivered to NASA for test in the gun structure.

Improvement of carbon nanotube field emission properties by ultrasonic nanowelding

NASA Astrophysics Data System (ADS)

Zhao, Bo; Yadian, Boluo; Chen, Da; Xu, Dong; Zhang, Yafei

2008-12-01

Ultrasonic nanowelding was used to improve the field emission properties of carbon nanotube (CNT) cathodes. The CNTs were deposited on the Ti-coated glass substrate by electrophoretic deposition. By pressing CNTs against metal (Ti) substrate under a vibrating force at ultrasonic frequency, a reliable and low resistance contact was obtained between CNTs and Ti. The scanning electron microscopy results show that CNTs are embedded into the metal substrate and act as stable field emitters. The welded cathode demonstrates an excellent field emission with high emission current density and good current stability.

Design, construction and long life endurance testing of cathode assemblies for use in microwave high-power transmitting tubes

NASA Technical Reports Server (NTRS)

Batra, R.; Marino, D.

1986-01-01

The cathode life test program sponsored by NASA Lewis Research Center at Watkins-Johnson Company has been in continuous operation since 1972. Its primary objective has been to evaluate the long life capability of barium dispenser cathodes to produce emission current densities of 2 A sq. cm. or more in an operational environment simulating that of a highpower microwave tube. The life test vehicles were equipped with convergent flow electron guns, drift space tubes with solenoid magnets for electron beam confinement and water-cooled depressed collectors. A variety of cathode types has been tested, including GE Tungstate, Litton Impregnated, Philips Type B and M, Semicon types S and M, and Spectra-Mat Type M. Recent emphasis has been on monitoring the performance of Philips Type M cathodes at 2 A sq. cm. and Sprectra-Mat and Semicon Type M cathodes at 4 A sq. cm. These cathodes have been operated at a constant current of 616 mA and a cathode anode voltage on the order of 10 kV. Cathode temperatures were maintained at 1010 C true as measured from black body holes in the backs of the cathodes. This report presents results of the cathode life test program from July l982 through April l986. The results include hours of operation and performance data in the form of normalized emission current density versus temperature curves (Miram plots).

Understanding the Impact of Field-Emitter Characteristics on Electron Beam Focusing in the VAPoR Time-of-Fight Mass Spectrometer

NASA Technical Reports Server (NTRS)

Southard, Adrian E.; Getty, Stephanie A.; Costen, Nicholas P.; Hidrobo, Gregory B.; Glavin, Daniel P.

2013-01-01

Simulations of field emission of electrons from an electron gun are used to determine the angular distribution of the emitted electron beam and the percentage of charge transmitted through the grid. The simulations are a first step towards understanding the spherical aberration present after focusing the electron beam. The effect of offset of the cathode with respect to the grid and the separation between cathode and grid on the angular distributions of emitted electrons and transmission of the grid are explored.

Oxygen transport in the internal xenon plasma of a dispenser hollow cathode

DOE Office of Scientific and Technical Information (OSTI.GOV)

Capece, Angela M., E-mail: acapece@pppl.gov; Shepherd, Joseph E.; Polk, James E.

2014-04-21

Reactive gases such as oxygen and water vapor modify the surface morphology of BaO dispenser cathodes and degrade the electron emission properties. For vacuum cathodes operating at fixed temperature, the emission current drops rapidly when oxygen adsorbs on top of the low work function surface. Previous experiments have shown that plasma cathodes are more resistant to oxygen poisoning and can operate with O{sub 2} partial pressures one to two orders of magnitude higher than vacuum cathodes before the onset of poisoning occurs. Plasma cathodes used for electric thrusters are typically operated with xenon; however, gas phase barium, oxygen, and tungstenmore » species may be found in small concentrations. The densities of these minor species are small compared with the plasma density, and thus, their presence in the discharge does not significantly alter the xenon plasma parameters. It is important, however, to consider the transport of these minor species as they may deposit on the emitter surface and affect the electron emission properties. In this work, we present the results of a material transport model used to predict oxygen fluxes to the cathode surface by solving the species conservation equations in a cathode with a 2.25 mm diameter orifice operated at a discharge current of 15 A, a Xe flow rate of 3.7 sccm, and 100 ppm of O{sub 2}. The dominant ionization process for O{sub 2} is resonant charge exchange with xenon ions. Ba is effectively recycled in the plasma; however, BaO and O{sub 2} are not. The model shows that the oxygen flux to the surface is not diffusion-limited; therefore, the high resistance to oxygen poisoning observed in plasma cathodes likely results from surface processes not considered here.« less

Diamond/diamond-like carbon coated nanotube structures for efficient electron field emission

NASA Technical Reports Server (NTRS)

Dimitrijevic, Steven (Inventor); Withers, James C. (Inventor); Loutfy, Raouf O. (Inventor)

2005-01-01

The present invention is directed to a nanotube coated with diamond or diamond-like carbon, a field emitter cathode comprising same, and a field emitter comprising the cathode. It is also directed to a method of preventing the evaporation of carbon from a field emitter comprising a cathode comprised of nanotubes by coating the nanotube with diamond or diamond-like carbon. In another aspect, the present invention is directed to a method of preventing the evaporation of carbon from an electron field emitter comprising a cathode comprised of nanotubes, which method comprises coating the nanotubes with diamond or diamond-like carbon.

Life test of a xenon hollow cathode for a space plasma contractor

NASA Technical Reports Server (NTRS)

Sarver-Verhey, Timothy R.

1994-01-01

A plasma contacting device using a hollow cathode for plasma production has been baselined for use on the Space Station. This application will require reliable, continuous operation of the cathode at electron emission currents of between 0.75 and 10 A for two years (17,500 hours). In order to validate life-time capability, a hollow cathode, operated in a diode configuration, has been tested for more than 8600 hours of stable discharge operation as of March 30, 1994. This cathode is operated at a steady-state emission current of 12.0 and a fixed xenon flow rate of 4.5 sccm. Discharge voltage and cathode temperature have remained relatively stable at approximately 12.9 V and 1260 C during the test. The test has experienced 7 shutdowns to date. In all instances, the cathode was reignited at about 42 V and resumed stable operation. This test represents the longest demonstration of stable operation of high current (greater than 1A) xenon hollow cathodes reported to date.

Lifetime experimental study of graphite cathode for relativistic backward wave oscillator

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wu, Ping; Science and Technology on High Power Microwave Laboratory, Northwest Institute of Nuclear Technology, Xi'an 710024; Sun, Jun

2016-07-21

Graphite cathodes are widely used due to their good emission properties, especially their long lifetime. Some previous papers have researched their lifetime under certain conditions and uncovered some important phenomena. This paper is dedicated to research the lifetime of the graphite cathode under higher power. In the lifetime test, the voltage and current amplitudes are about 970 kV and 9.7 kA, respectively. The repetition rate is 20 Hz. An X-band relativistic backward wave oscillator is used to generate high power microwave by utilizing the electron beam energy. The experimental results demonstrate that the emission property of the graphite cathode remains quite stable duringmore » 10{sup 5} pulses, despite some slight deteriorations regarding the beam and microwave parameters. The macroscopic morphology change of the cathode blade due to material evaporation is observed by a laser microscope. The mass loss of the graphite cathode is about 60 μg/C. Meanwhile, the observation by a scanning electron microscope uncovers that the original numerous flaky micro-structures are totally replaced by a relatively smooth surface at the mid region of the cathode blade and a large number of new micro-protrusions at the blade edges during the lifetime test.« less

Feedback model of secondary electron emission in DC gas discharge plasmas

NASA Astrophysics Data System (ADS)

Saravanan, ARUMUGAM; Prince, ALEX; Suraj, Kumar SINHA

2018-01-01

Feedback is said to exist in any amplifier when the fraction of output power in fed back as an input. Similarly, in gaseous discharge ions that incident on the cathode act as a natural feedback element to stabilize and self sustain the discharge. The present investigation is intended to emphasize the feedback nature of ions that emits secondary electrons (SEs) from the cathode surface in DC gas discharges. The average number of SEs emitted per incident ion and non ionic species (energetic neutrals, metastables and photons) which results from ion is defined as effective secondary electron emission coefficient (ESEEC,{γ }{{E}}). In this study, we derive an analytic expression that corroborates the relation between {γ }{{E}} and power influx by ion to the cathode based on the feedback theory of an amplifier. In addition, experimentally, we confirmed the typical positive feedback nature of SEE from the cathode in argon DC glow discharges. The experiment is done for three different cathode material of same dimension (tungsten (W), copper (Cu) and brass) under identical discharge conditions (pressure: 0.45 mbar, cathode bias: -600 V, discharge gab: 15 cm and operating gas: argon). Further, we found that the {γ }{{E}} value of these cathode material controls the amount of feedback power given by ions. The difference in feedback leads different final output i.e the power carried by ion at cathode ({P}{{i}}{\\prime }{| }{{C}}). The experimentally obtained value of {P}{{i}}{\\prime }{| }{{C}} is 4.28 W, 6.87 W and 9.26 W respectively for W, Cu and brass. In addition, the present investigation reveals that the amount of feedback power in a DC gas discharges not only affect the fraction of power fed back to the cathode but also the entire characteristics of the discharge.

Power-Efficient, High-Current-Density, Long-Life Thermionic Cathode Developed for Microwave Amplifier Applications

NASA Technical Reports Server (NTRS)

Wintucky, Edwin G.

2002-01-01

A power-efficient, miniature, easily manufactured, reservoir-type barium-dispenser thermionic cathode has been developed that offers the significant advantages of simultaneous high electron-emission current density (>2 A/sq cm) and very long life (>100,000 hr of continuous operation) when compared with the commonly used impregnated-type barium-dispenser cathodes. Important applications of this cathode are a wide variety of microwave and millimeter-wave vacuum electronic devices, where high output power and reliability (long life) are essential. We also expect it to enable the practical development of higher purveyance electron guns for lower voltage and more reliable device operation. The low cathode heater power and reduced size and mass are expected to be particularly beneficial in traveling-wave-tube amplifiers (TWTA's) for space communications, where future NASA mission requirements include smaller onboard spacecraft systems, higher data transmission rates (high frequency and output power) and greater electrical efficiency.

Surface studies on scandate cathodes and synthesized scandates

NASA Technical Reports Server (NTRS)

Lesny, Gary; Forman, Ralph

1990-01-01

Auger, ESCA, electron emission, evaporation, and desorption measurements were made on three different types of scandate surfaces. They are: (1) an impregnated top layer scandate cathode, (2) an unimpregnated top layer scandate cathode with a deposited barium or barium oxide adsorbate surface layer, and (3) a synthesized scandate surface, which replicates a scandate cathode surface. The purpose of these experiments was to determine the role that Sc2O3 plays in making the scandate cathode a more copious electron emitter than the conventional impregnated-type cathode. The synthesized scandate surface experiments consisted of depositing multilayer scandium on a tungsten surface, oxidizing the scandium, and then depositing either Ba or BaO on the scandium oxide surface. The results of these measurements showed that the low work function portions of the thin-film scandate cathode are where the Sc2O3 is the substrate and BaO is the adsorbate.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tierno, S. P., E-mail: sp.tierno@upm.es; Donoso, J. M.; Domenech-Garret, J. L.

The interaction between an electron emissive wall, electrically biased in a plasma, is revisited through a simple fluid model. We search for realistic conditions of the existence of a non-monotonic plasma potential profile with a virtual cathode as it is observed in several experiments. We mainly focus our attention on thermionic emission related to the operation of emissive probes for plasma diagnostics, although most conclusions also apply to other electron emission processes. An extended Bohm criterion is derived involving the ratio between the two different electron densities at the potential minimum and at the background plasma. The model allows amore » phase-diagram analysis, which confirms the existence of the non-monotonic potential profiles with a virtual cathode. This analysis shows that the formation of the potential well critically depends on the emitted electron current and on the velocity at the sheath edge of cold ions flowing from the bulk plasma. As a consequence, a threshold value of the governing parameter is required, in accordance to the physical nature of the electron emission process. The latter is a threshold wall temperature in the case of thermionic electrons. Experimental evidence supports our numerical calculations of this threshold temperature. Besides this, the potential well becomes deeper with increasing electron emission, retaining a fraction of the released current which limits the extent of the bulk plasma perturbation. This noninvasive property would explain the reliable measurements of plasma potential by using the floating potential method of emissive probes operating in the so-called strong emission regime.« less

Advanced electric propulsion and space plasma contactor research

NASA Technical Reports Server (NTRS)

Wilbur, P. J.

1986-01-01

A series of experiments performed on an 8 cm dia. ring cusp magnetic field ion thruster are described. The results show the effects of anode and cathode position and size, ring cusp axial location and discharge chamber length on plasma ion energy cost and extracted ion fraction. Thruster performance is shown to be improved substantially when optimum values of these parameters are used. Investigations into the basic plasma phenomena associated with the process of plasma contacting are described. The results show the process of electron collection from a background plasma to a hollow cathode plasma contactor exhibits a higher impedance than the process of electron emission from the hollow cathode. The importance of having cold ions present to facilitate the plasma contacting process is shown. Results of experiments into the behavior of hollow cathodes operating at high interelectrode pressures (up to approx. 100 Torr) on nitrogen and ammonia are presented. They suggest that diffuse emission from the insert of a hollow cathode can be sustained at high interelectrode pressures if the cathode is made of non-conducting material and the cathode internal pressure is reduced by evacuating the cathode interior. A theoretical model of discharge chamber operation developed for inert gas thrusters is extended so it can be used to evaluste the performance of mercury ion thrusters. Predictions of the model are compared to experimental results obtained on two 30 cm dia. thrusters.

Low-threshold field emission in planar cathodes with nanocarbon materials

NASA Astrophysics Data System (ADS)

Zhigalov, V.; Petukhov, V.; Emelianov, A.; Timoshenkov, V.; Chaplygin, Yu.; Pavlov, A.; Shamanaev, A.

2016-12-01

Nanocarbon materials are of great interest as field emission cathodes due to their low threshold voltage. In this work current-voltage characteristics of nanocarbon electrodes were studied. Low-threshold emission was found in planar samples where field enhancement is negligible (<10). Electron work function values, calculated by Fowler-Nordheim theory, are anomalous low (<1 eV) and come into collision with directly measured work function values in fabricated planar samples (4.1-4.4 eV). Non-applicability of Fowler-Nordheim theory for the nanocarbon materials was confirmed. The reasons of low-threshold emission in nanocarbon materials are discussed.

Microchannel plate for high-efficiency field emission display

NASA Astrophysics Data System (ADS)

Yi, Whikun; Jin, Sunghwan; Jeong, Taewon; Lee, Jeonghee; Yu, SeGi; Choi, Yongsoo; Kim, J. M.

2000-09-01

The efficiency of a field emission display was improved significantly with a newly developed microchannel plate. The key features of this unit and its fabrication are summarized as follows: (a) bulk alumina is used as a substrate material, (b) channel location is defined by a programed-hole puncher, and (c) thin film deposition is conducted by electroless plating followed by a sol-gel process. With the microchannel plate between the cathode and the anode of a field emission display, the brightness of luminescent light increases three- to fourfold by electron multiplication through an array of pores in the device. In addition, the fabricated microchannel plate prevents spreading of electrons emitted from the cathode tips, thus improving both display resolution and picture quality.

X-ray Diffraction Studies of the Structure and Thermochemistry of Alkaline-Earth Oxide-Coated Thermionic Cathodes

NASA Technical Reports Server (NTRS)

Karikari, E. K.; Bassey, E.; Wintucky, Edwin G.

1998-01-01

NASA LeRC has a broad, active cathode technology development program in which both experimental and theoretical studies are being employed to further development of thermionic cathodes for use as electron sources in vacuum devices for communications and other space applications. One important type of thermionic cathode under development is the alkaline-earth oxide-coated (BaO, SrO, CaO) cathode. Significant improvements in the emission characteristics of this cathode have been obtained through modification of the chemical composition and morphology of the oxide coating, with the best result thus far coming from the addition of In2O3 and Sc2O3. Whereas the In2O3 produces a finer, more uniform particle structure, the exact chemical state and role of the Sc2O3 in the emission enhancement is unknown. The purpose of this cooperative agreement is to combine the studies of the surface chemistry and electron emission at NASA LeRC of chemically modified oxide coatings with a study of the thermochemistry and crystal structure using X-ray diffraction equipment and expertise at Clark Atlanta University (CAU). The study at CAU is intended to provide the description and understanding of the structure and thermochemistry needed for further improvement and optimization of the modified coatings. A description of the experimental procedure, preliminary X-ray diffraction test results, together with the design of an ultrahigh vacuum chamber necessary for high temperature thermochemistry studies will be presented.

Characterization of the NEXT Hollow Cathode Inserts After Long-Duration Testing

NASA Technical Reports Server (NTRS)

Mackey, J.; Shastry, R.; Soulas, G.

2017-01-01

Hollow dispenser cathode inserts are a critical element of electric propulsion systems, and should therefore be well understood during long term operation to ensure reliable system performance. This work destructively investigated cathode inserts from the NEXT long-duration test which demonstrated 51,184 hours of high-voltage operation, 918 kg of propellant throughput, and 35.5 MN-s of total impulse. The characterization methods used include scanning electron microscopy with energy dispersive spectroscopy and X-ray diffraction. Microscopy analysis has been performed on fractured surfaces, emission surfaces, and metallographically polished cross-sections of post-test inserts and unused inserts. Impregnate distribution, etch region thickness, impregnate chemical content, emission surface topography, and emission surface phase identification are the primary factors investigated.

Drift waves control using emissive cathodes in the laboratory

NASA Astrophysics Data System (ADS)

Plihon, N.; Desangles, V.; De Giorgio, E.; Bousselin, G.; Marino, R.; Pustelnik, N.; Poye, A.

2017-12-01

Low frequency plasma fluctuations are known to be the cause of strong transport perpendicular to magnetic guiding field line. These low frequency drift waves have been studied in linear devices in the laboratory over the last two decades. Their excitation or mitigation have been addressed using different drives, such as ring biasing or electromagnetic low frequency fields. Here we present an experimental characterization of the behavior of drift waves when the profile of the background plasma rotation is controlled using hot emissive cathodes. We show that electron emission from the cathodes modify the plasma potential, which in turn controls the rotation profile. Mitigation or enhancement of drift waves (on the amplitude or azimuthal mode number) is observed depending on the plasma rotation profile.

Generation of anomalously energetic suprathermal electrons by an electron beam interacting with a nonuniform plasma

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sydorenko, D.; Kaganovich, I. D.; Chen, L.

Generation of anomalously energetic suprathermal electrons was observed in simulation of a high-voltage dc discharge with electron emission from the cathode. An electron beam produced by the emission interacts with the nonuniform plasma in the discharge via a two-stream instability. The energy transfer from the beam to the plasma electrons is ensured by the plasma nonuniformity. The electron beam excites plasma waves whose wavelength and phase speed gradually decrease towards anode. The waves with short wavelength near the anode accelerate plasma bulk electrons to suprathermal energies. The sheath near the anode reflects some of the accelerated electrons back into themore » plasma. These electrons travel through the plasma, reflect near the cathode, and enter the accelerating area again but with a higher energy than before. Such particles are accelerated to energies much higher than after the first acceleration. This mechanism plays a role in explaining earlier experimental observations of energetic suprathermal electrons in similar discharges.« less

High Power Microwaves for Defense and Accelerator Applications

DTIC Science & Technology

1990-06-11

pulsed power machines are typically made for laboratory simulation of charged particle and radiation spectra of nuclear explosions . Early on, it was...cathode and then explosive 10 ionization. After the first few nanoseconds, the electron emission is from a plasma produced at the cathode. Typically the...Virtually nothing is needed except an electron beam source. This power and simplicity makes vircators particularly interesting for single shot or explosively

Field-Induced Crystalline-to-Amorphous Phase Transformation on the Si Nano-Apex and the Achieving of Highly Reliable Si Nano-Cathodes

PubMed Central

Huang, Yifeng; Deng, Zexiang; Wang, Weiliang; Liang, Chaolun; She, Juncong; Deng, Shaozhi; Xu, Ningsheng

2015-01-01

Nano-scale vacuum channel transistors possess merits of higher cutoff frequency and greater gain power as compared with the conventional solid-state transistors. The improvement in cathode reliability is one of the major challenges to obtain high performance vacuum channel transistors. We report the experimental findings and the physical insight into the field induced crystalline-to-amorphous phase transformation on the surface of the Si nano-cathode. The crystalline Si tip apex deformed to amorphous structure at a low macroscopic field (0.6~1.65 V/nm) with an ultra-low emission current (1~10 pA). First-principle calculation suggests that the strong electrostatic force exerting on the electrons in the surface lattices would take the account for the field-induced atomic migration that result in an amorphization. The arsenic-dopant in the Si surface lattice would increase the inner stress as well as the electron density, leading to a lower amorphization field. Highly reliable Si nano-cathodes were obtained by employing diamond like carbon coating to enhance the electron emission and thus decrease the surface charge accumulation. The findings are crucial for developing highly reliable Si-based nano-scale vacuum channel transistors and have the significance for future Si nano-electronic devices with narrow separation. PMID:25994377

Proposal for Research on High-Brightness Cathodes for High-Power Free-Electron Lasers (FEL)

DTIC Science & Technology

2013-05-09

recent experiments involving single crystal diamond amplifier cathodes (DAC) at Brookhaven National Laboratory ( BNL ). While the emission surface of our...diamond grain in the entire structure, both surface and interior, is passivated with hydrogen. The aforementioned studies at BNL found that

Generation of runaway electrons and X-ray emission during breakdown of atmospheric-pressure air by voltage pulses with an ∼0.5-μs front duration

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kostyrya, I. D.; Tarasenko, V. F., E-mail: VFT@loi.hcei.tsc.ru

2015-03-15

Results are presented from experiments on the generation of runaway electron beams and X-ray emission in atmospheric-pressure air by using voltage pulses with an ∼0.5-μs front duration. It is shown that the use of small-curvature-radius spherical cathodes (or other cathodes with small curvature radii) decreases the intensity of the runaway electron beam and X-ray emission. It is found that, at sufficiently high voltages at the electrode gap (U{sub m} ∼ 100 kV), the gap breakdown, the formation of a spark channel, and the generation of a runaway electron beam occur over less than 10 ns. At high values of U{submore » m} behind the anode that were reached by increasing the cathode size and the electrode gap length, a supershort avalanche electron beam with a full width at half-maximum (FWHM) of up to ∼100 ps was detected. At voltages of ∼50 kV, the second breakdown regime was revealed in which a runaway electron beam with an FWHM of ∼2 ns was generated, whereas the FWHM of the X-ray pulse increased to ∼100 ns. It is established that the energy of the bulk of runaway electrons decreases with increasing voltage front duration and is ⩽30 keV in the first regime and ⩽10 keV in the second regime.« less

An experimental investigation of hollow cathode-based plasma contactors. Ph.D. Thesis

NASA Technical Reports Server (NTRS)

Williams, John D.

1991-01-01

Experimental results are presented which describe operation of the plasma environment associated with a hollow cathod-based plasma contactor collecting electrons from or emitting them to an ambient, low density Maxwellian plasma. A one-dimensional, phenomenological model of the near-field electron collection process, which was formulated from experimental observations, is presented. It considers three regions, namely, a plasma cloud adjacent to the contactor, an ambient plasma from which electrons are collected, and a double layer region that develops between the contactor plasma cloud and the ambient plasma regions. Results of the electron emission experiments are also presented. An important observation is made using a retarding potential analyzer (RPA) which shows that high energy ions generally stream from a contactor along with the electrons being emitted. A mechanism for this phenomenon is presented and it involves a high rate of ionization induced between electrons and atoms flowing together from the hollow cathode orifice. This can result in the development of a region of high positive potential. Langmuir and RPA probe data suggest that both electrons and ions expand spherically from this hill region. In addition to experimental observations, a one-dimensional model which describes the electron emission process and predicts the phenomena just mentioned is presented and shown to agree qualitatively with these observations.

Emission properties and back-bombardment for CeB{sub 6} compared to LaB{sub 6}

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bakr, Mahmoud, E-mail: m-a-bakr@iae.kyoto-u.ac.jp; Kawai, M.; Kii, T.

The emission properties of CeB{sub 6} compared to LaB{sub 6} thermionic cathodes have been measured using an electrostatic DC gun. Obtaining knowledge of the emission properties is the first step in understanding the back-bombardment effect that limits wide usage of thermionic radio-frequency electron guns. The effect of back-bombardment electrons on CeB{sub 6} compared to LaB{sub 6} was studied using a numerical simulation model. The results show that for 6 μs pulse duration with input radio-frequency power of 8 MW, CeB{sub 6} should experience 14% lower temperature increase and 21% lower current density rise compared to LaB{sub 6}. We conclude that CeB{submore » 6} has the potential to become the future replacement for LaB{sub 6} thermionic cathodes in radio-frequency electron guns.« less

Sintered wire cathode

DOEpatents

Falce, Louis R [San Jose, CA; Ives, R Lawrence [Saratoga, CA

2009-06-09

A porous cathode structure is fabricated from a plurality of wires which are placed in proximity to each other in elevated temperature and pressure for a sintering time. The sintering process produces the porous cathode structure which may be divided into a plurality of individual porous cathodes, one of which may be placed into a dispenser cathode support which includes a cavity for containing a work function reduction material such as BaO, CaO, and Al.sub.2O.sub.3. The work function reduction material migrates through the pores of the porous cathode from a work replenishment surface adjacent to the cavity of the dispenser cathode support to an emitting cathode surface, thereby providing a dispenser cathode which has a uniform work function and therefore a uniform electron emission.

Hollow - cathode electrode for high-power, high-pressure discharge devices

DOEpatents

Chang, Jim J.; Alger, Terry W.

1995-01-01

Several different cold cathode configurations for a gas discharge device each having a plurality of grooves of selected spacing, depth and width to improve the emission of electrons in a gas discharge device. Each of the cold cathode configurations can be machined from a single piece of a selected material. Several of the configurations can be assembled with individual elements which is easily seen from the various figures.

Explosive Emission and Gap Closure from a Relativistic Electron Beam Diode

DTIC Science & Technology

2013-06-01

relationship, impedance and perveance curves, plasma expansion velocity, and the time-resolved light emission on the surface of the cathode. I...indicating a cathode plasma density ~1017 cm-3 that migrates into the gap at ~50 cm/µs and an anode plasma of lower density ~1012 cm-3 that expands axially... plasma to the gap closure velocity. Initial estimates indicate the closure velocity for this relativistic diode is ~ 10 cm/µs. These measurements

Structural and emission characteristics of ion-irradiated Reticulated Vitreous Carbon

NASA Astrophysics Data System (ADS)

Chacon, Judith Rebecca

Cathodes formed from Reticulated Vitreous Carbon (RVC) were treated under varying conditions of Argon-ion beam current, beam voltage and irradiation duration. Surface structures, such as balls, cones, nanowires, and nanowhiskers were formed in the RVC network through a series of ion-impact sputtering and self-diffusion reactions. Raman shifts to the D and E2g' peak suggest C=C bonding within the original RVC structure was converted to the lesser-bound C-C bonding structure. Cathodes demonstrating the most stable electronic configuration exhibited significant vertical growth to graphitic domains as determined by calculations based on XRD measurements. Carbon nanotubes at the surface were observed at the surface through micro-Raman techniques. The surface structures formed by argon-bombardment, are responsible for cathodes exhibiting lower field-emission extraction fields. The electric field required for the onset of electron emission was measured to change from 6.03 V/micron in non-irradiated RVC to 1.62V/micron for RVC irradiated for 15 minutes at a beam voltage of 1200V and beam current of 200mA (ion-beam current density 2.24mA/cm2). Treated surfaces were also responsible for increased stability in emission over time. For untreated RVC, the field required for emission dropped 25% over a 48 hour training period, whilst modestly treated RVC (15min, 1200V, 100mA, or 1.52mA/cm2) rose as little as 3%. Field-emissive RVC, is an inexpensively produced, mechanically robust cathode with potential applications in lighting, displays and microwave sources.

Ferroelectric Emission Cathodes for Low-Power Electric Propulsion

NASA Technical Reports Server (NTRS)

Kovaleski, Scott D.; Burke, Tom (Technical Monitor)

2002-01-01

Low- or no-flow electron emitters are required for low-power electric thrusters, spacecraft plasma contactors, and electrodynamic tether systems to reduce or eliminate the need for propellant/expellant. Expellant-less neutralizers can improve the viability of very low-power colloid thrusters, field emission electric propulsion devices, ion engines, Hall thrusters, and gridded vacuum arc thrusters. The NASA Glenn Research Center (GRC) is evaluating ferroelectric emission (FEE) cathodes as zero expellant flow rate cathode sources for the applications listed above. At GRC, low voltage (100s to approx. 1500 V) operation of FEE cathodes is examined. Initial experiments, with unipolar, bipolar, and RF burst applied voltage, have produced current pulses 250 to 1000 ns in duration with peak currents of up to 2 A at voltages at or below 1500 V. In particular, FEE cathodes driven by RF burst voltages from 1400 to 2000 V peak to peak, at burst frequencies from 70 to 400 kHz, emitted average current densities from 0.1 to 0.7 A/sq cm. Pulse repeatability as a function of input voltage has been initially established. Reliable emission has been achieved in air background at pressures as high as 10(exp -6) Torr.

Surface and Bulk Characteristics of Cesium Iodide (CsI) coated Carbon (C) Fibers for High Power Microwave (HPM) Field Emission Cathodes

NASA Astrophysics Data System (ADS)

Vlahos, Vasilios; Morgan, Dane; Booske, John H.; Shiffler, Don

2008-11-01

CsI coated C fibers [1] are promising field emission cathodes for HPM applications. Ab initio computational modeling has shown that atomically-thin CsI coatings reduce the work function of C substrates by a surface dipole mechanism [2]. Characterization measurements of the composition and morphology of the CsI-coated C fibers are underway for determining the properties and characteristics of the following important regions of the fiber: (i) the surface on the tip of the fiber where the majority of electron emission is believed to occur, (ii) the surface covering the body of the fiber and its role on the emission properties of the system, and (iii) the interior volume of the fiber and its effects on the CsI surface re-supply process and rate. The results will be interpreted in terms of surface electronic properties and theoretical electron emission models. [1]D. Shiffler, et al., Phys. Plasmas 11 (2004) 1680. [2]V.Vlahos et al., Appl. Phys. Lett. 91 (2007) 144102.

Progress Toward a Gigawatt-Class Annular Beam Klystron with a Thermionic Electron Gun

NASA Astrophysics Data System (ADS)

Fazio, M.; Carlsten, B.; Farnham, J.; Habiger, K.; Haynes, W.; Myers, J.; Nelson, E.; Smith, J.; Arfin, B.; Haase, A.

2002-08-01

In an effort to reach the gigawatt power level in the microsecond pulse length regime Los Alamos, in collaboration with SLAC, is developing an annular beam klystron (ABK) with a thermionic electron gun. We hope to address the causes of pulse shortening in very high peak power tubes by building a "hard-vacuum" tube in the 10-10 Torr range with a thermionic electron gun producing a constant impedance electron-beam. The ABK has been designed to operate at 5 Hz pulse repetition frequency to allow for RF conditioning. The electron gun has a magnetron injection gun configuration and uses a dispenser cathode running at 1100 degC to produce a 4 kA electron beam at 800 kV. The cathode is designed to run in the temperature-limited mode to help maintain beam stability in the gun. The beam-stick consisting of the electron gun, an input cavity, an idler cavity, and drift tube, and the collector has been designed collaboratively, fabricated at SLAC, then shipped to Los Alamos for testing. On the test stand at Los Alamos a low voltage emission test was performed, but unfortunately as we prepared for high voltage testing a problem with the cathode heater was encountered that prevented the cathode from reaching a high enough temperature for electron emission. A post-mortem examination will be done shortly to determine the exact cause of the heater failure. The RF design has been proceeding and is almost complete. The output cavity presents a challenging design problem in trying to efficiently extract energy from the low impedance beam while maintaining a gap voltage low enough to avoid breakdown and a Q high enough to maintain mode purity. In the next iteration, the ABK will have a new cathode assembly installed along with the remainder of the RF circuit. This paper will discuss the electron gun and the design of the RF circuit along with a report on the status of the work.

A 13000-hour test of a mercury hollow cathode

NASA Technical Reports Server (NTRS)

Rawlin, V. K.

1973-01-01

A mercury-fed hollow cathode was tested for 12,979 hours in a bell jar at SERT 2 neutralizer operating conditions. The net electron current drawn to a collector was 0.25 ampere at average collector voltages between 21.8 and 36.7 volts. The mercury flow rate was varied from 5.6 to 30.8 equivalent milliamperes to give stable operation at the desired electrode voltages and currents. Variations with time in the neutralizer discharge characteristics were observed and hypothesized to be related to changes in the cathode orifice dimensions and the availability of electron emissive material. A facility failure caused abnormal test conditions for the last 876 hours and led to the cathode heater failure which concluded the test.

Noise limitations of multiplier phototubes in the radiation environment of space

NASA Technical Reports Server (NTRS)

Viehmann, W.; Eubanks, A. G.

1976-01-01

The contributions of Cerenkov emission, luminescence, secondary electron emission, and bremsstrahlung to radiation-induced data current and noise of multiplier phototubes were analyzed quantitatively. Fluorescence and Cerenkov emission in the tube window are the major contributors and can quantitatively account for dark count levels observed in orbit. Radiation-induced noise can be minimized by shielding, tube selection, and mode of operation. Optical decoupling of windows and cathode (side-window tubes) leads to further reduction of radiation-induced dark counts, as does reducing the window thickness and effective cathode area, and selection of window/cathode combinations of low fluorescence efficiency. In trapped radiation-free regions of near-earth orbits and in free space, Cerenkov emission by relativistic particles contributes predominantly to the photoelectron yield per event. Operating multiplier phototubes in the photon (pulse) counting mode will discriminate against these large pulses and substantially reduce the dark count and noise to levels determined by fluorescence.

Process for testing a xenon gas feed system of a hollow cathode assembly

NASA Technical Reports Server (NTRS)

Patterson, Michael J. (Inventor); Verhey, Timothy R. R. (Inventor); Soulas, George C. (Inventor)

2004-01-01

The design and manufacturing processes for Hollow Cathode Assemblies (HCA's) that operate over a broad range of emission currents up to 30 Amperes, at low potentials, with lifetimes in excess of 17,500 hours. The processes include contamination control procedures which cover hollow cathode component cleaning procedures, gas feed system designs and specifications, and hollow cathode activation and operating procedures to thereby produce cathode assemblies that have demonstrated stable and repeatable operating conditions, for both the discharge current and voltage. The HCA of this invention provides lifetimes of greater than 10,000 hours, and expected lifetimes of greater than 17,500 hours, whereas the present state-of-the-art is less than 500 hours at emission currents in excess of 1 Ampere. Stable operation is provided over a large range of operating emission currents, up to a 6:1 ratio, and this HCA can emit electron currents of up to 30 Amperes in magnitude to an external anode that simulates the current drawn to a space plasma, at voltages of less than 20 Volts.

Process for Ignition of Gaseous Electrical Discharge Between Electrodes of a Hollow Cathode Assembly

NASA Technical Reports Server (NTRS)

Patterson, Michael J. (Inventor); Verhey, Timothy R. R. (Inventor); Soulas, George C. (Inventor)

2000-01-01

The design and manufacturing processes for Hollow Cathode Assemblies (HCA's) that operate over a broad range of emission currents up to 30 Amperes, at low potentials, with lifetimes in excess of 17,500 hours. The processes include contamination control procedures which cover hollow cathode component cleaning procedures, gas feed system designs and specifications, and hollow cathode activation and operating procedures to thereby produce cathode assemblies that have demonstrated stable and repeatable operating conditions, for both the discharge current and voltage. The HCA of this invention provides lifetimes of greater than 10,000 hours, and expected lifetimes of greater than 17,500 hours, whereas the present state-of-the-art is less than 500 hours at emission currents in excess of 1 Ampere. Stable operation is provided over a large range of operating emission currents, up to a 6:1 ratio, and this HCA can emit electron currents of up to 30 Amperes in magnitude to an external anode that simulates the current drawn to a space plasma, at voltages of less than 20 Volts.

Hollow-cathode electrode for high-power, high-pressure discharge devices

DOEpatents

Chang, J.J.; Alger, T.W.

1995-08-22

Several different cold cathode configurations are disclosed for a gas discharge device each having a plurality of grooves of selected spacing, depth and width to improve the emission of electrons in a gas discharge device. Each of the cold cathode configurations can be machined from a single piece of a selected material. Several of the configurations can be assembled with individual elements which is easily seen from the various figures. 8 figs.

Laser-initiated explosive electron emission from flat germanium crystals

DOE Office of Scientific and Technical Information (OSTI.GOV)

Porshyn, V., E-mail: porshyn@uni-wuppertal.de; Mingels, S.; Lützenkirchen-Hecht, D.

2016-07-28

Flat Sb-doped germanium (100) crystals were investigated in the triode configuration under pulsed tunable laser illumination (pulse duration t{sub laser} = 3.5 ns and photon energy hν = 0.54–5.90 eV) and under DC voltages <10{sup 4} V. Large bunch charges up to ∼1 μC were extracted from the cathodes for laser pulses >1 MW/cm{sup 2} corresponding to a high quantum efficiency up to 3.3% and cathode currents up to 417 A. This laser-induced explosive electron emission (EEE) from Ge was characterized by its voltage-, laser power- and hν-sensitivity. The analysis of the macroscopic surface damage caused by the EEE is included as well. Moreover, we have carried out firstmore » direct measurements of electron energy distributions produced during the EEE from the Ge samples. The measured electron spectra hint for electron excitations to the vacuum level of the bulk and emission from the plasma plume with an average kinetic energy of ∼0.8 eV.« less

The theory of an auto-resonant field emission cathode relativistic electron accelerator for high efficiency microwave to direct current power conversion

NASA Technical Reports Server (NTRS)

Manning, Robert M.

1990-01-01

A novel method of microwave power conversion to direct current is discussed that relies on a modification of well known resonant linear relativistic electron accelerator techniques. An analysis is presented that shows how, by establishing a 'slow' electromagnetic field in a waveguide, electrons liberated from an array of field emission cathodes, are resonantly accelerated to several times their rest energy, thus establishing an electric current over a large potential difference. Such an approach is not limited to the relatively low frequencies that characterize the operation of rectennas, and can, with appropriate waveguide and slow wave structure design, be employed in the 300 to 600 GHz range where much smaller transmitting and receiving antennas are needed.

Moderate pressure plasma source of nonthermal electrons

NASA Astrophysics Data System (ADS)

Gershman, S.; Raitses, Y.

2018-06-01

Plasma sources of electrons offer control of gas and surface chemistry without the need for complex vacuum systems. The plasma electron source presented here is based on a cold cathode glow discharge (GD) operating in a dc steady state mode in a moderate pressure range of 2–10 torr. Ion-induced secondary electron emission is the source of electrons accelerated to high energies in the cathode sheath potential. The source geometry is a key to the availability and the extraction of the nonthermal portion of the electron population. The source consists of a flat and a cylindrical electrode, 1 mm apart. Our estimates show that the length of the cathode sheath in the plasma source is commensurate (~0.5–1 mm) with the inter-electrode distance so the GD operates in an obstructed regime without a positive column. Estimations of the electron energy relaxation confirm the non-local nature of this GD, hence the nonthermal portion of the electron population is available for extraction outside of the source. The use of a cylindrical anode presents a simple and promising method of extracting the high energy portion of the electron population. Langmuir probe measurements and optical emission spectroscopy confirm the presence of electrons with energies ~15 eV outside of the source. These electrons become available for surface modification and radical production outside of the source. The extraction of the electrons of specific energies by varying the anode geometry opens exciting opportunities for future exploration.

Modeling and simulation of RF photoinjectors for coherent light sources

NASA Astrophysics Data System (ADS)

Chen, Y.; Krasilnikov, M.; Stephan, F.; Gjonaj, E.; Weiland, T.; Dohlus, M.

2018-05-01

We propose a three-dimensional fully electromagnetic numerical approach for the simulation of RF photoinjectors for coherent light sources. The basic idea consists in incorporating a self-consistent photoemission model within a particle tracking code. The generation of electron beams in the injector is determined by the quantum efficiency (QE) of the cathode, the intensity profile of the driving laser as well as by the accelerating field and magnetic focusing conditions in the gun. The total charge emitted during an emission cycle can be limited by the space charge field at the cathode. Furthermore, the time and space dependent electromagnetic field at the cathode may induce a transient modulation of the QE due to surface barrier reduction of the emitting layer. In our modeling approach, all these effects are taken into account. The beam particles are generated dynamically according to the local QE of the cathode and the time dependent laser intensity profile. For the beam dynamics, a tracking code based on the Lienard-Wiechert retarded field formalism is employed. This code provides the single particle trajectories as well as the transient space charge field distribution at the cathode. As an application, the PITZ injector is considered. Extensive electron bunch emission simulations are carried out for different operation conditions of the injector, in the source limited as well as in the space charge limited emission regime. In both cases, fairly good agreement between measurements and simulations is obtained.

Secondary emission electron gun using external primaries

DOEpatents

Srinivasan-Rao, Triveni [Shoreham, NY; Ben-Zvi, Ilan [Setauket, NY

2009-10-13

An electron gun for generating an electron beam is provided, which includes a secondary emitter. The secondary emitter includes a non-contaminating negative-electron-affinity (NEA) material and emitting surface. The gun includes an accelerating region which accelerates the secondaries from the emitting surface. The secondaries are emitted in response to a primary beam generated external to the accelerating region. The accelerating region may include a superconducting radio frequency (RF) cavity, and the gun may be operated in a continuous wave (CW) mode. The secondary emitter includes hydrogenated diamond. A uniform electrically conductive layer is superposed on the emitter to replenish the extracted current, preventing charging of the emitter. An encapsulated secondary emission enhanced cathode device, useful in a superconducting RF cavity, includes a housing for maintaining vacuum, a cathode, e.g., a photocathode, and the non-contaminating NEA secondary emitter with the uniform electrically conductive layer superposed thereon.

Secondary emission electron gun using external primaries

DOEpatents

Srinivasan-Rao, Triveni [Shoreham, NY; Ben-Zvi, Ilan [Setauket, NY; Kewisch, Jorg [Wading River, NY; Chang, Xiangyun [Middle Island, NY

2007-06-05

An electron gun for generating an electron beam is provided, which includes a secondary emitter. The secondary emitter includes a non-contaminating negative-electron-affinity (NEA) material and emitting surface. The gun includes an accelerating region which accelerates the secondaries from the emitting surface. The secondaries are emitted in response to a primary beam generated external to the accelerating region. The accelerating region may include a superconducting radio frequency (RF) cavity, and the gun may be operated in a continuous wave (CW) mode. The secondary emitter includes hydrogenated diamond. A uniform electrically conductive layer is superposed on the emitter to replenish the extracted current, preventing charging of the emitter. An encapsulated secondary emission enhanced cathode device, useful in a superconducting RF cavity, includes a housing for maintaining vacuum, a cathode, e.g., a photocathode, and the non-contaminating NEA secondary emitter with the uniform electrically conductive layer superposed thereon.

Plasma-anode electron gun

NASA Astrophysics Data System (ADS)

Santoru, Joseph; Schumacher, Robert W.; Gregoire, Daniel J.

1994-11-01

The plasma-anode electron gun (PAG) is an electron source in which the thermionic cathode is replaced with a cold, secondary-electron-emitting electrode. Electron emission is stimulated by bombarding the cathode with high-energy ions. Ions are injected into the high-voltage gap through a gridded structure from a plasma source (gas pressure less than or equal to 50 mTorr) that is embedded in the anode electrode. The gridded structure serves as both a cathode for the plasma discharge and as an anode for the PAG. The beam current is modulated at near ground potential by modulating the plasma source, eliminating the need for a high-voltage modulator system. During laboratory tests, the PAG has demonstrated square-wave, 17-microsecond-long beam pulses at 100 kV and 10 A, and it has operated stably at 70 kV and 2.5 A for 210 microsecond pulse lengths without gap closure.

Development of a high average current polarized electron source with long cathode operational lifetime

DOE Office of Scientific and Technical Information (OSTI.GOV)

C. K. Sinclair; P. A. Adderley; B. M. Dunham

Substantially more than half of the electromagnetic nuclear physics experiments conducted at the Continuous Electron Beam Accelerator Facility of the Thomas Jefferson National Accelerator Facility (Jefferson Laboratory) require highly polarized electron beams, often at high average current. Spin-polarized electrons are produced by photoemission from various GaAs-based semiconductor photocathodes, using circularly polarized laser light with photon energy slightly larger than the semiconductor band gap. The photocathodes are prepared by activation of the clean semiconductor surface to negative electron affinity using cesium and oxidation. Historically, in many laboratories worldwide, these photocathodes have had short operational lifetimes at high average current, and havemore » often deteriorated fairly quickly in ultrahigh vacuum even without electron beam delivery. At Jefferson Lab, we have developed a polarized electron source in which the photocathodes degrade exceptionally slowly without electron emission, and in which ion back bombardment is the predominant mechanism limiting the operational lifetime of the cathodes during electron emission. We have reproducibly obtained cathode 1/e dark lifetimes over two years, and 1/e charge density and charge lifetimes during electron beam delivery of over 2?105???C/cm2 and 200 C, respectively. This source is able to support uninterrupted high average current polarized beam delivery to three experimental halls simultaneously for many months at a time. Many of the techniques we report here are directly applicable to the development of GaAs photoemission electron guns to deliver high average current, high brightness unpolarized beams.« less

Emission current from a single micropoint of explosive emission cathode

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wu, Ping; Science and Technology on High Power Microwave Laboratory, Northwest Institute of Nuclear Technology, Xi'an 710024; Sun, Jun

Explosive emission cathodes (EECs) are widely used due to their large current. There has been much research on the explosive electron emission mechanism demonstrating that a current density of 10{sup 8}–10{sup 9 }A/cm{sup 2} is necessary for a micropoint to explode in several nanoseconds and the micropoint size is in micron-scale according to the observation of the cathode surface. This paper, however, makes an effort to research the current density and the micropoint size in another way which considers the space charge screening effect. Our model demonstrates that the relativistic effect is insignificant for the micropoint emission due to the smallmore » size of the micropoint and uncovers that the micron-scale size is an intrinsic demand for the micropoint to reach a space charge limited current density of 10{sup 8}–10{sup 9 }A/cm{sup 2}. Meanwhile, our analysis shows that as the voltage increases, the micropoint emission will turn from a field limited state to a space charge limited state, which makes the steady-state micropoint current density independent of the cathode work function and much less dependent on the electric field and the field enhancement factor than that predicted by the Fowler-Nordheim formula.« less

Physical Processes in Hollow Cathode Discharge

DTIC Science & Technology

1989-12-01

State University. Finally, many thanks to my wife, Kyoung -Sook and my son, Frederick Teut, for their love and being supportive for two and half years...recommended for all electron emission purposes. 46 REFERENCES 1. Kim Gunther, "Hollow Cathode Plasma Source" ( Spectra-Mat Hollow Cathode Manual...59 Dong 401 Ho Seoul, Republic of Korea 8. Maj. Kim , Jong-Ryul 1 Postal Code 500-00 Book-Gu, Du-Am Dong, 874-14 Kwang-Ju, Republic of Korea 9. Maj

Pulsed electromagnetic gas acceleration

NASA Technical Reports Server (NTRS)

Jahn, R. G.; Vonjaskowsky, W. F.; Clark, K. E.

1975-01-01

Terminal voltage measurements with long cathodes in a high power, quasi-steady MPD discharge show that the critical current for the onset of voltage fluctuations, which was previously shown to be a function of cathode area, approaches an asymptote for cathodes of very large surface area. Floating potential measurements and photographs of the discharge luminosity indicate that the fluctuations are confined to the vicinity of the cathode and hence reflect a cathode emission process rather than a fundamental limit on MPD performance. Photoelectric measurements of particular argon neutral and ion transitions show that the higher electronic states are populated more heavily than would be calculated on the basis of Saha-Boltzmann equilibrium at the local electron temperature and number density. Preliminary optical depth measurements show that for a current of 4 kA and an argon mass flow of 12 g/sec, a population inversion exists between the upper and lower states of the 4880 A argon ion transition.

Correlation between microstructure and thermionic electron emission from Os-Ru thin films on dispenser cathodes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Swartzentruber, Phillip D.; John Balk, Thomas, E-mail: john.balk@uky.edu; Effgen, Michael P.

2014-07-01

Osmium-ruthenium films with different microstructures were deposited onto dispenser cathodes and subjected to 1000 h of close-spaced diode testing. Tailored microstructures were achieved by applying substrate biasing during deposition, and these were evaluated with scanning electron microscopy, x-ray diffraction, and energy dispersive x-ray spectroscopy before and after close-spaced diode testing. Knee temperatures determined from the close-spaced diode test data were used to evaluate cathode performance. Cathodes with a large (10-11) Os-Ru film texture possessed comparatively low knee temperatures. Furthermore, a low knee temperature correlated with a low effective work function as calculated from the close-spaced diode data. It is proposedmore » that the formation of strong (10-11) texture is responsible for the superior performance of the cathode with a multilayered Os-Ru coating.« less

Advanced electric propulsion and space plasma contactor research

NASA Technical Reports Server (NTRS)

Wilbur, Paul J.

1987-01-01

A theory of the plasma contacting process is described and experimental results obtained using three different hollow cathode-based plasma contactors are presented. The existence of a sheath across which the bulk of the voltage drop associated with the contacting process occurs is demonstrated. Test results are shown to agree with a model of a spherical, space-charge-limited double sheath. The concept of ignited mode contactor operation is discussed, which is shown to enhance contactor efficiency when it is collecting electrons. An investigation of the potentials in the plasma plumes downstream of contactors operating at typical conditions is presented. Results of tests performed on hollow cathodes operating at high interelectrode pressures (up to about 1000 Torr) on ammonia are presented and criteria that are necessary to ensure that the cathode will operate properly in this regime are presented. These results suggest that high pressure hollow cathode operation is difficult to achieve and that special care must be taken to assure that the electron emission region remains diffuse and attached to the low work function insert. Experiments conducted to verify results obtained previously using a ring cusp ion source equipped with a moveable anode are described and test results are reported. A theoretical study of hollow cathode operation at high electron emission currents is presented. Preliminary experiments using the constrained sheath optics concept to achieve ion extraction under conditions of high beam current density, low net accelerating voltage and well columniated beamlet formation are discussed.

Theory of Carbon Nanotube (CNT)-Based Electron Field Emitters

PubMed Central

Bocharov, Grigory S.; Eletskii, Alexander V.

2013-01-01

Theoretical problems arising in connection with development and operation of electron field emitters on the basis of carbon nanotubes are reviewed. The physical aspects of electron field emission that underlie the unique emission properties of carbon nanotubes (CNTs) are considered. Physical effects and phenomena affecting the emission characteristics of CNT cathodes are analyzed. Effects given particular attention include: the electric field amplification near a CNT tip with taking into account the shape of the tip, the deviation from the vertical orientation of nanotubes and electrical field-induced alignment of those; electric field screening by neighboring nanotubes; statistical spread of the parameters of the individual CNTs comprising the cathode; the thermal effects resulting in degradation of nanotubes during emission. Simultaneous consideration of the above-listed effects permitted the development of the optimization procedure for CNT array in terms of the maximum reachable emission current density. In accordance with this procedure, the optimum inter-tube distance in the array depends on the region of the external voltage applied. The phenomenon of self-misalignment of nanotubes in an array has been predicted and analyzed in terms of the recent experiments performed. A mechanism of degradation of CNT-based electron field emitters has been analyzed consisting of the bombardment of the emitters by ions formed as a result of electron impact ionization of the residual gas molecules. PMID:28348342

Excitation of Ion Acoustic Waves in Plasmas with Electron Emission from Walls

NASA Astrophysics Data System (ADS)

Khrabrov, A. V.; Wang, H.; Kaganovich, I. D.; Raitses, Y.; Sydorenko, D.

2015-11-01

Various plasma propulsion devices exhibit strong electron emission from the walls either as a result of secondary processes or due to thermionic emission. To understand details of electron kinetics in plasmas with strong emission, we have performed kinetic simulations of such plasmas using EDIPIC code. We show that excitation of ion acoustic waves is ubiquitous phenomena in many different plasma configurations with strong electron emission from walls. Ion acoustic waves were observed to be generated near sheath if the secondary electron emission from the walls is strong. Ion acoustic waves were also observed to be generated in the plasma bulk due to presence of an intense electron beam propagating from the cathode. This intense electron beam can excite strong plasma waves, which in turn drive the ion acoustic waves. Research supported by the U.S. Air Force Office of Scientific Research.

Ab initio investigation of barium-scandium-oxygen coatings on tungsten for electron emitting cathodes

NASA Astrophysics Data System (ADS)

Vlahos, Vasilios; Booske, John H.; Morgan, Dane

2010-02-01

Microwave, x-ray, and radio-frequency radiation sources require a cathode emitting electrons into vacuum. Thermionic B-type dispenser cathodes consist of BaxOz coatings on tungsten (W), where the surface coatings lower the W work function and enhance electron emission. The new and promising class of scandate cathodes modifies the B-type surface through inclusion of Sc, and their superior emissive properties are also believed to stem from the formation of a low work function surface alloy. In order to better understand these cathode systems, density-functional theory (DFT)-based ab initio modeling is used to explore the stability and work function of BaxScyOz on W(001) monolayer-type surface structures. It is demonstrated how surface depolarization effects can be calculated easily using ab initio calculations and fitted to an analytic depolarization equation. This approach enables the rapid extraction of the complete depolarization curve (work function versus coverage relation) from relatively few DFT calculations, useful for understanding and characterizing the emitting properties of novel cathode materials. It is generally believed that the B-type cathode has some concentration of Ba-O dimers on the W surface, although their structure is not known. Calculations suggest that tilted Ba-O dimers are the stable dimer surface configuration and can explain the observed work function reduction corresponding to various dimer coverages. Tilted Ba-O dimers represent a new surface coating structure not previously proposed for the activated B-type cathode. The thermodynamically stable phase of Ba and O on the W surface was identified to be the Ba0.25O configuration, possessing a significantly lower Φ value than any of the Ba-O dimer configurations investigated. The identification of a more stable Ba0.25O phase implies that if Ba-O dimers cover the surface of emitting B-type cathodes, then a nonequilibrium steady state must dominate the emitting surface. The identification of a stable and low work function Ba0.25Sc0.25O structure suggests that addition of Sc to the B-type cathode surface could form this alloy structure under operating conditions, leading to improved cathode performance and stability. Detailed comparison to previous experimental results of BaxScyOz on W surface coatings are made to both validate the modeling and aid in interpretation of experimental data. The studies presented here demonstrate that ab initio methods are powerful for understanding the fundamental physics of electron emitting materials systems and can potentially aid in the development of improved cathodes.

Estimation of the temporary service life of DC arc plasmatron cathode

NASA Astrophysics Data System (ADS)

Kulygin, V. M.; Pereslavtsev, A. V.; Tresvyatskii, S. S.

2017-09-01

The service life of the cathode of a DC arc plasmatron continuously working with tubular electrodes that operate in the air has been considered using the semi-phenomenological approach. The thermal emission, that ensures the necessary flow of electrons, and the evaporation of the cathode material, which determines its erosion, have been taken as the basic physical phenomena that constitute the workflow. The relationships that enable the estimation of the cathode's operating time have been obtained using the known regularities of these phenomena and experimental data available in the literature. The resulting evaluations coincide satisfactorily with the endurance test results.

Fast turn-on osmium coated cathode

NASA Astrophysics Data System (ADS)

Marrian, C. R. K.; Haas, G. A.; Shih, A.

1984-03-01

This abstract discloses a fast turn-on refractory coated cathode comprising a porous tungsten metal matrix impregnated with barium calcium aluminate and coated with osmium. The osmium coating has a planned series of interruptions with each interruption being on the order of several microns in width to thereby expose the tungsten. These interruptions permit the barium and oxygen from the impregnant to rise to the cathode surface during activation or reactivation to form a desired near monolayer of barium and oxygen to enhance electron emission. Thus, this cathode design provides a fast turn-on characteristic even after shelf storage.

The effect of plasma density and emitter geometry on space charge limits for field emitter array electron charge emission into a space plasma

NASA Astrophysics Data System (ADS)

Morris, Dave; Gilchrist, Brian; Gallimore, Alec

2001-02-01

Field Emitter Array Cathodes (FEACs) are a new technology being developed for several potential spacecraft electron emission and charge control applications. Instead of a single hot (i.e., high powered) emitter, or a gas dependant plasma contactor, FEAC systems consist of many (hundreds or thousands) of small (micron level) cathode/gate pairs printed on a semiconductor wafer that effect cold field emission at relatively low voltages. Each individual cathode emits only micro-amp level currents, but a functional array is capable of amp/cm2 current densities. It is hoped that thus FEAC offers the possibility of a relatively low-power, simple to integrate, and inexpensive technique for the high level of current emissions that are required for an electrodynamic tether (EDT) propulsion mission. Space charge limits are a significant concern for the EDT application. Vacuum chamber tests and PIC simulations are being performed at the University of Michigan Plasmadynamics and Electric Propulsion Laboratory and Space Physics Research Laboratory to determine the effect of plasma density and emitter geometry on space charge limitations. The results of this work and conclusions to date of how to best mitigate space charge limits will be presented. .

BRIEF COMMUNICATION: The negative ion flux across a double sheath at the formation of a virtual cathode

NASA Astrophysics Data System (ADS)

McAdams, R.; Bacal, M.

2010-08-01

For the case of negative ions from a cathode entering a plasma, the maximum negative ion flux and the positive ion flux before the formation of a virtual cathode have been calculated for particular plasma conditions. The calculation is based on a simple modification of an analysis of electron emission into a plasma containing negative ions. The results are in good agreement with a 1d3v PIC code model.

On the application of quantum transport theory to electron sources.

PubMed

Jensen, Kevin L

2003-01-01

Electron sources (e.g., field emitter arrays, wide band-gap (WBG) semiconductor materials and coatings, carbon nanotubes, etc.) seek to exploit ballistic transport within the vacuum after emission from microfabricated structures. Regardless of kind, all sources strive to minimize the barrier to electron emission by engineering material properties (work function/electron affinity) or physical geometry (field enhancement) of the cathode. The unique capabilities of cold cathodes, such as instant ON/OFF performance, high brightness, high current density, large transconductance to capacitance ratio, cold emission, small size and/or low voltage operation characteristics, commend their use in several advanced devices when physical size, weight, power consumption, beam current, and pulse repletion frequency are important, e.g., RF power amplifier such as traveling wave tubes (TWTs) for radar and communications, electrodynamic tethers for satellite deboost/reboost, and electric propulsion systems such as Hall thrusters for small satellites. The theoretical program described herein is directed towards models to evaluate emission current from electron sources (in particular, emission from WBG and Spindt-type field emitter) in order to assess their utility, capabilities and performance characteristics. Modeling efforts particularly include: band bending, non-linear and resonant (Poole-Frenkel) potentials, the extension of one-dimensional theory to multi-dimensional structures, and emission site statistics due to variations in geometry and the presence of adsorbates. Two particular methodologies, namely, the modified Airy approach and metal-semiconductor statistical hyperbolic/ellipsoidal model, are described in detail in their present stage of development.

Method to fabricate portable electron source based on nitrogen incorporated ultrananocrystalline diamond (N-UNCD)

DOEpatents

Sumant, Anirudha V.; Divan, Ralu; Posada, Chrystian M.; Castano, Carlos H.; Grant, Edwin J.; Lee, Hyoung K.

2016-03-29

A source cold cathode field emission array (FEA) source based on ultra-nanocrystalline diamond (UNCD) field emitters. This system was constructed as an alternative for detection of obscured objects and material. Depending on the geometry of the given situation a flat-panel source can be used in tomography, radiography, or tomosynthesis. Furthermore, the unit can be used as a portable electron or X-ray scanner or an integral part of an existing detection system. UNCD field emitters show great field emission output and can be deposited over large areas as the case with carbon nanotube "forest" (CNT) cathodes. Furthermore, UNCDs have better mechanical and thermal properties as compared to CNT tips which further extend the lifetime of UNCD based FEA.

Development of a high brightness ultrafast Transmission Electron Microscope based on a laser-driven cold field emission source.

PubMed

Houdellier, F; Caruso, G M; Weber, S; Kociak, M; Arbouet, A

2018-03-01

We report on the development of an ultrafast Transmission Electron Microscope based on a cold field emission source which can operate in either DC or ultrafast mode. Electron emission from a tungsten nanotip is triggered by femtosecond laser pulses which are tightly focused by optical components integrated inside a cold field emission source close to the cathode. The properties of the electron probe (brightness, angular current density, stability) are quantitatively determined. The measured brightness is the largest reported so far for UTEMs. Examples of imaging, diffraction and spectroscopy using ultrashort electron pulses are given. Finally, the potential of this instrument is illustrated by performing electron holography in the off-axis configuration using ultrashort electron pulses. Copyright © 2017 Elsevier B.V. All rights reserved.

Generalized Mechanism of Field Emission from Nanostructured Semiconductor Film Cathodes

PubMed Central

Wang, Ru-Zhi; Zhao, Wei; Yan, Hui

2017-01-01

Considering the effect of both the buffer layer and substrate, a series of ultrathin multilayered structure cathodes (UTMC) is constructed to simulate the field emission (FE) process of nanostructured semiconductor film cathodes (NSFCs). We find a generalized FE mechanism of the NSFCs, in which there are three distinct FE modes with the change of the applied field. Our results clearly show significant differences of FE between conventional emitters and nanofilm emitters, which the non-Fowler-Nordheim characteristics and the resonant FE will be inevitable for NSFCs. Moreover, the controllable FE can be realized by fine-tuning the quantum structure of NSFCs. The generalized mechanism of NSFCs presented here may be particularly useful for design high-speed and high-frequency vacuum nano-electronic devices.

Generalized Mechanism of Field Emission from Nanostructured Semiconductor Film Cathodes

NASA Astrophysics Data System (ADS)

Wang, Ru-Zhi; Zhao, Wei; Yan, Hui

2017-03-01

Considering the effect of both the buffer layer and substrate, a series of ultrathin multilayered structure cathodes (UTMC) is constructed to simulate the field emission (FE) process of nanostructured semiconductor film cathodes (NSFCs). We find a generalized FE mechanism of the NSFCs, in which there are three distinct FE modes with the change of the applied field. Our results clearly show significant differences of FE between conventional emitters and nanofilm emitters, which the non-Fowler-Nordheim characteristics and the resonant FE will be inevitable for NSFCs. Moreover, the controllable FE can be realized by fine-tuning the quantum structure of NSFCs. The generalized mechanism of NSFCs presented here may be particularly useful for design high-speed and high-frequency vacuum nano-electronic devices.

Investigation of Influence of Surface Nanoparticle on Emission Properties of Scandia-Doped Dispenser Cathodes

NASA Astrophysics Data System (ADS)

Zhang, Xizhu; Wang, Jinshu; Wang, Yiman; Liu, Wei; Zhou, Meiling; Gao, Zhiyuan

2013-06-01

The microstructure of a fully activated scandia doped dispenser (SDD) cathode has been studied by scanning electron microscope (SEM). The observation results display that nanoparticles appear at the growth steps and the surface of tungsten grains of the fully activated SDD cathode. To study the influence of the nanoparticles on the emission, the local electric field strengths around the nanoparticles have been calculated by Maxwell 2D code and Comsol. The calculation results show that the local electric field strengths are enhanced by 1.1 to 3.8 times to average value based on different model conditions. The highest field strength is about 1.54 × 105 V/cm at an average field strength of 40 KV/cm, which is related to a space-charge limited (SCL) current density of 100 A/cm2 in the experimental configuration. This implies the field strength is not high enough to cause field emission.

Multiphoton photoemission from a copper cathode illuminated by ultrashort laser pulses in an RF photoinjector.

PubMed

Musumeci, P; Cultrera, L; Ferrario, M; Filippetto, D; Gatti, G; Gutierrez, M S; Moody, J T; Moore, N; Rosenzweig, J B; Scoby, C M; Travish, G; Vicario, C

2010-02-26

In this Letter we report on the use of ultrashort infrared laser pulses to generate a copious amount of electrons by a copper cathode in an rf photoinjector. The charge yield verifies the generalized Fowler-Dubridge theory for multiphoton photoemission. The emission is verified to be prompt using a two pulse autocorrelation technique. The thermal emittance associated with the excess kinetic energy from the emission process is comparable with the one measured using frequency tripled uv laser pulses. In the high field of the rf gun, up to 50 pC of charge can be extracted from the cathode using a 80 fs long, 2 microJ, 800 nm pulse focused to a 140 mum rms spot size. Taking into account the efficiency of harmonic conversion, illuminating a cathode directly with ir laser pulses can be the most efficient way to employ the available laser power.

Mechanism of Runaway Electron Generation at Gas Pressures from a Few Atmospheres to Several Tens of Atmospheres

NASA Astrophysics Data System (ADS)

Zubarev, N. M.; Ivanov, S. N.

2018-04-01

The mechanism of runaway electron generation at gas pressures from a few atmospheres to several tens of atmospheres is proposed. According to this mechanism, the electrons pass into the runaway mode in the enhanced field zone that arises between a cathode micropoint—a source of field-emission electrons—and the region of the positive ion space charge accumulated near the cathode in the tails of the developing electron avalanches. As a result, volume gas ionization by runaway electrons begins with a time delay required for the formation of the enhanced field zone. This process determines the delay time of breakdown. The influence of the gas pressure on the formation dynamics of the space charge region is analyzed. At gas pressures of a few atmospheres, the space charge arises due to the avalanche multiplication of the very first field-emission electron, whereas at pressures of several tens of atmospheres, the space charge forms as a result of superposition of many electron avalanches with a relatively small number of charge carriers in each.

Instrumentation and Measurements for Electron Emission from Charged Insulators

NASA Technical Reports Server (NTRS)

Sim, Alec M.

2005-01-01

The electron was first discovered in 1898 by Sir John Joseph Thomson and has since been the subject of detailed study by nearly every scientific discipline. At nearly the same time Heinrich Rudolf Hertz conducted a series of experiments using cathode tubes, high potentials and ultraviolet light. When applying a large potential to a cathode he found that an arching event across the metal plates would occur. In addition, when shining an ultraviolet light on the metal he found that less potential was required to induce the spark. This result, taken together with other electrical phenomena brought about by the shining of light upon metal and was eventually termed the photoelectric effect. The work of Thomson and Hertz represent the beginning of electron emission studies and a body of ideas that pervade nearly all aspects of physics. In particular these ideas tell us a great deal about the nature of physical interactions within solids. In this thesis we will focus on the emission of electrons induced by an incident electron source over a range of energies, in which one can observe changes in emitted electron flux and energy distribution. In particular, when energetic particles impinge on a solid they can impart their energy, exciting electrons within the material. If this energy is sufficient to overcome surface energy barriers such as the work function, electron affinity or surface charge potential, electrons can escape from the material. The extent of electron emission from the material can be quantified as the ratio of incident particle flux to emitted particle flux, and is termed the electron yield.

Self-regenerating Nanotips: Indestructable Field-emission Cathodes for Low-power Electric Propulsion

DTIC Science & Technology

2010-09-27

Field Emission Scanning Electron Microscope. The chamber was evacuated using a series of three ion pumps and vacuum pressure of 10-7 Torr was...backed by a 110-L/min dry scroll pump . The chamber is also equipped with a 300-L/s combination ion/sublimation pump that can maintain pressure of...Torr for 2 to 24 hours and then the ion pump was turned off to let the vacuum pressure slowly increase while observing the electron emission

PIC-MCC analysis of electron multiplication in a cold-cathode Penning ion generator and its application to identify ignition voltage

NASA Astrophysics Data System (ADS)

Noori, H.; Ranjbar, A. H.; Mahjour-Shafiei, M.

2017-11-01

A cold-cathode Penning ion generator (PIG) has been developed in our laboratory to study the interaction of charged particles with matter. The ignition voltage was measured in the presence of the axial magnetic field in the range of 460-580 G. The performed measurements with stainless steel cathodes were in argon gas at pressure of 4 × 10-2 mbar. A PIC-MCC (particle-in-cell, Monte Carlo collision) technique has been used to calculate the electron multiplication coefficient M for various strength of axial magnetic field and applied voltage. An approach based on the coefficient M and the experimental values of the secondary electron emission coefficient γ, was proposed to determine the ignition voltages, theoretically. Applying the values of secondary coefficient γ leads to the average value of γM(V, B) to be = 1.05 ± 0.03 at the ignition of the PIG which satisfies the proposed ignition criterion. Thus, the ion-induced secondary electrons emitted from the cathode have dominant contribution to self-sustaining of the discharge process in a PIG.

Use of multiwavelength emission from hollow cathode lamp for measurement of state resolved atom density of metal vapor produced by electron beam evaporation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Majumder, A.; Dikshit, B.; Bhatia, M. S.

2008-09-15

State resolved atom population of metal vapor having low-lying metastable states departs from equilibrium value. It needs to be experimentally investigated. This paper reports the use of hollow cathode lamp based atomic absorption spectroscopy technique to measure online the state resolved atom density (ground and metastable) of metal vapor in an atomic beam produced by a high power electron gun. In particular, the advantage of availability of multiwavelength emission in hollow cathode lamp is used to determine the atom density in different states. Here, several transitions pertaining to a given state have also been invoked to obtain the mean valuemore » of atom density thereby providing an opportunity for in situ averaging. It is observed that at higher source temperatures the atoms from metastable state relax to the ground state. This is ascribed to competing processes of atom-atom and electron-atom collisions. The formation of collision induced virtual source is inferred from measurement of atom density distribution profile along the width of the atomic beam. The total line-of-sight average atom density measured by absorption technique using hollow cathode lamp is compared to that measured by atomic vapor deposition method. The presence of collisions is further supported by determination of beaming exponent by numerically fitting the data.« less

A brightness exceeding simulated Langmuir limit

NASA Astrophysics Data System (ADS)

Nakasuji, Mamoru

2013-08-01

When an excitation of the first lens determines a beam is parallel beam, a brightness that is 100 times higher than Langmuir limit is measured experimentally, where Langmuir limits are estimated using a simulated axial cathode current density which is simulated based on a measured emission current. The measured brightness is comparable to Langmuir limit, when the lens excitation is such that an image position is slightly shorter than a lens position. Previously measured values of brightness for cathode apical radii of curvature 20, 60, 120, 240, and 480 μm were 8.7, 5.3, 3.3, 2.4, and 3.9 times higher than their corresponding Langmuir limits, respectively, in this experiment, the lens excitation was such that the lens and the image positions were 180 mm and 400 mm, respectively. From these measured brightness for three different lens excitation conditions, it is concluded that the brightness depends on the first lens excitation. For the electron gun operated in a space charge limited condition, some of the electrons emitted from the cathode are returned to the cathode without having crossed a virtual cathode. Therefore, method that assumes a Langmuir limit defining method using a Maxwellian distribution of electron velocities may need to be revised. For the condition in which the values of the exceeding the Langmuir limit are measured, the simulated trajectories of electrons that are emitted from the cathode do not cross the optical axis at the crossover, thus the law of sines may not be valid for high brightness electron beam systems.

Mechanism of formation of subnanosecond current front in high-voltage pulse open discharge

NASA Astrophysics Data System (ADS)

Schweigert, I. V.; Alexandrov, A. L.; Zakrevsky, Dm. E.; Bokhan, P. A.

2014-11-01

The mechanism of subnanosecond current front rise observed previously in the experiment in high-voltage pulse open discharge in helium is studied in kinetic particle-in-cell simulations. The Boltzmann equations for electrons, ions, and fast atoms are solved self-consistently with the Poisson equations for the electrical potential. The partial contributions to the secondary electron emission from the ions, fast atoms, photons, and electrons, bombarding the electrode, are calculated. In simulations, as in the experiment, the discharge glows between two symmetrical cathodes and the anode grid in the midplane at P =6 Torr and the applied voltage of 20 kV. The electron avalanche development is considered for two experimental situations during the last stage of breakdown: (i) with constant voltage and (ii) with decreasing voltage. For case (i), the subnanosecond current front rise is set by photons from the collisional excitation transfer reactions. For the case (ii), the energetic electrons swamp the cathode during voltage drop and provide the secondary electron emission for the subnanosecond current rise, observed in the experiment.

Experimental research of different plasma cathodes for generation of high-current electron beams

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shafir, G.; Kreif, M.; Gleizer, J. Z.

2015-11-21

The results of experimental studies of different types of cathodes—carbon-epoxy rods, carbon-epoxy capillary, edged graphite, and metal-dielectric—under the application of high-voltage pulses with an amplitude of several hundreds of kV and pulse duration of several nanoseconds are presented. The best diode performance was achieved with the edged graphite and carbon-epoxy-based cathodes characterized by uniform and fast (<1 ns) formation of explosive emission plasma spots and quasi-constant diode impedance. This result was achieved for both annular cathodes in a strong magnetic field and planar cathodes of a similar diameter (∼2 cm) with no external magnetic field. The cathodes based on carbon-epoxy rods andmore » carbon-epoxy capillaries operating with an average current density up to 1 kA/cm{sup 2} showed insignificant erosion along 10{sup 6} pulses of the generator and the generated electron beam current showed excellent reproducibility in terms of the amplitude and waveform.« less

Cathode Formed by Thermal Evaporation of Ba:Al Alloy and Estimations of Barrier Height in an Organic LED

NASA Astrophysics Data System (ADS)

Ding, Lei; Zhang, Fang-Hui

2011-06-01

It is demonstrated that barium and aluminum alloy synthesized by melting in a glass tube under low vacuum is applicable for organic laser emitting diodes (LEDs) as a thin film cathode. The alloy film obtained by the thermal evaporation of pre-synthesized alloy is used in a single-boat organic LED device with the structure: indium tin oxide (ITO)/4,4'-bis[N-(1-naphthyl)-N-phenylamino]biphenyl(NPB)/tris-(8-hydroxyquinoline) aluminum(Alq3)/barium:aluminum alloy. The experimental results show that devices with this alloy film cathode exhibit better current density-voltage-luminance characteristics than those with a conventional pure Al cathode, and more weight of barium in aluminum leads to better performance of the devices. Characteristics of current density versus voltage for the electron-only devices are fitted by the Richardson—Schottky emission model, indicating that the electron injection barrier has a decrease of about 0.3 eV by this alloy cathode.

Device for providing high-intensity ion or electron beam

DOEpatents

McClanahan, Edwin D.; Moss, Ronald W.

1977-01-01

A thin film of a low-thermionic-work-function material is maintained on the cathode of a device for producing a high-current, low-pressure gas discharge by means of sputter deposition from an auxiliary electrode. The auxiliary electrode includes a surface with a low-work-function material, such as thorium, uranium, plutonium or one of the rare earth elements, facing the cathode but at a disposition and electrical potential so as to extract ions from the gas discharge and sputter the low-work-function material onto the cathode. By continuously replenishing the cathode film, high thermionic emissions and ion plasmas can be realized and maintained over extended operating periods.

The effect of zirconium-based surface treatment on the cathodic disbonding resistance of epoxy coated mild steel

NASA Astrophysics Data System (ADS)

Ghanbari, A.; Attar, M. M.

2014-10-01

The effect of zirconium-based surface treatment on the cathodic disbonding resistance and adhesion performance of an epoxy coated mild steel substrate was investigated. The obtained data from pull-off, cathodic disbonding test and electrochemical impedance spectroscopy (EIS) indicated that the zirconium conversion layer significantly improved the adhesion strength and cathodic disbonding resistance of the epoxy coating. This may be attributed to formation of some polar zirconium compounds on the surface and increment of surface roughness, that were evident in the results of field emission scanning electron microscopy (FE-SEM) and atomic force microscopy (AFM), respectively.

Electric thruster research

NASA Technical Reports Server (NTRS)

Kaufman, H. R.; Robinson, R. S.

1982-01-01

It has been customary to assume that ions flow nearly equally in all directions from the ion production region within an electron-bombardment discharge chamber. In general, the electron current through a magnetic field can alter the electron density, and hence the ion density, in such a way that ions tend to be directed away from the region bounded by the magnetic field. When this mechanism is understood, it becomes evident that many past discharge chamber designs have operated with a preferentially directed flow of ions. Thermal losses were calculated for an oxide-free hollow cathode. At low electron emissions, the total of the radiation and conduction losses agreed with the total discharge power. At higher emissions, though, the plasma collisions external to the cathode constituted an increasingly greater fraction of the discharge power. Experimental performance of a Hall-current thruster was adversely affected by nonuniformities in the magnetic field, produced by the cathode heating current. The technology of closed-drift thrusters was reviewed. The experimental electron diffusion in the acceleration channel was found to be within about a factor of 3 of the Bohm value for the better thruster designs at most operating conditions. Thruster efficiencies of about 0.5 appear practical for the 1000 to 2000 s range of specific impulse. Lifetime information is limited, but values of several thousands of hours should be possible with anode layer thrusters operated or = to 2000 s.

Testing a GaAs cathode in SRF gun

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, E.; Kewisch, J.; Ben-Zvi, I.

RF electron guns with a strained superlattice GaAs cathode are expected to generate polarized electron beams of higher brightness and lower emittance than do DC guns, due to their higher field gradient at the cathode's surface and lower cathode temperature. We plan to install a bulk GaAs:Cs in a SRF gun to evaluate the performance of both the gun and the cathode in this environment. The status of this project is: In our 1.3 GHz 1/2 cell SRF gun, the vacuum can be maintained at nearly 10{sup -12} Torr because of cryo-pumping at 2K. With conventional activation of bulk GaAs,more » we obtained a QE of 10% at 532 nm, with lifetime of more than 3 days in the preparation chamber and have shown that it can survive in transport from the preparation chamber to the gun. The beam line has been assembled and we are exploring the best conditions for baking the cathode under vacuum. We report here the progress of our test of the GaAs cathode in the SRF gun. Future particle accelerators, such as eRHIC and the ILC require high-brightness, high-current polarized electrons. Strained superlattice GaAs:Cs has been shown to be an efficient cathode for producing polarized electrons. Activation of GaAs with Cs,O(F) lowers the electron affinity and makes it energetically possible for all the electrons, excited into the conduction band that drift or diffuse to the emission surface, to escape into the vacuum. Presently, all operating polarized electron sources, such as the CEBAF, are DC guns. In these devices, the excellent ultra-high vacuum extends the lifetime of the cathode. However, the low field gradient on the photocathode's emission surface of the DC guns limits the beam quality. The higher accelerating gradients, possible in the RF guns, generate a far better beam. Until recently, most RF guns operated at room temperature, limiting the vacuum to {approx}10{sup -9} Torr. This destroys the GaAs's NEA surface. The SRF guns combine the excellent vacuum conditions of DC guns and the high accelerating gradient of the RF guns, potentially offering a long lived cathode with very low emittance. Testing this concept requires preparation of the cathode, transportation to the SRF gun and evaluation of the performance of the cathode and the gun at cryogenic temperatures. In our work at BNL, we successfully activated the bulk GaAs in the preparation chamber. The highest quantum efficient was 10% at 532 nm that fell to 0.5% after 100 hours. We explored three different ways to activate the GaAs. We verified that the GaAs photocathode remains stable for 30 hours in a 10{sup -11} Torr vacuum. Passing the photocathode through the low 10{sup -9} Torr transfer section in several seconds caused the QE to drop to 0.8%. The photocathode with 0.8% QE can be tested for the SRF gun. The gun and beam pipe were prepared and assembled. After baking at 200 C baking, the vacuum of the gun and beam pipe can sustain a low 10{sup -11} Torr at room temperature. The final test to extract electrons from the gun is ongoing. In this paper, we discuss our progress with this SRF gun and the results of the photocathode in preparation chamber and in magnet transfer line.« less

Ab initio study of the effects of thin CsI coatings on the work function of graphite cathodes

NASA Astrophysics Data System (ADS)

Vlahos, Vasilios; Booske, John H.; Morgan, Dane

2007-10-01

Cesium-iodide (CsI)-coated graphite cathodes are promising electron sources for high power microwave generators, but the mechanism driving the improved emission is not well understood. Therefore, an ab initio modeling investigation on the effects of thin CsI coatings on graphite has been carried out. It is demonstrated that the CsI coatings reduce the work function of the system significantly through a mechanism of induced dipoles. The results suggest that work function modification is a major contribution to the improved emission seen when CsI coatings are applied to C.

High-power, high-brightness pseudospark-produced electron beam driven by improved pulse line accelerator

DOE Office of Scientific and Technical Information (OSTI.GOV)

Junbino Zhu; Mingchang Wang; Zhijiang Wang

1995-12-31

A high power (200KV), intense current density, low emittance (71mmmrad), high brightness (8x10{sup 10}A/m rad) electron beam was generated in the 10cm long, high-voltage-resistive multi-gap hollow cathode pseudospark chamber filled with 15pa nitrogen and driven by an improved pulse line accelerator. The beam was ejected with the 1mm diameter, the 2.2KA beam current, and the 400ns pulse length, and could propagated 20cm in the drift tube. At a distance of 5cm from the anode it penetrated consecutively an acid-sensitive discoloring film and a 0.05mm-thick copper foil both stuck closely, left 0.6mm and 0.3mm holes on them, respectively. That 10 shotsmore » on an acid-sensitive film produced a hole of 1.6mm at 7cm downstream of anode showed its good repeatability. After 60 shots the pseudospark discharge chamber was disassembled and observed that almost no destructive damage traces left on the surfaces of its various electrodes and insulators. But on almost all the surfaces of changeable central hole parts installed on intermediate electrodes there are traces of electron emission from the sides facing the anode and of bombardment on the sides facing the cathode, in contrast with which on the front- and back-surfaces of hollow cathode no visible traces of electron emission from then was observed. In addition, there were different tints, strip-like regions on the side of anode facing the cathode. Another interesting phenomenon was that there were a set of concentric circular or elliptical ring pattern on the acid-sensitive discoloring film got at 5cm from the anode and observed tinder a metallograph. It seems that the pseudospark electron beam is Laminar beam i.e, being possessed of a multi-layer structure, at least in the case of multi-gap pseudospark discharge chamber. It was found experimentally that the quality of pseudospark electron beam is much better than that of the cold-cathode electron beam.« less

Nanostructural evolution during emission of CsI-coated carbon fiber cathodes

NASA Astrophysics Data System (ADS)

Drummy, Lawrence F.; Apt, Scott; Shiffler, Don; Golby, Ken; LaCour, Matt; Maruyama, Benji; Vaia, Richard A.

2010-06-01

Carbon-based nanofiber and microfiber cathodes exhibit very low voltages for the onset of electron emission, and thus provide exciting opportunities for applications ranging from high power microwave sources to field emission displays. CsI coatings have been experimentally shown to lower the work function for emission from the fiber tips, although little is known about the microstructure of the fibers themselves in their as-received state, after coating with CsI, or after being subjected to high voltage cycling. Longitudinal cross sections of the original, unused CsI-coated fibers produced by focused ion beam lift-out revealed a nanostructured graphitic core surrounded by an amorphous carbon shell with submicron sized islands of crystalline CsI on the outer surface. Aberration-corrected high resolution electron microscopy (HREM) of the fiber core achieved 0.10 nm resolution, with the graphite (200) clearly visible in digital fast Fourier transformations of the 2-4 nm highly ordered graphitic domains. As the cathode fibers are cycled at high voltage, HREM demonstrates that the graphitic ordering of the core increases with the number of cycles, however the structure and thickness of the amorphous carbon layer remains unchanged. These results are consistent with micro-Raman measurements of the fiber disordered/graphitic (D/G) band ratios. After high voltage cycling, a uniform ˜100 nm film at the fiber tip was evident in both bright field transmission electron microscopy (TEM) and high angle annular dark field scanning TEM (STEM). Low-dose electron diffraction techniques confirmed the amorphous nature of this film, and STEM with elemental mapping via x-ray energy dispersive spectroscopy indicates this layer is composed of CsIO. The oxidative evolution of tip composition and morphology due to impurities in the chamber, along with increased graphitization of the fiber core, contributes to changes in emission behavior with cycling.

Electron Thermionic Emission from Graphene and a Thermionic Energy Converter

NASA Astrophysics Data System (ADS)

Liang, Shi-Jun; Ang, L. K.

2015-01-01

In this paper, we propose a model to investigate the electron thermionic emission from single-layer graphene (ignoring the effects of the substrate) and to explore its application as the emitter of a thermionic energy converter (TIC). An analytical formula is derived, which is a function of the temperature, work function, and Fermi energy level. The formula is significantly different from the traditional Richardson-Dushman (RD) law for which it is independent of mass to account for the supply function of the electrons in the graphene behaving like massless fermion quasiparticles. By comparing with a recent experiment [K. Jiang et al., Nano Res. 7, 553 (2014)] measuring electron thermionic emission from suspended single-layer graphene, our model predicts that the intrinsic work function of single-layer graphene is about 4.514 eV with a Fermi energy level of 0.083 eV. For a given work function, a scaling of T3 is predicted, which is different from the traditional RD scaling of T2. If the work function of the graphene is lowered to 2.5-3 eV and the Fermi energy level is increased to 0.8-0.9 eV, it is possible to design a graphene-cathode-based TIC operating at around 900 K or lower, as compared with the metal-based cathode TIC (operating at about 1500 K). With a graphene-based cathode (work function=4.514 eV ) at 900 K and a metallic-based anode (work function=2.5 eV ) like LaB6 at 425 K, the efficiency of our proposed TIC is about 45%.

Development of 8-hydroxyquinoline metal based organic light-emitting diodes

NASA Astrophysics Data System (ADS)

Feng, Xiaodong

Because of its potential application for flat panel displays, solid-state lighting and 1.5 mum emitter for fiber optical communications, organic light-emitting diodes (OLEDs) have been intensively researched. One of the major problems with current OLED technology relates to inefficient electron injection at the cathode interface, which causes high driving voltage and poor device stability. Making a low resistance cathode contact for electron injection is critical to device performance. This work mainly focuses on cathode interface design and engineering. The Ohmic contact using a structure of C60/LiF/Al has been developed in electron only devices. It is found that application of the C60/LiF/Al contact to Alq based OLEDs leads to a dramatic reduction in driving voltages, a significant improvement in power efficiency, and a much slower aging process. A new cathode structure based on metal-organic-metal (MOM) tri-layer films has been developed. It is found that MOM cathodes reduce reflection by deconstructive optical interference from two metal films. The absolute reflectance from the MOM tr-ilayer films can be reduced to as low as 7% in the visible light spectrum. In actual working devices, the reflectance can be reduced from ˜80% to ˜20%. MOM cathodes provide a potential low-cost solution for high contrast full-color OLED displays. Low voltage Erq based OLEDs at 1.5 mum emission have been developed. The Erq/Ag cathode interface has been found to be efficient for electron injection. Dramatic improvement in driving voltage and power efficiency has been realized by implementing Bphen and C60 into Erq devices as an electron transport layer. Integration of Erq devices on Si wafers has also been demonstrated.

Destructive Evaluation of a Xenon Hollow Cathode after a 28,000 Hour Life Test

NASA Technical Reports Server (NTRS)

Sarver-Verhey, Timothy R.

1998-01-01

International Space Station (ISS) plasma contactor system requires a hollow cathode assembly (HCA) with a lifetime of at least 18,000 hours. In order to demonstrate the lifetime capability of the HCA, a series of hollow cathode wear tests was performed which included a life test operated at the maximum current of the HCA. This test sought to verify hollow cathode lifetime capability and contamination control protocols. This hollow cathode accumulated 27,800 hours of operation before it failed during a restart attempt. The cathode was subsequently destructively analyzed in order to determine the failure mechanism. Microscopic examination of the cathode interior determined that relatively small changes in the cathode physical geometry had occurred and barium tungstates, which are known to limit the emission process, had formed over a majority of the electron emitter surface. Because the final state of the insert was consistent with expected impregnate chemistry, the hollow cathode was believed to have reached the end of its usable life under the test conditions.

Mechanism of vacuum breakdown in radio-frequency accelerating structures

NASA Astrophysics Data System (ADS)

Barengolts, S. A.; Mesyats, V. G.; Oreshkin, V. I.; Oreshkin, E. V.; Khishchenko, K. V.; Uimanov, I. V.; Tsventoukh, M. M.

2018-06-01

It has been investigated whether explosive electron emission may be the initiating mechanism of vacuum breakdown in the accelerating structures of TeV linear electron-positron colliders (Compact Linear Collider). The physical processes involved in a dc vacuum breakdown have been considered, and the relationship between the voltage applied to the diode and the time delay to breakdown has been found. Based on the results obtained, the development of a vacuum breakdown in an rf electric field has been analyzed and the main parameters responsible for the initiation of explosive electron emission have been estimated. The formation of craters on the cathode surface during explosive electron emission has been numerically simulated, and the simulation results are discussed.

Advanced Thermal Conversion Systems

DTIC Science & Technology

2015-03-18

increase electron emission from the cathode. A two-stage, PETE topping stage followed by a thermoelectric bottoming stage, is projected to have a...illustrated in the by the energy-band diagrams in Fig. 1. In that aspect, PETE converters are similar to photovoltaic (PV) cells, but unlike PV cells, PETE... photovoltaic cells at 3000x concentration (~38%). As shown in Fig. 2(b), the highest conversion efficiencies are obtained by using photo-cathodes

Pulse Shaping a High-Current Relativistic Electron Beam in Vacuum

DTIC Science & Technology

1990-06-28

for cathode explosive field-emission initiation at the typical value of 200 kV/cm. The anode is 2.7 cm downstream from the cathode with an aperture of...R42 (J. Choe) I Attn: Dr. D. Prosnitz 1 R42 K. Boulais) 1 Dr. F. W. Chambers 1 R42 (J. Miller) 15 Dr. T. Orzechowski 1 R42 CD. Weidman) I P.O. Box

Cathodoluminescent UV-radiation sources

NASA Astrophysics Data System (ADS)

Vereschagina, N. Y.; Danilkin, M. I.; Kazaryan, M. A.; Ozol, D. I.; Sheshin, E. P.; Spassky, D. A.

2018-04-01

Mercury-free UV-radiation sources are described. An electron beam similar to cathode-ray tubes (CRT) excites a luminescent material in a vacuum bulb. A high density of excitation requires the cathode and the luminescent material to be resistant for that and provide the extended lifetime of the UV-radiation source. Carbon fibre and nano-carbon based field-emission cathodes produce long lasting stable emission with a high current density (up to 0.3-0.5 A/cm2 ). Li2B4O7:Cu and Li2B4O7:Ag luminescent ceramics survive under high radiation doses and provide UV luminescence bands peaked at 360-370 nm and 270 nm, respectively. The luminescence band at 360-370 nm has a good overlap with the fundamental absorption edge of TiO2, which is known as a photo-catalyst in air and water cleaning systems. The luminescence band at 270 nm overlaps with DNA absorption and provides a direct disinfection effect. We suggest the structure of complex luminescence centres and energy transfer mechanisms. The electron structure of lithium tetraborate and the contribution of impurities are also discussed in paper.

Field electron emission based on resonant tunneling in diamond/CoSi2/Si quantum well nanostructures

PubMed Central

Gu, Changzhi; Jiang, Xin; Lu, Wengang; Li, Junjie; Mantl, Siegfried

2012-01-01

Excellent field electron emission properties of a diamond/CoSi2/Si quantum well nanostructure are observed. The novel quantum well structure consists of high quality diamond emitters grown on bulk Si substrate with a nanosized epitaxial CoSi2 conducting interlayer. The results show that the main emission properties were modified by varying the CoSi2 thickness and that stable, low-field, high emission current and controlled electron emission can be obtained by using a high quality diamond film and a thicker CoSi2 interlayer. An electron resonant tunneling mechanism in this quantum well structure is suggested, and the tunneling is due to the long electron mean free path in the nanosized CoSi2 layer. This structure meets most of the requirements for development of vacuum micro/nanoelectronic devices and large-area cold cathodes for flat-panel displays. PMID:23082241

Field electron emission based on resonant tunneling in diamond/CoSi2/Si quantum well nanostructures.

PubMed

Gu, Changzhi; Jiang, Xin; Lu, Wengang; Li, Junjie; Mantl, Siegfried

2012-01-01

Excellent field electron emission properties of a diamond/CoSi(2)/Si quantum well nanostructure are observed. The novel quantum well structure consists of high quality diamond emitters grown on bulk Si substrate with a nanosized epitaxial CoSi(2) conducting interlayer. The results show that the main emission properties were modified by varying the CoSi(2) thickness and that stable, low-field, high emission current and controlled electron emission can be obtained by using a high quality diamond film and a thicker CoSi(2) interlayer. An electron resonant tunneling mechanism in this quantum well structure is suggested, and the tunneling is due to the long electron mean free path in the nanosized CoSi(2) layer. This structure meets most of the requirements for development of vacuum micro/nanoelectronic devices and large-area cold cathodes for flat-panel displays.

Studies of a plasma with a hot dense core in LAPD

NASA Astrophysics Data System (ADS)

van Compernolle, Bart; Gekelman, Walter; Pribyl, Patrick; Cooper, Chris

2009-11-01

Recently, considerable effort in the LArge Plasma Device at UCLA (LAPD) has gone into the study of large cathodes which would enable higher discharge currents and higher densities. The new cathode is made out of Lanthanum HexaBoride (LaB6). LaB6 has a low work function and has higher emissivity than Barium oxide coated cathodes. The operating temperature of LaB6 cathodes lies above 1600 degrees Celsius. Tests of this cathode in the Enormous Toroidal Plasma Device (ETPD) showed that densities in excess of 2 10^13 cm-3 and electron temperatures of 12 eV are feasible. Small LaB6 cathodes (3mm - 2cm) have been used before in LAPD in several experiments on heat transport and on magnetized flux ropes. The cathode presented in this paper has a 8 cm diameter, and can be positioned at different radial locations. The cathode will be pulsed into the standard background plasma (ne= 2 10^12 cm-3, .25 <=Te<=6 eV, dia = 60 cm, L = 18 m) creating a plasma with a hot dense core. We present the characterization of the core plasma at different conditions. Studies of the heat transport and density spreading at the interface between the core plasma and background plasma will be done by use of a variety of probes (Langmuir, magnetic, Mach, emissive) as well as fast photography.

Microanalysis of extended-test xenon hollow cathodes

NASA Technical Reports Server (NTRS)

Verhey, Timothy R.; Patterson, Michael J.

1991-01-01

Four hollow cathode electron sources were analyzed via boroscopy, scanning electron microscopy, energy dispersive x ray analysis, and x ray diffraction analysis. These techniques were used to develop a preliminary understanding of the chemistry of the devices that arise from contamination due to inadequate feed-system integrity and improper insert activation. Two hollow cathodes were operated in an ion thruster simulator at an emission current of 23.0 A for approximately 500 hrs. The two tests differed in propellant-feed systems, discharge power supplies, and activation procedures. Tungsten deposition and barium tungstate formation on the internal cathode surfaces occurred during the first test, which were believed to result from oxygen contamination of the propellant feed-system. Consequently, the test facility was upgraded to reduce contamination, and the test was repeated. The second hollow cathode was found to have experienced significantly less tungsten deposition. A second pair of cathodes examined were the discharge and the neutralizer hollow cathodes used in a life-test of a 30-cm ring-cusp ion thruster at a 5.5 kW power level. The cathodes' test history was documented and the post-test microanalyses are described. The most significant change resulting from the life-test was substantial tungsten deposition on the internal cathode surfaces, as well as removal of material from the insert surface. In addition, barium tungstate and molybdate were found on insert surfaces. As a result of the cathode examinations, procedures and approaches were proposed for improved discharge ignition and cathode longevity.

Advanced electric propulsion research

NASA Technical Reports Server (NTRS)

Wilbur, Paul J.

1988-01-01

Results are presented which show that hollow cathodes can be operated on ammonia but that sustained operation in the high pressures where arcjet thrusters operate (of the order of 1000 Torr) is difficult to achieve. The concept of using contoured, fine wire meshes attached across the screen grid apertures in an ion thruster to effect control of the ion beam divergence is introduced. The concept is compared to conventional (free sheath) ion extraction and is shown to be potentially attractive. The performance related effects of changing the anode and cathode locations and of interchanging hollow cathode and refractory filament electron sources within an 8-cm diameter, argon, ring cusp ion thruster discharge chamber are examined. The effects induced in discharge chamber performance by changes in magnetic field strength and configuration and in propellant flow distribution are also measured. Results are presented in terms of changes in the parameters that describe the effectiveness of primary electron utilization and ion extraction into the beam. The apparatus and instrumentation used to study hollow cathode operation at high electron emission levels (of the order of 100 A) is described.

The tungsten powder study of the dispenser cathode

NASA Astrophysics Data System (ADS)

Bao, Ji-xiu; Wan, Bao-fei

2006-06-01

The intercorrelation of tungsten powder properties, such as grain size, distribution and morphology, and porous matrix parameters with electron emission capability and longevity of Ba dispenser cathodes has been investigated for the different grain morphologies. It is shown that a fully cleaning step of the tungsten powder is so necessary that the tungsten powder will be reduction of oxide in hydrogen atmosphere above 700 °C. The porosity of the tungsten matrix distributes more even and the closed pore is fewer, the average granule size of the tungsten powder distributes more convergent. The porosity of the tungsten matrix and the evaporation of the activator are bigger and the pulse of the cathode is smaller when the granularity is bigger by the analysis of the electronic microscope and diode experiment.

Plasma interaction with emmissive surface with Debye-scale grooves

NASA Astrophysics Data System (ADS)

Schweigert, Irina; Burton, Thomas S.; Thompson, Gregory B.; Langendorf, Samuel; Walker, Mitchell L. R.; Keidar, Michael

2018-04-01

The sheath development over emissive grooved surface in dc discharge plasma controlled by an electron beam is studied in the experiment and in 2D kinetic simulations. Grooved hexagonal boron nitride surfaces with different aspect ratios, designed to mimic the erosion channels, were exposed to an argon plasma. The characteristic size of the grooves (1 mm and 5 mm) is about of the Debye length. The secondary electrons emission from the grooved surfaces is provided by the bombardment with energetic electrons originated from the heated powered cathode. The transition between a developed and a collapsed sheaths near emissive surface takes place with an increase of the beam electron energy. For grooved emissive surfaces, the sheath transition happens at essentially higher voltage compared to the planar one. This phenomenon is analyzed in the terms of the electron energy distribution function.

Performance of a carbon nanotube field emission electron gun

NASA Astrophysics Data System (ADS)

Getty, Stephanie A.; King, Todd T.; Bis, Rachael A.; Jones, Hollis H.; Herrero, Federico; Lynch, Bernard A.; Roman, Patrick; Mahaffy, Paul

2007-04-01

A cold cathode field emission electron gun (e-gun) based on a patterned carbon nanotube (CNT) film has been fabricated for use in a miniaturized reflectron time-of-flight mass spectrometer (RTOF MS), with future applications in other charged particle spectrometers, and performance of the CNT e-gun has been evaluated. A thermionic electron gun has also been fabricated and evaluated in parallel and its performance is used as a benchmark in the evaluation of our CNT e-gun. Implications for future improvements and integration into the RTOF MS are discussed.

Parametric study of rod-pinch diode using particle-in-cell simulation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kumar, R.; Biswas, D., E-mail: raghav@barc.gov.in; Chandra, R.

2014-07-01

We perform Particle-In-Cell (PIC) simulation of KALI-30 GW pulsed power generator based rod-pinch diode. It is shown that ions emitted from the anode-plasma play a crucial role in diode dynamics. It is found that ions not only help in compensating the space charge due to electron beam, but also lead to enhancement of the local electric field at the side walls of the cathode leading to additional electron emission from the side wall. Electrons emanating from one side wall of the cathode tend to converge at the anode tip. This can be used to design an improved Flash X-ray source.more » (author)« less

Locally Resolved Electron Emission Area and Unified View of Field Emission from Ultrananocrystalline Diamond Films

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chubenko, Oksana; Baturin, Stanislav S.; Kovi, Kiran K.

One of the common problems in case of field emission from polycrystalline diamond films, which typically have uniform surface morphology, is uncertainty in determining exact location of electron emission sites across the surface. Although several studies have suggested that grain boundaries are the main electron emission source, it is not particularly clear what makes some sites emit more than the others. It is also practically unclear how one could quantify the actual electron emission area and therefore field emission current per unit area. In this paper we study the effect of actual, locally resolved, field emission (FE) area on electronmore » emission characteristics of uniform planar highly conductive nitrogen-incorporated ultrananocrystalline diamond ((N)UNCD) field emitters. It was routinely found that field emission from as-grown planar (N)UNCD films is always confined to a counted number of discrete emitting centers across the surface which varied in size and electron emissivity. It was established that the actual FE area critically depends on the applied electric field, as well as that the actual FE area and the overall electron emissivity improve with sp2 fraction present in the film irrespectively of the original substrate roughness and morphology. To quantify the actual FE area and its dependence on the applied electric field, imaging experiments were carried out in a vacuum system in a parallel-plate configuration with a specialty anode phosphor screen. Electron emission micrographs were taken concurrently with I-V characteristics measurements. In addition, a novel automated image processing algorithm was developed to process extensive imaging datasets and calculate emission area per image. By doing so, it was determined that the emitting area was always significantly smaller than the FE cathode surface area. Namely, the actual FE area would change from 5×10-3 % to 1.5 % of the total cathode area with the applied electric field increased. Finally and most importantly, it was shown that when I-E curves as measured in the experiment were normalized by the field-dependent emission area, the resulting j-E curves demonstrated a strong kink and significant deviation from Fowler-Nordheim (FN) law, and eventually saturated at a current density of ~100 mA/cm2 . This value was nearly identical for all (N)UNCD films measured in this study, regardless of the substrate.« less

Plasma parameters of the cathode spot explosive electron emission cell obtained from the model of liquid-metal jet tearing and electrical explosion

NASA Astrophysics Data System (ADS)

Tsventoukh, M. M.

2018-05-01

A model has been developed for the explosive electron emission cell pulse of a vacuum discharge cathode spot that describes the ignition and extinction of the explosive pulse. The pulse is initiated due to hydrodynamic tearing of a liquid-metal jet which propagates from the preceding cell crater boundary and draws the ion current from the plasma produced by the preceding explosion. Once the jet neck has been resistively heated to a critical temperature (˜1 eV), the plasma starts expanding and decreasing in density, which corresponds to the extinction phase. Numerical and analytical solutions have been obtained that describe both the time behavior of the pulse plasma parameters and their average values. For the cell plasma, the momentum per transferred charge has been estimated to be some tens of g cm/(s C), which is consistent with the known measurements of ion velocity, ion erosion rate, and specific recoil force. This supports the model of the pressure-gradient-driven plasma acceleration mechanism for the explosive cathode spot cells. The ohmic electric field within the explosive current-carrying plasma has been estimated to be some tens of kV/cm, which is consistent with the known experimental data on cathode potential fall and explosive cell plasma size. This supports the model that assumes the ohmic nature of the cathode potential fall in a vacuum discharge.

A proposed physical model for the impregnated tungsten cathode based on Auger surface studies of the Ba-O-W system

NASA Technical Reports Server (NTRS)

Forman, R.

1979-01-01

Auger spectra and work function measurements are used to study the surface reactions between tungsten surface and adsorbed layers of barium, and barium and oxygen. The barium on an impregnated tungsten cathod seems to be an intermediate state, probably a coadsorbed barium-oxygen layer on tungsten. A slightly revised version of the previously suggested (1976) impregnated tungsten cathode model is proposed. This revised model assumes that the cathode surface during life has an adsorbed surface layer of a monolayer or less of both barium and oxygen on the surface. At end of life, steep drop in electron emission and resultant cathode failure occur. Recent NASA life test results on TWT type tubes are reported and explained by the proposed model.

High voltage pulse ignition of mercury discharge hollow cathodes

NASA Technical Reports Server (NTRS)

Wintucky, E. G.

1973-01-01

A high voltage pulse generated by a capacitor discharge into a step-up transformer has been demonstrated capable of consistently igniting hollow cathode mercury discharges at propellant flows and heater power levels much below those required by conventional cathode starting. Results are presented for 3.2-mm diameter enclosed and open keeper cathodes. Starting characteristics are shown to depend on keeper voltage, mercury flow rate, heater power, keeper orifice size, emissive materials, and electrode to which the pulse is applied. This starting technique has been used to start a cathode over 10,000 times without any degradation of starting capability. The starting reliability, propellant and power savings offered by the high voltage pulse start should favorably impact performance of electron bombardment thrusters in missions requiring many on-off duty cycles.

Simulation of a runaway electron avalanche developing in an atmospheric pressure air discharge

DOE Office of Scientific and Technical Information (OSTI.GOV)

Oreshkin, E. V., E-mail: oreshkinev@scalpnet.ru; Barengolts, S. A.; A. M. Prokhorov General Physics Institute, RAS, 119991 Moscow

2015-12-15

To gain a better understanding of the operation of atmospheric pressure air discharges, the formation of a runaway electron beam at an individual emission site on the cathode has been numerically simulated. The model provides a description of the dynamics of the fast electrons emitted into an air gap from the surface of the emission zone by solving numerically two-dimensional equations for the electrons. It is supposed that the electric field at the surface of the emission zone is enhanced, providing conditions for continuous acceleration of the emitted electrons. It is shown that the formation of a runaway electron beammore » in a highly overvolted discharge is largely associated with avalanche-type processes and that the number of electrons in the avalanche reaches 50% of the total number of runaway electrons.« less

On the energy deposition into the plasma for an inverted fireball geometry

NASA Astrophysics Data System (ADS)

Levko, Dmitry; Gruenwald, Johannes

2017-10-01

Energy deposition into a plasma for an inverted fireball geometry is studied using a self-consistent two-dimensional Particle-in-Cell Monte Carlo collision model. In this model, the cathode is a pin which injects the fixed electron current and the anode is a hollow metal tube covered with the metal grid. We obtain an almost constant ratio between the densities of plasmas generated in the cathode-grid gap and inside the hollow anode. The results of the simulations show that there is no energy exchange between the beam and plasma electrons at low emission currents. For increasing current, however, we observe the increasing coupling between the electron beam and the thermal plasma electrons. This leads to the heating of plasma electrons and the generation of the so-called supra-thermal electrons.

Improved operation of the nonambipolar electron source.

PubMed

Longmier, Ben; Hershkowitz, Noah

2008-09-01

Significant improvements have been made to the nonambipolar electron source (NES), a radio frequency (rf) plasma-based electron source that does not rely on electron emission at a cathode surface [B. Longmier, S. Baalrud, and N. Hershkowitz, Rev. Sci. Instrum. 77, 113504 (2006)]. A prototype NES has produced 30 A of continuous electron current, using 2 SCCM (SCCM denotes cubic centimeter per minute at STP) Xe, 1300 W rf power at 13.56 MHz, yielding a 180 times gas utilization factor. A helicon mode transition has also been identified during NES operation with an argon propellant, using 15 SCCM Ar, 1000 W rf, and 100 G magnetic field. This NES technology has the ability to replace hollow cathode electron sources and to enable high power electric propulsion missions, eliminating one of the lifetime restrictions that many ion thrusters have previously been faced with.

High temperature furnace

DOEpatents

Borkowski, Casimer J.

1976-08-03

A high temperature furnace for use above 2000.degree.C is provided that features fast initial heating and low power consumption at the operating temperature. The cathode is initially heated by joule heating followed by electron emission heating at the operating temperature. The cathode is designed for routine large temperature excursions without being subjected to high thermal stresses. A further characteristic of the device is the elimination of any ceramic components from the high temperature zone of the furnace.

Inert gas thrusters

NASA Technical Reports Server (NTRS)

Kaufman, H. R.; Robinson, R. S.

1979-01-01

Inert gas thrusters considered for space propulsion systems were investigated. Electron diffusion across a magnetic field was examined utilizing a basic model. The production of doubly charged ions was correlated using only overall performance parameters. The use of this correlation is therefore possible in the design stage of large gas thrusters, where detailed plasma properties are not available. Argon hollow cathode performance was investigated over a range of emission currents, with the positions of the inert, keeper, and anode varied. A general trend observed was that the maximum ratio of emission to flow rate increased at higher propellant flow rates. It was also found that an enclosed keeper enhances maximum cathode emission at high flow rates. The maximum cathode emission at a given flow rate was associated with a noisy high voltage mode. Although this mode has some similarities to the plume mode found at low flows and emissions, it is encountered by being initially in the spot mode and increasing emission. A detailed analysis of large, inert-gas thruster performance was carried out. For maximum thruster efficiency, the optimum beam diameter increases from less than a meter at under 2000 sec specific impulse to several meters at 10,000 sec. The corresponding range in input power ranges from several kilowatts to megawatts.

Emission current control system for multiple hollow cathode devices

NASA Technical Reports Server (NTRS)

Beattie, John R. (Inventor); Hancock, Donald J. (Inventor)

1988-01-01

An emission current control system for balancing the individual emission currents from an array of hollow cathodes has current sensors for determining the current drawn by each cathode from a power supply. Each current sensor has an output signal which has a magnitude proportional to the current. The current sensor output signals are averaged, the average value so obtained being applied to a respective controller for controlling the flow of an ion source material through each cathode. Also applied to each controller are the respective sensor output signals for each cathode and a common reference signal. The flow of source material through each hollow cathode is thereby made proportional to the current drawn by that cathode, the average current drawn by all of the cathodes, and the reference signal. Thus, the emission current of each cathode is controlled such that each is made substantially equal to the emission current of each of the other cathodes. When utilized as a component of a multiple hollow cathode ion propulsion motor, the emission current control system of the invention provides for balancing the thrust of the motor about the thrust axis and also for preventing premature failure of a hollow cathode source due to operation above a maximum rated emission current.

Effect of sputtered lanthanum hexaboride film thickness on field emission from metallic knife edge cathodes

NASA Astrophysics Data System (ADS)

Kirley, M. P.; Novakovic, B.; Sule, N.; Weber, M. J.; Knezevic, I.; Booske, J. H.

2012-03-01

We report experiments and analysis of field emission from metallic knife-edge cathodes, which are sputter-coated with thin films of lanthanum hexaboride (LaB6), a low-work function material. The emission current is found to depend sensitively on the thickness of the LaB6 layer. We find that films thinner than 10 nm greatly enhance the emitted current. However, cathodes coated with a thicker layer of LaB6 are observed to emit less current than the uncoated metallic cathode. This result is unexpected due to the higher work function of the bare metal cathode. We show, based on numerical calculation of the electrostatic potential throughout the structure, that the external (LaB6/vacuum) barrier is reduced with respect to uncoated samples for both thin and thick coatings. However, this behavior is not exhibited at the internal (metal/LaB6) barrier. In thinly coated samples, electrons tunnel efficiently through both the internal and external barrier, resulting in current enhancement with respect to the uncoated case. In contrast, the thick internal barrier in thickly coated samples suppresses current below the value for uncoated samples in spite of the lowered external barrier. We argue that this coating thickness variation stems from a relatively low (no higher than 1018 cm-3) free carrier density in the sputtered polycrystalline LaB6.

An Experiment on Thermionic Emission: Back to the Good Old Triode

ERIC Educational Resources Information Center

Azooz, A. A.

2007-01-01

A simple experiment to study thermionic emission, the Richardson-Dushman equation and the energy distribution function of thermionic electrons emitted from a hot cathode using a triode vacuum tube is described. It is pointed out that such a distribution function is directly proportional to the first derivative of the Edison anode current with…

Graphene oxide electrocatalyst on MnO2 air cathode as an efficient electron pump for enhanced oxygen reduction in alkaline solution

NASA Astrophysics Data System (ADS)

Basirun, Wan Jeffrey; Sookhakian, Mehran; Baradaran, Saeid; Endut, Zulkarnain; Mahmoudian, Mohammad Reza; Ebadi, Mehdi; Yousefi, Ramin; Ghadimi, Hanieh; Ahmed, Sohail

2015-03-01

Graphene oxide (GO) was deposited on the surface of a MnO2 air cathode by thermal evaporation at 50°C from a GO colloidal suspension. Fourier transformed infrared spectroscopy and field emission scanning electron microscopy confirmed the presence of GO on the MnO2 air cathode (GO-MnO2). Voltammetry and chrono-amperometry showed increased currents for the oxygen reduction reaction (ORR) in 6 M KOH solution for GO-MnO2 compared to the MnO2 cathode. The GO-MnO2 was used as an air cathode in an alkaline tin-air cell and produced a maximum power density of 13 mW cm-2, in contrast to MnO2, which produced a maximum power density of 9.2 mW cm-2. The electrochemical impedance spectroscopy results suggest that the chemical step for the ORR is the rate determining step, as proposed earlier by different researchers. It is suggested that the presence of GO and electrochemically reduced graphene oxide (ERGO) on the MnO2 surface are responsible for the increased rate of this step, whereby GO and ERGO accelerate the process of electron donation to the MnO2 and to adsorbed oxygen atoms.

Development of a laser ablation-hollow cathode glow discharge emission source and the application to the analysis of steel samples.

PubMed

Naeem, Tariq M; Matsuta, Hideyuki; Wagatsuma, Kazuaki

2004-12-01

A novel atomic emission spectrometry comprising laser ablation as a sampling source and hollow cathode plasma for the excitation of ablated sample atoms is proposed. In this arrangement, a conventional Grimm-type discharge lamp is employed, but the polarity of the power supply is reversed so that the cylindrical hollow tube acts as a cathode and the glow discharge plasma is produced within this tube. A laser is irradiated to introduce sample atoms into the discharge plasma. Ablated atoms are excited by collisions with electrons and gas species, and emit characteristic radiation upon de-excitation. The experiments were conducted only in an atmosphere of helium gas so as to avoid a rapid erosion of the cathode hollow tube. Phase-sensitive detection with a lock-in amplifier was utilized to reject the continuous background emission of the plasma gas and emissions of sputtered atoms from the tube material. The unique feature of this technique is that the sampling and excitation processes can be controlled independently. The proposed technique was employed for the determination of Cr, Mn, and Ni in low-alloyed steel samples. The obtained concentrations are in good agreement with the reported values. The relative standard deviation (RSD), a measure of the analytical precision, was estimated to be 2-9% for Cr, 3-4% for Mn, and 4-11% for Ni determination.

Plasma contactor research, 1989

NASA Technical Reports Server (NTRS)

Williams, John D.

1990-01-01

The characteristics of double layers observed by researchers investigating magnetospheric phenomena are contrasted to those observed in plasma contacting experiments. Experiments in the electron collection mode of the plasma contacting process were performed and the results confirm a simple model of this process for current levels ranging to 3 A. Experimental results were also obtained in a study of the process of electron emission from a hollow cathode plasma contactor. High energy ions are observed coming from the cathode in addition to the electrons and a phenomenological model that suggests a mechanism by which this could occur is presented. Experimental results showing the effects of the design parameters of the ambient plasma simulator on the plasma potential, electron temperature, electron density and plasma noise levels induced in plasma contacting experiments are presented. A preferred simulator design is selected on the basis of these results.

Electron beam emission from a diamond-amplifier cathode.

PubMed

Chang, Xiangyun; Wu, Qiong; Ben-Zvi, Ilan; Burrill, Andrew; Kewisch, Jorg; Rao, Triveni; Smedley, John; Wang, Erdong; Muller, Erik M; Busby, Richard; Dimitrov, Dimitre

2010-10-15

The diamond amplifier (DA) is a new device for generating high-current, high-brightness electron beams. Our transmission-mode tests show that, with single-crystal, high-purity diamonds, the peak current density is greater than 400  mA/mm², while its average density can be more than 100  mA/mm². The gain of the primary electrons easily exceeds 200, and is independent of their density within the practical range of DA applications. We observed the electron emission. The maximum emission gain measured was 40, and the bunch charge was 50  pC/0.5  mm². There was a 35% probability of the emission of an electron from the hydrogenated surface in our tests. We identified a mechanism of slow charging of the diamond due to thermal ionization of surface states that cancels the applied field within it. We also demonstrated that a hydrogenated diamond is extremely robust.

Field free, directly heated lanthanum boride cathode

DOEpatents

Leung, Ka-Ngo; Moussa, D.; Wilde, S.B.

1987-02-02

A directly heated cylindrical lanthanum boride cathode assembly is disclosed which minimizes generation of magnetic field which would interfere with electron emission from the cathode. The cathode assembly comprises a lanthanum boride cylinder in electrical contact at one end with a central support shaft which functions as one electrode to carry current to the lanthanum boride cylinder and in electrical contact, at its opposite end with a second electrode which is coaxially position around the central support shaft so that magnetic fields generated by heater current flowing in one direction through the central support shaft are cancelled by an opposite magnetic field generated by current flowing through the lanthanum boride cylinder and the coaxial electrode in a direction opposite to the current flow in the central shaft.

Real-time imaging, spectroscopy, and structural investigation of cathodic plasma electrolytic oxidation of molybdenum

NASA Astrophysics Data System (ADS)

Stojadinović, Stevan; Tadić, Nenad; Šišović, Nikola M.; Vasilić, Rastko

2015-06-01

In this paper, the results of the investigation of cathodic plasma electrolytic oxidation (CPEO) of molybdenum at 160 V in a mixed solution of borax, water, and ethylene glycol are presented. Real-time imaging and optical emission spectroscopy were used for the characterization of the CPEO. During the process, vapor envelope is formed around the cathode and strong electric field within the envelope caused the generation of plasma discharges. The spectral line shape analysis of hydrogen Balmer line Hβ (486.13 nm) shows that plasma discharges are characterized by the electron number density of about 1.4 × 1021 m-3. The electron temperature of 15 000 K was estimated by measuring molybdenum atomic lines intensity. Surface morphology, chemical, and phase composition of coatings formed by CPEO were characterized by scanning electron microscopy with energy dispersive x-ray spectroscopy and x-ray diffraction. The elemental components of CPEO coatings are Mo and O and the predominant crystalline form is MoO3.

Field Emission Enhancement and the Field-Screening Effect Reduction using Carbon Nanopipettes as Cold Cathodes

NASA Astrophysics Data System (ADS)

Safir, Abdelilah; Mudd, David; Yazdanpanah, Mehdi; Dobrokhotov, Vladimir; Sumanasekera, Gamini; Cohn, Robert

2008-03-01

In this work, we report a recent experimental study of high emission current densities exceeding 10mA/cm^2 and breakdown electric field lower than 5Volts/μm from novel cold cathodes such as conical shaped carbon nanopipettes (CNP). CNP were grown by CVD on Pt wire and have apex as sharp as 10nm with length between 3-6μm. The emission experiments were conducted under vacuum in a scanning electron microscope for individual CNP and in a dedicated chamber for bulk samples. CNP's conical bases and low density contribute significantly to the reduction of the screening effect and to the field emission enhancement. The experimental value for the field enhancement factor, γ, was about 867. Comparing emission results taken from CNP and aligned multiwall carbon nanotubes (MWNT) show that the ratio between γCNP and γMWNT is ˜1.6 which contributes to the reduction of screening effect. The emission from multilayers of graphene was also studied. High emission current (20μA) demonstrates promising emission properties of graphene.

Development of reverse biased p-n junction electron emission

NASA Technical Reports Server (NTRS)

Fowler, P.; Muly, E. C.

1971-01-01

A cold cathode emitter of hot electrons for use as a source of electrons in vacuum gauges and mass spectrometers was developed using standard Norton electroluminescent silicon carbide p-n diodes operated under reverse bias conditions. Continued development including variations in the geometry of these emitters was carried out such that emitters with an emission efficiency (emitted current/junction current) as high as 3 x 10-0.00001 were obtained. Pulse measurements of the diode characteristics were made and showed that higher efficiency can be attained under pulse conditions probably due to the resulting lower temperatures resulting from such operation.

Integrated structure vacuum tube: A Concept

NASA Technical Reports Server (NTRS)

Dimeff, J.; Kerwin, W. J.

1974-01-01

Cathode emission is made to occur by heating entire structure to 600 C, and positive potential is applied to anode with negative potential on grids. Electron flow takes place from ring to circular anode through electric field produced by grids.

Secondary Emission Calorimeter Sensor Development

NASA Astrophysics Data System (ADS)

Winn, David R.; Onel, Yasar

2012-12-01

In a Secondary Emission electron(SEe) detector module, Secondary Emission electrons (SEe) are generated from an SE surface/cathode, when charged hadronic or electromagnetic particles, particularly shower particles, penetrate an SE sampling module placed between absorber materials (Fe, Cu, Pb, W etc) in calorimeters. The SE cathode is a thin (10-50 nm thick) film (simple metal-oxides, or other higher yield materials) on the surface of a metal plate, which serves as the entrance “window” to a compact vacuum vessel (metal or metal-ceramic); this SE film cathode is analogous to a photocathode, and the SEe are similar to p.e., which are then amplified by dynodes, also is in a PMT. SE sensor modules can make use of electrochemically etched/machined or laser-cut metal mesh dynode sheets, as large as ~30 cm square, to amplify the Secondary Emission Electrons (SEe), much like those that compact metal mesh or mesh dynode PMT's use to amplify p.e.'s. The construction requirements easier than a PMT, since the entire final assembly can be done in air; there are no critical controlled thin film depositions, cesiation or other oxygen-excluded processes or other required vacuum activation, and consequently bake-out can be a refractory temperatures; the module is sealed by normal vacuum techniques (welding or brazing or other high temperature joinings), with a simple final heated vacuum pump-out and tip-off. The modules envisioned are compact, high gain, high speed, exceptionally radiation damage resistant, rugged, and cost effective, and can be fabricated in arbitrary tileable shapes. The SE sensor module anodes can be segmented transversely to sizes appropriate to reconstruct electromagnetic cores with high precision. The GEANT4 and existing calorimeter data estimated calorimeter response performance is between 35-50 Secondary Emission electrons per GeV, in a 1 cm thick Cu absorber calorimeter, with a gain per SEe > 105 per SEe, and an e/pi<1.2. The calorimeter pulse width is estimated to be <15 ns. With fine mesh sampling only (no thick absorbers) the resolution is ~25 MeV at 1 GeV.

International Space Station Cathode Life Testing

NASA Technical Reports Server (NTRS)

Soulas, George C.; Sarver-Verhey, Timothy R.

1997-01-01

Four hollow cathode assembly (HCA) life tests were initiated at operating conditions simulating on-orbit operation of the International Space Station plasma contactor. The objective of these tests is to demonstrate the mission-required 18,000 hour lifetime with high-fidelity development model HCAS. HCAs are operated with a continuous 6 sccm xenon flow rate and 3 A anode current. On-orbit emission current requirements are simulated with a square waveform consisting of 50 minutes at a 2.5 A emission current and 40 minutes with no emission current. One HCA test was terminated after approximately 8,000 hours so that a destructive analysis could be performed. The analysis revealed no life-limiting processes and the ultimate lifetime was projected to be greater than the mission requirement. Testing continues for the remaining three HCAs which have accumulated approximately 8,000 hours, 10,000 hours, and 11,000 hours, respectively, as of June 1997. Anode and bias voltages, strong indicators of cathode electron emitter condition, are within acceptable ranges and have exhibited no life- or performance-limiting phenomena to date.

Method of synthesizing small-diameter carbon nanotubes with electron field emission properties

NASA Technical Reports Server (NTRS)

Liu, Jie (Inventor); Du, Chunsheng (Inventor); Qian, Cheng (Inventor); Gao, Bo (Inventor); Qiu, Qi (Inventor); Zhou, Otto Z. (Inventor)

2009-01-01

Carbon nanotube material having an outer diameter less than 10 nm and a number of walls less than ten are disclosed. Also disclosed are an electron field emission device including a substrate, an optionally layer of adhesion-promoting layer, and a layer of electron field emission material. The electron field emission material includes a carbon nanotube having a number of concentric graphene shells per tube of from two to ten, an outer diameter from 2 to 8 nm, and a nanotube length greater than 0.1 microns. One method to fabricate carbon nanotubes includes the steps of (a) producing a catalyst containing Fe and Mo supported on MgO powder, (b) using a mixture of hydrogen and carbon containing gas as precursors, and (c) heating the catalyst to a temperature above 950.degree. C. to produce a carbon nanotube. Another method of fabricating an electron field emission cathode includes the steps of (a) synthesizing electron field emission materials containing carbon nanotubes with a number of concentric graphene shells per tube from two to ten, an outer diameter of from 2 to 8 nm, and a length greater than 0.1 microns, (b) dispersing the electron field emission material in a suitable solvent, (c) depositing the electron field emission materials onto a substrate, and (d) annealing the substrate.

Laser-triggered vacuum switch

DOEpatents

Brannon, Paul J.; Cowgill, Donald F.

1990-01-01

A laser-triggered vacuum switch has a material such as a alkali metal halide on the cathode electrode for thermally activated field emission of electrons and ions upon interaction with a laser beam, the material being in contact with the cathode with a surface facing the discharge gap. The material is preferably a mixture of KCl and Ti powders. The laser may either shine directly on the material, preferably through a hole in the anode, or be directed to the material over a fiber optic cable.

Laser-triggered vacuum switch

DOEpatents

Brannon, P.J.; Cowgill, D.F.

1990-12-18

A laser-triggered vacuum switch has a material such as a alkali metal halide on the cathode electrode for thermally activated field emission of electrons and ions upon interaction with a laser beam, the material being in contact with the cathode with a surface facing the discharge gap. The material is preferably a mixture of KCl and Ti powders. The laser may either shine directly on the material, preferably through a hole in the anode, or be directed to the material over a fiber optic cable. 10 figs.

An experimental investigation of cathode erosion in high current magnetoplasmadynamic arc discharges

NASA Astrophysics Data System (ADS)

Codron, Douglas A.

Since the early to mid 1960's, laboratory studies have demonstrated the unique ability of magnetoplasmadynamic (MPD) thrusters to deliver an exceptionally high level of specific impulse and thrust at large power processing densities. These intrinsic advantages are why MPD thrusters have been identified as a prime candidate for future long duration space missions, including piloted Mars, Mars cargo, lunar cargo, and other missions beyond low Earth orbit (LEO). The large total impulse requirements inherent of the long duration space missions demand the thruster to operate for a significant fraction of the mission burn time while requiring the cathodes to operate at 50 to 10,000 kW for 2,000 to 10,000 hours. The high current levels lead to high operational temperatures and a corresponding steady depletion of the cathode material by evaporation. This mechanism has been identified as the life-limiting component of MPD thrusters. In this research, utilizing subscale geometries, time dependent cathode axial temperature profiles under varying current levels (20 to 60 A) and argon gas mass flow rates (450 to 640 sccm) for both pure and thoriated solid tungsten cathodes were measured by means of both optical pyrometry and charged-coupled (CCD) camera imaging. Thoriated tungsten cathode axial temperature profiles were compared against those of pure tungsten to demonstrate the large temperature reducing effect lowered work function imparts by encouraging increased thermionic electron emission from the cathode surface. Also, Langmuir probing was employed to measure the electron temperature, electron density, and plasma potential near the "active zone" (the surface area of the cathode responsible for approximately 70% of the emitted current) in order to characterize the plasma environment and verify future model predictions. The time changing surface microstructure and elemental composition of the thoriated tungsten cathodes were analyzed using a scanning electron microscope (SEM) in conjunction with energy-dispersive X-ray spectroscopy (EDS). Such studies have provided a qualitative understanding of the typical pathways in which thorium diffuses and how it is normally redistributed along the cathode surface. Lastly, the erosion rates of both pure and thoriated tungsten cathodes were measured after various run times by use of an analytical scale. These measurements have revealed the ability of thoriated tungsten cathodes to run as long as that of pure tungsten but with significantly less material erosion.

Scanning Electron Microscopy with Samples in an Electric Field

PubMed Central

Frank, Ludĕk; Hovorka, Miloš; Mikmeková, Šárka; Mikmeková, Eliška; Müllerová, Ilona; Pokorná, Zuzana

2012-01-01

The high negative bias of a sample in a scanning electron microscope constitutes the “cathode lens” with a strong electric field just above the sample surface. This mode offers a convenient tool for controlling the landing energy of electrons down to units or even fractions of electronvolts with only slight readjustments of the column. Moreover, the field accelerates and collimates the signal electrons to earthed detectors above and below the sample, thereby assuring high collection efficiency and high amplification of the image signal. One important feature is the ability to acquire the complete emission of the backscattered electrons, including those emitted at high angles with respect to the surface normal. The cathode lens aberrations are proportional to the landing energy of electrons so the spot size becomes nearly constant throughout the full energy scale. At low energies and with their complete angular distribution acquired, the backscattered electron images offer enhanced information about crystalline and electronic structures thanks to contrast mechanisms that are otherwise unavailable. Examples from various areas of materials science are presented.

The hollow cathode in the quasi-steady MPD discharge

NASA Technical Reports Server (NTRS)

Von Jaskowsky, W. F.; Jahn, R. G.; Clark, K. E.; Krishnan, M.

1973-01-01

A large hollow cathode has been operated in a quasi-steady MPD discharge over a range of current from 7 to 30 kA and argon mass flow from 0.04 to 6.0 g/sec. The 1.3-cm-i.d. cathode cavity attains steady emission characteristics in some tens of microseconds without the assistance of auxiliary heating, low work function inserts, or external keeper electrodes. Measured current and potential distributions within the cavity reveal that the current attaches in a zone 1 to 2 cm long with a surface current density greater than 1000 A/sq cm and a local axial electric field less than 10 V/cm. Electron densities within the cavity, estimated from spectroscopic records, are above 10 to the 17th power per cu cm, at least one order of magnitude greater than has been reported for either ion engine hollow cathodes or conventional solid cathodes in similar arc discharges.

Vertically aligned diamond-graphite hybrid nanorod arrays with superior field electron emission properties

NASA Astrophysics Data System (ADS)

Ramaneti, R.; Sankaran, K. J.; Korneychuk, S.; Yeh, C. J.; Degutis, G.; Leou, K. C.; Verbeeck, J.; Van Bael, M. K.; Lin, I. N.; Haenen, K.

2017-06-01

A "patterned-seeding technique" in combination with a "nanodiamond masked reactive ion etching process" is demonstrated for fabricating vertically aligned diamond-graphite hybrid (DGH) nanorod arrays. The DGH nanorod arrays possess superior field electron emission (FEE) behavior with a low turn-on field, long lifetime stability, and large field enhancement factor. Such an enhanced FEE is attributed to the nanocomposite nature of the DGH nanorods, which contain sp2-graphitic phases in the boundaries of nano-sized diamond grains. The simplicity in the nanorod fabrication process renders the DGH nanorods of greater potential for the applications as cathodes in field emission displays and microplasma display devices.

Effect of energetic electrons on dust charging in hot cathode filament discharge

NASA Astrophysics Data System (ADS)

Kakati, B.; Kausik, S. S.; Saikia, B. K.; Bandyopadhyay, M.

2011-03-01

The effect of energetic electrons on dust charging for different types of dust is studied in hydrogen plasma. The hydrogen plasma is produced by hot cathode filament discharge method in a dusty plasma device. A full line cusped magnetic field cage is used to confine the plasma elements. To study the plasma parameters for various discharge conditions, a cylindrical Langmuir probe having 0.15 mm diameter and 10.0 mm length is used. An electronically controlled dust dropper is used to drop the dust particles into the plasma. For different discharge conditions, the dust current is measured using a Faraday cup connected to an electrometer. The effect of secondary emission as well as discharge voltage on charging of dust grains in hydrogen plasma is studied with different dust.

RHETT/EPDM Flight Hollow Cathode

NASA Technical Reports Server (NTRS)

Manzella, David; Patterson, Michael; Pastel, Michael

1997-01-01

Under the sponsorship of the BMDO Russian Hall Electric Thruster Technology program two xenon hollow cathodes, a flight unit and a flight spare were fabricated, acceptance tested and delivered to the Naval Research Laboratory for use on the Electric Propulsion Demonstration Module. These hollow cathodes, based on the International Space Station plasma contactor design, were fabricated at the NASA Lewis Research Center for use with a D-55 anode layer thruster in the first on-orbit operational application of this technology. The 2.2 Ampere nominal emission current of this device was obtained with a xenon flow rate of 0.6 mg/s. Ignition of the cathode discharge was accomplished through preheating the active electron emitter with a resistive heating element before application of a 650 volt ignition pulse between the emitter and an external starting electrode. The successful acceptance testing of the Electric Propulsion Demonstration Module utilizing these cathodes demonstrated the suitability of cathodes based on barium impregnated inserts in an enclosed keeper configuration for use with Hall thruster propulsion systems.

Thermionic emission from monolayer graphene, sheath formation and its feasibility towards thermionic converters

NASA Astrophysics Data System (ADS)

Misra, Shikha; Upadhyay Kahaly, M.; Mishra, S. K.

2017-02-01

A formalism describing the thermionic emission from a single layer graphene sheet operating at a finite temperature and the consequent formation of the thermionic sheath in its proximity has been established. The formulation takes account of two dimensional densities of state configuration, Fermi-Dirac (f-d) statistics of the electron energy distribution, Fowler's treatment of electron emission, and Poisson's equation. The thermionic current estimates based on the present analysis is found to be in reasonably good agreement with experimental observations (Zhu et al., Nano Res. 07, 1 (2014)). The analysis has further been simplified for the case where f-d statistics of an electron energy distribution converges to Maxwellian distribution. By using this formulation, the steady state sheath features, viz., spatial dependence of the surface potential and electron density structure in the thermionic sheath are derived and illustrated graphically for graphene parameters; the electron density in the sheath is seen to diminish within ˜10 s of Debye lengths. By utilizing the graphene based cathode in configuring a thermionic converter (TC), an appropriate operating regime in achieving the efficient energy conversion has been identified. A TC configured with the graphene based cathode (operating at ˜1200 K/work function 4.74 V) along with the metallic anode (operating at ˜400 K/ work function 2.0 V) is predicted to display ˜56% of the input thermal flux into the electrical energy, which infers approximately ˜84% of the Carnot efficiency.

Theory of step on leading edge of negative corona current pulse

NASA Astrophysics Data System (ADS)

Gupta, Deepak K.; Mahajan, Sangeeta; John, P. I.

2000-03-01

Theoretical models taking into account different feedback source terms (e.g., ion-impact electron emission, photo-electron emission, field emission, etc) have been proposed for the existence and explanation of the shape of negative corona current pulse, including the step on the leading edge. In the present work, a negative corona current pulse with the step on the leading edge is obtained in the presence of ion-impact electron emission feedback source only. The step on the leading edge is explained in terms of the plasma formation process and enhancement of the feedback source. Ionization wave-like movement toward the cathode is observed after the step. The conditions for the existence of current pulse, with and without the step on the leading edge, are also described. A qualitative comparison with earlier theoretical and experimental work is also included.

Breakdown in helium in high-voltage open discharge with subnanosecond current front rise

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schweigert, I. V., E-mail: ischweig@itam.nsc.ru; Alexandrov, A. L.; Bokhan, P. A.

Investigations of high-voltage open discharge in helium have shown a possibility of generation of current pulses with subnanosecond front rise, due to ultra-fast breakdown development. The open discharge is ignited between two planar cathodes with mesh anode in the middle between them. For gas pressure 6 Torr and 20 kV applied voltage, the rate of current rise reaches 500 A/(cm{sup 2} ns) for current density 200 A/cm{sup 2} and more. The time of breakdown development was measured for different helium pressures and a kinetic model of breakdown in open discharge is presented, based on elementary reactions for electrons, ions andmore » fast atoms. The model also includes various cathode emission processes due to cathode bombardment by ions, fast atoms, electrons and photons of resonant radiation with Doppler shift of frequency. It is shown, that the dominating emission processes depend on the evolution of the discharge voltage during the breakdown. In the simulations, two cases of voltage behavior were considered: (i) the voltage is kept constant during the breakdown; (ii) the voltage is reduced with the growth of current. For the first case, the exponentially growing current is maintained due to photoemission by the resonant photons with Doppler-shifted frequency. For the second case, the dominating factor of current growth is the secondary electron emission. In both cases, the subnanosecond rise of discharge current was obtained. Also the effect of gas pressure on breakdown development was considered. It was found that for 20 Torr gas pressure the time of current rise decreases to 0.1 ns, which is in agreement with experimental data.« less

Characteristics of Single Cathode Cascaded Bias Voltage Arc Plasma

NASA Astrophysics Data System (ADS)

Ou, Wei; Deng, Baiquan; Zeng, Xianjun; Gou, Fujun; Xue, Xiaoyan; Zhang, Weiwei; Cao, Xiaogang; Yang, Dangxiao; Cao, Zhi

2016-06-01

A single cathode with a cascaded bias voltage arc plasma source has been developed with a new quartz cathode chamber, instead of the previous copper chambers, to provide better diagnostic observation and access to the plasma optical emission. The cathode chamber cooling scheme is also modified to be naturally cooled only by light emission without cooling water to improve the optical thin performance in the optical path. A single-parameter physical model has been developed to describe the power dissipated in the cascaded bias voltage arc discharge argon plasmas, which have been investigated by utilizing optical emission spectroscopy (OES) and Langmuir probe. In the experiments, discharge currents from 50 A to 100 A, argon flow rates from 800 sccm to 2000 sccm and magnetic fields of 0.1 T and 0.2 T were chosen. The results show: (a) the relationship between the averaged resistivity and the averaged current density exhibits an empirical scaling law as \\barη \\propto \\bar {j}-0.63369 and the power dissipated in the arc has a strong relation with the filling factor; (b) through the quartz, the argon ions optical emission lines have been easily observed and are dominating with wavelengths between 340 nm and 520 nm, which are the emissions of Ar+-434.81 nm and Ar+-442.60 nm line, and the intensities are increasing with the arc current and decreasing with the inlet argon flow rate; and (c) the electron density and temperature can reach 2.0 × 1019 m-3 and 0.48 eV, respectively, under the conditions of an arc current of 90 A and a magnetic field of 0.2 T. The half-width of the ne radial profile is approximatively equal to a few Larmor radii of electrons and can be regarded as the diameter of the plasma jet in the experiments. supported by the International Thermonuclear Experimental Reactor (ITER) Program Special of Ministry of Science and Technology (No. 2013GB114003), and National Natural Science Foundation of China (Nos. 11275135, 11475122)

High power linear pulsed beam annealer. [Patent application

DOEpatents

Strathman, M.D.; Sadana, D.K.; True, R.B.

1980-11-26

A high power pulsed electron beam system for annealing semiconductors is comprised of an electron gun having a heated cathode, control grid and focus ring for confining the pulsed beam of electrons to a predetermined area, and a curved drift tube. The drift tube and an annular Faraday shield between the focus ring and the drift tube are maintained at a high positive voltage with respect to the cathode to accelerate electrons passing through the focus ring, thereby eliminating space charge limitations on the emission of electrons from said gun. A coil surrounding the curved drift tube provides a magnetic field which maintains the electron beam focused about the axis of the tube. The magnetic field produced by the coil around the curved tube imparts motion to electrons in a spiral path for shallow penetration of the electrons into a target. It also produces a scalloped profile of the electron beam. A second drift tube spaced a predetermined distance from the curved tube is positioned with its axis aligned with the axis of the first drift tube. The second drift tube and the target holder are maintained at a reference voltage between the cathode voltage and the curved tube voltage to decelerate the electrons. A second coil surrounding the second drift tube, maintains the electron beam focused about the axis of the second drift tube. The magnetic field of the second coil comprises the electron beam to the area of the semiconductor on the target holder.

Plasma contactor research, 1990

NASA Technical Reports Server (NTRS)

Williams, John D.; Wilbur, Paul J.

1991-01-01

Emissive and Langmuir probes were used to measure plasma potential profiles, plasma densities, electron energy distributions, and plasma noise levels near a hollow cathode-based plasma contactor emitting electrons. The effects of electron emission current (100 to 1500 mA) and contactor flowrate (2 to 10 sccm (Xenon)) on these data are examined. Retarding potential analyzer (RPA) measurements showing that high energy ions generally stream from a contactor along with the electrons being emitted are also presented, and a mechanism by which this occurs is postulated. This mechanism, which involves a high rate of ionization induced between electrons and atoms flowing together from the hollow cathode orifice, results in a region of high positive space charge and high positive potential. Langmuir and RPA probe data suggests that both electrons and ions expand spherically from this potential hill region. In addition to experimental observations, a simple one-dimensional model which describes the electron emission process and predicts the phenomena just mentioned is presented and is shown to agree qualitatively with these observations. Experimental results of the first stage of bilateral cooperation with the Italian Institute of Interplanetary Space Physics (IFSI CNR) are presented. Sharp, well-defined double layers were observed downstream of a contactor collecting electrons from an ambient plasma created in the IFSI Facility. The voltage drop across these double layers was observed to increase with the current drawn from the ambient plasma. This observation, which was not as clear in previous IFSI tests conducted at higher neutral pressures, is in agreement with previous experimental observations made at both Colorado State University and NASA Lewis Research Center. Greater double layer voltage drops, multiple double layers, and higher noise levels in the region near the double layers were also observed when a magnetic field was imposed and oriented perpendicular to the line joining the contactor and simulator.

Characteristics of a large vacuum wave precursor on the SABRE voltage adder MITL and extraction ion diode

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cuneo, M.E.; Hanson, D.L.; Menge, P.R.

SABRE (Sandia Accelerator and Beam Research Experiment) is a ten-cavity linear induction magnetically insulated voltage adder (6 MV, 300 kA) operated in positive polarity to investigate issues relevant to ion beam production and propagation for inertial confinement fusion. The voltage adder section is coupled to an applied-B extraction ion diode via a long coaxial output transmission line. Observations indicate that the power propagates in a vacuum wave prior to electron emission. After the electron emission threshold is reached, power propagates in a magnetically insulated wave. The precursor is observed to have a dominant impact on he turn-on, impedance history, andmore » beam characteristics of applied-B ion diodes since the precursor voltage is large enough to cause electron emission at the diode from both the cathode feed and cathode tips. The amplitude of the precursor at the load (3--4.5 MV) is a significant fraction of the maximum load voltage (5--6 MV) because (1) the transmission line gaps ( {approx} 9 cm at output) and therefore impedances are relatively large, and hence the electric field threshold for electron emission (200 to 300 kV/cm) is not reached until well into the power pulse rise time; and (2) the rapidly falling forward wave and diode impedance reduces the ratio of main pulse voltage to precursor voltage. Experimental voltage and current data from the transmission line and the ion diode will be presented and compared with TWOQUICK (2-D electromagnetic PIC code) simulations and analytic models.« less

Current transmission and nonlinear effects in un-gated thermionic cathode RF guns

DOE Office of Scientific and Technical Information (OSTI.GOV)

Edelen, J. P.; Harris, J. R.

Un-gated thermionic cathode RF guns are well known as a robust source of electrons for many accelerator applications. These sources are in principle scalable to high currents without degradation of the transverse emittance due to control grids but they are also known for being limited by back-bombardment. While back-bombardment presents a significant limitation, there is still a lack of general understanding on how emission over the whole RF period will affect the nature of the beams produced from these guns. In order to improve our understanding of how these guns can be used in general we develop analytical models thatmore » predict the transmission efficiency as a function of the design parameters, study how bunch compression and emission enhancement caused by Schottky barrier lowering affect the output current profile in the gun, and study the onset of space-charge limited effects and the resultant virtual cathode formation leading to a modulation in the output current distribution.« less

Theoretical analysis of field emission from a metal diamond cold cathode emitter

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lerner, P.; Cutler, P.H.; Miskovsky, N.M.

Recently, Geis {ital et al.} [J. Vac. Sci. Technol. B {bold 14}, 2060 (1996)] proposed a cold cathode emitter based on a Spindt-type design using a diamond film doped by substitutional nitrogen. The device is characterized by high field emission currents at very low power. Two properties, the rough surface of the metallic injector and the negative electron affinity of the (111) surface of the diamond are essential for its operation. We present a first consistent quantitative theory of the operation of a Geis{endash}Spindt diamond field emitter. Its essential features are predicated on nearly {ital zero-field conditions} in the diamondmore » beyond the depletion layer, {ital quasiballistic transport} in the conduction band, and applicability of a modified {ital Fowler{endash}Nordheim equation} to the transmission of electrons through the Schottky barrier at the metal-diamond interface. Calculated results are in good qualitative and quantitative agreement with the experimental results of Geis {ital et al.} {copyright} {ital 1997 American Vacuum Society.}« less

Steady and oscillatory plasma properties in the near-field plume of a hollow cathode

NASA Astrophysics Data System (ADS)

Zun, ZHANG; Kan, XIE; Jiting, OUYANG; Ning, GUO; Yu, QIN; Qimeng, XIA; Song, BAI; Xianming, WU; Zengjie, GU

2018-02-01

Hollow cathodes serve as electron sources in Hall thrusters, ion thrusters and other electric propulsion systems. One of the vital problems in their application is the cathode erosion. However, the basic erosion mechanism and the source of high-energy ions cause of erosion are not fully understood. In this paper, both potential measurements and simulation analyses were performed to explain the formation of high-energy ions. A high-speed camera, a single Langmuir probe and a floating emissive probe were used to determine the steady and oscillatory plasma properties in the near-field plume of a hollow cathode. The temporal structure, electron temperature, electron density, and both static and oscillation of plasma potentials of the plume have been obtained by the diagnostics mentioned above. The experimental results show that there exists a potential hill (about 30 V) and also severe potential oscillations in the near-plume region. Moreover, a simple 2D particle-in-cell model was used to analyze the energy transition between the potential hill and/or its oscillations and the ions. The simulation results show that the energy of ions gained from the static potential background is about 20 eV, but it could reach to 60 eV when the plasma oscillates.

Development of large volume double ring penning plasma discharge source for efficient light emissions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Prakash, Ram; Vyas, Gheesa Lal; Jain, Jalaj

In this paper, the development of large volume double ring Penning plasma discharge source for efficient light emissions is reported. The developed Penning discharge source consists of two cylindrical end cathodes of stainless steel having radius 6 cm and a gap 5.5 cm between them, which are fitted in the top and bottom flanges of the vacuum chamber. Two stainless steel anode rings with thickness 0.4 cm and inner diameters 6.45 cm having separation 2 cm are kept at the discharge centre. Neodymium (Nd{sub 2}Fe{sub 14}B) permanent magnets are physically inserted behind the cathodes for producing nearly uniform magnetic fieldmore » of {approx}0.1 T at the center. Experiments and simulations have been performed for single and double anode ring configurations using helium gas discharge, which infer that double ring configuration gives better light emissions in the large volume Penning plasma discharge arrangement. The optical emission spectroscopy measurements are used to complement the observations. The spectral line-ratio technique is utilized to determine the electron plasma density. The estimated electron plasma density in double ring plasma configuration is {approx}2 Multiplication-Sign 10{sup 11} cm{sup -3}, which is around one order of magnitude larger than that of single ring arrangement.« less

Development of large volume double ring penning plasma discharge source for efficient light emissions.

PubMed

Prakash, Ram; Vyas, Gheesa Lal; Jain, Jalaj; Prajapati, Jitendra; Pal, Udit Narayan; Chowdhuri, Malay Bikas; Manchanda, Ranjana

2012-12-01

In this paper, the development of large volume double ring Penning plasma discharge source for efficient light emissions is reported. The developed Penning discharge source consists of two cylindrical end cathodes of stainless steel having radius 6 cm and a gap 5.5 cm between them, which are fitted in the top and bottom flanges of the vacuum chamber. Two stainless steel anode rings with thickness 0.4 cm and inner diameters 6.45 cm having separation 2 cm are kept at the discharge centre. Neodymium (Nd(2)Fe(14)B) permanent magnets are physically inserted behind the cathodes for producing nearly uniform magnetic field of ~0.1 T at the center. Experiments and simulations have been performed for single and double anode ring configurations using helium gas discharge, which infer that double ring configuration gives better light emissions in the large volume Penning plasma discharge arrangement. The optical emission spectroscopy measurements are used to complement the observations. The spectral line-ratio technique is utilized to determine the electron plasma density. The estimated electron plasma density in double ring plasma configuration is ~2 × 10(11) cm(-3), which is around one order of magnitude larger than that of single ring arrangement.

Real-time imaging, spectroscopy, and structural investigation of cathodic plasma electrolytic oxidation of molybdenum

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stojadinović, Stevan, E-mail: sstevan@ff.bg.ac.rs; Tadić, Nenad; Šišović, Nikola M.

2015-06-21

In this paper, the results of the investigation of cathodic plasma electrolytic oxidation (CPEO) of molybdenum at 160 V in a mixed solution of borax, water, and ethylene glycol are presented. Real-time imaging and optical emission spectroscopy were used for the characterization of the CPEO. During the process, vapor envelope is formed around the cathode and strong electric field within the envelope caused the generation of plasma discharges. The spectral line shape analysis of hydrogen Balmer line H{sub β} (486.13 nm) shows that plasma discharges are characterized by the electron number density of about 1.4 × 10{sup 21 }m{sup −3}. The electron temperaturemore » of 15 000 K was estimated by measuring molybdenum atomic lines intensity. Surface morphology, chemical, and phase composition of coatings formed by CPEO were characterized by scanning electron microscopy with energy dispersive x-ray spectroscopy and x-ray diffraction. The elemental components of CPEO coatings are Mo and O and the predominant crystalline form is MoO{sub 3}.« less

Generation of Low-Energy High-Current Electron Beams in Plasma-Anode Electron Guns

NASA Astrophysics Data System (ADS)

Ozur, G. E.; Proskurovsky, D. I.

2018-01-01

This paper is a review of studies on the generation of low-energy high-current electron beams in electron guns with a plasma anode and an explosive-emission cathode. The problems related to the initiation of explosive electron emission under plasma and the formation and transport of high-current electron beams in plasma-filled systems are discussed consecutively. Considerable attention is given to the nonstationary effects that occur in the space charge layers of plasma. Emphasis is also placed on the problem of providing a uniform energy density distribution over the beam cross section, which is of critical importance in using electron beams of this type for surface treatment of materials. Examples of facilities based on low-energy high-current electron beam sources are presented and their applications in materials science and practice are discussed.

Single-layer nano-carbon film, diamond film, and diamond/nano-carbon composite film field emission performance comparison

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Xiaoping, E-mail: wxpchina64@aliyun.com, E-mail: wxpchina@sohu.com; Shanghai Key Laboratory of Modern Optical System, Shanghai 200093; Wang, Jinye

A series of single-layer nano-carbon (SNC) films, diamond films, and diamond/nano-carbon (D/NC) composite films have been prepared on the highly doped silicon substrate by using microwave plasma chemical vapor deposition techniques. The films were characterised by scanning electron microscopy, Raman spectroscopy, and field emission I-V measurements. The experimental results indicated that the field emission maximum current density of D/NC composite films is 11.8–17.8 times that of diamond films. And the field emission current density of D/NC composite films is 2.9–5 times that of SNC films at an electric field of 3.0 V/μm. At the same time, the D/NC composite film exhibitsmore » the advantage of improved reproducibility and long term stability (both of the nano-carbon film within the D/NC composite cathode and the SNC cathode were prepared under the same experimental conditions). And for the D/NC composite sample, a high current density of 10 mA/cm{sup 2} at an electric field of 3.0 V/μm was obtained. Diamond layer can effectively improve the field emission characteristics of nano-carbon film. The reason may be due to the diamond film acts as the electron acceleration layer.« less

Durable electrocatalytic-activity of Pt-Au/C cathode in PEMFCs.

PubMed

Selvaganesh, S Vinod; Selvarani, G; Sridhar, P; Pitchumani, S; Shukla, A K

2011-07-21

Longevity remains as one of the central issues in the successful commercialization of polymer electrolyte membrane fuel cells (PEMFCs) and primarily hinges on the durability of the cathode. Incorporation of gold (Au) to platinum (Pt) is known to ameliorate both the electrocatalytic activity and stability of cathode in relation to pristine Pt-cathodes that are currently being used in PEMFCs. In this study, an accelerated stress test (AST) is conducted to simulate prolonged fuel-cell operating conditions by potential cycling the carbon-supported Pt-Au (Pt-Au/C) cathode. The loss in performance of PEMFC with Pt-Au/C cathode is found to be ∼10% after 7000 accelerated potential-cycles as against ∼60% for Pt/C cathode under similar conditions. These data are in conformity with the electrochemical surface-area values. PEMFC with Pt-Au/C cathode can withstand >10,000 potential cycles with very little effect on its performance. X-ray diffraction and transmission electron microscopy studies on the catalyst before and after AST suggest that incorporating Au with Pt helps mitigate aggregation of Pt particles during prolonged fuel-cell operations while X-ray photoelectron spectroscopy reflects that the metallic nature of Pt is retained in the Pt-Au catalyst during AST in comparison to Pt/C that shows a major portion of Pt to be present as oxidic platinum. Field-emission scanning electron microscopy conducted on the membrane electrode assembly before and after AST suggests that incorporating Au with Pt helps mitigating deformations in the catalyst layer. This journal is © the Owner Societies 2011

Application of vitreous and graphitic large-area carbon surfaces as field-emission cathodes

NASA Astrophysics Data System (ADS)

Hunt, Charles E.; Wang, Yu

2005-09-01

Numerous carbon bulk or thin-film materials have been used as field-emission cathodes. Most of these can be made into large-area and high-current field-emission cathodes without the use of complex IC fabrication techniques. Some of these exhibit low-extraction field, low work-function, high ruggedness, chemical stability, uniform emission, and low-cost manufacturability. A comparison of all of these materials is presented. Two viable cathode materials, reticulated vitreous carbon (RVC) and graphite paste are examined here and compared.

Effect of thermionic cathode heating current self-magnetic field on gaseous plasma generator characteristics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lopatin, I. V., E-mail: lopatin@opee.hcei.tsc.ru; Akhmadeev, Yu. H.; Koval, N. N.

2015-10-15

The performance capabilities of the PINK, a plasma generator with a thermionic cathode mounted in the cavity of a hollow cathode, depending for its operation on a non-self-sustained low-pressure gas discharge have been investigated. It has been shown that when a single-filament tungsten cathode 2 mm in diameter is used and the peak filament current is equal to or higher than 100 A, the self-magnetic field of the filament current significantly affects the discharge current and voltage waveforms. This effect is due to changes in the time and space distributions of the emission current density from the hot cathode. Whenmore » the electron mean free path is close to the characteristic dimensions of the thermionic cathode, the synthesized plasma density distribution is nonuniform and the cathode is etched nonuniformly. The cathode lifetime in this case is 8–12 h. Using a cathode consisting of several parallel-connected tungsten filaments ∼0.8 mm in diameter moderates the effect of the self-magnetic field of the filament current and nearly doubles the cathode lifetime. The use of this type of cathode together with a discharge igniting electrode reduces the minimum operating pressure in the plasma generator to about one third of that required for the generator operation with a single-filament cathode (to 0.04 Pa)« less

Electrode erosion in steady-state electric propulsion engines

NASA Technical Reports Server (NTRS)

Pivirotto, Thomas J.; Deininger, William D.

1988-01-01

The anode and cathode of a 30 kW class arcjet engine were sectioned and analyzed. This arcjet was operated for a total time of 573 hr at power levels between 25 and 30 kW with ammonia at flow rates of 0.25 and 0.27 gm/s. The accumulated run time was sufficient to clearly establish erosion patterns and their causes. The type of electron emission from various parts of the cathode surface was made clear by scanning electron microscope analysis. A scanning electron microscope was used to study recrystallization on the hot anode surface. These electrodes were made of 2 percent thoriated tungsten and the surface thorium content and gradient perpendicular to the surfaces was determined by quantitative microprobe analysis. The results of this material analysis on the electrodes and recommendations for improving electrode operational life time are presented.

Segmented cold cathode display panel

NASA Technical Reports Server (NTRS)

Payne, Leslie (Inventor)

1998-01-01

The present invention is a video display device that utilizes the novel concept of generating an electronically controlled pattern of electron emission at the output of a segmented photocathode. This pattern of electron emission is amplified via a channel plate. The result is that an intense electronic image can be accelerated toward a phosphor thus creating a bright video image. This novel arrangement allows for one to provide a full color flat video display capable of implementation in large formats. In an alternate arrangement, the present invention is provided without the channel plate and a porous conducting surface is provided instead. In this alternate arrangement, the brightness of the image is reduced but the cost of the overall device is significantly lowered because fabrication complexity is significantly decreased.

Spinel lithium manganese oxide nanoparticles: unique molten salt synthesis strategy and excellent electrochemical performances.

PubMed

Wang, Xiong; Zhu, Juanjuan; Liu, Yingjie

2009-11-01

As a promising candidate cathode material, spinel lithium manganese oxide nanoparticles were successfully synthesized through a novel molten salt synthesis route at relatively low temperature, using manganese dioxide nanowires as precursor. A variety of techniques were applied to characterize the spinel nanomaterial, including X-ray diffraction, transmission electron microscopy, field-emission scanning electron microscopy, and X-ray photoelectron spectroscopy. The average particle size of the resulting spinel nanoparticles was about 80 nm with narrow distribution. As cathode material for rechargeable lithium ion battery, the electrochemical properties were investigated. All the results show that the electrochemical performances of the homogeneous spinel nanoparticles were improved, which might be ascribed to large specific surface area, fairly narrow size distribution, and the unique synthesis strategy.

A theoretical analysis of vacuum arc thruster performance

NASA Technical Reports Server (NTRS)

Polk, James E.; Sekerak, Mike; Ziemer, John K.; Schein, Jochen; Qi, Niansheng; Binder, Robert; Anders, Andre

2001-01-01

In vacuum arc discharges the current is conducted through vapor evaporated from the cathode surface. In these devices very dense, highly ionized plasmas can be created from any metallic or conducting solid used as the cathode. This paper describes theoretical models of performance for several thruster configurations which use vacuum arc plasma sources. This analysis suggests that thrusters using vacuum arc sources can be operated efficiently with a range of propellant options that gives great flexibility in specific impulse. In addition, the efficiency of plasma production in these devices appears to be largely independent of scale because the metal vapor is ionized within a few microns of the cathode electron emission sites, so this approach is well-suited for micropropulsion.

Investigation of hollow cathode performance for 30-cm thrusters

NASA Technical Reports Server (NTRS)

Mirtich, M. J.

1973-01-01

A parametric investigation of 6.35 mm diameter mercury hollow cathodes was carried out in a bell jar. The parameters that were varied were the amount of initial emissive mix, insert position, emission current, cathode temperature, orifice diameter, and mercury flow rate. Flow characteristic curves and performance as a function of time were obtained for the various cathodes. The results of a 3880 hr life test of a main cathode run at 15 amps emission current with no noticeable changes in keeper and collector voltages are also presented.

Detailed numerical simulation of cathode spots in vacuum arcs: Interplay of different mechanisms and ejection of droplets

NASA Astrophysics Data System (ADS)

Kaufmann, H. T. C.; Cunha, M. D.; Benilov, M. S.; Hartmann, W.; Wenzel, N.

2017-10-01

A model of cathode spots in high-current vacuum arcs is developed with account of all the potentially relevant mechanisms: the bombardment of the cathode surface by ions coming from a pre-existing plasma cloud; vaporization of the cathode material in the spot, its ionization, and the interaction of the produced plasma with the cathode; the Joule heat generation in the cathode body; melting of the cathode material and motion of the melt under the effect of the plasma pressure and the Lorentz force and related phenomena. After the spot has been ignited by the action of the cloud (which takes a few nanoseconds), the metal in the spot is melted and accelerated toward the periphery of the spot, with the main driving force being the pressure due to incident ions. Electron emission cooling and convective heat transfer are dominant mechanisms of cooling in the spot, limiting the maximum temperature of the cathode to approximately 4700-4800 K. A crater is formed on the cathode surface in this way. After the plasma cloud has been extinguished, a liquid-metal jet is formed and a droplet is ejected. No explosions have been observed. The modeling results conform to estimates of different mechanisms of cathode erosion derived from the experimental data on the net and ion erosion of copper cathodes.

Theoretical study of cathode surfaces and high-temperature superconductors

NASA Technical Reports Server (NTRS)

Mueller, Wolfgang

1995-01-01

Calculations are presented for the work functions of BaO on W, Os, Pt, and alloys of Re-W, Os-W, and Ir-W that are in excellent agreement with experiment. The observed emission enhancement for alloy relative to tungsten dispenser cathodes is attributed to properties of the substrate crystal structure and explained by the smaller depolarization of the surface dipole on hexagonal as compared to cubic substrates. For Ba and BaO on W(100), the geometry of the adsorbates has been determined by a comparison of inverse photoemission spectra with calculated densities of unoccupied states based on the fully relativistic embedded cluster approach. Results are also discussed for models of scandate cathodes and the electronic structure of oxygen on W(100) at room and elevated temperatures. A detailed comparison is made for the surface electronic structure of the high-temperature superconductor YBa2Cu3O7 as obtained with non-, quasi-, and fully relativistic cluster calculations.

[System of ns time-resolved spectroscopy diagnosis and radioprotection].

PubMed

Yao, Wei-Bo; Guo, Jian-Ming; Zhang, Yong-min; Tang, Jun-Ping; Cheng, Liang; Xu, Qi-fuo

2014-06-01

Cathode plasma of high current electron beam diode is an important research on high power microwave and strong pulsed radio accelerator. It is a reliable method to study cathode plasma by diagnosing the cathode plasma parameters with non-contact spectroscopy measurement system. The present paper introduced the work principle, system composition and performance of the nanosecond (ns) time-resolved spectroscopy diagnosis system. Furthermore, it introduced the implementing method and the temporal relation of lower jitter synchronous trigger system. Simultaneously, the authors designed electromagnetic and radio shield room to protect the diagnosis system due to the high electromagnetic and high X-ray and γ-ray radiation, which seriously interferes with the system. Time-resolved spectroscopy experiment on brass (H62) cathode shows that, the element and matter composition of cathode plasma is clearly increase with the increase in the diode pulsed voltage and current magnitude. The spectroscopy diagnosis system could be of up to 10 ns time resolve capability. It's least is 2 ns. Synchronous trigger system's jitter is less than 4 ns. The spectroscopy diagnosis system will open a new way to study the cathode emission mechanism in depth.

High-yield, ultrafast, surface plasmon-enhanced, Au nanorod optical field electron emitter arrays.

PubMed

Hobbs, Richard G; Yang, Yujia; Fallahi, Arya; Keathley, Philip D; De Leo, Eva; Kärtner, Franz X; Graves, William S; Berggren, Karl K

2014-11-25

Here we demonstrate the design, fabrication, and characterization of ultrafast, surface-plasmon enhanced Au nanorod optical field emitter arrays. We present a quantitative study of electron emission from Au nanorod arrays fabricated by high-resolution electron-beam lithography and excited by 35 fs pulses of 800 nm light. We present accurate models for both the optical field enhancement of Au nanorods within high-density arrays, and electron emission from those nanorods. We have also studied the effects of surface plasmon damping induced by metallic interface layers at the substrate/nanorod interface on near-field enhancement and electron emission. We have identified the peak optical field at which the electron emission mechanism transitions from a 3-photon absorption mechanism to strong-field tunneling emission. Moreover, we have investigated the effects of nanorod array density on nanorod charge yield, including measurement of space-charge effects. The Au nanorod photocathodes presented in this work display 100-1000 times higher conversion efficiency relative to previously reported UV triggered emission from planar Au photocathodes. Consequently, the Au nanorod arrays triggered by ultrafast pulses of 800 nm light in this work may outperform equivalent UV-triggered Au photocathodes, while also offering nanostructuring of the electron pulse produced from such a cathode, which is of interest for X-ray free-electron laser (XFEL) development where nanostructured electron pulses may facilitate more efficient and brighter XFEL radiation.

Space charge neutralization by electron-transparent suspended graphene

PubMed Central

Srisonphan, Siwapon; Kim, Myungji; Kim, Hong Koo

2014-01-01

Graphene possesses many fascinating properties originating from the manifold potential for interactions at electronic, atomic, or molecular levels. Here we report measurement of electron transparency and hole charge induction response of a suspended graphene anode on top of a void channel formed in a SiO2/Si substrate. A two-dimensional (2D) electron gas induced at the oxide interface emits into air and makes a ballistic transport toward the suspended graphene. A small fraction (>~0.1%) of impinging electrons are captured at the edge of 2D hole system in graphene, demonstrating good transparency to very low energy (<3 eV) electrons. The hole charges induced in the suspended graphene anode have the effect of neutralizing the electron space charge in the void channel. This charge compensation dramatically enhances 2D electron gas emission at cathode to the level far surpassing the Child-Langmuir's space-charge-limited emission. PMID:24441774

Phase control and fast start-up of a magnetron using modulation of an addressable faceted cathode

DOE Office of Scientific and Technical Information (OSTI.GOV)

Browning, J., E-mail: JimBrowning@BoiseState.edu; Fernandez-Gutierrez, S.; Lin, M. C.

The use of an addressable, faceted cathode has been proposed as a method of modulating current injection in a magnetron to improve performance and control phase. To implement the controllable electron emission, five-sided and ten-sided faceted planar cathodes employing gated field emitters are considered as these emitters could be fabricated on flat substrates. For demonstration, the conformal finite-difference time-domain particle-in-cell simulation, as implemented in VORPAL, has been used to model a ten-cavity, rising sun magnetron using the modulated current sources and benchmarked against a typical continuous current source. For the modulated, ten-sided faceted cathode case, the electrons are injected frommore » three emitter elements on each of the ten facets. Each emitter is turned ON and OFF in sequence at the oscillating frequency with five emitters ON at one time to drive the five electron spokes of the π-mode. The emitter duty cycle is then 1/6th the Radio-Frequency (RF) period. Simulations show a fast start-up time as low as 35 ns for the modulated case compared to 100 ns for the continuous current cases. Analysis of the RF phase using the electron spoke locations and the RF magnetic field components shows that the phase is controlled for the modulated case while it is random, as typical, for the continuous current case. Active phase control during oscillation was demonstrated by shifting the phase of the electron injection 180° after oscillations started. The 180° phase shift time was approximately 25 RF cycles.« less

Radial electron-beam-breakup transit-time oscillator

DOEpatents

Kwan, Thomas J. T.; Mostrom, Michael A.

1998-01-01

A radial electron-beam-breakup transit-time oscillator (RBTO) provides a compact high power microwave generator. The RBTO includes a coaxial vacuum transmission line having an outer conductor and an inner conductor. The inner conductor defines an annular cavity with dimensions effective to support an electromagnetic field in a TEM.sub.00m mode. A radial field emission cathode is formed on the outer conductor for providing an electron beam directed toward the annular cavity electrode. Microwave energy is then extracted from the annular cavity electrode.

Preliminary Results of Field Emission Cathode Tests

NASA Technical Reports Server (NTRS)

Sovey, James S.; Kovaleski, Scott D.

2001-01-01

Preliminary screening tests of field emission cathodes such as chemical vapor deposited (CVD) diamond, textured pyrolytic graphite, and textured copper were conducted at background pressures typical of electric thruster test facilities to assess cathode performance and stability. Very low power electric thrusters which provide tens to hundreds micronewtons of thrust may need field emission neutralizers that have a capability of tens to hundreds of microamperes. From current voltage characteristics, it was found that the CVD diamond and textured metals cathodes clearly satisfied the Fowler-Nordheim emission relation. The CVD diamond and a textured copper cathode had average current densities of 270 and 380 mA/sq cm, respectively, at the beginning-of-life. After a few hours of operation the cathode emission currents degraded by 40 to 75% at background pressures in the 10(exp -5) Pa to 10(exp -4) Pa range. The textured pyrolytic graphite had a modest current density at beginning-of-life of 84 mA/sq cm, but this cathode was the most stable of all. Extended testing of the most promising cathodes is warranted to determine if current degradation is a burn-in effect or whether it is a long-term degradation process. Preliminary experiments with ferroelectric emission cathodes, which are ceramics with spontaneous electric polarization, were conducted. Peak current densities of 30 to 120 mA/sq cm were obtained for pulse durations of about 500 ns in the 10(exp -4) Pa pressure range.

[Influence of MnO3 on Photoelectric Performance in Organic Light Emitting Diodes].

PubMed

Guan, Yun-xia; Chen, Li-jia; Chen, Ping; Fu, Xiao-qiang; Niu, Lian-bin

2016-03-01

Organic Light Emitting Diodes (OLEDs) has been a promising new research point that has received much attention recently. Emission in a conventional OLED originates from the recombination of carriers (electrons and holes) that are injected from external electrodes. In the device, Electrons, on the other hand, are injected from the Al cathode to an electron-transporting layer and travel to the same emissive zone. Holes are injected from the transparent ITO anode to a hole-transporting layer and holes reach an emitting zone through the holetransporting layer. Electrons and holes recombine at the emissive film to formsinglet excited states, followed by emissive light. It is because OLED is basically an optical device and its structure consists of organic or inorganic layers of sub-wavelength thickness with different refractive indices. When the electron and holes are injected through the electrodes, they combine in the emission zone emitting the photons. These photons will have the reflection and transmission at each interface and the interference will determine the intensity profile. The emissive light reflected at the interfaces or the metallic electrode returns to the emissive layer and affects the radiation current efficiency. Microcavity OLED can produce saturated colors and narrow the emission spetrum as a new kind of technique. In the paper, we fabricate microcavity OLED using glass substrate. Ag film acts as the anode reflector mirror; NPB serves as the hole-transporting material; Alq3 is electron-transporting material and organic emissive material; Ag film acts as cathode reflector mirror. The microcavity OLED structures named as A, B, C and D are glass/Ag(15 nm)/MoO3 (x nm)/NPB(50 nm)/Alq3 (60 nm)/A1(100 nm). Here, A, x = 4 nm; B, x = 7 nm; C, x = 10 nm; D, x = 13 nm. The characteristic voltage, brightness and current of these devices are investigated in the electric field. The luminance from the Devices A, B, C and D reaches the luminance of 928, 1 369, 2 550 and 2 035 cd x m(-2), respectively at 13 V. At 60 mA x cm(-2), the current efficiency of the microcavity OLEDs using MnO3 are about 2.2, 2.6, 3.1 and 2.6 cd x A(-2) respectively. It is found that electrons are majority carriers and holes are minority carriers in this microcavity OLEDs. MnO3 film can improve hole injection ability from 4 to 10 nm. In addition, hole injection ability is increased with the increasing thickness of the MnO3 film.

Operation of a high impedance applied-B extraction ion diode on the SABRE positive polarity linear induction accelerator

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hanson, D.L.; Cuneo, M.E.; McKay, P.F.

We present results from initial experiments with a high impedance applied-B extraction diode on the SABRE ten stage linear induction accelerator (6.7 MV, 300 kA). We have demonstrated efficient coupling of power from the accelerator through an extended MITL (Magnetically Insulated Transmission Line) into a high intensity ion beam. Both MITL electron flow in the diode region and ion diode behavior, including ion source turn-on, virtual cathode formation and evolution, enhancement delay, and ion coupling efficiency, are strongly influenced by the geometry of the diode insulating magnetic field. For our present diode electrode geometry, electrons from the diode feed stronglymore » influence the evolution of the virtual cathode. Both experimental data and particle-in-cell numerical simulations show that uniform insulation of these feed electrons is required for uniform ion emission and efficient diode operation.« less

Charge state distribution and emission characteristics in a table top reflex discharge - Effect of ion confinement and electrons accelerated across the sheath

DOE PAGES

Kumar, Deepak; Englesbe, Alexander; Parman, Matthew; ...

2015-11-05

Tabletop reflex discharges in a Penning geometry have many applications including ion sources and eXtreme Ultra-Violet (XUV) sources. The presence of primary electrons accelerated across the cathode sheaths is responsible for the distribution of ion charge states and of the unusually high XUV brightness of these plasmas. Absolutely calibrated space resolved XUV spectra from a table top reflex discharge operating with Al cathodes and Ne gas are presented. The spectra are analyzed with a new and complete model for ion charge distribution in similar reflex discharges. The plasma in the discharge was found to have a density of ~10 18mmore » –3 with a significant fraction >0.01 of fast primary electrons. As a result, the implications of the new model on the ion states achievable in a tabletop reflex plasma discharge are also discussed.« less

Investigation of hollow cathode performance for 30-cm thrusters

NASA Technical Reports Server (NTRS)

Mirtich, M. J.

1973-01-01

A parametric investigation of 6.35 mm diameter mercury hollow cathodes was carried out in a bell jar. The parameters that were varied were the amount of initial emissive mix, the insert position, the emission current, the cathode temperature, the orifice diameter, and the mercury flow rate. Flow characteristic curves and performance as a function of time were obtained for the various cathodes of interest. Also presented are the results of a 3880 hr life test of a main cathode run at 15 amps emission current with no noticeable changes in keeper and collector voltages.

The effect of a miniature argon flow rate on the spectral characteristics of a direct current atmospheric pressure glow micro-discharge between an argon microjet and a small sized flowing liquid cathode

NASA Astrophysics Data System (ADS)

Jamróz, Piotr; Żyrnicki, Wiesław; Pohl, Paweł

2012-07-01

A stable direct current atmospheric pressure glow microdischarge (dc-μAPGD) was generated between a miniature Ar flow microjet and a small sized flowing liquid cathode. The microdischarge was operated in the open to air atmosphere. High energy species, including OH, NH, NO, N2, H, O and Ar were identified in the emission spectra of this microdischarge. Additionally, atomic lines of metals dissolved in water solutions were easily excited. The near cathode and the near anode zones of the microdischarge were investigated as a function of an Ar flow rate up to 300 sccm. The spectroscopic parameters, i.e., the excitation, the vibrational and the rotational temperatures as well as the electron number density, were determined in the near cathode and the near anode regions of the microdischarge. In the near cathode region, the rotational temperatures obtained for OH (2000-2600 K) and N2 bands (1600-1950 K) were significantly lower than the excitation temperatures of Ar (7400 K-7800 K) and H (11 000-15 500 K) atoms. Vibrational temperatures of N2, OH and NO varied from 3400 to 4000 K, from 2900 to 3400 K and from 2700 to 3000 K, respectively. In the near anode region, rotational temperatures of OH (350-1750 K) and N2 (400-1350 K) and excitation temperatures of Ar (5200-5500 K) and H (3600-12 600 K) atoms were lower than those measured in the near cathode region. The effect of the introduction of a liquid sample on the microdischarge radiation and spectroscopic parameters was also investigated in the near cathode zone. The electron number density was calculated from the Stark broadening of the Hβ line and equals to (0.25-1.1) × 1015 cm- 3 and (0.68-1.2) × 1015 cm- 3 in the near cathode and the near anode zones, respectively. The intensity of the Na I emission line and the signal to background ratio (SBR) of this line were investigated in both zones to evaluate the excitation properties of the developed excitation microsource. The limit of detection for Na was determined at the level of 3 ng mL- 1.

Study of thermal-field emission properties and investigation of temperature dependent noise in the field emission current from vertical carbon nanotube emitters

NASA Astrophysics Data System (ADS)

Kolekar, Sadhu; Patole, S. P.; Patil, Sumati; Yoo, J. B.; Dharmadhikari, C. V.

2017-10-01

We have investigated temperature dependent field electron emission characteristics of vertical carbon nanotubes (CNTs). The generalized expression for electron emission from well-defined cathode surface is given by Millikan and Lauritsen [1] for the combination of temperature and electric field effect. The same expression has been used to explain the electron emission characteristics from vertical CNT emitters. Furthermore, this has been applied to explain the electron emission for different temperatures ranging from room temperature to 1500 K. The real-time field electron emission images at room temperature and 1500 K are recorded by using Charge Coupled Device (CCD) in order to understand the effect of temperature on distribution of electron emission spots and ring like structures in Field Emission Microscope (FEM) image. The FEM images could be used to calculate the total number of emitters per cm2 for electron emission. The calculated number of emitters per cm2 from FEM image is typically, 4.5 × 107 and the actual number emitters per cm2 present as per Atomic Force Microscopy (AFM) data is 1.2 × 1012. The measured Current-Voltage (I-V) characteristics exhibit non linear Folwer-Nordheim (F-N) type behavior. The fluctuations in the emission current were recorded at different temperatures and Fast Fourier transformed into temperature dependent power spectral density. The latter was found to obey power law relation S(f) = A(Iδ/fξ), where δ and ξ are temperature dependent current and frequency exponents respectively.

Gas temperature measurements in deuterium hollow cathode glow discharge

DOE Office of Scientific and Technical Information (OSTI.GOV)

Majstorović, Gordana, E-mail: gordana.majstorovic@va.mod.gov.rs; Šišović, Nikola, E-mail: nikolas@ff.bg.ac.rs

2016-03-25

We report results of optical emission spectroscopy measurements of rotational T{sub rot} and translational (gas) temperature of deuterium molecules in a hollow cathode (HC) glow discharge. The rotational temperature of excited electronic state of D{sub 2} was determined from the intensity distribution in the rotational structure of Q branch of the two Fulcher-α diagonal bands: (ν’=ν”=2) and (ν’=ν”=3). The population of excited energy levels, determined from relative line intensities, was used to derive radial rotational temperature distributions as well as gas temperature distribution of deuterium molecule.

Emission characteristics of dispenser cathodes with a fine-grained tungsten top layer

NASA Astrophysics Data System (ADS)

Kimura, S.; Higuchi, T.; Ouchi, Y.; Uda, E.; Nakamura, O.; Sudo, T.; Koyama, K.

1997-02-01

In order to improve the emission stability of the Ir-coated dispenser cathode under ion bombardment, a fine-grained tungsten top layer was applied on the substrate porous tungsten plug before Ir coating. The emission characteristics were studied after being assembled in a CRT gun. Cathode current was measured under pulse operation in a range of 0.1-9% duty. Remarkable anti-ion bombardment characteristics were observed over the range of 1-6% duty. The improved cathode showed 1.5 times higher emission current than that of a conventional Ir-coated dispenser cathode at 4% duty. AES analysis showed that the recovering rates of surface Ba and O atoms after ion bombardment were 2.5 times higher. From these results it is confirmed that the Ir coated cathode with a fine-grained tungsten top layer is provided with a good tolerance against the ion bombardment.

Transparent amorphous oxide semiconductors for organic electronics: Application to inverted OLEDs

PubMed Central

Hosono, Hideo; Toda, Yoshitake; Kamiya, Toshio; Watanabe, Satoru

2017-01-01

Efficient electron transfer between a cathode and an active organic layer is one key to realizing high-performance organic devices, which require electron injection/transport materials with very low work functions. We developed two wide-bandgap amorphous (a-) oxide semiconductors, a-calcium aluminate electride (a-C12A7:e) and a-zinc silicate (a-ZSO). A-ZSO exhibits a low work function of 3.5 eV and high electron mobility of 1 cm2/(V · s); furthermore, it also forms an ohmic contact with not only conventional cathode materials but also anode materials. A-C12A7:e has an exceptionally low work function of 3.0 eV and is used to enhance the electron injection property from a-ZSO to an emission layer. The inverted electron-only and organic light-emitting diode (OLED) devices fabricated with these two materials exhibit excellent performance compared with the normal type with LiF/Al. This approach provides a solution to the problem of fabricating oxide thin-film transistor-driven OLEDs with both large size and high stability. PMID:28028243

Dynamics of a high-current relativistic electron beam

DOE Office of Scientific and Technical Information (OSTI.GOV)

Strelkov, P. S., E-mail: strelkov@fpl.gpi.ru; Tarakanov, V. P., E-mail: karat@gmail.ru; Ivanov, I. E., E-mail: iei@fpl.gpi.ru

2015-06-15

The dynamics of a high-current relativistic electron beam is studied experimentally and by numerical simulation. The beam is formed in a magnetically insulated diode with a transverse-blade explosive-emission cathode. It is found experimentally that the radius of a 500-keV beam with a current of 2 kA and duration of 500 ns decreases with time during the beam current pulse. The same effect was observed in numerical simulations. This effect is explained by a change in the shape of the cathode plasma during the current pulse, which, according to calculations, leads to a change in the beam parameters, such as themore » electron pitch angle and the spread over the longitudinal electron momentum. These parameters are hard to measure experimentally; however, the time evolution of the radial profile of the beam current density, which can be measured reliably, coincides with the simulation results. This allows one to expect that the behavior of the other beam parameters also agrees with numerical simulations.« less

Electromagnetic radiation detector

DOEpatents

Benson, Jay L.; Hansen, Gordon J.

1976-01-01

An electromagnetic radiation detector including a collimating window, a cathode member having a photoelectric emissive material surface angularly disposed to said window whereby radiation is impinged thereon at acute angles, an anode, separated from the cathode member by an evacuated space, for collecting photoelectrons emitted from the emissive cathode surface, and a negatively biased, high transmissive grid disposed between the cathode member and anode.

Electron emission from ferroelectrics - a review

NASA Astrophysics Data System (ADS)

Riege, H.

1994-02-01

The strong pulsed emission of electrons from the surface of ferroelectric (FE) materials was discovered at CERN in 1987. Since then many aspects and properties of the method of generation and propagation of electron beams from FE have been studied experimentally. The method is based on macroscopic charge separation and self-emission of electrons under the influence of their own space-charge fields. Hence, this type of emission is not limited by the Langmuir-Child law as are conventional emission methods. Charge separation and electron emission can be achieved by rapid switching of the spontaneous, ferroelectric polarization. Polarization switching may be induced by application of electrical-field or mechanical-pressure pulses, as well as by thermal heating or laser illumination of the ferroelectric emitter. At higher emission intensities plasma formation assists the FE emission and leads to a strong growth of emitted current amplitude, which is no longer limited by the FE material and the surface properties. The most attractive features of FE emission are robustness and ease of manipulation of the emitter cathodes which can be transported through atmospheric air and used without any problems in vacuum, low-pressure gas or plasma environments. Large-area arrangements of multiple emitters, switched in interleaved mode, can produce electron beams of any shape, current amplitude or time structure. The successful application of FE emission in accelerator technology has been demonstrated experimentally in several cases, e.g. for triggering high-power gas switches, for photocathodes in electron guns, and for electron-beam generators intended to generate, neutralize and enhance ion beams in ion sources and ion linacs. Other applications can be envisaged in microwave power generators and in the fields of electronics and vacuum microelectronics.

Modeling electron emission and surface effects from diamond cathodes

NASA Astrophysics Data System (ADS)

Dimitrov, D. A.; Smithe, D.; Cary, J. R.; Ben-Zvi, I.; Rao, T.; Smedley, J.; Wang, E.

2015-02-01

We developed modeling capabilities, within the Vorpal particle-in-cell code, for three-dimensional simulations of surface effects and electron emission from semiconductor photocathodes. They include calculation of emission probabilities using general, piece-wise continuous, space-time dependent surface potentials, effective mass, and band bending field effects. We applied these models, in combination with previously implemented capabilities for modeling charge generation and transport in diamond, to investigate the emission dependence on applied electric field in the range from approximately 2 MV/m to 17 MV/m along the [100] direction. The simulation results were compared to experimental data. For the considered parameter regime, conservation of transverse electron momentum (in the plane of the emission surface) allows direct emission from only two (parallel to [100]) of the six equivalent lowest conduction band valleys. When the electron affinity χ is the only parameter varied in the simulations, the value χ = 0.31 eV leads to overall qualitative agreement with the probability of emission deduced from experiments. Including band bending in the simulations improves the agreement with the experimental data, particularly at low applied fields, but not significantly. Using surface potentials with different profiles further allows us to investigate the emission as a function of potential barrier height, width, and vacuum level position. However, adding surface patches with different levels of hydrogenation, modeled with position-dependent electron affinity, leads to the closest agreement with the experimental data.

Novel planar field emission of ultra-thin individual carbon nanotubes.

PubMed

Song, Xuefeng; Gao, Jingyun; Fu, Qiang; Xu, Jun; Zhao, Qing; Yu, Dapeng

2009-10-07

In this work, we proposed and realized a new prototype of planar field emission device based on as-grown individual carbon nanotubes (CNTs) on the surface of a Si-SiO2 substrate. The anode, cathode and the CNT tip all lie on the same surface, so the electron emission is reduced from three-dimensional to two-dimensional. The benefits of such a design include usage of thinner CNT emitters, integrity with planar technology, stable construction, better heat dissipation, etc. A tip-to-tip field emission device was presented besides the tip-to-electrode one. Real-time, in situ observation of the planar field emission was realized in a scanning electron microscope (SEM). Measurements showed that the minimum voltage for 10 nA field emission current was only 8.0 V and the maximum emission current density in an individual CNT emitter (1.0 nm in diameter) exceeded 5.7 x 10(8) A cm(-2). These results stand out in the comparison with recent works on individual CNT field emission, indicating that the planar devices based on ultra-thin individual CNTs are more competitive candidates for next-generation electron field emitters.

Improved DC Gun and Insulator Assembly

DOE Office of Scientific and Technical Information (OSTI.GOV)

Neubauer, Michael

Many user facilities such as synchrotron radiation light sources and free electron lasers rely on DC high voltage photoguns with internal field gradients as high as 10 to 15 MV/m. These high gradients often lead to field emission which poses serious problems for the photocathode used to generate the electron beam and the ceramic insulators used to bias the photocathode at high voltage. Ceramic insulators are difficult to manufacture, require long commissioning times, and have poor reliability, in part because energetic electrons bury themselves in the ceramic causing a buildup of charge and eventual puncture, and also because large diametermore » ceramics are difficult to braze reliably. The lifetimes of photo cathodes inside high current DC guns exhibiting field emission are limited to less than a hundred hours. Reducing the surface gradients on the metals reduces the field emission, which serves to maintain the required ultrahigh vacuum condition. A novel gun design with gradients around 5 MV/m and operating at 350 kV, a major improvement over existing designs, was proposed that allows for the in-situ replacement of photo cathodes in axially symmetric designs using inverted ceramics. In this project, the existing JLAB CEBAF asymmetric gun design with an inverted ceramic support was modeled and the beam dynamics characterized. An improved structure was designed that reduces the surface gradients and improves the beam optics. To minimize the surface gradients, a number of electrostatic gun designs were studied to determine the optimum configuration of the critical electrodes within the gun structure. Coating experiments were carried out to create a charge dissipative coating for cylindrical ceramics. The phase II proposal, which was not granted, included the design and fabrication of an axially symmetric DC Gun with an inverted ceramic that would operate with less than 5 MV/m at 350 kV and would be designed with an in-situ replaceable photo-cathode.« less

Application of M-type cathodes to high-power cw klystrons

NASA Astrophysics Data System (ADS)

Isagawa, S.; Higuchi, T.; Kobayashi, K.; Miyake, S.; Ohya, K.; Yoshida, M.

1999-05-01

Two types of high-power cw klystrons have been widely used at KEK in both TRISTAN and KEKB e +e - collider projects: one is a 0.8 MW/1.0 MW tube, called YK1302/YK1303 (Philips); the other is a 1.2 MW tube, called E3786/E3732 (Toshiba). Normally, the dispenser cathodes of the `B-type' and the `S-type' have been used, respectively, but for improved versions they have been replaced by low-temperature cathodes, called the `M-type'. An Os/Ru coating was applied to the former, whereas an Ir one was applied to the latter. Until now, all upgraded tubes installing M-type cathodes, 9 and 8 in number, respectively, have worked successfully without any dropout. A positive experience concerning the lifetime under real operation conditions has been obtained. M-type cathodes are, however, more easily poisoned. One tube installing an Os/Ru-coated cathode showed a gradual, and then sudden decrease in emission during an underheating test, although the emission could fortunately be recovered by aging at the KEK test field. Once sufficiently aged, the emission of an Ir-coated cathode proved to be very high and stable, and its lifetime is expected to be very long. One disadvantage of this cathode is, however, susceptibility to gas poisoning and the necessity of long-term initial aging. New techniques, like ion milling and fine-grained tungsten top layers, were not as successful as expected from their smaller scale applications to shorten the initial aging period. A burn-in process at higher cathode loading was efficient to make the poisoned cathode active and to decrease unwanted Wehnelt emission. On top of that, the emission cooling, and thus thermal conductivity near the emitting layer could play an important role in such large-current cathodes as ours.

Transmission-line-circuit model of an 85-TW, 25-MA pulsed-power accelerator

NASA Astrophysics Data System (ADS)

Hutsel, B. T.; Corcoran, P. A.; Cuneo, M. E.; Gomez, M. R.; Hess, M. H.; Hinshelwood, D. D.; Jennings, C. A.; Laity, G. R.; Lamppa, D. C.; McBride, R. D.; Moore, J. K.; Myers, A.; Rose, D. V.; Slutz, S. A.; Stygar, W. A.; Waisman, E. M.; Welch, D. R.; Whitney, B. A.

2018-03-01

We have developed a physics-based transmission-line-circuit model of the Z pulsed-power accelerator. The 33-m-diameter Z machine generates a peak electrical power as high as 85 TW, and delivers as much as 25 MA to a physics load. The circuit model is used to design and analyze experiments conducted on Z. The model consists of 36 networks of transmission-line-circuit elements and resistors that represent each of Zs 36 modules. The model of each module includes a Marx generator, intermediate-energy-storage capacitor, laser-triggered gas switch, pulse-forming line, self-break water switches, and tri-plate transmission lines. The circuit model also includes elements that represent Zs water convolute, vacuum insulator stack, four parallel outer magnetically insulated vacuum transmission lines (MITLs), double-post-hole vacuum convolute, inner vacuum MITL, and physics load. Within the vacuum-transmission-line system the model conducts analytic calculations of current loss. To calculate the loss, the model simulates the following processes: (i) electron emission from MITL cathode surfaces wherever an electric-field threshold has been exceeded; (ii) electron loss in the MITLs before magnetic insulation has been established; (iii) flow of electrons emitted by the outer-MITL cathodes after insulation has been established; (iv) closure of MITL anode-cathode (AK) gaps due to expansion of cathode plasma; (v) energy loss to MITL conductors operated at high lineal current densities; (vi) heating of MITL-anode surfaces due to conduction current and deposition of electron kinetic energy; (vii) negative-space-charge-enhanced ion emission from MITL anode surfaces wherever an anode-surface-temperature threshold has been exceeded; and (viii) closure of MITL AK gaps due to expansion of anode plasma. The circuit model is expected to be most accurate when the fractional current loss is small. We have performed circuit simulations of 52 Z experiments conducted with a variety of accelerator configurations and load-impedance time histories. For these experiments, the apparent fractional current loss varies from 0% to 20%. Results of the circuit simulations agree with data acquired on 52 shots to within 2%.

Numerical analysis of direct-current microdischarge for space propulsion applications using the particle-in-cell/Monte Carlo collision (PIC/MCC) method

NASA Astrophysics Data System (ADS)

Kong, Linghan; Wang, Weizong; Murphy, Anthony B.; Xia, Guangqing

2017-04-01

Microdischarges are an important type of plasma discharge that possess several unique characteristics, such as the presence of a stable glow discharge, high plasma density and intense excimer radiation, leading to several potential applications. The intense and controllable gas heating within the extremely small dimensions of microdischarges has been exploited in micro-thruster technologies by incorporating a micro-nozzle to generate the thrust. This kind of micro-thruster has a significantly improved specific impulse performance compared to conventional cold gas thrusters, and can meet the requirements arising from the emerging development and application of micro-spacecraft. In this paper, we performed a self-consistent 2D particle-in-cell simulation, with a Monte Carlo collision model, of a microdischarge operating in a prototype micro-plasma thruster with a hollow cylinder geometry and a divergent micro-nozzle. The model takes into account the thermionic electron emission including the Schottky effect, the secondary electron emission due to cathode bombardment by the plasma ions, several different collision processes, and a non-uniform argon background gas density in the cathode-anode gap. Results in the high-pressure (several hundreds of Torr), high-current (mA) operating regime showing the behavior of the plasma density, potential distribution, and energy flux towards the hollow cathode and anode are presented and discussed. In addition, the results of simulations showing the effect of different argon gas pressures, cathode material work function and discharge voltage on the operation of the microdischarge thruster are presented. Our calculated properties are compared with experimental data under similar conditions and qualitative and quantitative agreements are reached.

Efficient cold cathode emission in crystalline-amorphous hybrid: Study on carbon nanotube-cadmium selenide system

NASA Astrophysics Data System (ADS)

Sarkar, S.; Banerjee, D.; Das, N. S.; Ghorai, U. K.; Sen, D.; Chattopadhyay, K. K.

2018-03-01

Cadmium Selenide (CdSe) quantum dot (QD) decorated amorphous carbon nanotubes (a-CNTs) hybrids have been synthesized by simple chemical process. The samples were characterized by field emission scanning and transmission electron microscopy, Fourier transformed infrared spectroscopy, Raman and UV-Vis spectroscopy. Lattice image obtained from transmission electron microscopic study confirms the successful attachment of CdSe QDs. It is seen that hybrid samples show an enhanced cold emission properties with good stability. The results have been explained in terms of increased roughness, more numbers of emitting sites and favorable band bending induced electron transport. ANSYS software based calculation has also supported the result. Also a first principle based study has been done which shows that due to the formation of hybrid structure there is a profound upward shift in the Fermi level, i.e. a decrease of work function, which is believed to be another key reason for the observed improved field emission performance.

A vacuum-sealed compact x-ray tube based on focused carbon nanotube field-emission electrons

NASA Astrophysics Data System (ADS)

Jeong, Jin-Woo; Kim, Jae-Woo; Kang, Jun-Tae; Choi, Sungyoul; Ahn, Seungjoon; Song, Yoon-Ho

2013-03-01

We report on a fully vacuum-sealed compact x-ray tube based on focused carbon nanotube (CNT) field-emission electrons for various radiography applications. The specially designed two-step brazing process enabled us to accomplish a good vacuum level for the stable and reliable operation of the x-ray tube without any active vacuum pump. Also, the integrated focusing electrodes in the field-emission electron gun focused electron beams from the CNT emitters onto the anode target effectively, giving a small focal spot of around 0.3 mm with a large current of above 50 mA. The active-current control through the cathode electrode of the x-ray tube led a fast digital modulation of x-ray dose with a low voltage of below 5 V. The fabricated compact x-ray tube showed a stable and reliable operation, indicating good maintenance of a vacuum level of below 5 × 10-6 Torr and the possibility of field-emission x-ray tubes in a stand-alone device without an active pumping system.

Corrosion and Passivity Studies with Titanium

DTIC Science & Technology

1955-09-30

the (00.1) Face of a Titanium Single Crystal . - Part 3 Secondary Electron Emission from the Titanium Crystal , and from the Copper-Covered Titanium...ner upon the (00.1) face of a titaniuT single crystal . Low- energy electron diffraction is used to investigate the struc- ture of the deposit. Before...cathode emisaion is strongly dependent on the work function k. 8ince varies with crystal faces and the tip is generally so small that it is a single

High current density sheet-like electron beam generator

NASA Astrophysics Data System (ADS)

Chow-Miller, Cora; Korevaar, Eric; Schuster, John

Sheet electron beams are very desirable for coupling to the evanescent waves in small millimeter wave slow-wave circuits to achieve higher powers. In particular, they are critical for operation of the free-electron-laser-like Orotron. The program was a systematic effort to establish a solid technology base for such a sheet-like electron emitter system that will facilitate the detailed studies of beam propagation stability. Specifically, the effort involved the design and test of a novel electron gun using Lanthanum hexaboride (LaB6) as the thermionic cathode material. Three sets of experiments were performed to measure beam propagation as a function of collector current, beam voltage, and heating power. The design demonstrated its reliability by delivering 386.5 hours of operation throughout the weeks of experimentation. In addition, the cathode survived two venting and pump down cycles without being poisoned or losing its emission characteristics. A current density of 10.7 A/sq cm. was measured while operating at 50 W of ohmic heating power. Preliminary results indicate that the nearby presence of a metal plate can stabilize the beam.

High-efficiency AlxGa1-xAs/GaAs cathode for photon-enhanced thermionic emission solar energy converters

NASA Astrophysics Data System (ADS)

Feng, Cheng; Zhang, Yijun; Qian, Yunsheng; Wang, Ziheng; Liu, Jian; Chang, Benkang; Shi, Feng; Jiao, Gangcheng

2018-04-01

A theoretical emission model for AlxGa1-xAs/GaAs cathode with complex structure based on photon-enhanced thermionic emission is developed by utilizing one-dimensional steady-state continuity equations. The cathode structure comprises a graded-composition AlxGa1-xAs window layer and an exponential-doping GaAs absorber layer. In the deduced model, the physical properties changing with the Al composition are taken into consideration. Simulated current-voltage characteristics are presented and some important factors affecting the conversion efficiency are also illustrated. Compared with the graded-composition and uniform-doping cathode structure, and the uniform-composition and uniform-doping cathode structure, the graded-composition and exponential-doping cathode structure can effectively improve the conversion efficiency, which is ascribed to the twofold built-in electric fields. More strikingly, this graded bandgap structure is especially suitable for photon-enhanced thermionic emission devices since a higher conversion efficiency can be achieved at a lower temperature.

Electron gun for a multiple beam klystron with magnetic compression of the electron beams

DOEpatents

Ives, R. Lawrence; Tran, Hien T; Bui, Thuc; Attarian, Adam; Tallis, William; David, John; Forstall, Virginia; Andujar, Cynthia; Blach, Noah T; Brown, David B; Gadson, Sean E; Kiley, Erin M; Read, Michael

2013-10-01

A multi-beam electron gun provides a plurality N of cathode assemblies comprising a cathode, anode, and focus electrode, each cathode assembly having a local cathode axis and also a central cathode point defined by the intersection of the local cathode axis with the emitting surface of the cathode. Each cathode is arranged with its central point positioned in a plane orthogonal to a device central axis, with each cathode central point an equal distance from the device axis and with an included angle of 360/N between each cathode central point. The local axis of each cathode has a cathode divergence angle with respect to the central axis which is set such that the diverging magnetic field from a solenoidal coil is less than 5 degrees with respect to the projection of the local cathode axis onto a cathode reference plane formed by the device axis and the central cathode point, and the local axis of each cathode is also set such that the angle formed between the cathode reference plane and the local cathode axis results in minimum spiraling in the path of the electron beams in a homogenous magnetic field region of the solenoidal field generator.

Developing field emission electron sources based on ultrananocrystalline diamond for accelerators

DOE Office of Scientific and Technical Information (OSTI.GOV)

Baryshev, Sergey V.; Jing, Chunguang; Qiu, Jiaqi

Radiofrequency (RF) electron guns work by establishing an RF electromagnetic field inside a cavity having conducting walls. Electrons from a cathode are generated in the injector and immediately become accelerated by the RF electric field, and exit the gun as a series of electron bunches. Finding simple solutions for electron injection is a long standing problem. While energies of 30-50 MeV are achievable in linear accelerators (linacs), finding an electron source able to survive under MW electric loads and provide an average current of 1-10 mA is important. Meeting these requirements would open various linac applications for industry. The naturalmore » way to simplify and integrate RF injector architectures with the electron source would be to place the source directly into the RF cavity with no need for additional heaters/lasers. Euclid TechLabs in collaboration with Argonne National Lab are prototyping a family of highly effective field emission electron sources based on a nitrogen-incorporated ultrananocrystalline diamond ((N)UNCD) platform. Determined metrics suggest that our emitters are emissive enough to meet requirements for magnetized cooling at electron-ion colliders, linac-based radioisotope production and X-ray sterilization, and others.« less

Virtual cathode microwave generator having annular anode slit

DOEpatents

Kwan, Thomas J. T.; Snell, Charles M.

1988-01-01

A microwave generator is provided for generating microwaves substantially from virtual cathode oscillation. Electrons are emitted from a cathode and accelerated to an anode which is spaced apart from the cathode. The anode has an annular slit therethrough effective to form the virtual cathode. The anode is at least one range thickness relative to electrons reflecting from the virtual cathode. A magnet is provided to produce an optimum magnetic field having the field strength effective to form an annular beam from the emitted electrons in substantial alignment with the annular anode slit. The magnetic field, however, does permit the reflected electrons to axially diverge from the annular beam. The reflected electrons are absorbed by the anode in returning to the real cathode, such that substantially no reflexing electrons occur. The resulting microwaves are produced with a single dominant mode and are substantially monochromatic relative to conventional virtual cathode microwave generators.

Electron transfer from a carbon nanotube into vacuum under high electric fields

NASA Astrophysics Data System (ADS)

Filip, L. D.; Smith, R. C.; Carey, J. D.; Silva, S. R. P.

2009-05-01

The transfer of an electron from a carbon nanotube (CNT) tip into vacuum under a high electric field is considered beyond the usual one-dimensional semi-classical approach. A model of the potential energy outside the CNT cap is proposed in order to show the importance of the intrinsic CNT parameters such as radius, length and vacuum barrier height. This model also takes into account set-up parameters such as the shape of the anode and the anode-to-cathode distance, which are generically portable to any modelling study of electron emission from a tip emitter. Results obtained within our model compare well to experimental data. Moreover, in contrast to the usual one-dimensional Wentzel-Kramers-Brillouin description, our model retains the ability to explain non-standard features of the process of electron field emission from CNTs that arise as a result of the quantum behaviour of electrons on the surface of the CNT.

Stable synthesis of few-layered boron nitride nanotubes by anodic arc discharge.

PubMed

Yeh, Yao-Wen; Raitses, Yevgeny; Koel, Bruce E; Yao, Nan

2017-06-08

Boron nitride nanotubes (BNNTs) were successfully synthesized by a dc arc discharge using a boron-rich anode as synthesis feedstock in a nitrogen gas environment at near atmospheric pressure. The synthesis was achieved independent of the cathode material suggesting that under such conditions the arc operates in so-called anodic mode with the anode material being consumed by evaporation due to the arc heating. To sustain the arc current by thermionic electron emission, the cathode has to be at sufficiently high temperature, which for a typical arc current density of ~100 A/cm 2 , is above the boron melting point (2350 K). With both electrodes made from the same boron-rich alloy, we found that the arc operation unstable due to frequent sticking between two molten electrodes and formation of molten droplets. Stable and reliable arc operation and arc synthesis were achieved with the boron-rich anode and the cathode made from a refractory metal which has a melting temperature above the melting point of boron. Ex-situ characterization of synthesized BNNTs with electron microscopy and Raman spectroscopy revealed that independent of the cathode material, the tubes are primarily single and double walled. The results also show evidence of root-growth of BNNTs produced in the arc discharge.

Stable synthesis of few-layered boron nitride nanotubes by anodic arc discharge

DOE PAGES

Yeh, Yao-Wen; Raitses, Yevgeny; Koel, Bruce E.; ...

2017-06-08

Boron nitride nanotubes (BNNTs) were successfully synthesized by a dc arc discharge using a boron-rich anode as synthesis feedstock in a nitrogen gas environment at near atmospheric pressure. The synthesis was achieved independent of the cathode material suggesting that under such conditions the arc operates in so-called anodic mode with the anode material being consumed by evaporation due to the arc heating. In order to sustain the arc current by thermionic electron emission, the cathode has to be at sufficiently high temperature, which for a typical arc current density of similar to 100 A/cm 2, is above the boron meltingmore » point (2350 K). With both electrodes made from the same boron-rich alloy, we found that the arc operation unstable due to frequent sticking between two molten electrodes and formation of molten droplets. We achieved a stable and reliable arc operation and arc synthesis with the boronrich anode and the cathode made from a refractory metal which has a melting temperature above the melting point of boron. Ex-situ characterization of synthesized BNNTs with electron microscopy and Raman spectroscopy revealed that independent of the cathode material, the tubes are primarily single and double walled. Our results also show evidence of root-growth of BNNTs produced in the arc discharge.« less

Stable synthesis of few-layered boron nitride nanotubes by anodic arc discharge

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yeh, Yao-Wen; Raitses, Yevgeny; Koel, Bruce E.

Boron nitride nanotubes (BNNTs) were successfully synthesized by a dc arc discharge using a boron-rich anode as synthesis feedstock in a nitrogen gas environment at near atmospheric pressure. The synthesis was achieved independent of the cathode material suggesting that under such conditions the arc operates in so-called anodic mode with the anode material being consumed by evaporation due to the arc heating. In order to sustain the arc current by thermionic electron emission, the cathode has to be at sufficiently high temperature, which for a typical arc current density of similar to 100 A/cm 2, is above the boron meltingmore » point (2350 K). With both electrodes made from the same boron-rich alloy, we found that the arc operation unstable due to frequent sticking between two molten electrodes and formation of molten droplets. We achieved a stable and reliable arc operation and arc synthesis with the boronrich anode and the cathode made from a refractory metal which has a melting temperature above the melting point of boron. Ex-situ characterization of synthesized BNNTs with electron microscopy and Raman spectroscopy revealed that independent of the cathode material, the tubes are primarily single and double walled. Our results also show evidence of root-growth of BNNTs produced in the arc discharge.« less

Analysis of XeC1 Emission in a Hollow Cathode Discharge.

DTIC Science & Technology

1981-06-01

excited homopolar molecule, e.g., Xe2 , Hg2 The term exciplex refers to an electronically excited heteropolar complex, e.g., KrF , XeOH , XeCl , which...HCI Products, k9 = 5.4 x 10 cm /sec. (25) Figure 9 summarizes the main energy pathways for XeCI exciplex formation via three body recombination and

Modeling of Microplasmas with Nano-Engineered Electrodes

NASA Astrophysics Data System (ADS)

Macheret, Sergey; Tholeti, Siva Shashank; Alexeenko, Alina

2015-09-01

Microplasmas can potentially be used as unique tunable dielectrics for reconfigurable radio-frequency systems, if electron densities of 1010-1012 cm-3 can be sustained in cavities smaller than 100 micron. However, for low loss tangent, gas pressures below 10 mTorr would be required, whereas the physics of electron impact ionization dictates the pd scaling so that microplasmas must operate at high gas pressures, hundreds of Torr, and also high voltages. We analyze a new principle of plasma generation that goes well beyond the pd scaling by eliminating electron impact ionization. In the new concept, electrons are generated at the cathode by field emission from nanotubes, and ions are independently produced in field ionization at atomically-sharp tips on the anode. The electrons and ions then move in the opposite directions, mix, and create a plasma. The low pressure results in collisionless motion with no electron-impact ionization. One-dimensional PIC/MCC calculations show that emitters such as carbon nanotubes placed sparsely on the cathode, combined with field ionization nanorods at the anode, can indeed ensure steady-state electron densities of up to 1012 cm-3 at gas pressure lower than 10 mTorr with only 50-100 Volts applied cross a 40-50 μm gap.

Ion and advanced electric thruster research

NASA Technical Reports Server (NTRS)

Wilbur, P. J.

1980-01-01

A phenomenological model of the orificed, hollow cathode based on the field enhanced, thermionic mechanism of electron emission is presented. High frequency oscillations associated with the orificed, hollow cathode are shown to be a consequence of current flow through the cathode orifice. A procedure for Langmuir probing of the hollow cathode discharge and analyzing the resulting probe characteristics is discussed. The results of sputter yield measurements made for molybdenum, tantalum, type 304 stainless steel and copper surfaces being bombarded by low energy argon or mercury ions are also given. The effects of nitrogen and alternated copper layers on the sputter yields of molybdenum, tantalum and 304 stainless steel are also discussed. A dynamic model of electrothermal rocket and ramjet thrusters is developed. The gross performance of these devices is compared to that of an electromagnetic gun for the case of a high acceleration, Earth launch mission. The theoretical performance of electrothermal rockets and ramjets is shown to be comparable to that of the electromagnetic gun.

Nano-Filament Field Emission Cathode Development Final Report CRADA No. TSB-0731-93

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bernhardt, Tony; Fahlen, Ted

At the time the CRADA was established, Silicon Video Corporation, of Cupertino, CA was a one-year-old rapidly growing start-up company. SVC was developing flat panel displays (FPDs) to replace Cathode Ray Terminals (CRTs) for personal computers, work stations and televisions. They planned to base their products on low cost and energy efficient field emission technology. It was universally recognized that the display was both the dominant cost item and differentiating feature of many products such as laptop computers and hand-held electronics and that control of the display technology through U.S. sources was essential to success in these markets. The purposemore » of this CRADA project was to determine if electrochemical planarization would be a viable, inexpensive alternative to current optical polishing techniques for planarizing the surface of a ceramic backplate of a thin film display.« less

Structural and Electrical Properties of Lithium-Ion Rechargeable Battery Using the LiFePO4/Carbon Cathode Material.

PubMed

Kim, Young-Sung; Jeoung, Tae-Hoon; Nam, Sung-Pill; Lee, Seung-Hwan; Kim, Jea-Chul; Lee, Sung-Gap

2015-03-01

LiFePO4/C composite powder as cathode material and graphite powder as anode material for Li-ion batteries were synthesized by using the sol-gel method. An electrochemical improvement of LiFePO4 materials has been achieved by adding polyvinyl alcohol as a carbon source into as-prepared materials. The samples were characterized by elemental analysis (EA), X-ray diffraction (XRD), and field emission scanning electron microscopy (FE-EM). The chemical composition of LiFePO4/C powders was in a good agreement with that of the starting solution. The capacity loss after 500 cycles of LiFePO4/C cell is 11.1% in room temperature. These superior electrochemical properties show that LiFePO4/C composite materials are promising candidates as cathode materials.

Method of depositing multi-layer carbon-based coatings for field emission

DOEpatents

Sullivan, John P.; Friedmann, Thomas A.

1999-01-01

A novel field emitter device for cold cathode field emission applications, comprising a multi-layer resistive carbon film. The multi-layered film of the present invention is comprised of at least two layers of a resistive carbon material, preferably amorphous-tetrahedrally coordinated carbon, such that the resistivities of adjacent layers differ. For electron emission from the surface, the preferred structure comprises a top layer having a lower resistivity than the bottom layer. For edge emitting structures, the preferred structure of the film comprises a plurality of carbon layers, wherein adjacent layers have different resistivities. Through selection of deposition conditions, including the energy of the depositing carbon species, the presence or absence of certain elements such as H, N, inert gases or boron, carbon layers having desired resistivities can be produced. Field emitters made according the present invention display improved electron emission characteristics in comparison to conventional field emitter materials.

Method of depositing multi-layer carbon-based coatings for field emission

DOEpatents

Sullivan, J.P.; Friedmann, T.A.

1999-08-10

A novel field emitter device is disclosed for cold cathode field emission applications, comprising a multi-layer resistive carbon film. The multi-layered film of the present invention is comprised of at least two layers of a resistive carbon material, preferably amorphous-tetrahedrally coordinated carbon, such that the resistivities of adjacent layers differ. For electron emission from the surface, the preferred structure comprises a top layer having a lower resistivity than the bottom layer. For edge emitting structures, the preferred structure of the film comprises a plurality of carbon layers, wherein adjacent layers have different resistivities. Through selection of deposition conditions, including the energy of the depositing carbon species, the presence or absence of certain elements such as H, N, inert gases or boron, carbon layers having desired resistivities can be produced. Field emitters made according the present invention display improved electron emission characteristics in comparison to conventional field emitter materials. 8 figs.

Photon-enhanced thermionic emission for solar concentrator systems.

PubMed

Schwede, Jared W; Bargatin, Igor; Riley, Daniel C; Hardin, Brian E; Rosenthal, Samuel J; Sun, Yun; Schmitt, Felix; Pianetta, Piero; Howe, Roger T; Shen, Zhi-Xun; Melosh, Nicholas A

2010-09-01

Solar-energy conversion usually takes one of two forms: the 'quantum' approach, which uses the large per-photon energy of solar radiation to excite electrons, as in photovoltaic cells, or the 'thermal' approach, which uses concentrated sunlight as a thermal-energy source to indirectly produce electricity using a heat engine. Here we present a new concept for solar electricity generation, photon-enhanced thermionic emission, which combines quantum and thermal mechanisms into a single physical process. The device is based on thermionic emission of photoexcited electrons from a semiconductor cathode at high temperature. Temperature-dependent photoemission-yield measurements from GaN show strong evidence for photon-enhanced thermionic emission, and calculated efficiencies for idealized devices can exceed the theoretical limits of single-junction photovoltaic cells. The proposed solar converter would operate at temperatures exceeding 200 degrees C, enabling its waste heat to be used to power a secondary thermal engine, boosting theoretical combined conversion efficiencies above 50%.

LASER APPLICATIONS AND OTHER TOPICS IN QUANTUM ELECTRONICS: Study of emission of a volume nanosecond discharge plasma in xenon, krypton and argon at high pressures

NASA Astrophysics Data System (ADS)

Baksht, E. Kh; Lomaev, Mikhail I.; Rybka, D. V.; Tarasenko, Viktor F.

2006-06-01

The emission properties of a volume nanosecond discharge plasma produced in xenon, krypton and argon at high pressures in a discharge gap with a cathode having a small radius of curvature are studied. Spectra in the range 120-850 nm and amplitude—time characteristics of xenon emission at different regimes and excitation techniques are recorded and analysed. It is shown that upon excitation of the volume discharge initiated by a beam of avalanche electrons, at least 90% of the energy in the spectral range 120-850 nm is emitted by xenon dimers. For xenon at a pressure of 1.2 atm, ~45 mJ of the spontaneous emission energy was obtained in the full solid angle in a pulse with the full width at half-maximum ~130 ns.

Tracking Electron Uptake from a Cathode into Shewanella Cells: Implications for Energy Acquisition from Solid-Substrate Electron Donors

PubMed Central

Rajeev, Pournami; Jain, Abhiney; Pirbadian, Sahand; Okamoto, Akihiro; Gralnick, Jeffrey A.; El-Naggar, Mohamed Y.; Nealson, Kenneth H.

2018-01-01

ABSTRACT While typically investigated as a microorganism capable of extracellular electron transfer to minerals or anodes, Shewanella oneidensis MR-1 can also facilitate electron flow from a cathode to terminal electron acceptors, such as fumarate or oxygen, thereby providing a model system for a process that has significant environmental and technological implications. This work demonstrates that cathodic electrons enter the electron transport chain of S. oneidensis when oxygen is used as the terminal electron acceptor. The effect of electron transport chain inhibitors suggested that a proton gradient is generated during cathode oxidation, consistent with the higher cellular ATP levels measured in cathode-respiring cells than in controls. Cathode oxidation also correlated with an increase in the cellular redox (NADH/FMNH2) pool determined with a bioluminescence assay, a proton uncoupler, and a mutant of proton-pumping NADH oxidase complex I. This work suggested that the generation of NADH/FMNH2 under cathodic conditions was linked to reverse electron flow mediated by complex I. A decrease in cathodic electron uptake was observed in various mutant strains, including those lacking the extracellular electron transfer components necessary for anodic-current generation. While no cell growth was observed under these conditions, here we show that cathode oxidation is linked to cellular energy acquisition, resulting in a quantifiable reduction in the cellular decay rate. This work highlights a potential mechanism for cell survival and/or persistence on cathodes, which might extend to environments where growth and division are severely limited. PMID:29487241

Design of indirectly heated thoriated tungsten cathode based strip electron gun

DOE Office of Scientific and Technical Information (OSTI.GOV)

Maiti, Namita; Thakur, K.B.; Patil, D.S.

Design of indirectly heated solid cathode based electron gun (200 kW, 45 kV, 270 degree bent strip type electron gun) has been presented. The solid cathode is made of thoriated tungsten. The solid cathode design has been suitably done to achieve required electron beam cross section. The design approach consists of simulation followed by extensive experimentation. In the design, the effort has been put to reduce the non-uniformity of the heat flux from the filament to the solid cathode to obtain better uniformity of temperature on the solid cathode. Trial beam experiments shows that the modified design achieves one tomore » one correspondence of the solid cathode length and the electron beam length. (author)« less

Photo-stimulated low electron temperature high current diamond film field emission cathode

DOEpatents

Shurter,; Roger Philips, Devlin [Los Alamos, NM; David James, Moody [Santa Fe, NM; Nathan Andrew, Taccetti [Los Alamos, NM; Jose Martin, Russell [Santa Fe, NM; John, Steven [Los Alamos, NM

2012-07-24

An electron source includes a back contact surface having a means for attaching a power source to the back contact surface. The electron source also includes a layer comprising platinum in direct contact with the back contact surface, a composite layer of single-walled carbon nanotubes embedded in platinum in direct contact with the layer comprising platinum. The electron source also includes a nanocrystalline diamond layer in direct contact with the composite layer. The nanocrystalline diamond layer is doped with boron. A portion of the back contact surface is removed to reveal the underlying platinum. The electron source is contained in an evacuable container.

Emission efficiency optimization of RE 2O 3 doped molybdenum thermionic cathode by application of pattern recognition method

NASA Astrophysics Data System (ADS)

Wang, Jinshu; Liu, Wei; Liu, Yanqin; Zhou, Meiling

2005-09-01

As an alternative for thoriated tungsten thermionic cathodes, molybdenum doped with either a single rare earth oxide such as La 2O 3, Y 2O 3 and Sc 2O 3 or a mixture thereof has been produced by powder metallurgy. It is shown that carbonization can greatly improve the emission properties (i.e. emission capability and stability) of RE 2O 3 doped molybdenum due to the formation of a (metallic) rare earth atomic layer on the surface of the cathode by the reduction reaction of molybdenum carbide and rare earth oxide. Among all the carbonized samples, La 2O 3 and Y 2O 3 co-doped molybdenum cathode showed the best performance in emission. In addition, computer pattern recognition technique has been used to optimize the composition of the material and of the cathode preparation technique. We derive the equation of the emission efficiency as a function of cathode composition and carbonization degree. Based on the projecting coordinates obtained from the equation, the optimum projection region was identified, which can serve as guide for the composition and carbonization degree design.

Electron-emission characteristics of tungsten alloys: Mee 492. [No data; plasma anode tube

DOE Office of Scientific and Technical Information (OSTI.GOV)

Moon, H.M.

A plasma-anode tube was constructed to investigate the electron-emission characteristics for rhenium, 1% thorium tungsten, and 2% thorium tungsten. The tube consists of cathode, anode, cesium reservoir, and three probes. Inside of tube is a rough vacuum by using a Varian liquid-nitrogen-cooled cryovalve and further vacuum by using a Varian absorption pumpt to 4 X IO/sup -5/ pa. The tube was sealed off from the vacuum pump after the cesium ampoule was broken. The entire plasma-anode tube except the cesiunm reservoir was placed in a Blue M Electric Company furnace whose door had been modified to permit viewing of themore » tube.« less

Laser-photofield emission from needle cathodes for low-emittance electron beams.

PubMed

Ganter, R; Bakker, R; Gough, C; Leemann, S C; Paraliev, M; Pedrozzi, M; Le Pimpec, F; Schlott, V; Rivkin, L; Wrulich, A

2008-02-15

Illumination of a ZrC needle with short laser pulses (16 ps, 266 nm) while high voltage pulses (-60 kV, 2 ns, 30 Hz) are applied, produces photo-field emitted electron bunches. The electric field is high and varies rapidly over the needle surface so that quantum efficiency (QE) near the apex can be much higher than for a flat photocathode due to the Schottky effect. Up to 150 pC (2.9 A peak current) have been extracted by photo-field emission from a ZrC needle. The effective emitting area has an estimated radius below 50 microm leading to a theoretical intrinsic emittance below 0.05 mm mrad.

Band-to-Band Tunneling-Dominated Thermo-Enhanced Field Electron Emission from p-Si/ZnO Nanoemitters.

PubMed

Huang, Zhizhen; Huang, Yifeng; Xu, Ningsheng; Chen, Jun; She, Juncong; Deng, Shaozhi

2018-06-13

Thermo-enhancement is an effective way to achieve high performance field electron emitters, and enables the individually tuning on the emission current by temperature and the electron energy by voltage. The field emission current from metal or n-doped semiconductor emitter at a relatively lower temperature (i.e., < 1000 K) is less temperature sensitive due to the weak dependence of free electron density on temperature, while that from p-doped semiconductor emitter is restricted by its limited free electron density. Here, we developed full array of uniform individual p-Si/ZnO nanoemitters and demonstrated the strong thermo-enhanced field emission. The mechanism of forming uniform nanoemitters with well Si/ZnO mechanical joint in the nanotemplates was elucidated. No current saturation was observed in the thermo-enhanced field emission measurements. The emission current density showed about ten-time enhancement (from 1.31 to 12.11 mA/cm 2 at 60.6 MV/m) by increasing the temperature from 323 to 623 K. The distinctive performance did not agree with the interband excitation mechanism but well-fit to the band-to-band tunneling model. The strong thermo-enhancement was proposed to be benefit from the increase of band-to-band tunneling probability at the surface portion of the p-Si/ZnO nanojunction. This work provides promising cathode for portable X-ray tubes/panel, ionization vacuum gauges and low energy electron beam lithography, in where electron-dose control at a fixed energy is needed.

Metal Photocathodes for Free Electron Laser Applications

NASA Astrophysics Data System (ADS)

Greaves, Corin Michael Ricardo

Synchrotron x-ray radiation sources have revolutionized many areas of science from elucidating the atomic structure of proteins to understanding the electronic structure of complex materials such as the cuprate superconductors. In a Free Electron Laser (FEL), the main difference to the synchrotron radiation mechanism is that the light field acts on the electron beam, over a long distance in an undulator, and causes electron bunching at the optical wavelength. Electrons in different parts of the electron bunch are therefore correlated, and so emit coherently, with a brightness that scales as the square of the number of electrons. In order to lase, the electron beam in a FEL must have a transverse geometric emittance less than the wavelength of the light to be produced. For the generation of x-ray wavelengths, this is one of the most difficult challenges in the design and construction of a FEL. The geometric emittance can be "compressed" by acceleration to very high energy, but with the penalty of very large physical size and very large cost. The motivation for this work was provided by the desire to investigate the fundamental origin of the emittance of an electron beam as it is born at a photocathode. If this initial, or "thermal" emittance can be reduced, the energy, scale and cost of accelerators potentially would be reduced. As the LCLS used copper as its photocathode, this material was the one studied in this work. Copper was used in the LCLS as it represented a "robust" material that could stand the very high accelerating gradients used in the photoinjector of the FEL. Metals are also prompt photoemitters, and so can be used to produce very short electron bunches. This can be a useful property for creation of extremely short FEL pulses, and also for creation of beams that are allowed to expand under space charge forces, but in a way that results in linear fields, allowing subsequent recompression. An ideal photocathode for FEL photoinjector should have high quantum efficiency (QE), small emittance, fast temporal response, long lifetime, and minimal complexity. High QE of cathodes require less power for driving laser and also reduce the risk of damaging the cathode materials. Small emittance reduce the scale of the accelerator, therefore, the cost. Metal photocathodes such as copper exhibit long lifetime and fast response, but have quite low quantum efficiency ( < 10-4). The aim in this work was to understand the quantum yield of the metal, and the transverse momentum spectrum, as the product of the latter and the cathode beam spot size gives the transverse emittance. Initial x-ray diffraction work provided evidence that the LCLS photocathode consisted of large low index single crystal grains, and so work focused on the study of single crystals that could be produced with atomically ordered surfaces, rather than a polycrystalline material. Present theories of quantum yield and transverse emittance assume the basic premise that the metal is entirely disordered, and work here shows that this is fundamentally incorrect, and that the order of the surface plays a critical role in determining the characteristics of emission. In order to investigate these surfaces, I constructed a laser-based ultra-low energy angle resolved photoemission system, capable of measuring the momentum spectrum of the emission and wavelength and angle dependent electron yield. This system has been commissioned, and data taken on low index surfaces of copper. Results from this work on single crystal copper demonstrates that emitted electrons from the band structure of a material can exhibit small emittance and high quantum efficiency. We show that the emission from the Cu(111) surface state is highly correlated between angle of incidence and excitation energy. This manifests itself in the form of a truncated emission cone, rather than the isotropic emission predicted from the normal model. This clearly then reduces the emittance from the normal values. It also results in extremely strong polarization dependence, with p-s asymmetry of up to 16 at low photon energy. It also directly suggests ways through changing materials, or by material design to significantly reduce emittance, at the same time increasing electron yield. These results show the benefits that could be gained from electronic engineering of cathodes and should have direct impact in the design of future FEL photoinjectors. (Abstract shortened by UMI.)

Bio-electrochemical synthesis of commodity chemicals by autotrophic acetogens utilizing CO2 for environmental remediation.

PubMed

Jabeen, Gugan; Farooq, Robina

2016-09-01

Bio-electrochemical synthesis (BES) is a technique in which electro-autotrophic bacteria such as Clostridium ljungdahlii utilize electric currents as an electron source from the cathode to reduce CO2 to extracellular, multicarbon, exquisite products through autotrophic conversion. The BES of volatile fatty acids and alcohols directly from CO2 is a sustainable alternative for non-renewable, petroleum-based polymer production. This conversion of CO2 implies reduction of greenhouse gas emissions. The synthesis of heptanoic acid, heptanol, hexanoic acid and hexanol, for the first time, by Clostridium ljungdahlii was a remarkable achievement of BES. In our study, these microorganisms were cultivated on the cathode of a bio-electrochemical cell at -400 mV by a DC power supply at 37 degree Centrigrade, pH 6.8, and was studied for both batch and continuous systems. Pre-enrichment of bio-cathode enhanced the electroactivity of cells and resulted in maximizing extracellular products in less time. The main aim of the research was to investigate the impact of low-cost substrate CO2, and the longer cathode recovery range was due to bacterial reduction of CO2 to multicarbon chemical commodities with electrons driven from the cathode. Reactor design was simplified for cost-effectiveness and to enhance energy efficiencies. The Columbic recovery of ethanoic acid, ethanol, ethyl butyrate, hexanoic acid, heptanoic acid and hexanol being in excess of 80 percent proved that BES was a remarkable technology.

Development of Thin Films as Potential Structural Cathodes to Enable Multifunctional Energy-Storage Structural Composite Batteries for the U.S. Army’s Future Force

DTIC Science & Technology

2011-09-01

glancing angle X - ray diffraction (GAXRD), atomic force microscopy (AFM), scanning electron microscopy (SEM), and electrochemical...Emission SEM FWHM full width at half maximum GAXRD glancing angle X - ray diffraction H3COCH2CH2OH 2-methoxyethanol LiMn2O4 lithium manganese oxide...were characterized by scanning electron microscopy (SEM), X - ray diffraction (XRD), and atomic force microscopy (AFM). In addition,

Field-Emission Staggered Structure Based on Diamond-Graphite Clusters

NASA Astrophysics Data System (ADS)

Davidovich, M. V.; Yafarov, R. K.

2018-02-01

We have proposed and designed a vacuum field-emission triode structure with high-resistivity semiconducting or insulating micrometer-size right parallelepipeds deposited in the staggered order on the conducting substrate (cathode), as well as a structure with a nanofilm on the cathode, which is formed by evaporated diamond-graphite clusters. It has been shown theoretically and experimentally that the emissivity of these structures is much higher than that of an uncoated cathode.

Modeling electron emission and surface effects from diamond cathodes

DOE PAGES

Dimitrov, D. A.; Smithe, D.; Cary, J. R.; ...

2015-02-05

We developed modeling capabilities, within the Vorpal particle-in-cell code, for three-dimensional (3D) simulations of surface effects and electron emission from semiconductor photocathodes. They include calculation of emission probabilities using general, piece-wise continuous, space-time dependent surface potentials, effective mass and band bending field effects. We applied these models, in combination with previously implemented capabilities for modeling charge generation and transport in diamond, to investigate the emission dependence on applied electric field in the range from approximately 2 MV/m to 17 MV/m along the [100] direction. The simulation results were compared to experimental data. For the considered parameter regime, conservation of transversemore » electron momentum (in the plane of the emission surface) allows direct emission from only two (parallel to [100]) of the six equivalent lowest conduction band valleys. When the electron affinity χ is the only parameter varied in the simulations, the value χ = 0.31 eV leads to overall qualitative agreement with the probability of emission deduced from experiments. Including band bending in the simulations improves the agreement with the experimental data, particularly at low applied fields, but not significantly. In this study, using surface potentials with different profiles further allows us to investigate the emission as a function of potential barrier height, width, and vacuum level position. However, adding surface patches with different levels of hydrogenation, modeled with position-dependent electron affinity, leads to the closest agreement with the experimental data.« less

Work function and surface stability of tungsten-based thermionic electron emission cathodes

NASA Astrophysics Data System (ADS)

Jacobs, Ryan; Morgan, Dane; Booske, John

2017-11-01

Materials that exhibit a low work function and therefore easily emit electrons into vacuum form the basis of electronic devices used in applications ranging from satellite communications to thermionic energy conversion. W-Ba-O is the canonical materials system that functions as the thermionic electron emitter commercially used in a range of high-power electron devices. However, the work functions, surface stability, and kinetic characteristics of a polycrystalline W emitter surface are still not well understood or characterized. In this study, we examined the work function and surface stability of the eight lowest index surfaces of the W-Ba-O system using density functional theory methods. We found that under the typical thermionic cathode operating conditions of high temperature and low oxygen partial pressure, the most stable surface adsorbates are Ba-O species with compositions in the range of Ba0.125O-Ba0.25O per surface W atom, with O passivating all dangling W bonds and Ba creating work function-lowering surface dipoles. Wulff construction analysis reveals that the presence of O and Ba significantly alters the surface energetics and changes the proportions of surface facets present under equilibrium conditions. Analysis of previously published data on W sintering kinetics suggests that fine W particles in the size range of 100-500 nm may be at or near equilibrium during cathode synthesis and thus may exhibit surface orientation fractions well described by the calculated Wulff construction.

Self-aligned gated field emission devices using single carbon nanofiber cathodes

NASA Astrophysics Data System (ADS)

Guillorn, M. A.; Melechko, A. V.; Merkulov, V. I.; Hensley, D. K.; Simpson, M. L.; Lowndes, D. H.

2002-11-01

We report on the fabrication and operation of integrated gated field emission devices using single vertically aligned carbon nanofiber (VACNF) cathodes where the gate aperture has been formed using a self-aligned technique based on chemical mechanical polishing. We find that this method for producing gated cathode devices easily achieves structures with gate apertures on the order of 2 mum that show good concentric alignment to the VACNF emitter. The operation of these devices was explored and field emission characteristics that fit well to the Fowler-Nordheim model of emission was demonstrated.

High power microwave generator

DOEpatents

Minich, Roger W.

1988-01-01

A device (10) for producing high-powered and coherent microwaves is described. The device comprises an evacuated, cylindrical, and hollow real cathode (20) that is driven to inwardly field emit relativistic electrons. The electrons pass through an internally disposed cylindrical and substantially electron-transparent cylindrical anode (24), proceed toward a cylindrical electron collector electrode (26), and form a cylindrical virtual cathode (32). Microwaves are produced by spatial and temporal oscillations of the cylindrical virtual cathode (32), and by electrons that reflex back and forth between the cylindrical virtual cathode (32) and the cylindrical real cathode (20).

Investigation on emission characteristics of metal-ceramic cathode applied to industrial X-ray diode.

PubMed

Xun, Ma; Jianqiang, Yuan; Hongwei, Liu; Hongtao, Li; Lingyun, Wang; Ping, Jiang

2016-06-01

The industrial x-ray diode with high impedance configuration is usually adopted to generate repetitive x-ray, but its performance would be worsened due to lower electric field on the cathode of diode when a voltage of several hundreds of kV is applied. To improve its performance, a novel metal-ceramic cathode is proposed in this paper. Key factors (width, relative permittivity of ceramic, and so on) affecting electric field distribution on triple points are analyzed by electrostatic field calculation program, so as to optimize the design of this novel cathode. Experiments are done to study the characteristics including emission current of cathode, diode voltage duration, diode mean dynamic impedance, and diode impedance drop velocity within diode power duration. The results show that metal-ceramic cathode could improve diode performance by enhancing emission current and stabling impedance; the impedance drop velocity of diode with spoke-shaped metal-ceramic cathode was reduced to -5 Ω ns(-1) within diode power duration, comparing to -15 Ω ns(-1) with metal foil cathode.

Radiation transport in kinetic simulations and the influence of photoemission on electron current in self-sustaining discharges

DOE PAGES

Fierro, Andrew S.; Moore, Christopher Hudson; Scheiner, Brett; ...

2017-01-12

A kinetic description for electronic excitation of helium for principal quantum number nmore » $$\\leqslant $$ 4 has been included into a particle-in-cell (PIC) simulation utilizing direct simulation Monte Carlo (DSMC) for electron-neutral interactions. The excited electronic levels radiate state-dependent photons with wavelengths from the extreme ultraviolet (EUV) to visible regimes. Photon wavelengths are chosen according to a Voigt distribution accounting for the natural, pressure, and Doppler broadened linewidths. This method allows for reconstruction of the emission spectrum for a non-thermalized electron energy distribution function (EEDF) and investigation of high energy photon effects on surfaces, specifically photoemission. A parallel plate discharge with a fixed field (i.e. space charge neglected) is used to investigate the effects of including photoemission for a Townsend discharge. When operating at a voltage near the self-sustaining discharge threshold, it is observed that the electron current into the anode is higher when including photoemission from the cathode than without even when accounting for self-absorption from ground state atoms. As a result, the photocurrent has been observed to account for as much as 20% of the total current from the cathode under steady-state conditions.« less

Initial Plasma Testing of the Ion Proportional Surface Emission Cathode

DTIC Science & Technology

2008-07-15

REPRINT 3. DATES COVERED (From - To) 4. TITLE AND SUBTITLE Initial Plasma Testing of the Ion Proportional Surface Emission Cathode 5a. CONTRACT NUMBER...substrate and an adjacent metal cathode element. The substrate potential is held positive of the cathode with gate elements. In plasma , the gate is...eliminated due to ambient ion flux which maintains the substrate potential near plasma ground. Prototype devices have been tested using a laboratory plasma

A vacuum sealed high emission current and transmission efficiency carbon nanotube triode

DOE Office of Scientific and Technical Information (OSTI.GOV)

Di, Yunsong; Jiangsu Key Laboratory of Optoelectronic Technology, Nanjing Normal University, Nanjing 210023; Wang, Qilong

A vacuum sealed carbon nanotubes (CNTs) triode with a concave and spoke-shaped Mo grid is presented. Due to the high aperture ratio of the grid, the emission current could be modulated at a relatively high electric field. Totally 75 mA emission current has been obtained from the CNTs cathode with the average applied field by the grid shifting from 8 to 13 V/μm. Whilst with the electron transmission efficiency of the grid over 56%, a remarkable high modulated current electron beam over 42 mA has been collected by the anode. Also contributed by the high aperture ration of the grid,more » desorbed gas molecules could flow away from the emission area rapidly when the triode has been operated at a relative high emission current, and finally collected by a vacion pump. The working pressure has been maintained at ∼1 × 10{sup −7} Torr, seldom spark phenomena occurred. Nearly perfect I-V curve and corresponding Fowler-Nordheim (FN) plot confirmed the accuracy of the measured data, and the emission current was long term stable and reproducible. Thusly, this kind of triode would be used as a high-power electron source.« less

Microwave generator

DOEpatents

Kwan, T.J.T.; Snell, C.M.

1987-03-31

A microwave generator is provided for generating microwaves substantially from virtual cathode oscillation. Electrons are emitted from a cathode and accelerated to an anode which is spaced apart from the cathode. The anode has an annular slit there through effective to form the virtual cathode. The anode is at least one range thickness relative to electrons reflecting from the virtual cathode. A magnet is provided to produce an optimum magnetic field having the field strength effective to form an annular beam from the emitted electrons in substantial alignment with the annular anode slit. The magnetic field, however, does permit the reflected electrons to axially diverge from the annular beam. The reflected electrons are absorbed by the anode in returning to the real cathode, such that substantially no reflexing electrons occur. The resulting microwaves are produced with a single dominant mode and are substantially monochromatic relative to conventional virtual cathode microwave generators. 6 figs.

Barium Depletion in Hollow Cathode Emitters

NASA Technical Reports Server (NTRS)

Polk, James E.; Capece, Angela M.; Mikellides, Ioannis G.; Katz, Ira

2009-01-01

The effect of tungsten erosion, transport and redeposition on the operation of dispenser hollow cathodes was investigated in detailed examinations of the discharge cathode inserts from an 8200 hour and a 30,352 hour ion engine wear test. Erosion and subsequent re-deposition of tungsten in the electron emission zone at the downstream end of the insert reduces the porosity of the tungsten matrix, preventing the ow of barium from the interior. This inhibits the interfacial reactions of the barium-calcium-aluminate impregnant with the tungsten in the pores. A numerical model of barium transport in the internal xenon discharge plasma shows that the barium required to reduce the work function in the emission zone can be supplied from upstream through the gas phase. Barium that flows out of the pores of the tungsten insert is rapidly ionized in the xenon discharge and pushed back to the emitter surface by the electric field and drag from the xenon ion flow. This barium ion flux is sufficient to maintain a barium surface coverage at the downstream end greater than 0.6, even if local barium production at that point is inhibited by tungsten deposits. The model also shows that the neutral barium pressure exceeds the equilibrium vapor pressure of the impregnant decomposition reaction over much of the insert length, so the reactions are suppressed. Only a small region upstream of the zone blocked by tungsten deposits is active and supplies the required barium. These results indicate that hollow cathode failure models based on barium depletion rates in vacuum dispenser cathodes are very conservative.

Bioelectrochemical approach for control of methane emission from wetlands.

PubMed

Liu, Shentan; Feng, Xiaojuan; Li, Xianning

2017-10-01

To harvest electricity and mitigate methane emissions from wetlands, a novel microbial fuel cell coupled constructed wetland (MFC-CW) was assembled with an anode placing in the rhizosphere and a cathode on the water surface. Plant-mediated methane accounted for 71-82% of the total methane fluxes. The bioanode served as an inexhaustible source of electron acceptors and resulted in reduced substantial methane emissions owing to electricigens outcompeting methanogens for carbon and electrons when substrate was deficient. However, when supplying sufficient organic carbon, both electricity and methane increased, indicating that electrogenesis and methanogenesis could co-exist in harmony. Direct methane emission (diffusion/ebullition) and plant-mediated methane emission were affected by operating conditions. Methanogenesis was significantly suppressed (∼98%) at HRT of 96h and with external resistance of 200Ω, accompanied with improved coulombic efficiency of 14.9% and current density of 187mA/m 2 . Contrarily, change of electrode polarity in the rhizosphere led to more methane efflux. Copyright © 2017 Elsevier Ltd. All rights reserved.

Design, Fabrication, and Characterization of Carbon Nanotube Field Emission Devices for Advanced Applications

NASA Astrophysics Data System (ADS)

Radauscher, Erich Justin

Carbon nanotubes (CNTs) have recently emerged as promising candidates for electron field emission (FE) cathodes in integrated FE devices. These nanostructured carbon materials possess exceptional properties and their synthesis can be thoroughly controlled. Their integration into advanced electronic devices, including not only FE cathodes, but sensors, energy storage devices, and circuit components, has seen rapid growth in recent years. The results of the studies presented here demonstrate that the CNT field emitter is an excellent candidate for next generation vacuum microelectronics and related electron emission devices in several advanced applications. The work presented in this study addresses determining factors that currently confine the performance and application of CNT-FE devices. Characterization studies and improvements to the FE properties of CNTs, along with Micro-Electro-Mechanical Systems (MEMS) design and fabrication, were utilized in achieving these goals. Important performance limiting parameters, including emitter lifetime and failure from poor substrate adhesion, are examined. The compatibility and integration of CNT emitters with the governing MEMS substrate (i.e., polycrystalline silicon), and its impact on these performance limiting parameters, are reported. CNT growth mechanisms and kinetics were investigated and compared to silicon (100) to improve the design of CNT emitter integrated MEMS based electronic devices, specifically in vacuum microelectronic device (VMD) applications. Improved growth allowed for design and development of novel cold-cathode FE devices utilizing CNT field emitters. A chemical ionization (CI) source based on a CNT-FE electron source was developed and evaluated in a commercial desktop mass spectrometer for explosives trace detection. This work demonstrated the first reported use of a CNT-based ion source capable of collecting CI mass spectra. The CNT-FE source demonstrated low power requirements, pulsing capabilities, and average lifetimes of over 320 hours when operated in constant emission mode under elevated pressures, without sacrificing performance. Additionally, a novel packaged ion source for miniature mass spectrometer applications using CNT emitters, a MEMS based Nier-type geometry, and a Low Temperature Cofired Ceramic (LTCC) 3D scaffold with integrated ion optics were developed and characterized. While previous research has shown other devices capable of collecting ion currents on chip, this LTCC packaged MEMS micro-ion source demonstrated improvements in energy and angular dispersion as well as the ability to direct the ions out of the packaged source and towards a mass analyzer. Simulations and experimental design, fabrication, and characterization were used to make these improvements. Finally, novel CNT-FE devices were developed to investigate their potential to perform as active circuit elements in VMD circuits. Difficulty integrating devices at micron-scales has hindered the use of vacuum electronic devices in integrated circuits, despite the unique advantages they offer in select applications. Using a combination of particle trajectory simulation and experimental characterization, device performance in an integrated platform was investigated. Solutions to the difficulties in operating multiple devices in close proximity and enhancing electron transmission (i.e., reducing grid loss) are explored in detail. A systematic and iterative process was used to develop isolation structures that reduced crosstalk between neighboring devices from 15% on average, to nearly zero. Innovative geometries and a new operational mode reduced grid loss by nearly threefold, thereby improving transmission of the emitted cathode current to the anode from 25% in initial designs to 70% on average. These performance enhancements are important enablers for larger scale integration and for the realization of complex vacuum microelectronic circuits.

Single-stage EHD thruster response to several simulation conditions in nitrogen gas

NASA Astrophysics Data System (ADS)

Granados, Victor H.; Pinheiro, Mario J.; Sá, Paulo A.

2017-09-01

We use a numerical model to investigate the influence of pressure from 0.5 Torr (66.7 Pa) to 100 Torr (13.3 kPa) and temperature (190-400 K) on the performance (thrust, fluid velocity, and thrust-to-power-ratio) of a single stage electrohydrodynamic thruster made of a rod anode and funnel-like cathode geometry, using nitrogen as the working gas. The model includes the following nitrogen species: N, N+, N2, N2+ , and N4+ . Additional factors are investigated: (i) the ballast resistance, (ii) the secondary electron emission from the cathode (in the range of 10-5 -10°), and (iii) the influence of the gap between electrodes on the discharge. As expected, higher pressures increase the net thrust, thrust efficiency, and peak gas velocity; however, with increasing temperatures, the trend reverses. We notice that gas flow velocity diminishes for the increasing values of the secondary emission coefficient, and it is possible to identify two working regimes presenting different behaviors: in the first region, for values of the secondary electron emission coefficient between 10-5 and 10-2 , thrust was not affected, and in the second region, between 10-2 and 1, a clear decrease in thrust is observed, accompanied by an increase in the discharge current, an undesired effect for the purpose of thrust production.

Large area directly heated lanthanum hexaboride cathode structure having predetermined emission profile

DOEpatents

Leung, Ka-Ngo; Gordon, K.C.; Kippenhan, D.O.; Purgalis, P.; Moussa, D.; Williams, M.D.; Wilde, S.B.; West, M.W.

1987-10-16

A large area directly heated lanthanum hexaboride (LaB/sub 6/) cathode system is disclosed. The system comprises a LaB/sub 6/ cathode element generally circular in shape about a central axis. The cathode element has a head with an upper substantially planar emission surface, and a lower downwardly and an intermediate body portion which diminishes in cross-section from the head towards the base of the cathode element. A central rod is connected to the base of the cathode element and extends along the central axis. Plural upstanding spring fingers are urged against an outer peripheral contact surface of the head end to provide a mechanical and electrical connection to the cathode element. 7 figs

Effect of lost charged particles on the breakdown characteristics of the gaseous electrical discharge in non-uniform axial electric field

NASA Astrophysics Data System (ADS)

Noori, H.; Ranjbar, A. H.

2017-10-01

The secondary emission coefficient is a valuable parameter for numerical modeling of the discharge process in gaseous insulation. A theoretical model has been developed to consider the effects of the radial electric field, non-uniformity of the axial electric field, and radial diffusion of charged particles on the secondary emission coefficient. In the model, a modified breakdown criterion is employed to determine the effective secondary electron emission, γeff. Using the geometry factor gi which is introduced based on the effect of radial diffusion of charged particles on the fraction of ions which arrive at the cathode, the geometry-independent term of γeff (Δi) was obtained as a function of the energy of the incident ions on the cathode. The results show that Δi is approximately a unique function of the ion energy for the ratios of d/R = 39, 50, 77, 115, and 200. It means that the considered mechanisms in the model are responsible for the deviation from Paschen's law.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Korolev, Yu. D.; Landl, N. V., E-mail: landl@lnp.hcei.tsc.ru; Geyman, V. G.

Results from studies of a low-current glow discharge with a hollow cathode are presented. A specific feature of the discharge conditions was that a highly emissive tablet containing cesium carbonate was placed in the cathode cavity. In the absence of a tablet, the discharge ignition voltage was typically ≥3.5 kV, while the burning voltage was in the range of 500–600 V. The use of the tablet made it possible to decrease the ignition voltage to 280 V and maintain the discharge burning voltage at a level of about 130 V. A model of the current sustainment in a hollow-cathode dischargemore » is proposed. Instead of the conventional secondary emission yield, the model uses a generalized emission yield that takes into account not only ion bombardment of the cathode, but also the emission current from an external source. The model is used to interpret the observed current−voltage characteristics. The results of calculations agree well with the experimental data. It is shown that, in some discharge modes, the external emission current from the cathode can reach 25% of the total discharge current.« less

Time evolution of nanosecond runaway discharges in air and helium at atmospheric pressure

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yatom, S.; Vekselman, V.; Krasik, Ya. E.

2012-12-15

Time- and space-resolved fast framing photography was employed to study the discharge initiated by runaway electrons in air and He gas at atmospheric pressure. Whereas in the both cases, the discharge occurs in a nanosecond time scale and its front propagates with a similar velocity along the cathode-anode gap, the later stages of the discharge differ significantly. In air, the main discharge channels develop and remain in the locations with the strongest field enhancement. In He gas, the first, diode 'gap bridging' stage, is similar to that obtained in air; however, the development of the discharge that follows is dictatedmore » by an explosive electron emission from micro-protrusions on the edge of the cathode. These results allow us to draw conclusions regarding the different conductivity of the plasma produced in He and air discharges.« less

Plasma mixing glow discharge device for analytical applications

DOEpatents

Pinnaduwage, Lal A.

1999-01-01

An instrument for analyzing a sample has an enclosure that forms a chamber containing an anode which divides the chamber into a discharge region and an analysis region. A gas inlet and outlet are provided to introduce and exhaust a rare gas into the discharge region. A cathode within the discharge region has a plurality of pins projecting in a geometric pattern toward the anode for exciting the gas and producing a plasma discharge between the cathode and the anode. Low energy electrons (e.g. <0.5 eV) pass into the analysis region through an aperture. The sample to be analyzed is placed into the analysis region and bombarded by the metastable rare gas atoms and the low energy electrons extracted into from the discharge region. A mass or optical spectrometer can be coupled to a port of the analysis region to analyze the resulting ions and light emission.

Plasma mixing glow discharge device for analytical applications

DOEpatents

Pinnaduwage, L.A.

1999-04-20

An instrument for analyzing a sample has an enclosure that forms a chamber containing an anode which divides the chamber into a discharge region and an analysis region. A gas inlet and outlet are provided to introduce and exhaust a rare gas into the discharge region. A cathode within the discharge region has a plurality of pins projecting in a geometric pattern toward the anode for exciting the gas and producing a plasma discharge between the cathode and the anode. Low energy electrons (e.g. <0.5 eV) pass into the analysis region through an aperture. The sample to be analyzed is placed into the analysis region and bombarded by the metastable rare gas atoms and the low energy electrons extracted into from the discharge region. A mass or optical spectrometer can be coupled to a port of the analysis region to analyze the resulting ions and light emission. 3 figs.

HIGH CURRENT COAXIAL PHOTOMULTIPLIER TUBE

DOEpatents

Glass, N.W.

1960-01-19

A medium-gain photomultiplier tube having high current output, fast rise- time, and matched output impedance was developed. The photomultiplier tube comprises an elongated cylindrical envelope, a cylindrical anode supported at the axis of the envelope, a plurality of elongated spaced opaque areas on the envelope, and a plurality of light admitting windows. A photo-cathode is supported adjacent to each of the windows, and a plurality of secondary emissive dynodes are arranged in two types of radial arrays which are alternately positioned to fill the annular space between the anode and the envelope. The dynodes are in an array being radially staggered with respect to the dynodes in the adjacent array, the dynodes each having a portion arranged at an angle with respect to the electron path, such that electrons emitted by each cathode undergo multiplication upon impingement on a dynode and redirected flight to the next adjacent dynode.

Process system and method for fabricating submicron field emission cathodes

DOEpatents

Jankowski, A.F.; Hayes, J.P.

1998-05-05

A process method and system for making field emission cathodes exists. The deposition source divergence is controlled to produce field emission cathodes with height-to-base aspect ratios that are uniform over large substrate surface areas while using very short source-to-substrate distances. The rate of hole closure is controlled from the cone source. The substrate surface is coated in well defined increments. The deposition source is apertured to coat pixel areas on the substrate. The entire substrate is coated using a manipulator to incrementally move the whole substrate surface past the deposition source. Either collimated sputtering or evaporative deposition sources can be used. The position of the aperture and its size and shape are used to control the field emission cathode size and shape. 3 figs.

Process system and method for fabricating submicron field emission cathodes

DOEpatents

Jankowski, Alan F.; Hayes, Jeffrey P.

1998-01-01

A process method and system for making field emission cathodes exists. The deposition source divergence is controlled to produce field emission cathodes with height-to-base aspect ratios that are uniform over large substrate surface areas while using very short source-to-substrate distances. The rate of hole closure is controlled from the cone source. The substrate surface is coated in well defined increments. The deposition source is apertured to coat pixel areas on the substrate. The entire substrate is coated using a manipulator to incrementally move the whole substrate surface past the deposition source. Either collimated sputtering or evaporative deposition sources can be used. The position of the aperture and its size and shape are used to control the field emission cathode size and shape.

Material and Energy Flows in the Materials Production, Assembly, and End-of-Life Stages of the Automotive Lithium-Ion Battery Life Cycle

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dunn, Jennifer B.; Gaines, Linda; Barnes, Matthew

2014-01-01

This document contains material and energy flows for lithium-ion batteries with an active cathode material of lithium manganese oxide (LiMn₂O₄). These data are incorporated into Argonne National Laboratory’s Greenhouse gases, Regulated Emissions, and Energy use in Transportation (GREET) model, replacing previous data for lithium-ion batteries that are based on a nickel/cobalt/manganese (Ni/Co/Mn) cathode chemistry. To identify and determine the mass of lithium-ion battery components, we modeled batteries with LiMn₂O₄ as the cathode material using Argonne’s Battery Performance and Cost (BatPaC) model for hybrid electric vehicles, plug-in hybrid electric vehicles, and electric vehicles. As input for GREET, we developed new ormore » updated data for the cathode material and the following materials that are included in its supply chain: soda ash, lime, petroleum-derived ethanol, lithium brine, and lithium carbonate. Also as input to GREET, we calculated new emission factors for equipment (kilns, dryers, and calciners) that were not previously included in the model and developed new material and energy flows for the battery electrolyte, binder, and binder solvent. Finally, we revised the data included in GREET for graphite (the anode active material), battery electronics, and battery assembly. For the first time, we incorporated energy and material flows for battery recycling into GREET, considering four battery recycling processes: pyrometallurgical, hydrometallurgical, intermediate physical, and direct physical. Opportunities for future research include considering alternative battery chemistries and battery packaging. As battery assembly and recycling technologies develop, staying up to date with them will be critical to understanding the energy, materials, and emissions burdens associated with batteries.« less

Pulsed electromagnetic gas accelleration. [incorporation of hollow cathode in plasma discharge and suitability determination of MPD discharge as plasmadynamic laser source

NASA Technical Reports Server (NTRS)

Jahn, R. G.

1973-01-01

Direct measurement with thermocouples of the power deposited in the anode of a multi-megawatt magnetoplasmadynamic discharge has shown the fractional anode power to decrease from 50% at 200 kW to 10% at 20 MW. Using local measurements of current density, electric potential, and electron temperature, the traditional model for heat conduction to the anode is found to be inadequate. Other experiments in which the voltage-current characteristics and exhaust velocities of MPD arcs using Plexiglas and boron nitride chamber insulators and various mass injection configurations show that ablation can affect nominal accelerator operation in several distinct ways. The incorporation of a hollow cathode in a 7 kA plasma discharge has shown that a stable current attachment can be realized in the cavity without the aid of cathode heaters, keeper electrodes, or emissive coatings.

Theory and simulation of electron beam dynamics in the AWE superswarf magnetically immersed diode

DOE Office of Scientific and Technical Information (OSTI.GOV)

Oliver, B.V.; Welch, D.R.; Olson, C.L.

1999-07-01

Results from numerical simulation and analytic theory of magnetically immersed diode behavior on the United Kingdom's Atomic Weapons Establishment (AWE) Superswarf accelerator are presented. The immersed diode consists of a cylindrical needle point cathode immersed in a strong {approximately}10--20 T solenoidal magnetic field. The anode-cathode (A-K) accelerating gap is held at vacuum and is {approximately}5--10 cm in length, with the anode/target located at the mid-plane of the solenoid. Typical accelerator parameters are 5--6 MeV and 40 kA. Ions emitted from the anode target stream toward the cathode and interact strongly with the electron beam. Collective oscillations between the beam electronsmore » and counter-streaming ions are driven unstable and results in a corkscrew rotation of the beam, yielding a time-integrated spot size substantially larger than that expected from single particle motion. This magnetized ion-hose instability is three dimensional. On the other hand, beam transverse temperature variations, although slightly enhanced in 3D, are primarily due to changes in the effective potential at the cathode (a combination of both the electrostatic and vector potential) and are manifest in 2D. Simulation studies examining spot and dose variation with varying cathode diameter and A-K gap distance are presented and confirm the above mentioned trends. Conclusions are that the diode current is determined by standard di-polar space-charge limited emissions, the minimum beam spot-size is limited by the ion-hose instability saturation amplitude, and the beam transverse temperature at the target is a function of the initial conditions on the cathode. Comparison to existing data will also be presented.« less

Structure and properties of ZrB2, ZrSiB and ZrAlSiB cathode materials and coatings obtained by their magnetron sputtering

NASA Astrophysics Data System (ADS)

Iatsyuk, I. V.; Lemesheva, M. V.; Kiryukhantsev-Korneev, Ph V.; Levashov, E. A.

2018-04-01

The ceramic ZrB2, ZrSiB, and ZrAlSiB cathodes were manufactured by means of self-propagating high-temperature synthesis (SHS). The parameters of SHS process including dependence of the combustion temperature and rate on the initial temperature of the reaction mixtures, as well as values of effective activation energy were estimated. Cathodes were subjected to the magnetron sputtering in the argon atmosphere. The structure and properties of cathodes and coatings were studied by means of X-ray diffraction, scanning electron microscopy, energy-dispersive and glow discharge optical emission spectroscopy. Bulk ceramic samples and coatings were characterised in terms of their hardness, elastic modulus, elastic recovery, density, and residual porosity. Results obtained shows that cathodes posses homogeneous structure with low porosity level in range 2-6% and hardness between 10 and 17 GPa. Coatings demonstrate dense defect-free structure and contain nanocrystallites of h-ZrB2 phase. The grain size and hardness decrease from 8 down to 2 nm and from 37 down to 16 GPa with the addition of the silicon and aluminum dopes.

On the coupling of hydride generation with atmospheric pressure glow discharge in contact with the flowing liquid cathode for the determination of arsenic, antimony and selenium with optical emission spectrometry.

PubMed

Greda, Krzysztof; Jamroz, Piotr; Jedryczko, Dominika; Pohl, Pawel

2015-05-01

The miniaturized atmospheric pressure glow discharge (APGD) sustained between a liquid flowing cathode and a He nozzle jet anode was combined with hydride generation (HG) to improve the performance of the determination of As, Sb and Se with optical emission spectrometry (OES). As(III), Sb(III) and Se(IV) species were converted into volatile hydrides in the reaction with NaBH4 and right after that they were delivered to the near-anode region of APGD through the nozzle. The transport efficiency of As, Sb and Se to the discharge was several times higher, while intensities of atomic emission lines of As, Sb and Se were improved 3 orders of magnitude (as compared to intensities acquired for the near-cathode region in a APGD system with a typical introduction of analytes through sputtering of the flowing liquid cathode). The effect of the concentration of NaBH4 and HCl in a sample solution, the discharge current, the flow rate of He carrier/jet-supporting and He shielding gases on the emission yield coming from As, Sb, Se, He and H atomic lines and OH and N2 band heads as well as the electron number density was thoroughly studied. Under compromised conditions, limits of detection (3σ criterion) of As, Sb and Se were respectively 4.2, 1.2 and 3.1 µg L(-1). Usefulness of the method was confirmed by the analysis of Sniadecki and Marchlewski highly mineralized spring waters (Kudowa Zdroj, Poland) on the content of As, Sb and Se. Recoveries of elements added to these spring waters were within 90.3-103.7% proving good accuracy of the HG-APGD-OES method. Copyright © 2015 Elsevier B.V. All rights reserved.

Technology of fast spark gaps

NASA Astrophysics Data System (ADS)

Standler, Ronald B.

1989-09-01

To protect electronic systems from the effects of electromagnetic pulse (EMP) form nuclear weapons and high-power microwave (HPM) weapons, it is desirable to have fast responding protection components. The gas-filled spark gap appears to be an attractive protection component, except that it can be slow to conduct under certain conditions. This report reviews the literature and presents ideas for construction of a spark gap that will conduct in less than one nanosecond. The key concept to making a fast-responding spark gap is to produce a large number of free electrons quickly. Seven different mechanisms for production of free electrons are reviewed, and several that are relevant to miniature spark gaps for protective applications are discussed in detail. These mechanisms include: inclusion of radioactive materials, photoelectric effect, secondary electrode emission from the anode, and field emission from the cathode.

Enhanced flashover strength in polyethylene nanodielectrics by secondary electron emission modification

NASA Astrophysics Data System (ADS)

Wang, Weiwang; Li, Shengtao; Min, Daomin

2016-04-01

This work studies the correlation between secondary electron emission (SEE) characteristics and impulse surface flashover in polyethylene nanodielectrics both theoretically and experimentally, and illustrates the enhancement of flashover voltage in low-density polyethylene (LDPE) through incorporating Al2O3 nanoparticles. SEE characteristics play key roles in surface charging and gas desorption during surface flashover. This work demonstrates that the presence of Al2O3 nanoparticles decreases the SEE coefficient of LDPE and enhances the impact energy at the equilibrium state of surface charging. These changes can be explained by the increase of surface roughness and of surface ionization energy, and the strong interaction between nanoparticles and the polymer dielectric matrix. The surface charge and flashover voltage are calculated according to the secondary electron emission avalanche (SEEA) model, which reveals that the positive surface charges are reduced near the cathode triple point, while the presence of more nanoparticles in high loading samples enhances the gas desorption. Consequently, the surface flashover performance of LDPE/Al2O3 nanodielectrics is improved.

Direct Synthesis of Carbon Nanotube Field Emitters on Metal Substrate for Open-Type X-ray Source in Medical Imaging.

PubMed

Gupta, Amar Prasad; Park, Sangjun; Yeo, Seung Jun; Jung, Jaeik; Cho, Chonggil; Paik, Sang Hyun; Park, Hunkuk; Cho, Young Chul; Kim, Seung Hoon; Shin, Ji Hoon; Ahn, Jeung Sun; Ryu, Jehwang

2017-07-29

We report the design, fabrication and characterization of a carbon nanotube enabled open-type X-ray system for medical imaging. We directly grew the carbon nanotubes used as electron emitter for electron gun on a non-polished raw metallic rectangular-rounded substrate with an area of 0.1377 cm² through a plasma enhanced chemical vapor deposition system. The stable field emission properties with triode electrodes after electrical aging treatment showed an anode emission current of 0.63 mA at a gate field of 7.51 V/μm. The 4.5-inch cubic shape open type X-ray system was developed consisting of an X-ray aperture, a vacuum part, an anode high voltage part, and a field emission electron gun including three electrodes with focusing, gate and cathode electrodes. Using this system, we obtained high-resolution X-ray images accelerated at 42-70 kV voltage by digital switching control between emitter and ground electrode.

Direct Synthesis of Carbon Nanotube Field Emitters on Metal Substrate for Open-Type X-ray Source in Medical Imaging

PubMed Central

Gupta, Amar Prasad; Park, Sangjun; Yeo, Seung Jun; Jung, Jaeik; Cho, Chonggil; Paik, Sang Hyun; Park, Hunkuk; Cho, Young Chul; Kim, Seung Hoon; Shin, Ji Hoon; Ahn, Jeung Sun; Ryu, Jehwang

2017-01-01

We report the design, fabrication and characterization of a carbon nanotube enabled open-type X-ray system for medical imaging. We directly grew the carbon nanotubes used as electron emitter for electron gun on a non-polished raw metallic rectangular-rounded substrate with an area of 0.1377 cm2 through a plasma enhanced chemical vapor deposition system. The stable field emission properties with triode electrodes after electrical aging treatment showed an anode emission current of 0.63 mA at a gate field of 7.51 V/μm. The 4.5-inch cubic shape open type X-ray system was developed consisting of an X-ray aperture, a vacuum part, an anode high voltage part, and a field emission electron gun including three electrodes with focusing, gate and cathode electrodes. Using this system, we obtained high-resolution X-ray images accelerated at 42–70 kV voltage by digital switching control between emitter and ground electrode. PMID:28773237

Influence of quantum effects on the parameters of a cold cathode with carbon nanotubes

NASA Astrophysics Data System (ADS)

Glukhova, O. E.; Kolesnikova, A. S.; Slepchenkov, M. M.

2016-01-01

We consider the effect of an external electric field on the parameters of a cold cathode on carbon nanotubes using the quantum-mechanical approach to the description of the interaction of the field with the atomic structure of nanoemitters. It is established for the first time that an increase in the length of the emitting edge of the tube in a field of 10-11 V/nm increases the field emission current of electrons by 3-10%. It is found that in a field of 11 V/nm and higher, atoms of the upper edge of a carbon nanotube are detached with the subsequent destruction of the atomic core.

Improved field emission properties of carbon nanotubes grown on stainless steel substrate and its application in ionization gauge

NASA Astrophysics Data System (ADS)

Li, Detian; Cheng, Yongjun; Wang, Yongjun; Zhang, Huzhong; Dong, Changkun; Li, Da

2016-03-01

Vertically aligned carbon nanotube (CNT) arrays were fabricated by chemical vapor deposition (CVD) technique on different substrates. Microstructures and field emission characteristics of the as-grown CNT arrays were investigated systematically, and its application in ionization gauge was also evaluated preliminarily. The results indicate that the as-grown CNT arrays are vertically well-aligned relating to the substrate surfaces, but the CNTs grown on stainless steel substrate are longer and more crystalline than the ones grown on silicon wafer substrate. The field emission behaviors of the as-grown CNT arrays are strongly dependent upon substrate properties. Namely, the CNT array grown on stainless steel substrate has better field emission properties, including lower turn on and threshold fields, better emission stability and repeatability, compared with the one grown on silicon wafer substrate. The superior field emission properties of the CNT array grown on stainless steel substrate are mainly attributed to low contact resistance, high thermal conductivity, good adhesion strength, etc. In addition, the metrological behaviors of ionization gauge with the CNT array grown on stainless steel substrate as an electron source were investigated, and this novel cathode ionization gauge extends the lower limit of linear pressure measurement to 10-8 Pa, which is one order of magnitude lower than the result reported for the same of gauge with CNT cathode.

Note: design and development of improved indirectly heated cathode based strip electron gun.

PubMed

Maiti, Namita; Bade, Abhijeet; Tembhare, G U; Patil, D S; Dasgupta, K

2015-02-01

An improved design of indirectly heated solid cathode based electron gun (200 kW, 45 kV, 270° bent strip type electron gun) has been presented. The solid cathode is made of thoriated tungsten, which acts as an improved source of electron at lower temperature. So, high power operation is possible without affecting structural integrity of the electron gun. The design issues are addressed based on the uniformity of temperature on the solid cathode and the single long filament based design. The design approach consists of simulation followed by extensive experimentation. In the design, the effort has been put to tailor the non-uniformity of the heat flux from the filament to the solid cathode to obtain better uniformity of temperature on the solid cathode. Trial beam experiments have been carried out and it is seen that the modified design achieves one to one correspondence of the solid cathode length and the electron beam length.

Note: Design and development of improved indirectly heated cathode based strip electron gun

DOE Office of Scientific and Technical Information (OSTI.GOV)

Maiti, Namita; Patil, D. S.; Dasgupta, K.

An improved design of indirectly heated solid cathode based electron gun (200 kW, 45 kV, 270° bent strip type electron gun) has been presented. The solid cathode is made of thoriated tungsten, which acts as an improved source of electron at lower temperature. So, high power operation is possible without affecting structural integrity of the electron gun. The design issues are addressed based on the uniformity of temperature on the solid cathode and the single long filament based design. The design approach consists of simulation followed by extensive experimentation. In the design, the effort has been put to tailor themore » non-uniformity of the heat flux from the filament to the solid cathode to obtain better uniformity of temperature on the solid cathode. Trial beam experiments have been carried out and it is seen that the modified design achieves one to one correspondence of the solid cathode length and the electron beam length.« less

Large area directly heated lanthanum hexaboride cathode structure having predetermined emission profile

DOEpatents

Leung, Ka-Ngo; Gordon, Keith C.; Kippenham, Dean O.; Purgalis, Peter; Moussa, David; Williams, Malcom D.; Wilde, Stephen B.; West, Mark W.

1989-01-01

A large area directly heated lanthanum hexaboride (LaB.sub.6) cathode system (10) is disclosed. The system comprises a LaB.sub.6 cathode element (11) generally circular in shape about a central axis. The cathode element (11) has a head (21) with an upper substantially planar emission surface (23), and a lower downwardly and an intermediate body portion (26) which diminishes in cross-section from the head (21) towards the base (22) of the cathode element (11). A central rod (14) is connected to the base (22) of the cathode element (11) and extends along the central axis. Plural upstanding spring fingers (37) are urged against an outer peripheral contact surface (24) of the head end (21) to provide a mechanical and electrical connection to the cathode element (11).

Organic light emitting device architecture for reducing the number of organic materials

DOEpatents

D'Andrade, Brian [Westampton, NJ; Esler, James [Levittown, PA

2011-10-18

An organic light emitting device is provided. The device includes an anode and a cathode. A first emissive layer is disposed between the anode and the cathode. The first emissive layer includes a first non-emitting organic material, which is an organometallic material present in the first emissive layer in a concentration of at least 50 wt %. The first emissive layer also includes a first emitting organic material. A second emissive layer is disposed between the first emissive layer and the cathode, preferably, in direct contact with the first emissive layer. The second emissive material includes a second non-emitting organic material and a second emitting organic material. The first and second non-emitting materials, and the first and second emitting materials, are all different materials. A first non-emissive layer is disposed between the first emissive layer and the anode, and in direct contact with the first emissive layer. The first non- emissive layer comprises the first non-emissive organic material.

Optimization of cathodic arc deposition and pulsed plasma melting techniques for growing smooth superconducting Pb photoemissive films for SRF injectors

NASA Astrophysics Data System (ADS)

Nietubyć, Robert; Lorkiewicz, Jerzy; Sekutowicz, Jacek; Smedley, John; Kosińska, Anna

2018-05-01

Superconducting photoinjectors have a potential to be the optimal solution for moderate and high current cw operating free electron lasers. For this application, a superconducting lead (Pb) cathode has been proposed to simplify the cathode integration into a 1.3 GHz, TESLA-type, 1.6-cell long purely superconducting gun cavity. In the proposed design, a lead film several micrometres thick is deposited onto a niobium plug attached to the cavity back wall. Traditional lead deposition techniques usually produce very non-uniform emission surfaces and often result in a poor adhesion of the layer. A pulsed plasma melting procedure reducing the non-uniformity of the lead photocathodes is presented. In order to determine the parameters optimal for this procedure, heat transfer from plasma to the film was first modelled to evaluate melting front penetration range and liquid state duration. The obtained results were verified by surface inspection of witness samples. The optimal procedure was used to prepare a photocathode plug, which was then tested in an electron gun. The quantum efficiency and the value of cavity quality factor have been found to satisfy the requirements for an injector of the European-XFEL facility.

Effect of MWCNT on prepared cathode material (Li2Mn(x)Fe(1-x)SiO4) for energy storage applications

NASA Astrophysics Data System (ADS)

Agnihotri, Shruti; Rattan, Sangeeta; Sharma, A. L.

2016-05-01

The electrode material Li2MnFeSiO4 was successfully synthesized by standard sol-gel method and further modified with multiwalled carbon nano tube (MWCNT) to achieve better electrochemical properties. Our strategy helps us to improve the performance and storage capacity as compared with the bared material. This novel composite structure constructs an efficient cation (Li+) and electron channel which significantly enhance the Li+ ion diffusion coefficient and reduced charge transfer resistance. Hence leads to high conductivity and specific capacity. Characterization technique like Field emission scanning electron microscopy (FESEM) has been used to confirm its morphology, structure and particle size which comes out to be of the order of ˜20 to 30 nm. Lesser particle size reveals better electrochemical properties. Electrical conductivity (˜10-5 Scm-1) of MWCNT doped oxide cathode materials was recorded using ac impedance spectroscopy technique which reflects tenfold increment when compared with pure oxide cathode materials. Cyclic voltametery analysis has been done to calculate specific capacity and potential window of materials with and without CNTs. The results obtained from different techniques are well correlated and suitable for energy storage applications.

Design of a LaB 6 gun using EGN2 and INTMAG

NASA Astrophysics Data System (ADS)

Becker, R.; Herrmannsfeldt, W. B.

1990-12-01

In order to launch a high-density electron beam to be focused in the 5 T superconducting solenoid of the Frankfurt EBIS [R. Becker et al., Nucl. Instr. and Meth. B24 (1987) 838], an electron gun has been designed, with a 0.5 mm diameter LaB 6 cathode (FEI Comp., Beaverton, USA) in a 70 mm diameter electrode geometry. The emitting surface is placed in the axial fringing field of the solenoid, modified by an axial shielding disk and a bucking coil, to provide either immersed flow or Brillouin flow conditions for the focused beam. Since the cathode diameter is small as compared to the electrodes, a new feature of EGN2 [W.B. Herrmannsfeldt, SLAC-331 (1988)] had to be used in order to have a sufficient number of meshes along the emitting surface. By starting a field line in the large geometry, a curved Neumann boundary is found for a subdivided part of the gun, which represents the influence of the larger part. EGN2 writes the coordinates of this field line on a file, which can be used by POLYGON [R. Becker, Nucl. Instr. and Meth. B42 (1989) 162] (a boundary setup program for EGN2) to define a curved Neumann boundary. By this procedure, it becomes possible to get a reliable simulation of the emission properties of a small cathode in large gun electrodes. The magnetostatic field calculations have been performed with INTMAG [R. Becker, Nucl. Instr. and Meth. B42 (1989) 303], which is a new program of the boundary element method type. Due to the integration calculus, the results do not need smoothing or "Maxwellisation" for the use in EGN2, where the off-axis fields are evaluated by radial expansion. INTMAG provides an output file, which is suitably formatted to be read in by EGN2. The gun design is based on space-charge-limited emission, but no Pierce-type electrode has been provided in the vicinity of the cathode; instead a Wehnelt electrode on negative bias with respect to the cathode is used to create the correct Pierce-type equipotential in free space, ending on the cathode edge with the correct angle. This gives an additional adjustment tool, if the axial position of the gun is not perfect and it relaxes the radial tolerance requirements considerably.

Photoemission experiments of a large area scandate dispenser cathode

NASA Astrophysics Data System (ADS)

Zhang, Huang; Liu, Xing-guang; Chen, Yi; Chen, De-biao; Jiang, Xiao-guo; Yang, An-min; Xia, Lian-sheng; Zhang, Kai-zhi; Shi, Jin-shui; Zhang, Lin-wen

2010-09-01

A 100-mm-diameter scandate dispenser cathode was tested as a photocathode with a 10 ns Nd:YAG laser (266 nm) on an injector test stand for linear induction accelerators. This thermionic dispenser cathode worked at temperatures ranging from room temperature to 930 °C (below or near the thermionic emission threshold) while the vacuum was better than 4×10 -7 Torr. The laser pulse was synchronized with a 120 ns diode voltage pulse stably and they were in single pulse mode. Emission currents were measured by a Faraday cup. The maximum peak current collected at the anode was about 100 A. The maximum quantum efficiency measured at low laser power was 2.4×10 -4. Poisoning effect due to residual gas was obvious and uninterrupted heating was needed to keep cathode's emission capability. The cathode was exposed to air one time between experiments and recovered after being reconditioned. Photoemission uniformity of the cathode was also explored by changing the laser spot's position.

Space charge effects on the current-voltage characteristics of gated field emitter arrays

NASA Astrophysics Data System (ADS)

Jensen, K. L.; Kodis, M. A.; Murphy, R. A.; Zaidman, E. G.

1997-07-01

Microfabricated field emitter arrays (FEAs) can provide the very high electron current densities required for rf amplifier applications, typically on the order of 100 A/cm2. Determining the dependence of emission current on gate voltage is important for the prediction of emitter performance for device applications. Field emitters use high applied fields to extract current, and therefore, unlike thermionic emitters, the current densities can exceed 103A/cm2 when averaged over an array. At such high current densities, space charge effects (i.e., the influence of charge between cathode and collector on emission) affect the emission process or initiate conditions which can lead to failure mechanisms for field emitters. A simple model of a field emitter will be used to calculate the one-dimensional space charge effects on the emission characteristics by examining two components: charge between the gate and anode, which leads to Child's law, and charge within the FEA unit cell, which gives rise to a field suppression effect which can exist for a single field emitter. The predictions of the analytical model are compared with recent experimental measurements designed to assess space charge effects and predict the onset of gate current. It is shown that negative convexity on a Fowler-Nordheim plot of Ianode(Vgate) data can be explained in terms of field depression at the emitter tip in addition to reflection of electrons by a virtual cathode created when the anode field is insufficient to extract all of the current; in particular, the effects present within the unit cell constitute a newly described effect.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Qin, Fen; Key Laboratory on High Power Microwave Technology, Institute of Applied Electronics, China Academy of Engineering Physics, Mianyang 621900; Wang, Dong, E-mail: mr20001@sina.com

We present the repetitive operation research results of an L-band magnetically insulated transmission line oscillator with metal array cathode (MAC-MILO) in this paper. To ensure a more uniform emission of electrons emitted from the cathode, metal plates with different outer radii and thicknesses are periodically arranged in longitudinal direction on the cathode substrate to act as emitters. The higher order mode depressed MILO (HDMILO) structure is applied to ensure stability of the tube. Comparison experiments are carried out between velvet cathode and MAC MILO driven by a 20 GW/40 Ω/40 ns/20 Hz pulse power system. Experimental results reveal that themore » MAC has much lower outgassing rate, much longer life time, and higher repetitive stability. The MAC-MILO could work stably with a rep-rate up to 20 Hz at a power level of 550 MW when employing a 350 kV/35 kA electric pulse. The TE{sub 11} mode radiation pattern in the farfield region reveals the tube works steadily on the dominant mode. More than 2000 shots have been tested in repetitive mode without any obvious degradation of the detected microwave parameters.« less

An electromagnetic/electrostatic dual cathode system for electron beam instruments

NASA Technical Reports Server (NTRS)

Bradley, J. G.; Conley, J. M.; Wittry, D. B.; Albee, A. L.

1986-01-01

A method of providing cathode redundancy which consists of two fixed cathodes and uses electromagnetic and/or electrostatic fields to direct the electron beam to the electron optical axis is presented, with application to the cathode system of the Scanning Electron Microscope and Particle Analyzer proposed for NASA's Mariner Mark II Comet Rendezvous/Asteroid Flyby projected for the 1990s. The symmetric double deflection system chosen has the optical property that the image of the effective electron source is formed above the magnet assembly near the apparent position of the effective source, and it makes the transverse positions of the electron sources independent of the electron beam energy. Good performance of the system is found, with the sample imaging resolution being the same as for the single-axis cathode.

Energy-filtered real- and k-space secondary and energy-loss electron imaging with Dual Emission Electron spectro-Microscope: Cs/Mo(110).

PubMed

Grzelakowski, Krzysztof P

2016-05-01

Since its introduction the importance of complementary k||-space (LEED) and real space (LEEM) information in the investigation of surface science phenomena has been widely demonstrated over the last five decades. In this paper we report the application of a novel kind of electron spectromicroscope Dual Emission Electron spectroMicroscope (DEEM) with two independent electron optical channels for reciprocal and real space quasi-simultaneous imaging in investigation of a Cs covered Mo(110) single crystal by using the 800eV electron beam from an "in-lens" electron gun system developed for the sample illumination. With the DEEM spectromicroscope it is possible to observe dynamic, irreversible processes at surfaces in the energy-filtered real space and in the corresponding energy-filtered kǁ-space quasi-simultaneously in two independent imaging columns. The novel concept of the high energy electron beam sample illumination in the cathode lens based microscopes allows chemically selective imaging and analysis under laboratory conditions. Copyright © 2015 Elsevier B.V. All rights reserved.

Influence of surface emission processes on a fast-pulsed dielectric barrier discharge in air at atmospheric pressure

NASA Astrophysics Data System (ADS)

Pechereau, François; Bonaventura, Zdeněk; Bourdon, Anne

2016-08-01

This paper presents simulations of an atmospheric pressure air discharge in a point-to-plane geometry with a dielectric layer parallel to the cathode plane. Experimentally, a discharge reignition in the air gap below the dielectrics has been observed. With a 2D fluid model, it is shown that due to the fast rise of the high voltage applied and the sharp point used, a first positive spherical discharge forms around the point. Then this discharge propagates axially and impacts the dielectrics. As the first discharge starts spreading on the upper dielectric surface, in the second air gap with a low preionization density of {{10}4}~\\text{c}{{\\text{m}}-3} , the 2D fluid model predicts a rapid reignition of a positive discharge. As in experiments, the discharge reignition is much slower, a discussion on physical processes to be considered in the model to increase the reignition delay is presented. The limit case with no initial seed charges in the second air gap has been studied. First, we have calculated the time to release an electron from the cathode surface by thermionic and field emission processes for a work function φ \\in ≤ft[3,4\\right] eV and an amplification factor β \\in ≤ft[100,220\\right] . Then a 3D Monte Carlo model has been used to follow the dynamics of formation of an avalanche starting from a single electron emitted at the cathode. Due to the high electric field in the second air gap, we have shown that in a few nanoseconds, a Gaussian cloud of seed charges is formed at a small distance from the cathode plane. This Gaussian cloud has been used as the initial condition of the 2D fluid model in the second air gap. In this case, the propagation of a double headed discharge in the second air gap has been observed and the reignition delay is in rather good agreement with experiments.

Energy-Sensitive Ion- and Cathode-Luminescent Radiation-Beam Monitors Based on Multilayer Thin-Film Designs.

PubMed

Gil-Rostra, Jorge; Ferrer, Francisco J; Espinós, Juan Pedro; González-Elipe, Agustín R; Yubero, Francisco

2017-05-17

A multilayer luminescent design concept is presented to develop energy-sensitive radiation-beam monitors on the basis of colorimetric analysis. Each luminescent layer within the stack consists of rare-earth-doped transparent oxides of optical quality and a characteristic luminescent emission under excitation with electron or ion beams. For a given type of particle beam (electron, protons, α particles, etc.), its penetration depth and therefore its energy loss at a particular buried layer within the multilayer stack depend on the energy of the initial beam. The intensity of the luminescent response of each layer is proportional to the energy deposited by the radiation beam within the layer, so characteristic color emission will be achieved if different phosphors are considered in the layers of the luminescent stack. Phosphor doping, emission efficiency, layer thickness, and multilayer structure design are key parameters relevant to achieving a broad colorimetric response. Two case examples are designed and fabricated to illustrate the capabilities of these new types of detector to evaluate the kinetic energy of either electron beams of a few kilo-electron volts or α particles of a few mega-electron volts.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shao, Jiahang; Antipov, Sergey P.; Baryshev, Sergey V.

Field emission from a solid metal surface has been continuously studied for a century over macroscopic to atomic scales. It is general knowledge that, other than the surface properties, the emitted current is governed solely by the applied electric field. A pin cathode has been used to study the dependence of field emission on stored energy in an L-band rf gun. The stored energy was changed by adjusting the axial position (distance between the cathode base and the gun back surface) of the cathode while the applied electric field on the cathode tip is kept constant. Avery strong correlation ofmore » the field-emission current with the stored energy has been observed. While eliminating all possible interfering sources, an enhancement of the current by a factor of 5 was obtained as the stored energy was increased by a factor of 3. It implies that under certain circumstances a localized field emission may be significantly altered by the global parameters in a system.« less

Cathode fall model and current-voltage characteristics of field emission driven direct current microplasmas

DOE Office of Scientific and Technical Information (OSTI.GOV)

Venkattraman, Ayyaswamy

2013-11-15

The post-breakdown characteristics of field emission driven microplasma are studied theoretically and numerically. A cathode fall model assuming a linearly varying electric field is used to obtain equations governing the operation of steady state field emission driven microplasmas. The results obtained from the model by solving these equations are compared with particle-in-cell with Monte Carlo collisions simulation results for parameters including the plasma potential, cathode fall thickness, ion number density in the cathode fall, and current density vs voltage curves. The model shows good overall agreement with the simulations but results in slightly overpredicted values for the plasma potential andmore » the cathode fall thickness attributed to the assumed electric field profile. The current density vs voltage curves obtained show an arc region characterized by negative slope as well as an abnormal glow discharge characterized by a positive slope in gaps as small as 10 μm operating at atmospheric pressure. The model also retrieves the traditional macroscale current vs voltage theory in the absence of field emission.« less

Tunable blue organic light emitting diode based on aluminum calixarene supramolecular complex

NASA Astrophysics Data System (ADS)

Legnani, C.; Reyes, R.; Cremona, M.; Bagatin, I. A.; Toma, H. E.

2004-07-01

In this letter, the results of supramolecular organic light emitting diodes using a calix[4] arene complex thin film as emitter and electron transporting layer are presented. The devices were grown onto glass substrates coated with indium-tin-oxide layer and aluminum thick (150nm) cathode. By applying a dc voltage between the device electrodes in forward bias condition, a blue light emission in the active area of the device was observed. It was found that the electroluminescent emission peak can be tuned between 470 and 510nm changing the applied voltage bias from 4.3 to 5.4V. The observed tunable emission can be associated with an energy transfer from the calixarene compound.

Electron collection enhancement arising from neutral gas jets on a charged vehicle in the ionosphere

NASA Technical Reports Server (NTRS)

Gilchrist, Brian E.; Banks, Peter M.; Neubert, Torsten; Williamson, P. Roger; Myers, Neil B.

1990-01-01

Observations of current collection enhancements due to cold nitrogen gas control jet emissions from a highly charged, isolated rocket payload in the ionosphere have been made during the cooperative high altitude rocket gun experiment (CHARGE) 2 using an electrically tethered mother/daughter payload system. The current collection enhancement was observed on a platform (daughter payload) located 100 to 400 m away from the main payload firing an energetic electron beam (mother payload). These results are interpreted in terms of an electrical discharge forming in close proximity to the daughter vehicle during the short periods of gas emission. The results indicate that it is possible to enhance the electron current collection capability of positively charged vehicles by means of deliberate neutral gas releases into an otherwise undisturbed space plasma. The results are also compared with recent laboratory observations of hollow cathode plasma contactors operating in the 'ignited' mode.

Electron Density and Two-Channel Neutron Emission Measurements in Steady-State Spherical Inertial-Electrostatically Confined Plasmas, with Review of the 1-D Kinetic Model

NASA Technical Reports Server (NTRS)

Dobson, Chris C.; Hrbud, Ivana

2004-01-01

Electron density measurements have been made in steady-state plasmas in a spherical inertial electrostatic confinement (IEC) discharge using microwave interferometry. Plasma cores interior to two cathodes, having diameters of 15 and 23 cm, respectively, were probed over a transverse range of 10 cm with a spatial resolution of about 1.4 cm for buffer gas pressures from 0.2 to 6 Pa in argon and deuterium. The transverse profiles are generally flat, in some cases with eccentric symmetric minima, and give mean densities of from approx. = 0.4 to 7x 10(exp 10)/cu cm, the density generally increasing with the neutral gas pressure. Numerical solutions of the 1-D Poisson equation for EC plasmas are reviewed and energy distribution functions are identified which give flat transverse profiles. These functions are used with the plasma approximation to obtain solutions which also give densities consistent with the measurements, and a double potential well solution is obtained which has minima qualitatively similar to those observed. Explicit consideration is given to the compatibility of the solutions interior and exterior to the cathode, and to grid transparency. Deuterium fusion neutron emission rates were also measured and found to be isotropic, to within the measurement error, over two simultaneous directions. Anisotropy was observed in residual emissions during operation with non-fusing hydrogen-1. The deuterium rates are consistent with predictions from the model.

Miniature Reservoir Cathode: An Update

NASA Technical Reports Server (NTRS)

Vancil, Bernard K.; Wintucky, Edwin G.

2002-01-01

We report on recent work to produce a small low power, low cost reservoir cathode capable of long life (more than 100,000 hours) at high loading (> 5 A/sq cm). Our objective is a highly manufacturable, commercial device costing less than $30. Small highly loaded cathodes are needed, especially for millimeter wave tubes, where focusing becomes difficult when area convergence ratios are too high. We currently have 3 models ranging from .060-inch diameter to. 125-inch diameter. Reservoir type barium dispenser cathodes have a demonstrated capability for simultaneous high emission density and long life. Seven reservoir cathodes continue to operate on the cathode life test facility at NSWC, Crane, Indiana at 2 and 4 amps/sq cm. They have accumulated nearly 100,000 hours with practically no change in emission levels or knee temperature.

CdS-metal contact at higher current densities.

NASA Technical Reports Server (NTRS)

Stirn, R. J.; Boeer, K. W.; Dussel, G. A.

1973-01-01

An investigation is conducted concerning the mechanisms by which a steady flow of current proceeds through the contact when an external voltage is applied. The main characteristics of current mechanisms are examined, giving attention to photoemission from the cathode, thermionic emission, minority-carrier extraction, and the tunneling of electrons. A high-field domain analysis is conducted together with experimental studies. Particular attention is given to the range in which tunneling predominates.

Life Model of Hollow Cathodes Using a Barium Calcium Aluminate Impregnated Tungsten Emitter

NASA Technical Reports Server (NTRS)

Kovaleski, S. D.; Burke, Tom (Technical Monitor)

2001-01-01

Hollow cathodes with barium calcium aluminate impregnated tungsten emitters for thermionic emission are widely used in electric propulsion. These high current, low power cathodes are employed in ion thrusters, Hall thrusters, and on the International Space Station in plasma contactors. The requirements on hollow cathode life are growing more stringent with the increasing use of electric propulsion technology. The life limiting mechanism that determines the entitlement lifetime of a barium impregnated thermionic emission cathode is the evolution and transport of barium away from the emitter surface. A model is being developed to study the process of barium transport and loss from the emitter insert in hollow cathodes. The model accounts for the production of barium through analysis of the relevant impregnate chemistry. Transport of barium through the approximately static gas is also being treated. Finally, the effect of temperature gradients within the cathode are considered.

Modeling and simulation for the field emission of carbon nanotubes array

NASA Astrophysics Data System (ADS)

Wang, X. Q.; Wang, M.; Ge, H. L.; Chen, Q.; Xu, Y. B.

2005-12-01

To optimize the field emission of the infinite carbon nanotubes (CNTs) array on a planar cathode surface, the numerical simulation for the behavior of field emission with finite difference method was proposed. By solving the Laplace equation with computer, the influence of the intertube distance, the anode-cathode distance and the opened/capped CNT on the field emission of CNTs array were taken into account, and the results could accord well with the experiments. The simulated results proved that the field enhancement factor of individual CNT is largest, but the emission current density is little. Due to the enhanced screening of the electric field, the enhancement factor of CNTs array decreases with decreasing the intertube distance. From the simulation the field emission can be optimized when the intertube distance is close to the tube height. The anode-cathode distance hardly influences the field enhancement factor of CNTs array, but can low the threshold voltage by decreasing the anode-cathode distance. Finally, the distribution of potential of the capped CNTs array and the opened CNTs array was simulated, which the results showed that the distribution of potential can be influenced to some extent by the anode-cathode distance, especially at the apex of the capped CNTs array and the brim of the opened CNTs array. The opened CNTs array has larger field enhancement factor and can emit more current than the capped one.

Stable blue phosphorescent organic light emitting devices

DOEpatents

Forrest, Stephen R.; Thompson, Mark; Giebink, Noel

2014-08-26

Novel combination of materials and device architectures for organic light emitting devices is provided. An organic light emitting device, is provided, having an anode, a cathode, and an emissive layer disposed between the anode and the cathode. The emissive layer includes a host and a phosphorescent emissive dopant having a peak emissive wavelength less than 500 nm, and a radiative phosphorescent lifetime less than 1 microsecond. Preferably, the phosphorescent emissive dopant includes a ligand having a carbazole group.

Nanomaterial-based x-ray sources

NASA Astrophysics Data System (ADS)

Cole, Matthew T.; Parmee, R. J.; Milne, William I.

2016-02-01

Following the recent global excitement and investment in the emerging, and rapidly growing, classes of one and two-dimensional nanomaterials, we here present a perspective on one of the viable applications of such materials: field electron emission based x-ray sources. These devices, which have a notable history in medicine, security, industry and research, to date have almost exclusively incorporated thermionic electron sources. Since the middle of the last century, field emission based cathodes were demonstrated, but it is only recently that they have become practicable. We outline some of the technological achievements of the past two decades, and describe a number of the seminal contributions. We explore the foremost market hurdles hindering their roll-out and broader industrial adoption and summarise the recent progress in miniaturised, pulsed and multi-source devices.

Reactive Black 5 as electron donor and/or electron acceptor in dual chamber of solar photocatalytic fuel cell.

PubMed

Khalik, Wan Fadhilah; Ho, Li-Ngee; Ong, Soon-An; Voon, Chun-Hong; Wong, Yee-Shian; Yusuf, Sara Yasina; Yusoff, NikAthirah; Lee, Sin-Li

2018-07-01

The role of azo dye Reactive Black 5 (RB5) as an electron donor and/or electron acceptor could be distinguished in dual chamber of photocatalytic fuel cell (PFC). The introduction of RB5 in anode chamber increased the voltage generation in the system since degradation of RB5 might produce electrons which also would transfer through external circuit to the cathode chamber. The removal efficiency of RB5 with open and closed circuit was 8.5% and 13.6%, respectively and removal efficiency for open circuit was low due to the fact that recombination of electron-hole pairs might happen in anode chamber since without connection to the cathode, electron cannot be transferred. The degradation of RB5 in cathode chamber with absence of oxygen showed that electrons from anode chamber was accepted by dye molecules to break its azo bond. The presence of oxygen in cathode chamber would improve the oxygen reduction rate which occurred at Platinum-loaded carbon (Pt/C) cathode electrode. The V oc , J sc and P max for different condition of ultrapure water at cathode chamber also affected their fill factor. The transportation of protons to cathode chamber through Nafion membrane could decrease the pH of ultrapure water in cathode chamber and undergo hydrogen evolution reaction in the absence of oxygen which then increased degradation rate of RB5 as well as its electricity generation. Copyright © 2018 Elsevier Ltd. All rights reserved.

Evaluating the Field Emission Characteristics of Aluminum for DC High Voltage Photo-Electron Guns

NASA Astrophysics Data System (ADS)

Taus, Rhys; Poelker, Matthew; Forman, Eric; Mamun, Abdullah

2014-03-01

High current photoguns require high power laser light, but only a small portion of the laser light illuminating the photocathode produces electron beam. Most of the laser light (~ 65%) simply serves to heat the photocathode, which leads to evaporation of the chemicals required to create the negative electron affinity condition necessary for photoemission. Photocathode cooling techniques have been employed to address this problem, but active cooling of the photocathode is complicated because the cooling apparatus must float at high voltage. This work evaluates the field emission characteristics of cathode electrodes manufactured from materials with high thermal conductivity: aluminum and copper. These electrodes could serve as effective heat sinks, to passively cool the photocathode that resides within such a structure. However, literature suggests ``soft'' materials like aluminum and copper are ill suited for photogun applications, due to excessive field emission when biased at high voltage. This work provides an evaluation of aluminum and copper electrodes inside a high voltage field emission test stand, before and after coating with titanium nitride (TiN), a coating that enhances surface hardness. National Science Foundation Award Number: 1062320 and the Department of Defence ASSURE program.

Development of plasma cathode electron guns

NASA Astrophysics Data System (ADS)

Oks, Efim M.; Schanin, Peter M.

1999-05-01

The status of experimental research and ongoing development of plasma cathode electron guns in recent years is reviewed, including some novel upgrades and applications to various technological fields. The attractiveness of this kind of e-gun is due to its capability of creating high current, broad or focused beams, both in pulsed and steady-state modes of operation. An important characteristic of the plasma cathode electron gun is the absence of a thermionic cathode, a feature which leads to long lifetime and reliable operation even in the presence of aggressive background gas media and at fore-vacuum gas pressure ranges such as achieved by mechanical pumps. Depending on the required beam parameters, different kinds of plasma discharge systems can be used in plasma cathode electron guns, such as vacuum arcs, constricted gaseous arcs, hollow cathode glows, and two kinds of discharges in crossed E×B fields: Penning and magnetron. At the present time, plasma cathode electron guns provide beams with transverse dimension from fractional millimeter up to about one meter, beam current from microamperes to kiloamperes, beam current density up to about 100 A/cm2, pulse duration from nanoseconds to dc, and electron energy from several keV to hundreds of keV. Applications include electron beam melting and welding, surface treatment, plasma chemistry, radiation technologies, laser pumping, microwave generation, and more.

Nanomodulated electron beams via electron diffraction and emittance exchange for coherent x-ray generation

NASA Astrophysics Data System (ADS)

Nanni, E. A.; Graves, W. S.; Moncton, D. E.

2018-01-01

We present a new method for generation of relativistic electron beams with current modulation on the nanometer scale and below. The current modulation is produced by diffracting relativistic electrons in single crystal Si, accelerating the diffracted beam and imaging the crystal structure, then transferring the image into the temporal dimension via emittance exchange. The modulation period can be tuned by adjusting electron optics after diffraction. This tunable longitudinal modulation can have a period as short as a few angstroms, enabling production of coherent hard x-rays from a source based on inverse Compton scattering with total accelerator length of approximately ten meters. Electron beam simulations from cathode emission through diffraction, acceleration, and image formation with variable magnification are presented along with estimates of the coherent x-ray output properties.

Modeling of thermal expansion coefficient of perovskite oxide for solid oxide fuel cell cathode

NASA Astrophysics Data System (ADS)

Heydari, F.; Maghsoudipour, A.; Alizadeh, M.; Khakpour, Z.; Javaheri, M.

2015-09-01

Artificial intelligence models have the capacity to eliminate the need for expensive experimental investigation in various areas of manufacturing processes, including the material science. This study investigates the applicability of adaptive neuro-fuzzy inference system (ANFIS) approach for modeling the performance parameters of thermal expansion coefficient (TEC) of perovskite oxide for solid oxide fuel cell cathode. Oxides (Ln = La, Nd, Sm and M = Fe, Ni, Mn) have been prepared and characterized to study the influence of the different cations on TEC. Experimental results have shown TEC decreases favorably with substitution of Nd3+ and Mn3+ ions in the lattice. Structural parameters of compounds have been determined by X-ray diffraction, and field emission scanning electron microscopy has been used for the morphological study. Comparison results indicated that the ANFIS technique could be employed successfully in modeling thermal expansion coefficient of perovskite oxide for solid oxide fuel cell cathode, and considerable savings in terms of cost and time could be obtained by using ANFIS technique.

Theory and Numerical Simulation of Plasma-wall Interactions in Electric Propulsion

NASA Astrophysics Data System (ADS)

Mikellides, Ioannis

2016-10-01

Electric propulsion (EP) can be an enabling technology for many science missions considered by NASA because it can produce high exhaust velocities, which allow for less propellant mass compared to typical chemical systems. Over the last decade two EP technologies have emerged as primary candidates for several proposed science missions, mainly due to their superior performance and proven record in space flight: the Ion and Hall thrusters. As NASA looks ahead to increasingly ambitious science goals, missions demand higher endurance from the propulsion system. So, by contrast to the early years of development of these thrusters, when the focus was on performance, considerable focus today is shifting towards extending their service life. Considering all potentially life-limiting mechanisms in Ion and Hall thrusters two are of primary concern: (a) the erosion of the acceleration channel in Hall thrusters and (b) the erosion of the hollow cathode. The plasma physics leading to material wear in these devices are uniquely challenging. For example, soon after the propellant is introduced into the hollow cathode it becomes partially ionized as it traverses a region of electron emission. Electron emission involves highly non-linear boundary conditions. Also, the sheath size is typically many times smaller than the characteristic physical scale of the device, yet energy gained by ions through the sheath must be accounted for in the erosion calculations. The plasma-material interactions in Hall thruster channels pose similar challenges that are further exacerbated by the presence of a strong applied magnetic field. In this presentation several complexities associated with plasma-wall interactions in EP will be discussed and numerical simulation results of key plasma properties in two examples, Hall thrusters and hollow cathodes, will be presented.

Integration of transmissible organic electronic devices for sensor application

NASA Astrophysics Data System (ADS)

Tam, Hoi Lam; Wang, Xizu; Zhu, Furong

2013-09-01

A high performance proximity sensor that integrates a front semitransparent organic photodiode (OPD) and an organic light-emitting diode (OLED) is demonstrated. A 0.3-nm-thick plasma-polymerized fluorocarbon film (CFX)-modified thin silver interlayer, serving simultaneously as a semitransparent cathode for the OPD and an anode for OLED, is used to vertically connect the functional organic electronic components. A microcavity OLED is formed between a semitransparent Ag/CFX interlayer and the rear Al cathode enhancing the forward electroluminescence emission in the integrated device. The semitransparent-OPD/OLED stack is designed using an optical admittance analysis method. In the integrated sensor, the front semitransparent OPD component enables a high transmission of light emitted by the integrated OLED unit and a high absorption when light is reflected from objects, thereby to increase the signal/noise ratio. The design and fabrication flexibility of an integrated semitransparent-OPD/OLED device also has cost benefit, making it possible for application in organic proximity sensors.

High Current Hollow Cathode Plasma Plume Measurements

NASA Technical Reports Server (NTRS)

Thomas, Robert E.; Kamhawi, Hani; Williams, George J., Jr.

2014-01-01

Plasma plume measurements are reported for a hollow cathode assembly (HCA) operated at discharge currents of 50, 70, and 100 A at xenon flow rates between 19 - 46 standard cubic centimeter per minute. The HCA was centrally mounted in the NASA-300MS Hall Thruster and was operated in the "spot" and "plume" modes with additional data taken with an applied magnetic field. Langmuir probes, retarding potential analyzers, and optical emission spectroscopy were employed to measure plasma properties near the orifice of the HCA and to assess the charge state of the near-field plasma. Electron temperatures (2-6 electron volt) and plasma potentials are consistent with probe-measured values in previous investigations. Operation with an applied-field yields higher discharge voltages, increased Xe III production, and increased signals from the 833.5 nm C I line. While operating in plume mode and with an applied field, ion energy distribution measurements yield ions with energies significantly exceeding the applied discharge voltage. These findings are correlated with high-frequency oscillations associated with each mode.

Spatial resolution of imaging plate with flash X-rays and its utilization for radiography

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shaikh, A. M., E-mail: shaikham@barc.gov.in; Romesh, C.; Kolage, T. S.

2015-06-24

A flash X-ray source developed using pulsed electron accelerator with electron energy range of 400keV to 1030keV and a field emission cathode is characterized using X-ray imaging plates. Spatial resolution of the imaging system is measured using edge spread function fitted to data obtained from radiograph of Pb step wedge. A spatial resolution of 150±6 µm is obtained. The X-ray beam size is controlled by the anode-cathode configuration. Optimum source size of ∼13±2 mm diameter covering an area with intensity of ∼27000 PSL/mm{sup 2} is obtained on the imaging plate kept at a distance of ∼200 mm from the tip of the anode.more » It is used for recording radiographs of objects like satellite cable cutter, aero-engine turbine blade and variety of pyro-devices used in aerospace industry.« less

Screening effect in matrix graphene / SiC planar field emmiters

NASA Astrophysics Data System (ADS)

Jityaev, I. L.; Svetlichnyi, A. M.; Kolomiytsev, A. S.; Ageev, O. A.

2017-11-01

The paper describes simulation of matrix field emission nanostructures on the basis of graphene on a semi-insulating silicon carbide. The planar spike-type field emission cathodes were measured. The electric field distribution in an interelectrode gap of the emission structure was obtained. The models take into account the distance between cathode tops. Screening effect condition was detected in planar field emission structure and a way of eliminating was proposed.

Plasma Emission Characteristics from a High Current Hollow Cathode in an Ion Thruster Discharge Chamber

NASA Technical Reports Server (NTRS)

Foster, John E.; Patterson, Michael J.

2002-01-01

The presence of energetic ions produced by a hollow cathodes operating at high emission currents (greater than 5A) has been documented in the literature. In order to further elucidate these findings, an investigation of a high current cathode operating in an ion thruster discharge chamber has been undertaken. Using Langmuir probes, a low energy charged particle analyzer and emission spectroscopy, the behavior of the near-cathode plasma and the emitted ion energy distribution was characterized. The presence of energetic ions was confirmed. It was observed that these ions had energies in excess of the discharge voltage and thus cannot be simply explained by ions falling out of plasma through a potential difference of this order. Additionally, evidence provided by Langmuir probes suggests the existence of a double layer essentially separating the hollow cathode plasma column from the main discharge. The radial potential difference associated with this double layer was measured to be of order the ionization potential.

Hydrogenase-independent uptake and metabolism of electrons by the archaeon Methanococcus maripaludis.

PubMed

Lohner, Svenja T; Deutzmann, Jörg S; Logan, Bruce E; Leigh, John; Spormann, Alfred M

2014-08-01

Direct, shuttle-free uptake of extracellular, cathode-derived electrons has been postulated as a novel mechanism of electron metabolism in some prokaryotes that may also be involved in syntrophic electron transport between two microorganisms. Experimental proof for direct uptake of cathodic electrons has been mostly indirect and has been based on the absence of detectable concentrations of molecular hydrogen. However, hydrogen can be formed as a transient intermediate abiotically at low cathodic potentials (<-414 mV) under conditions of electromethanogenesis. Here we provide genetic evidence for hydrogen-independent uptake of extracellular electrons. Methane formation from cathodic electrons was observed in a wild-type strain of the methanogenic archaeon Methanococcus maripaludis as well as in a hydrogenase-deletion mutant lacking all catabolic hydrogenases, indicating the presence of a hydrogenase-independent mechanism of electron catabolism. In addition, we discovered a new route for hydrogen or formate production from cathodic electrons: Upon chemical inhibition of methanogenesis with 2-bromo-ethane sulfonate, hydrogen or formate accumulated in the bioelectrochemical cells instead of methane. These results have implications for our understanding on the diversity of microbial electron uptake and metabolism.

Enhanced flashover strength in polyethylene nanodielectrics by secondary electron emission modification

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Weiwang; Li, Shengtao, E-mail: sli@xjtu.edu.cn; Min, Daomin

2016-04-15

This work studies the correlation between secondary electron emission (SEE) characteristics and impulse surface flashover in polyethylene nanodielectrics both theoretically and experimentally, and illustrates the enhancement of flashover voltage in low-density polyethylene (LDPE) through incorporating Al{sub 2}O{sub 3} nanoparticles. SEE characteristics play key roles in surface charging and gas desorption during surface flashover. This work demonstrates that the presence of Al{sub 2}O{sub 3} nanoparticles decreases the SEE coefficient of LDPE and enhances the impact energy at the equilibrium state of surface charging. These changes can be explained by the increase of surface roughness and of surface ionization energy, and themore » strong interaction between nanoparticles and the polymer dielectric matrix. The surface charge and flashover voltage are calculated according to the secondary electron emission avalanche (SEEA) model, which reveals that the positive surface charges are reduced near the cathode triple point, while the presence of more nanoparticles in high loading samples enhances the gas desorption. Consequently, the surface flashover performance of LDPE/Al{sub 2}O{sub 3} nanodielectrics is improved.« less

Pulsed Plasma Electron Sources

NASA Astrophysics Data System (ADS)

Krasik, Yakov

2008-11-01

Pulsed (˜10-7 s) electron beams with high current density (>10^2 A/cm^2) are generated in diodes with electric field of E > 10^6 V/cm. The source of electrons in these diodes is explosive emission plasma, which limits pulse duration; in the case E < 10^5 V/cm this plasma is not uniform and there is a time delay in its formation. Thus, there is a continuous interest in research of electron sources which can be used for generation of uniform electron beams produced at E <= 10^5 V/cm. In the present report, several types of plasma electron source (PES) will be considered. The first type of PES is fiber-based cathodes, with and without CsI coating. The operation of these cathodes is governed by the formation of the flashover plasma which serves as a source of electrons. The second type of PES is the ferroelectric plasma source (FPS). The operation of FPS, characterized by the formation of dense surface flashover plasma is accompanied also by the generation of fast microparticles and energetic neutrals. The latter was explained by Coulomb micro-explosions of the ferroelectric surface due to an large time-varying electric field at the front of the expanding plasma. A short review of recent achievements in the operation of a multi-FPS-assisted hollow anode to generate a large area electron beam will be presented as well. Finally, parameters of the plasma produced by a multi-capillary cathode with FPS and velvet igniters will be discussed. Ya. E. Krasik, J. Z. Gleizer, D. Yarmolich, A. Krokhmal, V. Ts. Gurovich, S.Efimov, J. Felsteiner V. Bernshtam, and Yu. M. Saveliev, J. Appl. Phys. 98, 093308 (2005). Ya. E. Krasik, A. Dunaevsky, and J. Felsteiner, Phys. Plasmas 8, 2466 (2001). D. Yarmolich, V. Vekselman, V. Tz. Gurovich, and Ya. E. Krasik, Phys. Rev. Lett. 100, 075004 (2008). J. Z. Gleizer, Y. Hadas and Ya. E. Krasik, Europhysics Lett. 82, 55001 (2008).

Tungsten and Barium Transport in the Internal Plasma of Hollow Cathodes

NASA Technical Reports Server (NTRS)

Polk, James E.; Mikellides, Ioannis G.; Katz, Ira; Capece, Angela M.

2008-01-01

The effect of tungsten erosion, transport and redeposition on the operation of dispenser hollow cathodes was investigated in detailed examinations of the discharge cathode inserts from an 8200 hour and a 30,352 hour ion engine wear test. Erosion and subsequent re-deposition of tungsten in the electron emission zone at the downstream end of the insert reduces the porosity of the tungsten matrix, preventing the flow of barium from the interior. This inhibits the interfacial reactions of the barium-calcium-aluminate impregnant with the tungsten in the pores. A numerical model of barium transport in the internal xenon discharge plasma shows that the barium required to reduce the work function in the emission zone can be supplied from upstream through the gas phase. Barium that flows out of the pores of the tungsten insert is rapidly ionized in the xenon discharge and pushedback to the emitter surface by the electric field and drag from the xenon ion flow. Thisbarium ion flux is sufficient to maintain a barium surface coverage at the downstream endgreater than 0.6, even if local barium production at that point is inhibited by tungsten deposits. The model also shows that the neutral barium pressure exceeds the equilibrium vapor pressure of the impregnant decomposition reaction over much of the insert length,so the reactions are suppressed. Only a small region upstream of the zone blocked by tungsten deposits is active and supplies the required barium. These results indicate that hollowcathode failure models based on barium depletion rates in vacuum dispenser cathodes are very conservative.

Freestanding and flexible graphene papers as bioelectrochemical cathode for selective and efficient CO2 conversion.

PubMed

Aryal, Nabin; Halder, Arnab; Zhang, Minwei; Whelan, Patrick R; Tremblay, Pier-Luc; Chi, Qijin; Zhang, Tian

2017-08-22

During microbial electrosynthesis (MES) driven CO 2 reduction, cathode plays a vital role by donating electrons to microbe. Here, we exploited the advantage of reduced graphene oxide (RGO) paper as novel cathode material to enhance electron transfer between the cathode and microbe, which in turn facilitated CO 2 reduction. The acetate production rate of Sporomusa ovata-driven MES reactors was 168.5 ± 22.4 mmol m -2 d -1 with RGO paper cathodes poised at -690 mV versus standard hydrogen electrode. This rate was approximately 8 fold faster than for carbon paper electrodes of the same dimension. The current density with RGO paper cathodes of 2580 ± 540 mA m -2 was increased 7 fold compared to carbon paper cathodes. This also corresponded to a better cathodic current response on their cyclic voltammetric curves. The coulombic efficiency for the electrons conversion into acetate was 90.7 ± 9.3% with RGO paper cathodes and 83.8 ± 4.2% with carbon paper cathodes, respectively. Furthermore, more intensive cell attachment was observed on RGO paper electrodes than on carbon paper electrodes with confocal laser scanning microscopy and scanning electron microscopy. These results highlight the potential of RGO paper as a promising cathode for MES from CO 2 .

Optimization of cathodic arc deposition and pulsed plasma melting techniques for growing smooth superconducting Pb photoemissive films for SRF injectors

DOE PAGES

Nietubyc, Robert; Lorkiewicz, Jerzy; Sekutowicz, Jacek; ...

2018-02-14

Superconducting photoinjectors have a potential to be the optimal solution for moderate and high current cw operating free electron lasers. For this application, a superconducting lead (Pb) cathode has been proposed to simplify the cathode integration into a 1.3 GHz, TESLA-type, 1.6-cell long purely superconducting gun cavity. In the proposed design, a lead film several micrometres thick is deposited onto a niobium plug attached to the cavity back wall. Traditional lead deposition techniques usually produce very non-uniform emission surfaces and often result in a poor adhesion of the layer. A pulsed plasma melting procedure reducing the non-uniformity of the leadmore » photocathodes is presented. In order to determine the parameters optimal for this procedure, heat transfer from plasma to the film was first modelled to evaluate melting front penetration range and liquid state duration. The obtained results were verified by surface inspection of witness samples. The optimal procedure was used to prepare a photocathode plug, which was then tested in an electron gun. In conclusion, the quantum efficiency and the value of cavity quality factor have been found to satisfy the requirements for an injector of the European-XFEL facility.« less

Optimization of cathodic arc deposition and pulsed plasma melting techniques for growing smooth superconducting Pb photoemissive films for SRF injectors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nietubyc, Robert; Lorkiewicz, Jerzy; Sekutowicz, Jacek

Superconducting photoinjectors have a potential to be the optimal solution for moderate and high current cw operating free electron lasers. For this application, a superconducting lead (Pb) cathode has been proposed to simplify the cathode integration into a 1.3 GHz, TESLA-type, 1.6-cell long purely superconducting gun cavity. In the proposed design, a lead film several micrometres thick is deposited onto a niobium plug attached to the cavity back wall. Traditional lead deposition techniques usually produce very non-uniform emission surfaces and often result in a poor adhesion of the layer. A pulsed plasma melting procedure reducing the non-uniformity of the leadmore » photocathodes is presented. In order to determine the parameters optimal for this procedure, heat transfer from plasma to the film was first modelled to evaluate melting front penetration range and liquid state duration. The obtained results were verified by surface inspection of witness samples. The optimal procedure was used to prepare a photocathode plug, which was then tested in an electron gun. In conclusion, the quantum efficiency and the value of cavity quality factor have been found to satisfy the requirements for an injector of the European-XFEL facility.« less

Investigation of accelerating ion triode with magnetic insulation for neutron generation

NASA Astrophysics Data System (ADS)

Shikanov, A. E.; Kozlovskij, K. I.; Vovchenko, E. D.; Rashchikov, V. I.; Shatokhin, V. L.; Isaev, A. A.

2017-12-01

Vacuum accelerating tube (AT) for neutron generation with the secondary electron emission suppressed by helical line pulse magnetic field which allocated inside accelerating gap in front of hollow conical cathodeis discussed. The central anode was covered by the hollow cathode. This technical solution of AT is an ion triode in which helical line serve as a grid. Computer simulation results of longitudinal magnetic field distributional along the axis are presented.

Multi-layer carbon-based coatings for field emission

DOEpatents

Sullivan, John P.; Friedmann, Thomas A.

1998-01-01

A multi-layer resistive carbon film field emitter device for cold cathode field emission applications. The multi-layered film of the present invention consists of at least two layers of a conductive carbon material, preferably amorphous-tetrahedrally coordinated carbon, where the resistivities of adjacent layers differ. For electron emission from the surface, the preferred structure can be a top layer having a lower resistivity than the bottom layer. For edge emitting structures, the preferred structure of the film can be a plurality of carbon layers, where adjacent layers have different resistivities. Through selection of deposition conditions, including the energy of the depositing carbon species, the presence or absence of certain elements such as H, N, inert gases or boron, carbon layers having desired resistivities can be produced.

A theoretical study of electron multiplication coefficient in a cold-cathode Penning ion generator

NASA Astrophysics Data System (ADS)

Noori, H.; Ranjbar, A. H.; Rahmanipour, R.

2017-11-01

The discharge mechanism of a Penning ion generator (PIG) is seriously influenced by the electron ionization process. A theoretical approach has been proposed to formulate the electron multiplication coefficient, M, of a PIG as a function of the axial magnetic field and the applied voltage. A numerical simulation was used to adjust the free parameters of expression M. Using the coefficient M, the values of the effective secondary electron emission coefficient, γeff, were obtained to be from 0.09 to 0.22. In comparison to the experimental results, the average value of γeff differs from the secondary coefficient of clean and dirty metals by the factors 1.4 and 0.5, respectively.

Repetitive nanosecond electron accelerators type URT-1 for radiation technology

NASA Astrophysics Data System (ADS)

Sokovnin, S. Yu.; Balezin, M. E.

2018-03-01

The electron accelerator URT-1М-300 for mobile installation was created for radiation disinfecting to correct drawbacks that were found the URT-1M electron accelerator operation (the accelerating voltage up to 1 МV, repetition rate up to 300 pps, electron beam size 400 × 100 mm, the pulse width about 100 ns). Accelerator configuration was changed that allowed to reduce significantly by 20% tank volume with oil where is placed the system of formation high-voltage pulses, thus the average power of the accelerator is increased by 6 times at the expense of increase in pulses repetition rate. Was created the system of the computerized monitoring parameters (output parameters and thermal mode) and remote control of the accelerator (charge voltage, pulse repetition rate), its elements and auxiliary systems (heat of the thyratron, vacuum system), the remote control panel is connected to the installation by the fiber-optical channel, what lightens the work for service personnel. For generating an electron beam up to 400 mm wide there are used metal- ceramic] and metal-dielectric cold cathodes of several emission elements (plates) with a non-uniform distribution of the electron beam current density on the output foil ± 15%. It was found that emission drop of both type of cathodes, during the operation at the high repetition rate (100 pps) is substantial at the beginning of the process, and then proceeds rather slowly that allows for continuous operation up to 40 h. Experiments showed that linear dependence of the voltage and a signal from the pin-diode remains within the range of the charge voltage 45-65 kV. Thus, voltage increases from 690 to 950 kV, and the signal from the pin-diode - from (2,8-4,6)*104 Gy/s. It allows to select electron energy quite precisely with consideration of the radiation technology requirements.

A multiple gap plasma cathode electron gun and its electron beam analysis in self and trigger breakdown modes.

PubMed

Kumar, Niraj; Pal, Dharmendra Kumar; Jadon, Arvind Singh; Pal, Udit Narayan; Rahaman, Hasibur; Prakash, Ram

2016-03-01

In the present paper, a pseudospark discharge based multiple gap plasma cathode electron gun is reported which has been operated separately in self and trigger breakdown modes using two different gases, namely, argon and hydrogen. The beam current and beam energy have been analyzed using a concentric ring diagnostic arrangement. Two distinct electron beams are clearly seen with hollow cathode and conductive phases. The hollow cathode phase has been observed for ∼50 ns where the obtained electron beam is having low beam current density and high energy. While in conductive phase it is high current density and low energy electron beam. It is inferred that in the hollow cathode phase the beam energy is more for the self breakdown case whereas the current density is more for the trigger breakdown case. The tailor made operation of the hollow cathode phase electron beam can play an important role in microwave generation. Up to 30% variation in the electron beam energy has been achieved keeping the same gas and by varying the breakdown mode operations. Also, up to 32% variation in the beam current density has been achieved for the trigger breakdown mode at optimized trigger position by varying the gas type.

Soft x-ray spectroscopy studies of novel electronic materials using synchrotron radiation

NASA Astrophysics Data System (ADS)

Newby, David, Jr.

Soft x-ray spectroscopy can provide a wealth of information on the electronic structure of solids. In this work, a suite of soft x-ray spectroscopies is applied to organic and inorganic materials with potential applications in electronic and energy generation devices. Using the techniques of x-ray absorption (XAS), x-ray emission spectroscopy (XES), and x-ray photoemission spectroscopy (XPS), the fundamental properties of these different materials are explored. Cycloparaphenylenes (CPPs) are a recently synthesized family of cyclic hydrocarbons with very interesting properties and many potential applications. Unusual UV/Visible fluorescence trends have spurred a number of theoretical investigations into the electronic properties of the CPP family, but thus far no comprehensive electronic structure measurements have been conducted. XPS, XAS, and XES data for two varieties, [8]- and [10]-CPP, are presented here, and compared with the results of relevant DFT calculations. Turning towards more application-centered investigations, similar measurements are applied to two materials commonly used in solid oxide fuel cell (SOFC) cathodes: La1-xSrxMnO 3 (LSMO) and La1-xSr1- xCo1-yFe yO3 (LSCF). Both materials are structurally perovskites, but they exhibit strikingly different electronic properties. SOFC systems very efficiently produce electricity by catalyzing reactions between oxygen and petroleum-based hydrocarbons at high temperatures (> 800 C). Such systems are already utilized to great effect in many industries, but more widespread adoption could be had if the cells could operate at lower temperatures. Understanding the electronic structure and operational evolution of the cathode materials is essential for the development of better low-temperature fuel cells. LSCF is a mixed ion-electron conductor which holds promise for low-temperature SOFC applications. XPS spectra of LSCF thin films are collected as the films are heated and gas-dosed in a controlled environment. The surface evolution of these films is discussed, and the effects of different gas environments on oxygen vacancy concentration are elucidated. LSMO is commonly used in commercial fuel cell devices. Here the resonant soft x-ray emission (RIXS) spectrum of LSMO is examined, and it is shown that the inelastic x-ray emission structure of LSMO arises from local atomic multiplet effects.

Field Emission Characteristics of Carbon Nanotubes and Their Applications in Sensors and Devices

NASA Astrophysics Data System (ADS)

Vaseashta, Ashok

2003-03-01

FIELD EMISSION CHARACTERISTICS OF CARBON NANOTUBES AND THEIR APPLICATIONS IN SENSORS AND DEVICES A. Vaseashta, C. Shaffer, M. Collins, A. Mwuara Dept of Physics, Marshall University, Huntington, WV V. Pokropivny Institute for Materials Sciences of NASU, Kiev, Ukraine. D. Dimova-Malinovska Bulgarian Academy of Sciences, Sofia, Bulgaria. The dimensionality of a system has profound influence on its physical behavior. With advances in technology over the past few decades, it has become possible to fabricate and study reduced-dimensional systems, such as carbon nanotubes (CNTs). Carbon nanotubes are especially promising candidate for cold cathode field emitter because of their electrical properties, high aspect ratio, and small radius of curvature at the tips. Electron emission from the carbon nanotubes was investigated. Based upon the field emission investigation of carbon nanotubes, several prototype devices have been suggested that operate with low swing voltages with sufficient high current densities. Characteristics that allow improved current stability and long lifetime operation for electrical and opto-electronics devices are presented. The aim of this brief overview is to illustrate the useful characteristics of carbon nanotubes and its possible application.

Hydrogenase-independent uptake and metabolism of electrons by the archaeon Methanococcus maripaludis

PubMed Central

Lohner, Svenja T; Deutzmann, Jörg S; Logan, Bruce E; Leigh, John; Spormann, Alfred M

2014-01-01

Direct, shuttle-free uptake of extracellular, cathode-derived electrons has been postulated as a novel mechanism of electron metabolism in some prokaryotes that may also be involved in syntrophic electron transport between two microorganisms. Experimental proof for direct uptake of cathodic electrons has been mostly indirect and has been based on the absence of detectable concentrations of molecular hydrogen. However, hydrogen can be formed as a transient intermediate abiotically at low cathodic potentials (<−414 mV) under conditions of electromethanogenesis. Here we provide genetic evidence for hydrogen-independent uptake of extracellular electrons. Methane formation from cathodic electrons was observed in a wild-type strain of the methanogenic archaeon Methanococcus maripaludis as well as in a hydrogenase-deletion mutant lacking all catabolic hydrogenases, indicating the presence of a hydrogenase-independent mechanism of electron catabolism. In addition, we discovered a new route for hydrogen or formate production from cathodic electrons: Upon chemical inhibition of methanogenesis with 2-bromo-ethane sulfonate, hydrogen or formate accumulated in the bioelectrochemical cells instead of methane. These results have implications for our understanding on the diversity of microbial electron uptake and metabolism. PMID:24844759

Motion of a virtual cathode in a cylindrical channel with electron beam transport in the “compressed” state

DOE Office of Scientific and Technical Information (OSTI.GOV)

Belomyttsev, S. Ya.; Grishkov, A. A.; Tsygankov, R. V.

2014-03-15

This paper studies the motion of a virtual cathode in a two-section drift tube with the formation and breakup of the “compressed” state of an electron beam. Experimental arrangements to intercept part of the injected current during the voltage pulse and to provide virtual cathode motion toward the collector are proposed. The arrangements were implemented on the SINUS-7 high-current electron accelerator. Theoretical and experimental dependences of the virtual cathode velocity on the injected current and cathode voltage are presented. The experimental data on virtual cathode motion agree with its theoretical model based on analytical solutions of equations assisted by computermore » simulation with the PIC code KARAT. The results of the work demonstrate the feasibility of controlling the virtual cathode motion which can be used in collective ion acceleration and microwave generation.« less

Single-Layer Halide Perovskite Light-Emitting Diodes with Sub-Band Gap Turn-On Voltage and High Brightness.

PubMed

Li, Junqiang; Shan, Xin; Bade, Sri Ganesh R; Geske, Thomas; Jiang, Qinglong; Yang, Xin; Yu, Zhibin

2016-10-03

Charge-carrier injection into an emissive semiconductor thin film can result in electroluminescence and is generally achieved by using a multilayer device structure, which requires an electron-injection layer (EIL) between the cathode and the emissive layer and a hole-injection layer (HIL) between the anode and the emissive layer. The recent advancement of halide perovskite semiconductors opens up a new path to electroluminescent devices with a greatly simplified device structure. We report cesium lead tribromide light-emitting diodes (LEDs) without the aid of an EIL or HIL. These so-called single-layer LEDs have exhibited a sub-band gap turn-on voltage. The devices obtained a brightness of 591 197 cd m -2 at 4.8 V, with an external quantum efficiency of 5.7% and a power efficiency of 14.1 lm W -1 . Such an advancement demonstrates that very high efficiency of electron and hole injection can be obtained in perovskite LEDs even without using an EIL or HIL.

Single Crystal Diamond Needle as Point Electron Source.

PubMed

Kleshch, Victor I; Purcell, Stephen T; Obraztsov, Alexander N

2016-10-12

Diamond has been considered to be one of the most attractive materials for cold-cathode applications during past two decades. However, its real application is hampered by the necessity to provide appropriate amount and transport of electrons to emitter surface which is usually achieved by using nanometer size or highly defective crystallites having much lower physical characteristics than the ideal diamond. Here, for the first time the use of single crystal diamond emitter with high aspect ratio as a point electron source is reported. Single crystal diamond needles were obtained by selective oxidation of polycrystalline diamond films produced by plasma enhanced chemical vapor deposition. Field emission currents and total electron energy distributions were measured for individual diamond needles as functions of extraction voltage and temperature. The needles demonstrate current saturation phenomenon and sensitivity of emission to temperature. The analysis of the voltage drops measured via electron energy analyzer shows that the conduction is provided by the surface of the diamond needles and is governed by Poole-Frenkel transport mechanism with characteristic trap energy of 0.2-0.3 eV. The temperature-sensitive FE characteristics of the diamond needles are of great interest for production of the point electron beam sources and sensors for vacuum electronics.

Single Crystal Diamond Needle as Point Electron Source

NASA Astrophysics Data System (ADS)

Kleshch, Victor I.; Purcell, Stephen T.; Obraztsov, Alexander N.

2016-10-01

Diamond has been considered to be one of the most attractive materials for cold-cathode applications during past two decades. However, its real application is hampered by the necessity to provide appropriate amount and transport of electrons to emitter surface which is usually achieved by using nanometer size or highly defective crystallites having much lower physical characteristics than the ideal diamond. Here, for the first time the use of single crystal diamond emitter with high aspect ratio as a point electron source is reported. Single crystal diamond needles were obtained by selective oxidation of polycrystalline diamond films produced by plasma enhanced chemical vapor deposition. Field emission currents and total electron energy distributions were measured for individual diamond needles as functions of extraction voltage and temperature. The needles demonstrate current saturation phenomenon and sensitivity of emission to temperature. The analysis of the voltage drops measured via electron energy analyzer shows that the conduction is provided by the surface of the diamond needles and is governed by Poole-Frenkel transport mechanism with characteristic trap energy of 0.2-0.3 eV. The temperature-sensitive FE characteristics of the diamond needles are of great interest for production of the point electron beam sources and sensors for vacuum electronics.

Foundations of DC plasma sources

NASA Astrophysics Data System (ADS)

Tomas Gudmundsson, Jon; Hecimovic, Ante

2017-12-01

A typical dc discharge is configured with the negative cathode at one end and a positive anode at the other end, separated by a gas filled gap, placed inside a long glass cylinder. A few hundred volts between the cathode and anode is required to maintain the discharge. The type of discharge that is formed between the two electrodes depends upon the pressure of the working gas, the nature of the working gas, the applied voltage and the geometry of the discharge. We discuss the current-voltage characteristics of the discharge as well as the distinct structure that develops in the glow discharge region. The dc glow discharge appears in the discharge current range from μA to mA at 0.5-300 Pa pressure. We discuss the various phenomena observed in the dc glow discharge, including the cathode region, the positive column, and striations. The dc glow discharge is maintained by the emission of secondary electrons from the cathode target due to the bombardment of ions. For decades, the dc glow discharge has been used as a sputter source. Then it is often operated as an obstructed abnormal glow discharge and the required applied voltage is in the range 2-5 kV. Typically, the cathode target (the material to be deposited) is connected to a negative voltage supply (dc or rf) and the substrate holder faces the target. The relatively high operating pressure, in the range from 2 to 4 Pa, high applied voltages, and the necessity to have a conductive target limit the application of dc glow discharge as a sputter source. In order to lower the discharge voltage and expand the operation pressure range, the lifetime of the electrons in target vicinity is increased through applying magnetic field, by adding permanent magnets behind the cathode target. This arrangement is coined the magnetron sputtering discharge. The various configurations of the magnetron sputtering discharge and its applications are described. Furthermore, the use of dc discharges for chemical analysis, the Penning discharge and the hollow cathode discharges and some of its applications are briefly discussed.

A method for achieving ignition of a low voltage gas discharge device

DOEpatents

Kovarik, Vincent J.; Hershcovitch, Ady; Prelec, Krsto

1988-01-01

An electronic device of the type wherein current flow is conducted by an ionized gas comprising a cathode of the type heated by ionic bombardment, an anode, means for maintaining a predetermined pressure in the region between the anode and the cathode and means for maintaining a field in the region. The field, which is preferably a combined magnetic and electric field, is oriented so that the mean distance traveled by electrons before reaching the anode is increased. Because of this increased distance traveled electrons moving to the anode will ionize a larger number of gas atoms, thus reducing the voltage necesary to initiate gas breakdown. In a preferred embodiment the anode is a main hollow cathode and the cathode is a smaller igniter hollow cathode located within and coaxial with the main hollow cathode. An axial magnetic field is provided in the region between the hollow cathodes in order to facilitate gas breakdown in that region and initiate plasma discharge from the main hollow cathode.

Low-voltage gas-discharge device

DOEpatents

Kovarik, V.J.; Hershcovitch, A.; Prelec, K.

1982-06-08

An electronic device of the type wherein current flow is conducted by an ionized gas comprising a cathode of the type heated by ionic bombardment, an anode, means for maintaining a predetermined pressure in the region between the anode and the cathode and means for maintaining a field in the region is described. The field, which is preferably a combined magnetic and electric field, is oriented so that the mean distance traveled by electrons before reaching the anode is increased. Because of this increased distance traveled electrons moving to the anode will ionize a large number of gas atoms, thus reducing the voltage necessary to initiate gas breakdown. In a preferred embodiment the anode is a main hollow cathode and the cathode is a smaller igniter hollow cathode located within and coaxial with the main hollow cathode. An axial magnetic field is provided in the region between the hollow cathodes in order to facilitate gas breakdown in that region and initiate plasma discharge from the main hollow cathode.

Operation of a long-pulse backward-wave oscillator using a disk cathode

NASA Astrophysics Data System (ADS)

Hahn, Kelly; Fuks, Mikhail I.; Schamiloglu, Edl

2001-08-01

Recent work at the University of New Mexico has studied the use of a circular disk cathode as the electron source in a long-pulse Backward Wave Oscillator (BWO) experiment. The use of this cathode was motivated by recent studies by Loza and Strelkov of the General Physics Institute in Russia that demonstrated that a relativistic electron beam with stable cross section could be sustained for over one microsecond. In our first investigations using this new cathode configuration we found that the microwave pulse length generated from a long pulse BWO increased somewhat compared to the case when a traditional annular `cookie-cutter' cathode was used. We attribute this pulse lengthening to the hypothesis that the disk cathode generates a relativistic electron beam that is less likely to radially expand, thereby minimizing wall interception and the generation of unwanted plasma. In this paper we describe details of work- in-progress relating to a comparison of microwave generation from a disk cathode and annular cathode in a long-pulse BWO.

Investigation into key interfacial reactions within lithium-ion batteries

NASA Astrophysics Data System (ADS)

Vissers, Daniel Richard

Given the concern of global climate change and the understanding that carbon dioxide emissions are driving this change, much effort has been invested into lowering carbon dioxide emissions. One approach to reduce carbon dioxide emissions is to curtail the carbon dioxide emissions from vehicles through the introduction of hybrid electric vehicles, plug-in hybrid electric vehicles, and electric vehicles. Today, lithium cobalt oxide materials are widely used in consumer electronic applications, yet these materials are cost prohibitive for larger scale vehicle applications. As a result, alternative materials with higher energy densities and lower costs are being investigated. One key alternative to cobalt that has received much attention is manganese. Manganese is of interest for its lower cost and favorable environmental friendliness. The use of manganese has led to numerous cathode materials such as Li 1-deltaMn2O4 (4V spinel), Li1-deltaMn 1.5Ni0.25O4 (5V spinel), Li1-(Mn 1-x-yNiyCox)O2 (layered), Li2MnO 3-Li1-delta(Mn1-x-yNiyCox)O 2 (layered-layered), and Li2MnO3-Li1-delta (Mn1-x-yNiyCox)1O2 -Li1-deltaMn2O4 (layered-layered-spinel). The work disclosed in the dissertation focuses on two topics associated with these manganese based cathodes. The first topic is the exceptional cyclic-ability of a high power, high energy density, 5V spinel cathode material (Li 1-deltaMn1.5Ni0.25O4) with a core-shell architecture, and the second is the severe capacity fade associated with manganese dissolution from cathodes at elevated operating temperatures. Both topics are of interest to the Li-ion battery industry. For instance, a 5V spinel cathode represents a viable path to increase both the power and energy density of Li-ion batteries. As its name implies, the 5V spinel operates at 5V that is higher than the conventional 4V lithium ion batteries. Since power and energy are directly proportional to the potential, moving from an operating potential of 4V to 5V represents an increase in both power and energy densities of 25%. When the 5V spinel cathode is coupled with a graphite anode, an energy density of up to 240 Wh kg-1 is possible [2]. Secondly, the severe capacity fade associated with the manganese dissolution generally leads to a design with oversized battery packs, like those for the General Motors Chevy Volt, to meet warranty requirements. The result of this work led to deeper understandings of the underlying mechanisms for the exceptional cyclic-ability of the core-shell 5V spinel and for the severe capacity fade associated with manganese dissolution from the cathode and to a rational approach to resolve the severe capacity fade associated with manganese dissolution.

Outgassing rate analysis of a velvet cathode and a carbon fiber cathode

NASA Astrophysics Data System (ADS)

Li, An-Kun; Fan, Yu-Wei; Qian, Bao-Liang; Zhang, Zi-cheng; Xun, Tao

2017-11-01

In this paper, the outgassing-rates of a carbon fiber array cathode and a polymer velvet cathode are tested and discussed. Two different methods of measurements are used in the experiments. In one scheme, a method based on dynamic equilibrium of pressure is used. Namely, the cathode works in the repetitive mode in a vacuum diode, a dynamic equilibrium pressure would be reached when the outgassing capacity in the chamber equals the pumping capacity of the pump, and the outgassing rate could be figured out according to this equilibrium pressure. In another scheme, a method based on static equilibrium of pressure is used. Namely, the cathode works in a closed vacuum chamber (a hard tube), and the outgassing rate could be calculated from the pressure difference between the pressure in the chamber before and after the work of the cathode. The outgassing rate is analyzed from the real time pressure evolution data which are measured using a magnetron gauge in both schemes. The outgassing rates of the carbon fiber array cathode and the velvet cathode are 7.3 ± 0.4 neutrals/electron and 85 ± 5 neutrals/electron in the first scheme and 9 ± 0.5 neutrals/electron and 98 ± 7 neutrals/electron in the second scheme. Both the results of two schemes show that the outgassing rate of the carbon fiber array cathode is an order smaller than that of the velvet cathode under similar conditions, which shows that this carbon fiber array cathode is a promising replacement of the velvet cathode in the application of magnetically insulated transmission line oscillators and relativistic magnetrons.

Nanomodulated electron beams via electron diffraction and emittance exchange for coherent x-ray generation

DOE PAGES

Nanni, E. A.; Graves, W. S.; Moncton, D. E.

2018-01-19

We present a new method for generation of relativistic electron beams with current modulation on the nanometer scale and below. The current modulation is produced by diffracting relativistic electrons in single crystal Si, accelerating the diffracted beam and imaging the crystal structure, then transferring the image into the temporal dimension via emittance exchange. The modulation period can be tuned by adjusting electron optics after diffraction. This tunable longitudinal modulation can have a period as short as a few angstroms, enabling production of coherent hard x-rays from a source based on inverse Compton scattering with total accelerator length of approximately tenmore » meters. Electron beam simulations from cathode emission through diffraction, acceleration, and image formation with variable magnification are presented along with estimates of the coherent x-ray output properties.« less

Spacecraft potential control on ISEE-1

NASA Technical Reports Server (NTRS)

Gonfalone, A.; Pedersen, A.; Fahleson, U. V.; Faelthammar, C. G.; Mozer, F. S.; Torbert, R. B.

1979-01-01

Active control of the potential of the ISEE-1 satellite by the use of electron guns is reviewed. The electron guns contain a special cathode capable of emitting an electron current selectable between 10 to the -8th power and 10 to the -3rd power at energies from approximately .6 to 41 eV. Results obtained during flight show that the satellite potential can be stabilized at a value more positive than the normally positive floating potential. The electron guns also reduce the spin modulation of the spacecraft potential which is due to the aspect dependent photoemission of the long booms. Plasma parameters like electron temperature and density can be deduced from the variation of the spacecraft potential as a function of the gun current. The effects of electron beam emission on other experiments are briefly mentioned.

Nanomodulated electron beams via electron diffraction and emittance exchange for coherent x-ray generation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nanni, E. A.; Graves, W. S.; Moncton, D. E.

We present a new method for generation of relativistic electron beams with current modulation on the nanometer scale and below. The current modulation is produced by diffracting relativistic electrons in single crystal Si, accelerating the diffracted beam and imaging the crystal structure, then transferring the image into the temporal dimension via emittance exchange. The modulation period can be tuned by adjusting electron optics after diffraction. This tunable longitudinal modulation can have a period as short as a few angstroms, enabling production of coherent hard x-rays from a source based on inverse Compton scattering with total accelerator length of approximately tenmore » meters. Electron beam simulations from cathode emission through diffraction, acceleration, and image formation with variable magnification are presented along with estimates of the coherent x-ray output properties.« less

WE-G-BRD-09: Novel MRI Compatible Electron Accelerator for MRI-Linac Radiotherapy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Whelan, B; Keall, P; Gierman, S

Purpose: MRI guided radiotherapy is a rapidly growing field; however current linacs are not designed to operate in MRI fringe fields. As such, current MRI- Linac systems require magnetic shielding, impairing MR image quality and system flexibility. Here, we present a bespoke electron accelerator concept with robust operation in in-line magnetic fields. Methods: For in-line MRI-Linac systems, electron gun performance is the major constraint on accelerator performance. To overcome this, we propose placing a cathode directly within the first accelerating cavity. Such a configuration is used extensively in high energy particle physics, but not previously for radiotherapy. Benchmarked computational modellingmore » (CST, Darmstadt, Germany) was employed to design and assess a 5.5 cell side coupled accelerator with a temperature limited thermionic cathode in the first accelerating cell. This simulation was coupled to magnetic fields from a 1T MRI model to assess robustness in magnetic fields for Source to Isocenter Distance between 1 and 2 meters. Performance was compared to a conventional electron gun based system in the same magnetic field. Results: A temperature limited cathode (work function 1.8eV, temperature 1245K, emission constant 60A/K/cm{sup 2}) will emit a mean current density of 24mA/mm{sup 2} (Richardson’s Law). We modeled a circular cathode with radius 2mm and mean current 300mA. Capture efficiency of the device was 43%, resulting in target current of 130 mA. The electron beam had a FWHM of 0.2mm, and mean energy of 5.9MeV (interquartile spread of 0.1MeV). Such an electron beam is suitable for radiotherapy, comparing favourably to conventional systems. This model was robust to operation the MRI fringe field, with a maximum current loss of 6% compared to 85% for the conventional system. Conclusion: The bespoke electron accelerator is robust to operation in in-line magnetic fields. This will enable MRI-Linacs with no accelerator magnetic shielding, and minimise painstaking optimisation of the MRI fringe field. This work was supported by US (NIH) and Australian (NHMRC & Cancer Institute NSW) government research funding. In addition, I would like to thank cancer institute NSW and the Ingham Institute for scholarship support.« less

Microstructure control of SOFC cathode material: The role of dispersing agent

NASA Astrophysics Data System (ADS)

Ismail, Ismariza; Jani, Abdul Mutalib Md; Osman, Nafisah

2017-09-01

In the present works, La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) cathode powders were synthesized by a sol-gel method with the aid of ethylene glycol which served as the dispersing agent. The phase formation and morphology of the powders were examined by X-Ray diffractometer (XRD) and field emission scanning electron microscopy (FESEM), respectively. The electrochemical properties of the synthesized cathode were obtained using an electrochemical impedance spectroscopy (EIS). The characteristic peaks for LSCF phase appears in the X-ray diffractogram after calcined at 500 °C and complete formation of LSCF single phase was attained at 700 °C. FESEM micrographs showed the presence of spherical particles of the powders with approximate particle size between 10 to 60 nm along with agglomerate morphologies. Well dispersed particles and fewer aggregates were observed for samples prepared with addition of ethylene glycol as the synthesizing aid. The surface area obtained for powder sample prepared with the aid of dispersing agent is 12.0 m2g-1. The EIS measurement results depicts a lower area specific resistance (ASR) obtained for sample prepared with addition of the ethylene glycol as compared to the pristine sample. The present results encourage the optimization of the cathode particle design in order to further improve the cathode performance.

A survey of Kaufman thruster cathodes

NASA Technical Reports Server (NTRS)

Weigand, A. J.; Nakanishi, S.

1971-01-01

A survey is presented of the various cathodes which were developed and used in the Kaufman ion thruster. The electron bombardment type ion source is briefly described. The general design, operating characteristics, and power requirements are shown for each type of cathode from the refractory metals used in 1960 to the plasma discharge hollow cathodes of today. A detailed discussion of the hollow cathode is given, including starting and cyclic operating characteristics as well as more fundamental design parameters. Tests to date show that the plasma hollow cathode is an efficient electron source with demonstrated durability over 10,000 hours.

Enhanced Electron Injection and Exciton Confinement for Pure Blue Quantum-Dot Light-Emitting Diodes by Introducing Partially Oxidized Aluminum Cathode.

PubMed

Wang, Zhibin; Cheng, Tai; Wang, Fuzhi; Bai, Yiming; Bian, Xingming; Zhang, Bing; Hayat, Tasawar; Alsaedi, Ahmed; Tan, Zhan'ao

2018-05-31

Stable and efficient red (R), green (G), and blue (B) light sources based on solution-processed quantum dots (QDs) play important roles in next-generation displays and solid-state lighting technologies. The brightness and efficiency of blue QDs-based light-emitting diodes (LEDs) remain inferior to their red and green counterparts, due to the inherently unfavorable energy levels of different colors of light. To solve these problems, a device structure should be designed to balance the injection holes and electrons into the emissive QD layer. Herein, through a simple autoxidation strategy, pure blue QD-LEDs which are highly bright and efficient are demonstrated, with a structure of ITO/PEDOT:PSS/Poly-TPD/QDs/Al:Al2O3. The autoxidized Al:Al2O3 cathode can effectively balance the injected charges and enhance radiative recombination without introducing an additional electron transport layer (ETL). As a result, high color-saturated blue QD-LEDs are achieved with a maximum luminance over 13,000 cd m -2 , and a maximum current efficiency of 1.15 cd A -1 . The easily controlled autoxidation procedure paves the way for achieving high-performance blue QD-LEDs.

A multiple gap plasma cathode electron gun and its electron beam analysis in self and trigger breakdown modes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kumar, Niraj; Pal, Udit Narayan; Prakash, Ram

In the present paper, a pseudospark discharge based multiple gap plasma cathode electron gun is reported which has been operated separately in self and trigger breakdown modes using two different gases, namely, argon and hydrogen. The beam current and beam energy have been analyzed using a concentric ring diagnostic arrangement. Two distinct electron beams are clearly seen with hollow cathode and conductive phases. The hollow cathode phase has been observed for ∼50 ns where the obtained electron beam is having low beam current density and high energy. While in conductive phase it is high current density and low energy electronmore » beam. It is inferred that in the hollow cathode phase the beam energy is more for the self breakdown case whereas the current density is more for the trigger breakdown case. The tailor made operation of the hollow cathode phase electron beam can play an important role in microwave generation. Up to 30% variation in the electron beam energy has been achieved keeping the same gas and by varying the breakdown mode operations. Also, up to 32% variation in the beam current density has been achieved for the trigger breakdown mode at optimized trigger position by varying the gas type.« less

The PROPEL Electrodynamic Tether Mission and Connecting to the Ionosphere

NASA Technical Reports Server (NTRS)

Gilchrist, Brian; Bilen, Sven; Hoyt, Rob; Stone,Nobie; Vaughn, Jason; Fuhrhop, Keith; Krause, Linda; Khazanov, George; Johnson, Les

2012-01-01

The exponential increase of launch system size.and cost.with delta-V makes missions that require large total impulse cost prohibitive. Led by NASA's Marshall Space Flight Center, a team from government, industry, and academia has developed a flight demonstration mission concept of an integrated electrodynamic (ED) tethered satellite system called PROPEL: "Propulsion using Electrodynamics". The PROPEL Mission is focused on demonstrating a versatile configuration of an ED tether to overcome the limitations of the rocket equation, enable new classes of missions currently unaffordable or infeasible, and significantly advance the Technology Readiness Level (TRL) to an operational level. We are also focused on establishing a far deeper understanding of critical processes and technologies to be able to scale and improve tether systems in the future. Here, we provide an overview of the proposed PROPEL mission. One of the critical processes for efficient ED tether operation is the ability to inject current to and collect current from the ionosphere. Because the PROPEL mission is planned to have both boost and deboost capability using a single tether, the tether current must be capable of flowing in both directions and at levels well over 1 A. Given the greater mobility of electrons over that of ions, this generally requires that both ends of the ED tether system can both collect and emit electrons. For example, hollow cathode plasma contactors (HCPCs) generally are viewed as state-of-the-art and high TRL devices; however, for ED tether applications important questions remain of how efficiently they can operate as both electron collectors and emitters. Other technologies will be highlighted that are being investigated as possible alternatives to the HCPC such as Solex that generates a plasma cloud from a solid material (Teflon) and electron emission (only) technologies such as cold-cathode electron field emission or photo-electron beam generation (PEBG) techniques.

Technology Area Roadmap for In-Space Propulsion Technologies

NASA Technical Reports Server (NTRS)

Johnson, Les; Meyer, Michael; Palaszewski, Bryan; Coote, David; Goebel, Dan; White, Harold

2012-01-01

The exponential increase of launch system size.and cost.with delta-V makes missions that require large total impulse cost prohibitive. Led by NASA fs Marshall Space Flight Center, a team from government, industry, and academia has developed a flight demonstration mission concept of an integrated electrodynamic (ED) tethered satellite system called PROPEL: \\Propulsion using Electrodynamics.. The PROPEL Mission is focused on demonstrating a versatile configuration of an ED tether to overcome the limitations of the rocket equation, enable new classes of missions currently unaffordable or infeasible, and significantly advance the Technology Readiness Level (TRL) to an operational level. We are also focused on establishing a far deeper understanding of critical processes and technologies to be able to scale and improve tether systems in the future. Here, we provide an overview of the proposed PROPEL mission. One of the critical processes for efficient ED tether operation is the ability to inject current to and collect current from the ionosphere. Because the PROPEL mission is planned to have both boost and deboost capability using a single tether, the tether current must be capable of flowing in both directions and at levels well over 1 A. Given the greater mobility of electrons over that of ions, this generally requires that both ends of the ED tether system can both collect and emit electrons. For example, hollow cathode plasma contactors (HCPCs) generally are viewed as state-of-the-art and high TRL devices; however, for ED tether applications important questions remain of how efficiently they can operate as both electron collectors and emitters. Other technologies will be highlighted that are being investigated as possible alternatives to the HCPC such as Solex that generates a plasma cloud from a solid material (Teflon) and electron emission (only) technologies such as cold-cathode electron field emission or photo-electron beam generation (PEBG) techniques

Mixed Conducting Electrodes for Better AMTEC Cells

NASA Technical Reports Server (NTRS)

Ryan, Margaret; Williams, Roger; Homer, Margie; Lara. Liana

2003-01-01

Electrode materials that exhibit mixed conductivity (that is, both electronic and ionic conductivity) have been investigated in a continuing effort to improve the performance of the alkali metal thermal-to-electric converter (AMTEC). These electrode materials are intended primarily for use on the cathode side of the sodium-ion-conducting solid electrolyte of a sodium-based AMTEC cell. They may also prove useful in sodium-sulfur batteries, which are under study for use in electric vehicles. An understanding of the roles played by the two types of conduction in the cathode of a sodium-based AMTEC cell is prerequisite to understanding the advantages afforded by these materials. In a sodium-based AMTEC cell, the anode face of an anode/solid-electrolyte/cathode sandwich is exposed to Na vapor at a suitable pressure. Upon making contact with the solid electrolyte on the anode side, Na atoms oxidize to form Na+ ions and electrons. Na+ ions then travel through the electrolyte to the cathode. Na+ ions leave the electrolyte at the cathode/electrolyte interface and are reduced by electrons that have been conducted through an external electrical load from the anode to the cathode. Once the Na+ ions have been reduced to Na atoms, they travel through the cathode to vaporize into a volume where the Na vapor pressure is much lower than it is on the anode side. Thus, the cathode design is subject to competing requirements to be thin enough to allow transport of sodium to the low-pressure side, yet thick enough to afford adequate electronic conductivity. The concept underlying the development of the present mixed conducting electrode materials is the following: The constraint on the thickness of the cathode can be eased by incorporating Na+ -ionconducting material to facilitate transport of sodium through the cathode in ionic form. At the same time, by virtue of the electronically conducting material mixed with the ionically conducting material, reduction of Na+ ions to Na atoms can take place throughout the thickness of the cathode. The net effect is to reduce the diffusion and flow resistance to sodium through the electrode while reducing the electronic resistance by providing shorter conduction paths for electrons. Reduced resistance to both sodium transport and electronic conductivity results in an increase in electric power output.

2D particle-in-cell simulation of the entire process of surface flashover on insulator in vacuum

NASA Astrophysics Data System (ADS)

Wang, Hongguang; Zhang, Jianwei; Li, Yongdong; Lin, Shu; Zhong, Pengfeng; Liu, Chunliang

2018-04-01

With the introduction of an external circuit model and a gas desorption model, the surface flashover on the plane insulator-vacuum interface perpendicular to parallel electrodes is simulated by a Particle-In-Cell method. It can be seen from simulations that when the secondary electron emission avalanche (SEEA) occurs, the current sharply increases because of the influence of the insulator surface charge on the cathode field emission. With the introduction of the gas desorption model, the current keeps on increasing after SEEA, and then the feedback of the external circuit causes the voltage between the two electrodes to decrease. The cathode emission current decreases, while the anode current keeps growing. With the definition that flashover occurs when the diode voltage drops by more than 20%, we obtained the simulated flashover voltage which agrees with the experimental value with the use of the field enhancement factor β = 145 and the gas molecule desorption coefficient γ=0.25 . From the simulation results, we can also see that the time delay of flashover decreases exponentially with voltage. In addition, from the gas desorption model, the gas density on the insulator surface is found to be proportional to the square of the gas desorption rate and linear with time.

Individually addressable cathodes with integrated focusing stack or detectors

DOEpatents

Thomas, Clarence E.; Baylor, Larry R.; Voelkl, Edgar; Simpson, Michael L.; Paulus, Michael J.; Lowndes, Douglas; Whealton, John; Whitson, John C.; Wilgen, John B.

2005-07-12

Systems and method are described for addressable field emission array (AFEA) chips. A plurality of individually addressable cathodes are integrated with an electrostatic focusing stack and/or a plurality of detectors on the addressable field emission array. The systems and methods provide advantages including the avoidance of space-charge blow-up.

High resolution x-ray absorption and emission spectroscopy of Li x CoO2 single crystals as a function delithiation

NASA Astrophysics Data System (ADS)

Simonelli, L.; Paris, E.; Iwai, C.; Miyoshi, K.; Takeuchi, J.; Mizokawa, T.; Saini, N. L.

2017-03-01

The effect of delithiation in Li x CoO2 is studied by high resolution Co K-edge x-ray absorption and x-ray emission spectroscopy. Polarization dependence of the x-ray absorption spectra on single crystal samples is exploited to reveal information on the anisotropic electronic structure. We find that the electronic structure of Li x CoO2 is significantly affected by delithiation in which the Co ions oxidation state tending to change from 3+  to 4+. The Co intersite (intrasite) 4p-3d hybridization suffers a decrease (increase) by delithiation. The unoccupied 3d t 2g orbitals with a 1g symmetry, containing substantial O 2p character, hybridize isotropically with Co 4p orbitals and likely to have itinerant character unlike anisotropically hybridized 3d e g orbitals. Such a peculiar electronic structure could have significant effect on the mobility of Li in Li x CoO2 cathode and hence the battery characteristics.

Passage of the discharge current through the plasma-electrode interface in the electromagnetic rail accelerator channel

NASA Astrophysics Data System (ADS)

Zhukov, B. G.; Reznikov, B. I.; Kurakin, R. O.; Ponyaev, S. A.; Bobashev, S. V.

2016-11-01

We investigate the phenomena that accompany the acceleration of a free plasma piston (without a striker) in the electromagnetic rail accelerator channel filled with different gases (argon, helium). An intense glow appears in the shock-compressed layer (SCL) in the case of strong shock waves that produce a high electron concentration ( 1017-1018 cm-3) behind the front. We have proposed that explosive electron emission (EEE) ensures the high-intensity emission of electrons, the passage of a part of the discharge current through the SCL, and the glow of the SCL. The velocity of a shock wave for which the strong electric field in the Debye layer at the cathode causes EEE from its surface and the passage of the current in the SCL has been determined. It has been concluded that, for high velocities of the plasma, the EEE is a universal mechanism that ensure the passage of a strong current through the interface between the cold electrode and the plasma.

Denitrifying Bacterial Communities Affect Current Production and Nitrous Oxide Accumulation in a Microbial Fuel Cell

PubMed Central

Vilar-Sanz, Ariadna; Puig, Sebastià; García-Lledó, Arantzazu; Trias, Rosalia; Balaguer, M. Dolors; Colprim, Jesús; Bañeras, Lluís

2013-01-01

The biocathodic reduction of nitrate in Microbial Fuel Cells (MFCs) is an alternative to remove nitrogen in low carbon to nitrogen wastewater and relies entirely on microbial activity. In this paper the community composition of denitrifiers in the cathode of a MFC is analysed in relation to added electron acceptors (nitrate and nitrite) and organic matter in the cathode. Nitrate reducers and nitrite reducers were highly affected by the operational conditions and displayed high diversity. The number of retrieved species-level Operational Taxonomic Units (OTUs) for narG, napA, nirS and nirK genes was 11, 10, 31 and 22, respectively. In contrast, nitrous oxide reducers remained virtually unchanged at all conditions. About 90% of the retrieved nosZ sequences grouped in a single OTU with a high similarity with Oligotropha carboxidovorans nosZ gene. nirS-containing denitrifiers were dominant at all conditions and accounted for a significant amount of the total bacterial density. Current production decreased from 15.0 A·m−3 NCC (Net Cathodic Compartment), when nitrate was used as an electron acceptor, to 14.1 A·m−3 NCC in the case of nitrite. Contrarily, nitrous oxide (N2O) accumulation in the MFC was higher when nitrite was used as the main electron acceptor and accounted for 70% of gaseous nitrogen. Relative abundance of nitrite to nitrous oxide reducers, calculated as (qnirS+qnirK)/qnosZ, correlated positively with N2O emissions. Collectively, data indicate that bacteria catalysing the initial denitrification steps in a MFC are highly influenced by main electron acceptors and have a major influence on current production and N2O accumulation. PMID:23717427

Denitrifying bacterial communities affect current production and nitrous oxide accumulation in a microbial fuel cell.

PubMed

Vilar-Sanz, Ariadna; Puig, Sebastià; García-Lledó, Arantzazu; Trias, Rosalia; Balaguer, M Dolors; Colprim, Jesús; Bañeras, Lluís

2013-01-01

The biocathodic reduction of nitrate in Microbial Fuel Cells (MFCs) is an alternative to remove nitrogen in low carbon to nitrogen wastewater and relies entirely on microbial activity. In this paper the community composition of denitrifiers in the cathode of a MFC is analysed in relation to added electron acceptors (nitrate and nitrite) and organic matter in the cathode. Nitrate reducers and nitrite reducers were highly affected by the operational conditions and displayed high diversity. The number of retrieved species-level Operational Taxonomic Units (OTUs) for narG, napA, nirS and nirK genes was 11, 10, 31 and 22, respectively. In contrast, nitrous oxide reducers remained virtually unchanged at all conditions. About 90% of the retrieved nosZ sequences grouped in a single OTU with a high similarity with Oligotropha carboxidovorans nosZ gene. nirS-containing denitrifiers were dominant at all conditions and accounted for a significant amount of the total bacterial density. Current production decreased from 15.0 A · m(-3) NCC (Net Cathodic Compartment), when nitrate was used as an electron acceptor, to 14.1 A · m(-3) NCC in the case of nitrite. Contrarily, nitrous oxide (N2O) accumulation in the MFC was higher when nitrite was used as the main electron acceptor and accounted for 70% of gaseous nitrogen. Relative abundance of nitrite to nitrous oxide reducers, calculated as (qnirS+qnirK)/qnosZ, correlated positively with N2O emissions. Collectively, data indicate that bacteria catalysing the initial denitrification steps in a MFC are highly influenced by main electron acceptors and have a major influence on current production and N2O accumulation.

Electron reversal ionizer for detection of trace species using a spherical cathode

NASA Technical Reports Server (NTRS)

Boumsellek, Said (Inventor); Chutjian, Ara (Inventor)

1994-01-01

A reversal electron, high-current ionizer capable of focusing a beam of electrons to a reversal region employs an indirectly heated cathode having a concave emitting surface of width of W less than 2r, where r is the radius of curvature and preferably a ratio of width to radius approximately equal to one for optimum high current for a given cathode width.

Hollow cathodes as electron emitting plasma contactors Theory and computer modeling

NASA Technical Reports Server (NTRS)

Davis, V. A.; Katz, I.; Mandell, M. J.; Parks, D. E.

1987-01-01

Several researchers have suggested using hollow cathodes as plasma contactors for electrodynamic tethers, particularly to prevent the Shuttle Orbiter from charging to large negative potentials. Previous studies have shown that fluid models with anomalous scattering can describe the electron transport in hollow cathode generated plasmas. An improved theory of the hollow cathode plasmas is developed and computational results using the theory are compared with laboratory experiments. Numerical predictions for a hollow cathode plasma source of the type considered for use on the Shuttle are presented, as are three-dimensional NASCAP/LEO calculations of the emitted ion trajectories and the resulting potentials in the vicinity of the Orbiter. The computer calculations show that the hollow cathode plasma source makes vastly superior contact with the ionospheric plasma compared with either an electron gun or passive ion collection by the Orbiter.

Numerical investigation of the double-arcing phenomenon in a cutting arc torch

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mancinelli, B. R., E-mail: bmancinelli@frvt.utn.edu.ar; Minotti, F. O.; Kelly, H.

2014-07-14

A numerical investigation of the double-arcing phenomenon in a cutting arc torch is reported. The dynamics of the double-arcing were simulated by using a two-dimensional model of the gas breakdown development in the space-charge layer contiguous to the nozzle of a cutting arc torch operated with oxygen. The kinetic scheme includes ionization of heavy particles by electron impact, electron attachment, electron detachment, electron–ion recombination, and ion–ion recombination. Complementary measurements during double-arcing phenomena were also conducted. A marked rise of the nozzle voltage was found. The numerical results showed that the dynamics of a cathode spot at the exit of themore » nozzle inner surface play a key role in the raising of the nozzle voltage, which in turn allows more electrons to return to the wall at the nozzle inlet. The return flow of electrons thus closes the current loop of the double-arcing. The increase in the (floating) nozzle voltage is due to the fact that the increased electron emission at the spot is mainly compensated by the displacement current (the ions do not play a relevant role due to its low-mobility) until that the stationary state is achieved and the electron return flow fully-compensates the electron emission at the spot. A fairly good agreement was found between the model and the experiment for a spot emission current growth rate of the order of 7 × 10{sup 4} A/s.« less

Initiation of vacuum breakdown and failure mechanism of the carbon nanotube during thermal field emission

NASA Astrophysics Data System (ADS)

Dan, Cai; Lie, Liu; Jin-Chuan, Ju; Xue-Long, Zhao; Hong-Yu, Zhou; Xiao, Wang

2016-04-01

The carbon nanotube (CNT)-based materials can be used as vacuum device cathodes. Owing to the excellent field emission properties of CNT, it has great potentials in the applications of an explosive field emission cathode. The falling off of CNT from the substrate, which frequently appears in experiments, restricts its application. In addition, the onset time of vacuum breakdown limits the performance of the high-power explosive-emission-cathode-based diode. In this paper, the characteristics of the CNT, electric field strength, contact resistance and the kind of substrate material are varied to study the parameter effects on the onset time of vacuum breakdown and failure mechanism of the CNT by using the finite element method. Project supported by the National Natural Science Foundation of China (Grant Nos. 11305263 and 61401484).

Secondary electron emission yield dependence on the Fermi level in Silicon

NASA Astrophysics Data System (ADS)

Urrabazo, David; Goeckner, Matthew; Overzet, Lawrence

2013-09-01

Secondary Electron Emission (SEE) by ion bombardment plays a key role in determining the properties of many plasmas. As a result, significant efforts have been expended to control the SEE coefficient (increasing or decreasing it) by tailoring the electron work function of surfaces. A few recent publications point to the possibility of controlling the SEE coefficient of semiconductor surfaces in real time through controlling the numbers of electrons in the conduction band near the surface. Large control over the plasma was achieved by injecting electrons into the semiconductor just under the cathode surface via a subsurface PN junction. The hypothesis was that SEE is dependent on the numbers of electrons in the conduction band near the surface (which is related to the position of the Fermi level near the surface). We are testing the validity of this hypothesis. We have begun fundamental ion beam studies to explore this possible dependence of SEE on the Fermi energy level using Si. Various doping levels and dopants are being evaluated and the results of these tests will be presented. This work was supported in part by US Dept. of Energy. Acknowledgement to Dr. L. Raja at UT Austin.

Long-Life/Low-Power Ion-Gun Cathode

NASA Technical Reports Server (NTRS)

Fitzgerald, D. J.

1982-01-01

New cathode has form of hollow tube through which gas enters region of high electron density, produced by electric discharge with auxiliary electrode referred to as "keeper." Ion-gun cathode emits electrons that bombard gas in chamber. Ions accelerated out of source are used to dope semiconductor material.

Numerical model of the plasma formation at electron beam welding

NASA Astrophysics Data System (ADS)

Trushnikov, D. N.; Mladenov, G. M.

2015-01-01

The model of plasma formation in the keyhole in liquid metal as well as above the electron beam welding zone is described. The model is based on solution of two equations for the density of electrons and the mean electron energy. The mass transfer of heavy plasma particles (neutral atoms, excited atoms, and ions) is taken into account in the analysis by the diffusion equation for a multicomponent mixture. The electrostatic field is calculated using the Poisson equation. Thermionic electron emission is calculated for the keyhole wall. The ionization intensity of the vapors due to beam electrons and high-energy secondary and backscattered electrons is calibrated using the plasma parameters when there is no polarized collector electrode above the welding zone. The calculated data are in good agreement with experimental data. Results for the plasma parameters for excitation of a non-independent discharge are given. It is shown that there is a need to take into account the effect of a strong electric field near the keyhole walls on electron emission (the Schottky effect) in the calculation of the current for a non-independent discharge (hot cathode gas discharge). The calculated electron drift velocities are much bigger than the velocity at which current instabilities arise. This confirms the hypothesis for ion-acoustic instabilities, observed experimentally in previous research.

Effect of CO on the field emission properties of tetrapod zinc oxide cathode.

PubMed

Wang, Jinchan; Zhang, Xiaobing; Lei, Wei; Mao, Fuming; Cui, Yunkang; Xiao, Mei

2012-08-01

Tetrapod zinc oxide (T-ZnO), being a kind of nano-material, has large specific surface area and surface binding energy, which will make it sensitive to the ambient gas condition. So the field emission properties will be influenced by the gas adsorption when being applied as the cathode materials of field emission devices. Carbon monoxide is the main residual gas in T-ZnO field emission devices. In this paper, carbon monoxide was introduced into a field emission device with T-ZnO emitters. The field emission currents of tetrapod ZnO were compared before and after exposure to CO.

Temperature management of photo cathodes at MAMI and MESA

NASA Astrophysics Data System (ADS)

Aulenbacher, K.; Friederich, S.; Tyukin, V.

2018-05-01

Production of highly polarized electron current is limited by cathode heating which leads to the destruction of the active layer. For the new electron accelerator MESA a more efficient solution for the cathode cooling problem is required, with the goal to achieve acceptable temperatures at an incident power of about 1 Watt. The current status of temperature management of photo cathodes at MAMI and MESA is presented.

Electron Beam Misalignment Study of MIG for 42 GHz, 200 kW Gyrotron

NASA Astrophysics Data System (ADS)

Sharma, S. K.; Singh, Udaybir; Kumar, Nitin; Sahu, Naveen; Shekhawat, Narendra; Srivastava, Deepak; Alaria, M. K.; Bera, A.; Jain, P. K.; Sinha, A. K.

2017-10-01

This paper presents the electron beam misalignment study with respect to cathode position and cathode magnetic field of 42 GHz, 200 kW gyrotron. The performance of gyrotron is affected with the misalignment of cathode position. The simulation results confirm the tolerance of cathode misalignment with respect to the design parameters such as the transverse-to-axial velocity ratio, the maximum transverse velocity spread, etc.

Relativistic electron beam device

DOEpatents

Freeman, J.R.; Poukey, J.W.; Shope, S.L.; Yonas, G.

1975-07-01

A design is given for an electron beam device for irradiating spherical hydrogen isotope bearing targets. The accelerator, which includes hollow cathodes facing each other, injects an anode plasma between the cathodes and produces an approximately 10 nanosecond, megajoule pulse between the anode plasma and the cathodes. Targets may be repetitively positioned within the plasma between the cathodes, and accelerator diode arrangement permits materials to survive operation in a fusion power source. (auth)

Multi-layer carbon-based coatings for field emission

DOEpatents

Sullivan, J.P.; Friedmann, T.A.

1998-10-13

A multi-layer resistive carbon film field emitter device for cold cathode field emission applications is disclosed. The multi-layered film of the present invention consists of at least two layers of a conductive carbon material, preferably amorphous-tetrahedrally coordinated carbon, where the resistivities of adjacent layers differ. For electron emission from the surface, the preferred structure can be a top layer having a lower resistivity than the bottom layer. For edge emitting structures, the preferred structure of the film can be a plurality of carbon layers, where adjacent layers have different resistivities. Through selection of deposition conditions, including the energy of the depositing carbon species, the presence or absence of certain elements such as H, N, inert gases or boron, carbon layers having desired resistivities can be produced. 8 figs.

Gridded thermionic gun and integral superconducting ballistic bunch compression cavity

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schultheiss, Thomas

Electron-Ion colliders such as the Medium energy Electron Ion Collider (MEIC) being developed by JLAB require high current electrons with low energy spread for electron cooling of the collider ring. Accelerator techniques for improving bunch charge, average current, emittance, and energy spread are required for Energy Recovery Linacs (ERLs) and Circulator Rings (CR) for next generation colliders for nuclear physics experiments. Example candidates include thermionic-cathode electron guns with RF accelerating structures. Thermionic cathodes are known to produce high currents and have excellent lifetime. The success of the IR and THz Free-Electron Laser (FEL) designed and installed by Advanced Energy Systemsmore » at the Fritz Haber Institute (FHI) of the Max Planck Society in Berlin [1,2] demonstrates that gridded thermionic cathodes and rf systems be considered for next generation collider technology. In Phase 1 Advanced Energy Systems (AES) developed and analyzed a design concept using a superconducting cavity pair and gridded thermionic cathode. Analysis included Beam Dynamics and thermal analysis to show that a design of this type is feasible. The latest design goals for the MEIC electron cooler were for electron bunches of 420 pC at a frequency of 952.6 MHz with a magnetic field on the cathode of 2kG. This field magnetizes the beam imparting angular momentum that provides for helical motion of the electrons in the cooling solenoid. The helical motion increases the interaction time and improves the cooling efficiency. A coil positioned around the cathode providing 2kG field was developed. Beam dynamics simulations were run to develop the particle dynamics near the cathode and grid. Lloyd Young added capability to Tstep to include space charge effects between two plates and include image charge effects from the grid. He also added new pepper-pot geometry capability to account for honeycomb grids. These additions were used to develop the beam dynamics for this gun. The general design is a modified ballistic compression cavity pair with two independently powered cells [3]. The first is a cathode cell that includes the thermionic cathode and grid to provide for beam bunching. The second is a full cell with independent phasing and field levels designed to minimize energy spread. The primary goal for Phase II is to manufacture a superconducting gun with a thermionic cathode and imbedded coil. The system developed here is applicable to many high current electron accelerators. The analysis and design constraints imposed by the magnetized cathode make the cathode system developed here more complicated and limited than one without the magnetized beam constraints. High power ERLs would benefit by a gun with the capabilities shown here, 400 mA or more of current. ERLs hold great promise for electron cooling experiments, advanced light sources and Free Electron Lasers. This high current electron injector is a technological advance that will place the requirements for an ERL capable of providing quality bunches needed for cooling within the MEIC circulator ring within reach. This injector would have application to future ERLs around the world.« less

Plasmatic ion source

NASA Astrophysics Data System (ADS)

Semenov, A. P.

1986-02-01

A plasmatic ion source was built in which the hollow cathode above the two discharge chamber cathodes is readily replaced upon depletion after 250 to 300 h. The emission outlet hole is restored to original size by replacement of the cathode insert, while gas is continuously admitted by means of a spring mechanism. The source operates in the Penning discharge mode, with argon as the working gas. The hollow cathode is 36 mm long and has an inside diameter of 4 mm. The other two cathodes serve as pole shoes of a toroidal ferrite magnet which produces a longitudinal magnet field of 0.1 T induction in the discharge chamber. All three cathodes are made of magnetic steel and are insulated from cylindrical copper anode by teflon spacers. Heat is dissipated by oil, which carries it away to a water cooled housing compartment. The source generates an ion emission current of 20 mA with a discharge current of 200 mA at a pull voltage of 20kV.

Rapid start of oscillations in a magnetron with a "transparent" cathode.

PubMed

Fuks, Mikhail; Schamiloglu, Edl

2005-11-11

We report on the improvement of conditions for the rapid start of oscillations in magnetrons by increasing the amplitude of the operating wave that is responsible for the capture of electrons into spokes. This amplitude increase is achieved by using a hollow cathode with longitudinal strips removed, thereby making the cathode transparent to the wave electric field with azimuthal polarization. In addition, an optimal choice of the number and position of cathode strips provide favorable prebunching of the electron flow over the cathode for fast excitation of the operating mode. Particle-in-cell simulations of the A6 magnetron demonstrate these advantages of this novel cathode.

A survey of Kaufman thruster cathodes.

NASA Technical Reports Server (NTRS)

Weigand, A. J.; Nakanishi, S.

1971-01-01

A survey is presented of various cathodes which have been developed and used in the Kaufman ion thruster. The electron-bombardment type ion source used in the thruster is briefly described. The general design, operating characteristics, and power requirements are shown for each type of cathode from the refractory metals used in 1960 to the plasma discharge hollow cathodes of today. A detailed discussion of the hollow cathode is given describing starting and cyclic operating characteristics as well as more fundamental design parameters. Tests to date show that the plasma hollow cathode is an efficient electron source with demonstrated durability over 10,000 hours and should offer further performance and life improvements.

Ultrabright fluorescent OLEDS using triplet sinks

DOEpatents

Zhang, Yifan; Forrest, Stephen R; Thompson, Mark

2013-06-04

A first device is provided. The first device further comprises an organic light emitting device. The organic light emitting device further comprises an anode, a cathode, and an emissive layer disposed between the anode and the cathode. The emissive layer further comprises an organic host compound, an organic emitting compound capable of fluorescent emission at room temperature, and an organic dopant compound. The triplet energy of the dopant compound is lower than the triplet energy of the host compound. The dopant compound does not strongly absorb the fluorescent emission of the emitting compound.

Generation of multicomponent ion beams by a vacuum arc ion source with compound cathode.

PubMed

Savkin, K P; Yushkov, Yu G; Nikolaev, A G; Oks, E M; Yushkov, G Yu

2010-02-01

This paper presents the results of time-of-flight mass spectrometry studies of the elemental and mass-to-charge state compositions of metal ion beams produced by a vacuum arc ion source with compound cathode (WC-Co(0.5), Cu-Cr(0.25), Ti-Cu(0.1)). We found that the ion beam composition agrees well with the stoichiometric composition of the cathode material from which the beam is derived, and the maximum ion charge state of the different plasma components is determined by the ionization capability of electrons within the cathode spot plasma, which is common to all components. The beam mass-to-charge state spectrum from a compound cathode features a greater fraction of multiply charged ions for those materials with lower electron temperature in the vacuum arc cathode spot, and a smaller fraction for those with higher electron temperature within the spot. We propose a potential diagram method for determination of attainable ion charge states for all components of the compound cathodes.

Analysis of magnetically immersed electron guns with non-adiabatic fields

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pikin, Alexander; Alessi, James G.; Beebe, Edward N.

Electron diode guns, which have strongly varying magnetic or electric fields in a cathode-anode gap, were investigated in order to generate laminar electron beams with high current density using magnetically immersed guns. By creating a strongly varying radial electric field in a cathode-anode gap of the electron gun, it was demonstrated that the optical properties of the gun can be significantly altered, which allows the generation of a laminar, high-current electron beam with relatively low magnetic field on the cathode. The relatively high magnetic compression of the electron beam achieved by this method is important for producing electron beams withmore » high current density. A similar result can be obtained by inducing a strong variation of the magnetic field in a cathode-anode gap. It was observed that creating a dip in the axial magnetic field in the cathode-anode gap of an adiabatic electron gun has an optical effect similar to guns with strong variation of radial electric field. By analyzing the electron trajectories angles and presenting the results in a gun performance map different geometries of magnetically immersed electron guns with non-adiabatic fields are compared with each other and with a more traditional adiabatic electron gun. Some advantages and limitations of guns with non-adiabatic fields are outlined. In conclusion, the tests results of non-adiabatic electron gun with modified magnetic field are presented.« less

Analysis of magnetically immersed electron guns with non-adiabatic fields

DOE PAGES

Pikin, Alexander; Alessi, James G.; Beebe, Edward N.; ...

2016-11-08

Electron diode guns, which have strongly varying magnetic or electric fields in a cathode-anode gap, were investigated in order to generate laminar electron beams with high current density using magnetically immersed guns. By creating a strongly varying radial electric field in a cathode-anode gap of the electron gun, it was demonstrated that the optical properties of the gun can be significantly altered, which allows the generation of a laminar, high-current electron beam with relatively low magnetic field on the cathode. The relatively high magnetic compression of the electron beam achieved by this method is important for producing electron beams withmore » high current density. A similar result can be obtained by inducing a strong variation of the magnetic field in a cathode-anode gap. It was observed that creating a dip in the axial magnetic field in the cathode-anode gap of an adiabatic electron gun has an optical effect similar to guns with strong variation of radial electric field. By analyzing the electron trajectories angles and presenting the results in a gun performance map different geometries of magnetically immersed electron guns with non-adiabatic fields are compared with each other and with a more traditional adiabatic electron gun. Some advantages and limitations of guns with non-adiabatic fields are outlined. In conclusion, the tests results of non-adiabatic electron gun with modified magnetic field are presented.« less

Analysis of magnetically immersed electron guns with non-adiabatic fields.

PubMed

Pikin, Alexander; Alessi, James G; Beebe, Edward N; Raparia, Deepak; Ritter, John

2016-11-01

Electron diode guns, which have strongly varying magnetic or electric fields in a cathode-anode gap, were investigated in order to generate laminar electron beams with high current density using magnetically immersed guns. By creating a strongly varying radial electric field in a cathode-anode gap of the electron gun, it was demonstrated that the optical properties of the gun can be significantly altered, which allows the generation of a laminar, high-current electron beam with relatively low magnetic field on the cathode. The relatively high magnetic compression of the electron beam achieved by this method is important for producing electron beams with high current density. A similar result can be obtained by inducing a strong variation of the magnetic field in a cathode-anode gap. It was observed that creating a dip in the axial magnetic field in the cathode-anode gap of an adiabatic electron gun has an optical effect similar to guns with strong variation of radial electric field. By analyzing the electron trajectories angles and presenting the results in a gun performance map, different geometries of magnetically immersed electron guns with non-adiabatic fields are compared with each other and with a more traditional adiabatic electron gun. Some advantages and limitations of guns with non-adiabatic fields are outlined. The tests' results of a non-adiabatic electron gun with modified magnetic field are presented.

Cylindrical electron beam diode

DOEpatents

Bolduc, Paul E.

1976-01-01

A diode discharge device may include a tubular anode concentrically encircled by and spaced from a tubular cathode electrode with ends intermediate the ends of said anode electrode, and a metal conductive housing having a tubular wall disposed around the cathode electrode with end walls connected to the anode electrode. High energy electron current coupling is through an opening in the housing tubular wall to a portion of the cathode electrode intermediate its ends. Suitable utilization means may be within the anode electrode at positions to be irradiated by electrons emitted from the cathode electrode and transmitted through the anode walls.

Increase of intrinsic emittance induced by multiphoton photoemission from copper cathodes illuminated by femtosecond laser pulses

NASA Astrophysics Data System (ADS)

An, Chenjie; Zhu, Rui; Xu, Jun; Liu, Yaqi; Hu, Xiaopeng; Zhang, Jiasen; Yu, Dapeng

2018-05-01

Electron sources driven by femtosecond laser have important applications in many aspects, and the research about the intrinsic emittance is becoming more and more crucial. The intrinsic emittance of polycrystalline copper cathode, which was illuminated by femtosecond pulses (FWHM of the pulse duration was about 100 fs) with photon energies above and below the work function, was measured with an extremely low bunch charge (single-electron pulses) based on free expansion method. A minimum emittance was obtained at the photon energy very close to the effective work function of the cathode. When the photon energy decreased below the effective work function, emittance increased rather than decreased or flattened out to a constant. By investigating the dependence of photocurrent density on the incident laser intensity, we found the emission excited by pulsed photons with sub-work-function energies contained two-photon photoemission. In addition, the portion of two-photon photoemission current increased with the reduction of photon energy. We attributed the increase of emittance to the effect of two-photon photoemission. This work shows that conventional method of reducing the photon energy of excited light source to approach the room temperature limit of the intrinsic emittance may be infeasible for femtosecond laser. There would be an optimized photon energy value near the work function to obtain the lowest emittance for pulsed laser pumped photocathode.

Compact High Current Rare-Earth Emitter Hollow Cathode for Hall Effect Thrusters

NASA Technical Reports Server (NTRS)

Goebel, Dan M. (Inventor); Watkins, Ronnie M. (Inventor); Hofer, Richard R. (Inventor)

2012-01-01

An apparatus and method for achieving an efficient central cathode in a Hall effect thruster is disclosed. A hollow insert disposed inside the end of a hollow conductive cathode comprises a rare-earth element and energized to emit electrons from an inner surface. The cathode employs an end opening having an area at least as large as the internal cross sectional area of the rare earth insert to enhance throughput from the cathode end. In addition, the cathode employs a high aspect ratio geometry based on the cathode length to width which mitigates heat transfer from the end. A gas flow through the cathode and insert may be impinged by the emitted electrons to yield a plasma. One or more optional auxiliary gas feeds may also be employed between the cathode and keeper wall and external to the keeper near the outlet.

Effect of Li2O/Al cathode in Alq3 based organic light-emitting diodes.

PubMed

Shin, Eun Chul; Ahn, Hui Chul; Han, Wone Keun; Kim, Tae Wan; Lee, Won Jae; Hong, Jin Woong; Chung, Dong Hoe; Song, Min Jong

2008-09-01

An effect of bilayer cathode Li20/Al was studied in Alq3 based organic light-emitting diodes with a variation of Li2O layer thickness. The current-luminance-voltage characteristics of ITO/TPD/Alq3/Li2O/Al device were measured at ambient condition to investigate the effect of Li2O/Al. It was found that when the thickness of Li2O layer is in the range of 0.5-1 nm, there are improvements in luminance, efficiency, and turn-on voltage of the device. A current density and a luminance are increased by about 100 times, a turn-on voltage is lowered from 6 V to 3 V, a maximum current efficiency is improved by a factor of 2.3, and a maximum power efficiency is improved by a factor of 3.2 for a device with a use of thin Li2O layer compared to those of the one without the Li2Otron-barrier height for electron injection from the cathode to the emissive layer.

Structured electron beams from nano-engineered cathodes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lueangaramwong, A.; Mihalcea, D.; Andonian, G.

The ability to engineer cathodes at the nano-scale have open new possibilities such as enhancing quantum eciency via surface-plasmon excitation, forming ultra-low-emittance beams, or producing structured electron beams. In this paper we present numerical investigations of the beam dynamics associated to this class of cathode in the weak- and strong-field regimes.We finally discuss the possible applications of some of the achievable cathode patterns when coupled with other phase space manipulations.

Pulsed electromagnetic gas acceleration. [magnetohydrodynamics, plasma power sources and plasma propulsion

NASA Technical Reports Server (NTRS)

Jahn, R. G.; Vonjaskowsky, W. F.; Clark, K. E.

1975-01-01

Terminal voltage measurements with various cathodes and anodes in a high power, quasi-steady magnetoplasmadynamic (MPD) are discussed. The magnitude of the current at the onset of voltage fluctuations is shown to be an increasing function of cathode area and a weaker decreasing function of anode area. Tests with a fluted cathode indicated that the fluctuations originate in the plasma adjacent to the cathode rather than at the cathode surface. Measurements of radiative output from an optical cavity aligned to examine the current-carrying portion of a two-dimensional, 56 kA magnetoplasmadynamic discharge reveal no lasing in that region, consistent with calculations of electron excitation and resonance radiation trapping. A voltage-swept double probe technique allows single-shot determination of electron temperature and electron number density in the recombining MPD exhaust flow. Current distributions within the cavity of MPD hollow cathodes for various static prefills with no injected mass flow are examined.

The Nanophysics of Electron Emission and Breakdown for High Power Microwave Source

DTIC Science & Technology

2009-12-21

Professor John E. Scharer, Professor Dane Morgan, Professor Xin He, Graduate Student Nishant Sule, Graduate Student Vasilios Vlahos , Graduate...A231-A260 (2005), invited. 52. Vlahos , V., Booske, J.H., Morgan, D.D., “The Effects of Thin CsI coatings on the Work Function of Graphite Cathodes...using Ab-initio Modeling,” Appl. Phys. Lett. 91, paper 144102, 3 pages (2007). 53. Vlahos , V., Lee, Y.-L., Booske, J.H., Morgan, D., Turek, L

Thin films of aluminum nitride and aluminum gallium nitride for cold cathode applications

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sowers, A.T.; Christman, J.A.; Bremser, M.D.

1997-10-01

Cold cathode structures have been fabricated using AlN and graded AlGaN structures (deposited on n-type 6H-SiC) as the thin film emitting layer. The cathodes consist of an aluminum grid layer separated from the nitride layer by a SiO{sub 2} layer and etched to form arrays of either 1, 3, or 5 {mu}m holes through which the emitting nitride surface is exposed. After fabrication, a hydrogen plasma exposure was employed to activate the cathodes. Cathode devices with 5 {mu}m holes displayed emission for up to 30 min before failing. Maximum emission currents ranged from 10{endash}100 nA and required grid voltages rangingmore » from 20{endash}110 V. The grid currents were typically 1 to 10{sup 4} times the collector currents. {copyright} {ital 1997 American Institute of Physics.}« less

A fluorescent stilbenoid dendrimer for solution-processed blue light emitting diodes

NASA Astrophysics Data System (ADS)

Coya, C.; Álvarez, A. L.; Ramos, M.; de Andrés, A.; Zaldo, C.; Gómez, R.; Segura, J. L.; Seoane, C.

2008-04-01

We report a solution processed blue stilbenoid dendrimer based on a 1, 3, 5 - benzene core and endowed with a periphery of electron donating and solubilizing alkoxy chains. Raman analysis it is revealed as a helpful tool to investigate changes from the pristine material to the material in the OLED structure, explaining the differences between the dendrimer single layer thin film photoluminescence (PL) and the electroluminescence (EL) dendrimer active layer emission in the device. We report a blue EL emission (439 nm) and a very promising effective mobility value of 2.55 × 10 -5 cm2/(V•s) suggesting good transport properties for non doped blue OLEDs that use air stable Al as the cathode.

Graphene enhanced field emission from InP nanocrystals.

PubMed

Iemmo, L; Di Bartolomeo, A; Giubileo, F; Luongo, G; Passacantando, M; Niu, G; Hatami, F; Skibitzki, O; Schroeder, T

2017-12-08

We report the observation of field emission (FE) from InP nanocrystals (NCs) epitaxially grown on an array of p-Si nanotips. We prove that FE can be enhanced by covering the InP NCs with graphene. The measurements are performed inside a scanning electron microscope chamber with a nano-controlled W-thread used as an anode. We analyze the FE by Fowler-Nordheim theory and find that the field enhancement factor increases monotonically with the spacing between the anode and the cathode. We also show that InP/p-Si junction has a rectifying behavior, while graphene on InP creates an ohmic contact. Understanding the fundamentals of such nanojunctions is key for applications in nanoelectronics.

Graphene enhanced field emission from InP nanocrystals

NASA Astrophysics Data System (ADS)

Iemmo, L.; Di Bartolomeo, A.; Giubileo, F.; Luongo, G.; Passacantando, M.; Niu, G.; Hatami, F.; Skibitzki, O.; Schroeder, T.

2017-12-01

We report the observation of field emission (FE) from InP nanocrystals (NCs) epitaxially grown on an array of p-Si nanotips. We prove that FE can be enhanced by covering the InP NCs with graphene. The measurements are performed inside a scanning electron microscope chamber with a nano-controlled W-thread used as an anode. We analyze the FE by Fowler-Nordheim theory and find that the field enhancement factor increases monotonically with the spacing between the anode and the cathode. We also show that InP/p-Si junction has a rectifying behavior, while graphene on InP creates an ohmic contact. Understanding the fundamentals of such nanojunctions is key for applications in nanoelectronics.

Field emission and photoluminescence characteristics of ZnS nanowires via vapor phase growth

NASA Astrophysics Data System (ADS)

Chang, Yongqin; Wang, Mingwei; Chen, Xihong; Ni, Saili; Qiang, Weijing

2007-05-01

Large-area ZnS nanowires were synthesized through a vapor phase deposition method. X-ray diffraction and electron microscopy results show that the products are composed of single crystalline ZnS nanowires with a cubic structure. The nanowires have sharp tips and are distributed uniformly on silicon substrates. The diameter of the bases is in the range of 320-530 nm and that of the tips is around 20-30 nm. The strong ultraviolet emission in the photoluminescence spectra also demonstrates that the ZnS nanowires are of high crystalline perfection. Field emission measurements reveal that the ZnS nanowires have a fairly low threshold field, which may be ascribed to their very sharp tips, rough surfaces and high crystal quality. The perfect field emission ability of the ZnS nanowires makes them a promising candidate for the fabrication of flexible cold cathodes.

Ultrafast transmission electron microscopy using a laser-driven field emitter: Femtosecond resolution with a high coherence electron beam.

PubMed

Feist, Armin; Bach, Nora; Rubiano da Silva, Nara; Danz, Thomas; Möller, Marcel; Priebe, Katharina E; Domröse, Till; Gatzmann, J Gregor; Rost, Stefan; Schauss, Jakob; Strauch, Stefanie; Bormann, Reiner; Sivis, Murat; Schäfer, Sascha; Ropers, Claus

2017-05-01

We present the development of the first ultrafast transmission electron microscope (UTEM) driven by localized photoemission from a field emitter cathode. We describe the implementation of the instrument, the photoemitter concept and the quantitative electron beam parameters achieved. Establishing a new source for ultrafast TEM, the Göttingen UTEM employs nano-localized linear photoemission from a Schottky emitter, which enables operation with freely tunable temporal structure, from continuous wave to femtosecond pulsed mode. Using this emission mechanism, we achieve record pulse properties in ultrafast electron microscopy of 9Å focused beam diameter, 200fs pulse duration and 0.6eV energy width. We illustrate the possibility to conduct ultrafast imaging, diffraction, holography and spectroscopy with this instrument and also discuss opportunities to harness quantum coherent interactions between intense laser fields and free-electron beams. Copyright © 2016 The Authors. Published by Elsevier B.V. All rights reserved.

High Current Density Cathodes for Future Vacuum Electronics Applications

DTIC Science & Technology

2008-05-30

Tube - device for generating high levels of RF power DARPA Defense Advanced Research Agency PBG Photonic band gap W- Band 75-111 GHz dB Decibels GHz...Extended interaction klystron 1. Introduction All RF vacuum electron sources require a high quality electron beam for efficient operation. Research on...with long life. Pres- ently, only thermionic dispenser cathodes are practical for high power RF sources. Typical thermi- onic cathodes consists of a

Electron current extraction from a permanent magnet waveguide plasma cathode.

PubMed

Weatherford, B R; Foster, J E; Kamhawi, H

2011-09-01

An electron cyclotron resonance plasma produced in a cylindrical waveguide with external permanent magnets was investigated as a possible plasma cathode electron source. The configuration is desirable in that it eliminates the need for a physical antenna inserted into the plasma, the erosion of which limits operating lifetime. Plasma bulk density was found to be overdense in the source. Extraction currents over 4 A were achieved with the device. Measurements of extracted electron currents were similar to calculated currents, which were estimated using Langmuir probe measurements at the plasma cathode orifice and along the length of the external plume. The influence of facility effects and trace ionization in the anode-cathode gap are also discussed. © 2011 American Institute of Physics

Gated Field-Emission Cathode Radio-Frequency (RF) Gun

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fermi Research Alliance, Fermi Alliance

The goal of this CRADA was to procure the carbon nanotube cathode from Radiabeam, install it in HBESL and make current measurements as a function of the gun gradient. The gun was operated at 1.3 GHz. After testing, send the cathode back to RadiaBeam for surface analysis.

An Overview of Electron Acceptors in Microbial Fuel Cells

PubMed Central

Ucar, Deniz; Zhang, Yifeng; Angelidaki, Irini

2017-01-01

Microbial fuel cells (MFC) have recently received increasing attention due to their promising potential in sustainable wastewater treatment and contaminant removal. In general, contaminants can be removed either as an electron donor via microbial catalyzed oxidization at the anode or removed at the cathode as electron acceptors through reduction. Some contaminants can also function as electron mediators at the anode or cathode. While previous studies have done a thorough assessment of electron donors, cathodic electron acceptors and mediators have not been as well described. Oxygen is widely used as an electron acceptor due to its high oxidation potential and ready availability. Recent studies, however, have begun to assess the use of different electron acceptors because of the (1) diversity of redox potential, (2) needs of alternative and more efficient cathode reaction, and (3) expanding of MFC based technologies in different areas. The aim of this review was to evaluate the performance and applicability of various electron acceptors and mediators used in MFCs. This review also evaluated the corresponding performance, advantages and disadvantages, and future potential applications of select electron acceptors (e.g., nitrate, iron, copper, perchlorate) and mediators. PMID:28469607

Neutralization of an ion beam from the end-Hall ion source by a plasma electron source based on a discharge in crossed E × H fields

NASA Astrophysics Data System (ADS)

Dostanko, A. P.; Golosov, D. A.

2009-10-01

The possibility of using a plasma electron source (PES) with a discharge in crossed E × H field for compensating the ion beam from an end-Hall ion source (EHIS) is analyzed. The PES used as a neutralizer is mounted in the immediate vicinity of the EHIS ion generation and acceleration region at 90° to the source axis. The behavior of the discharge and emission parameters of the EHIS is determined for operation with a filament neutralizer and a plasma electron source. It is found that the maximal discharge current from the ion source attains a value of 3.8 A for operation with a PES and 4 A for operation with a filament compensator. It is established that the maximal discharge current for the ion source strongly depends on the working gas flow rate for low flow rates (up to 10 ml/min) in the EHIS; for higher flow rates, the maximum discharge current in the EHIS depends only on the emissivity of the PES. Analysis of the emission parameters of EHISs with filament and plasma neutralizers shows that the ion beam current and the ion current density distribution profile are independent of the type of the electron source and the ion current density can be as high as 0.2 mA/cm2 at a distance of 25 cm from the EHIS anode. The balance of currents in the ion source-electron source system is considered on the basis of analysis of operation of EHISs with various sources of electrons. It is concluded that the neutralization current required for operation of an ion source in the discharge compensation mode must be equal to or larger than the discharge current of the ion source. The use of PES for compensating the ion beam from an end-Hall ion source proved to be effective in processes of ion-assisted deposition of thin films using reactive gases like O2 or N2. The application of the PES technique makes it possible to increase the lifetime of the ion-assisted deposition system by an order of magnitude (the lifetime with a Ti cathode is at least 60 h and is limited by the replacement life of the deposited cathode insertion).

Energetic Charged Particle Emission from Hydrogen-Loaded pd and ti Cathodes and its Enhancement by He-4 Implantation

NASA Astrophysics Data System (ADS)

Lipson, A. G.; Miley, G. H.; Lipson, A. G.; Lyakhov, B. F.; Roussetski, A. S.

2006-02-01

In this paper, we demonstrate reproducible emissions of energetic alphas and protons appearing in an energy range where both cosmic ray interference and possible alpha emissions from contamination (e.g., radon) is assumed to be negligible. We also show that He4 doping of Pd and Ti cathodes leads to a significant enhancement of the energetic charged particles emission (ECPE). This measurement of the emissions of energetic (MeV) particles, in a region of low background interference plus their enhancement by He4 doping provides very strong support for the existence of LENR processes in the crystalline lattice of deuterated metals.

Cathode performance during two beam operation of the high current high polarization electron gun for eRHIC

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rahman, O.; Ben-Zvi, I.; Degen, C.

Two electron beams from two activated bulk GaAs photocathodes were successfully combined during the recent beam test of the High Current High Polarization Electron gun for eRHIC. The beam test took place in Stangenes Industries in Palo Alto, CA, where the cathodes were placed in diagonally opposite locations inside the high voltage shroud. No significant cross talking between the cathodes was found for the pertinent vacuum and low average current operation, which is very promising towards combining multiple beams for higher average current. This paper describes the cathode preparation, transport and cathode performance in the gun for the combining test,more » including the QE and lifetimes of the photocathodes at various steps of the experiment.« less

Design and development of indirectly heated solid cathode for strip type electron gun.

PubMed

Maiti, Namita; Mukherjee, S; Kumar, Bhunesh; Barve, U D; Suryawanshi, V B; Das, A K

2010-01-01

Design analysis of a high power indirectly heated solid cathode (for a 200 kW, 45 kV, and 270 degrees bent strip type electron gun) has been presented. The design approach consists of simulation followed by extensive experimentation with different cathode configurations. The preferred cathode is of trapezoidal section (8 x 4 x 2 mm(3)) with an emitting area of 110 x 4 mm(2) made up of tantalum operating at about 2500 K. The solid cathode at the operating temperature of 2500 K generated a well defined electron beam. Electromagnetic and thermomechanical simulation is used to optimize the shape of the beam. Thermal modeling has also been used to analyze the temperature and stress distribution on the electrodes. The simulation results are validated by experimental measurement.

Experimental observation of polarized electroluminescence from edge-emission organic light emitting devices

NASA Astrophysics Data System (ADS)

Ran, G. Z.; Jiang, D. F.; Kan, Q.; Chen, H. D.

2010-12-01

We have observed a strongly polarized edge-emission from an organic light emitting device (OLED) with a silicon anode and a stacked Sm/Au (or Ag) cathode. For the OLED with a Sm/Au cathode, the transverse magnetic (TM) mode is stronger than the transverse electric (TE) mode by a factor of 2, while the polarization ratio of TM:TE is close to 300 for that with a Sm/Ag cathode. The polarization results from the scattering of surface plasmon polaritons at the device boundary. Such a silicon-based OLED is potentially an electrically excited SPP source in plasmonics.

Hollow-Cathode Source Generates Plasma

NASA Technical Reports Server (NTRS)

Deininger, W. D.; Aston, G.; Pless, L. C.

1989-01-01

Device generates argon, krypton, or xenon plasma via thermionic emission and electrical discharge within hollow cathode and ejects plasma into surrounding vacuum. Goes from cold start up to full operation in less than 5 s after initial application of power. Exposed to moist air between operations without significant degradation of starting and running characteristics. Plasma generated by electrical discharge in cathode barrel sustained and aided by thermionic emission from emitter tube. Emitter tube does not depend on rare-earth oxides, making it vulnerable to contamination by exposure to atmosphere. Device modified for use as source of plasma in laboratory experiments or industrial processes.

Microgap ultra-violet detector

DOEpatents

Wuest, Craig R.; Bionta, Richard M.

1994-01-01

A microgap ultra-violet detector of photons with wavelengths less than 400 run (4000 Angstroms) which comprises an anode and a cathode separated by a gas-filled gap and having an electric field placed across the gap. Either the anode or the cathode is semi-transparent to UV light. Upon a UV photon striking the cathode an electron is expelled and accelerated across the gap by the electric field causing interactions with other electrons to create an electron avalanche which contacts the anode. The electron avalanche is detected and converted to an output pulse.

Microgap ultra-violet detector

DOEpatents

Wuest, C.R.; Bionta, R.M.

1994-09-20

A microgap ultra-violet detector of photons with wavelengths less than 400 run (4,000 Angstroms) which comprises an anode and a cathode separated by a gas-filled gap and having an electric field placed across the gap is disclosed. Either the anode or the cathode is semi-transparent to UV light. Upon a UV photon striking the cathode an electron is expelled and accelerated across the gap by the electric field causing interactions with other electrons to create an electron avalanche which contacts the anode. The electron avalanche is detected and converted to an output pulse. 2 figs.

Quantum efficiency temporal response and lifetime of a GaAs cathode in SRF electron gun

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, E.; Ben-Zvi, I.; Kewisch, J.

2010-05-23

RF electron guns with a strained super lattice GaAs cathode can generate polarized electron beam of higher brightness and lower emittance than do DC guns, due to their higher field gradient at the cathode's surface. In a normal conducting RF gun, the extremely high vaccum required by these cathodes can not be met. We report on an experiment with a superconducting SRF gun, which can maintain a vacuum of nearly 10-12 torr because of cryo-pumping at the temperature of 4.2K. With conventional activation, we obtained a QE of 3% at 532 nm, with lifetime of nearly 3 days in themore » preparation chamber. We plan to use this cathode in a 1.3 GHz 1/2 cell SRF gun to study its performance. In addition, we studied the multipacting at the location of cathode. A new model based on the Forkker-Planck equation which can estimate the bunch length of the electron beam is discussed in this paper. Future particle accelerators such as eRHIC and ILC require high brightness, high current polarized electrons Recently, using a superlattice crystal, the maximum polarization of 95% was reached. Activation with Cs,O lowers the electron affinity and makes it energetically possible for all the electrons excited in to the conduction band and reach the surface to escape into the vacuum. Presently the polarized electron sources are based on DC gun, such as that at the CEBAF at Jlab. In these devices, the life time of the cathode is extended due to the reduced back bombardment in their UHV conditions. However, the low accelerating gradient of the DC guns lead to poor longitudinal emittance. The higher accelerating gradient of the RF gun generates low emittance beams. Superconducting RF guns combine the excellent vacuum conditions of the DC guns with the higher accelerating gradients of the RF guns and provide potentially a long lived cathode with very low transverse and longitudinal emittance. In our work at BNL, we successfully activated the GaAs. The quantum efficient is 3% at 532 nm and is expected to improve further. In addition, we studied the multipacting at the location of cathode. A new model based on the Forkker-Planck equation which can estimate the bunch length of the electron beam is discussed in this paper.« less

Single Crystal Diamond Needle as Point Electron Source

PubMed Central

Kleshch, Victor I.; Purcell, Stephen T.; Obraztsov, Alexander N.

2016-01-01

Diamond has been considered to be one of the most attractive materials for cold-cathode applications during past two decades. However, its real application is hampered by the necessity to provide appropriate amount and transport of electrons to emitter surface which is usually achieved by using nanometer size or highly defective crystallites having much lower physical characteristics than the ideal diamond. Here, for the first time the use of single crystal diamond emitter with high aspect ratio as a point electron source is reported. Single crystal diamond needles were obtained by selective oxidation of polycrystalline diamond films produced by plasma enhanced chemical vapor deposition. Field emission currents and total electron energy distributions were measured for individual diamond needles as functions of extraction voltage and temperature. The needles demonstrate current saturation phenomenon and sensitivity of emission to temperature. The analysis of the voltage drops measured via electron energy analyzer shows that the conduction is provided by the surface of the diamond needles and is governed by Poole-Frenkel transport mechanism with characteristic trap energy of 0.2–0.3 eV. The temperature-sensitive FE characteristics of the diamond needles are of great interest for production of the point electron beam sources and sensors for vacuum electronics. PMID:27731379

Simplifying microbial electrosynthesis reactor design.

PubMed

Giddings, Cloelle G S; Nevin, Kelly P; Woodward, Trevor; Lovley, Derek R; Butler, Caitlyn S

2015-01-01

Microbial electrosynthesis, an artificial form of photosynthesis, can efficiently convert carbon dioxide into organic commodities; however, this process has only previously been demonstrated in reactors that have features likely to be a barrier to scale-up. Therefore, the possibility of simplifying reactor design by both eliminating potentiostatic control of the cathode and removing the membrane separating the anode and cathode was investigated with biofilms of Sporomusa ovata. S. ovata reduces carbon dioxide to acetate and acts as the microbial catalyst for plain graphite stick cathodes as the electron donor. In traditional 'H-cell' reactors, where the anode and cathode chambers were separated with a proton-selective membrane, the rates and columbic efficiencies of microbial electrosynthesis remained high when electron delivery at the cathode was powered with a direct current power source rather than with a potentiostat-poised cathode utilized in previous studies. A membrane-less reactor with a direct-current power source with the cathode and anode positioned to avoid oxygen exposure at the cathode, retained high rates of acetate production as well as high columbic and energetic efficiencies. The finding that microbial electrosynthesis is feasible without a membrane separating the anode from the cathode, coupled with a direct current power source supplying the energy for electron delivery, is expected to greatly simplify future reactor design and lower construction costs.

A centre-triggered magnesium fuelled cathodic arc thruster uses sublimation to deliver a record high specific impulse

NASA Astrophysics Data System (ADS)

Neumann, Patrick R. C.; Bilek, Marcela; McKenzie, David R.

2016-08-01

The cathodic arc is a high current, low voltage discharge that operates in vacuum and provides a stream of highly ionised plasma from a solid conducting cathode. The high ion velocities, together with the high ionisation fraction and the quasineutrality of the exhaust stream, make the cathodic arc an attractive plasma source for spacecraft propulsion applications. The specific impulse of the cathodic arc thruster is substantially increased when the emission of neutral species is reduced. Here, we demonstrate a reduction of neutral emission by exploiting sublimation in cathode spots and enhanced ionisation of the plasma in short, high-current pulses. This, combined with the enhanced directionality due to the efficient erosion profiles created by centre-triggering, substantially increases the specific impulse. We present experimentally measured specific impulses and jet power efficiencies for titanium and magnesium fuels. Our Mg fuelled source provides the highest reported specific impulse for a gridless ion thruster and is competitive with all flight rated ion thrusters. We present a model based on cathode sublimation and melting at the cathodic arc spot explaining the outstanding performance of the Mg fuelled source. A further significant advantage of an Mg-fuelled thruster is the abundance of Mg in asteroidal material and in space junk, providing an opportunity for utilising these resources in space.

Development and Experimental Operation of a Flashboard Plasma Cathode Test Stand

DTIC Science & Technology

2012-06-01

grid-controlled system [31]. J.R. Bayless and his group developed a new type of plasma cathode electron gun qualified for pulsed and continuous...Interferometry of flashboard and cable- gun plasma opening switches on hawk,” IEEE Trans. Plasma Sci., vol. 25, no. 2, pp. 189–195, Apr. 1997. [29] C...The plasma -cathode electron gun ,” IEEE Journal of Quantum Electronics, vol. 10, no. 2, pp. 213–218, Feb 1974. [33] Ady Hershcovitch

A new design of indirectly heated cathode based strip type electron gun.

PubMed

Maiti, Namita; Lijeesh, K; Barve, U D; Quadri, Nishad; Tembhare, G U; Mukherjee, S; Thakur, K B; Das, A K

2013-08-01

A new design of indirectly heated solid cathode based electron gun (200 kW, 45 kV, 270° bent strip type electron gun) has been presented. The design issue addressed is the uniformity of temperature on the solid cathode using (a) a multi-segmented filament with variable height as the primary heat source and (b) trapezoidal shaped single long filament as the primary heat source. The proposed design in this paper is based on computer simulation and validated by extensive experimentations. The design emphasis is on maintaining uniform temperature on the solid cathode. The designed multi-segment filament and the single long filament provide a temperature uniformity on the solid cathode of about 250 K and 110 K, respectively. The better temperature uniformity inspite of the thermal expansion, in case of a single long filament tightly clamped at two ends, has been possible due to shaping of the single filament with a number of constituent sections such that the thermal expansion of different sections forming the actual filament takes care of not only the mechanical stability but also does not affect the emitting surface of the filament. Experiments show that the modified design achieves a one to one correspondence of the solid cathode length and the electron beam length emitted from the solid cathode.

Anode initiated surface flashover switch

DOEpatents

Brainard, John P.; Koss, Robert J.

2003-04-29

A high voltage surface flashover switch has a pair of electrodes spaced by an insulator. A high voltage is applied to an anode, which is smaller than the opposing, grounded, cathode. When a controllable source of electrons near the cathode is energized, the electrons are attracted to the anode where they reflect to the insulator and initiate anode to cathode breakdown.

Long lifetime hollow cathodes for 30-cm mercury ion thrusters

NASA Technical Reports Server (NTRS)

Mirtich, M. J.; Kerslake, W. R.

1976-01-01

An experimental investigation of hollow cathodes for 30-cm Hg bombardment thrusters was carried out. Both main and neutralizer cathode configurations were tested with both rolled foil inserts coated with low work function material and impregnated porous tungsten inserts. Temperature measurements of an impregnated insert at various positions in the cathode were made. These, along with the cathode thermal profile are presented. A theory for rolled foil and impregnated insert operation and lifetime in hollow cathodes is developed. Several endurance tests, as long as 18000 hours at emission currents of up to 12 amps were attained with no degradation in performance.

Prediction of field emitter cathode lifetime based on measurement of I- V curves

NASA Astrophysics Data System (ADS)

Bormashov, V. S.; Nikolski, K. N.; Baturin, A. S.; Sheshin, E. P.

2003-06-01

A technique is presented, which allows the prediction of field emitter cathode lifetime without long-term direct measurements of cathode parameters stability. This technique is based on periodic measurements of cathode I- V characteristics. Moreover, it allows performing a post-experiment optimization for the appropriate choice of the feedback system to provide a stable operation during a long time. The proposed technique was applied to study the emission properties of reticulated vitreous carbon (RVC) and thermo-enlarged graphite (TEG). For the given cathodes, the characteristic time of the cathode destruction was estimated.

Electricity generation and pollutant degradation using a novel biocathode coupled photoelectrochemical cell.

PubMed

Du, Yue; Feng, Yujie; Qu, Youpeng; Liu, Jia; Ren, Nanqi; Liu, Hong

2014-07-01

The photoelectrochemical cell (PEC) is a promising tool for the degradation of organic pollutants and simultaneous electricity recovery, however, current cathode catalysts suffer from high costs and short service lives. Herein, we present a novel biocathode coupled PEC (Bio-PEC) integrating the advantages of photocatalytic anode and biocathode. Electrochemical anodized TiO2 nanotube arrays fabricated on Ti substrate were used as Bio-PEC anodes. Field-emission scanning electron microscope images revealed that the well-aligned TiO2 nanotubes had inner diameters of 60-100 nm and wall-thicknesses of about 5 nm. Linear sweep voltammetry presented the pronounced photocurrent output (325 μA/cm(2)) under xenon illumination, compared with that under dark conditions. Comparing studies were carried out between the Bio-PEC and PECs with Pt/C cathodes. The results showed that the performance of Pt/C cathodes was closely related with the structure and Pt/C loading amounts of cathodes, while the Bio-PEC achieved similar methyl orange (MO) decoloration rate (0.0120 min(-1)) and maximum power density (211.32 mW/m(2)) to the brush cathode PEC with 50 mg Pt/C loading (Brush-PEC, 50 mg). The fill factors of Bio-PEC and Brush-PEC (50 mg) were 39.87% and 43.06%, respectively. The charge transfer resistance of biocathode was 13.10 Ω, larger than the brush cathode with 50 mg Pt/C (10.68 Ω), but smaller than the brush cathode with 35 mg Pt/C (18.35 Ω), indicating the comparable catalytic activity with Pt/C catalyst. The biocathode was more dependent on the nutrient diffusion, such as nitrogen and inorganic carbon, thus resulting in relatively higher diffusion resistance compared to the brush cathode with 50 mg Pt/C loading that yielded similar MO removal and power output. Considering the performance and cost of PEC system, the biocathode was a promising alternative for the Pt/C catalyst.

Microsecond Electron Beam Source with Electron Energy Up to 400 Kev and Plasma Anode

NASA Astrophysics Data System (ADS)

Abdullin, É. N.; Basov, G. F.; Shershnev, S.

2017-12-01

A new high-power source of electrons with plasma anode for producing high-current microsecond electron beams with electron energy up to 400 keV has been developed, manufactured, and put in operation. To increase the cross section and pulse current duration of the beam, a multipoint explosive emission cathode is used in the electron beam source, and the beam is formed in an applied external guiding magnetic field. The Marx generator with vacuum insulation is used as a high-voltage source. Electron beams with electron energy up to 300-400 keV, current of 5-15 kA, duration of 1.5-3 μs, energy up to 4 kJ, and cross section up to 150 cm2 have been produced. The operating modes of the electron beam source are realized in which the applied voltage is influenced weakly on the current. The possibility of source application for melting of metal surfaces is demonstrated.

High voltage threshold for stable operation in a dc electron gun

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yamamoto, Masahiro, E-mail: masahiro@post.kek.jp; Nishimori, Nobuyuki, E-mail: n-nishim@tagen.tohoku.ac.jp

We report clear observation of a high voltage (HV) threshold for stable operation in a dc electron gun. The HV hold-off time without any discharge is longer than many hours for operation below the threshold, while it is roughly 10 min above the threshold. The HV threshold corresponds to the minimum voltage where discharge ceases. The threshold increases with the number of discharges during HV conditioning of the gun. Above the threshold, the amount of gas desorption per discharge increases linearly with the voltage difference from the threshold. The present experimental observations can be explained by an avalanche discharge modelmore » based on the interplay between electron stimulated desorption (ESD) from the anode surface and subsequent secondary electron emission from the cathode by the impact of ionic components of the ESD molecules or atoms.« less

Diagnostics for a 1.2 kA, 1 MeV, electron induction injector

NASA Astrophysics Data System (ADS)

Houck, T. L.; Anderson, D. E.; Eylon, S.; Henestroza, E.; Lidia, S. M.; Vanecek, D. L.; Westenskow, G. A.; Yu, S. S.

1998-12-01

We are constructing a 1.2 kA, 1 MeV, electron induction injector as part of the RTA program, a collaborative effort between LLNL and LBNL to develop relativistic klystrons for Two-Beam Accelerator applications. The RTA injector will also be used in the development of a high-gradient, low-emittance, electron source and beam diagnostics for the second axis of the Dual Axis Radiographic Hydrodynamic Test (DARHT) Facility. The electron source will be a 3.5″-diameter, thermionic, flat-surface, m-type cathode with a maximum shroud field stress of approximately 165 kV/cm. Additional design parameters for the injector include a pulse length of over 150 ns flat top (1% energy variation), and a normalized edge emittance of less than 200 π-mm-mr. Precise measurement of the beam parameters is required so that performance of the RTA injector can be confidently scaled to the 4 kA, 3 MeV, and 2-microsecond pulse parameters of the DARHT injector. Planned diagnostics include an isolated cathode with resistive divider for direct measurement of current emission, resistive wall and magnetic probe current monitors for measuring beam current and centroid position, capacitive probes for measuring A-K gap voltage, an energy spectrometer, and a pepperpot emittance diagnostic. Details of the injector, beam line, and diagnostics are presented.

Direct current H- source for the medicine accelerator (invited)

NASA Astrophysics Data System (ADS)

Belchenko, Yu.; Savkin, V.

2004-05-01

A compact cw hydrogen negative ion source having reliable operation and a simplified maintenance is developed at Budker Institute of Nuclear Physics for a tandem accelerator of boron capture neutron therapy installation. The source uses a Penning discharge with a hydrogen and cesium feed through the hollows in the cathodes. Discharge voltage is about 60-80 V, current 9 A, hydrogen pressure 4-5 Pa, magnetic field 0.05-0.1 T, and cesium seed <1 mg/h. Negative ions are mainly produced on the cesiated anode surface due to conversion of hydrogen atoms. An optimal anode temperature is 250-350 °C. Negative ion beam current is directly proportional to the discharge current and to the emission hole area. A triode system for the beam extraction and acceleration system is used. The flux of accompanying extracted electrons was decreased by filtering in the transverse magnetic field. This electron flux was intercepted to the special electrode, biased at 4 kV potential with respect to the anode. Source stable cw operation for several hour runs was multiply tested. A H- ion beam with current up to 8 mA, beam energy 23 keV was produced regularly. Negative ion current of heavy impurities had a value of about 3% of the total beam current. Beam normalized emittance is about 0.3 π mm mrad and emission current density -0.1 A/cm2. A built-in cathode heater provides the operation quick start.

Solenoid and monocusp ion source

DOEpatents

Brainard, John Paul; Burns, Erskine John Thomas; Draper, Charles Hadley

1997-01-01

An ion source which generates hydrogen ions having high atomic purity incorporates a solenoidal permanent magnets to increase the electron path length. In a sealed envelope, electrons emitted from a cathode traverse the magnetic field lines of a solenoid and a monocusp magnet between the cathode and a reflector at the monocusp. As electrons collide with gas, the molecular gas forms a plasma. An anode grazes the outer boundary of the plasma. Molecular ions and high energy electrons remain substantially on the cathode side of the cusp, but as the ions and electrons are scattered to the aperture side of the cusp, additional collisions create atomic ions. The increased electron path length allows for smaller diameters and lower operating pressures.

Solenoid and monocusp ion source

DOEpatents

Brainard, J.P.; Burns, E.J.T.; Draper, C.H.

1997-10-07

An ion source which generates hydrogen ions having high atomic purity incorporates a solenoidal permanent magnets to increase the electron path length. In a sealed envelope, electrons emitted from a cathode traverse the magnetic field lines of a solenoid and a monocusp magnet between the cathode and a reflector at the monocusp. As electrons collide with gas, the molecular gas forms a plasma. An anode grazes the outer boundary of the plasma. Molecular ions and high energy electrons remain substantially on the cathode side of the cusp, but as the ions and electrons are scattered to the aperture side of the cusp, additional collisions create atomic ions. The increased electron path length allows for smaller diameters and lower operating pressures. 6 figs.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Matsubara, Y.; Tahara, H.; Nogawa, S.

A new type of electron source for ion sources, which serves as a cathode has been developed. In this cathode, a high-density microwave plasma is produced under the electron-cyclotron-resonance (ECR) condition, and a high electron current of several amperes can be extracted from it. The structure of this microwave plasma (MP) cathode is very simple and compact. A rod antenna connected to a coaxial line for introducing the microwave power (2.45 GHz) and a rare-earth metal permanent magnet for producing the ECR condition are major components. Since there is no filament in this MP cathode, it has a longer lifetimemore » than the equivalent thermionic filament electron emitter. It offers a great advantage to the operation with reactive as well as inert gases. This MP cathode has been adapted in Kaufman-type ion source and have successfully obtained an argon ion-beam current of 110 mA and an oxygen ion-beam current of 43 mA in 25 mm diameter.« less

Robust Low-Cost Cathode for Commercial Applications

NASA Technical Reports Server (NTRS)

Patterson, Michael J.

2007-01-01

Under funding from the NASA Commercial Technology Office, a cathode assembly was designed, developed, fabricated, and tested for use in plasma sources for ground-based materials processing applications. The cathode development activity relied on the large prior NASA investment and successful development of high-current, high-efficiency, long-life hollow cathodes for use on the International Space Station Plasma Contactor System. The hollow cathode was designed and fabricated based on known engineering criteria and manufacturing processes for compatibility with the requirements of the plasma source. The transfer of NASA GRC-developed hollow cathode technology for use as an electron emitter in the commercial plasma source is anticipated to yield a significant increase in process control, while eliminating the present issues of electron emitter lifetime and contamination.

PVP-Assisted Synthesis of Uniform Carbon Coated Li2S/CB for High-Performance Lithium-Sulfur Batteries.

PubMed

Chen, Lin; Liu, Yuzi; Zhang, Fan; Liu, Caihong; Shaw, Leon L

2015-11-25

The lithium-sulfur (Li-S) battery is a great alternative to the state-of-the-art lithium ion batteries due to its high energy density. However, low utilization of active materials, the insulating nature of sulfur or lithium sulfide (Li2S), and polysulfide dissolution in organic liquid electrolyte lead to low initial capacity and fast performance degradation. Herein, we propose a facile and viable approach to address these issues. This new approach entails synthesis of Li2S/carbon black (Li2S/CB) cores encapsulated by a nitrogen-doped carbon shell with polyvinylpyrrolidone (PVP) assistance. Combining energy-filtered transmission electron microscopy (EFTEM) elemental mappings, XPS and FTIR measurements, it is confirmed that the as-synthesized material has a structure of a Li2S/CB core with a nitrogen-doped carbon shell (denoted as Li2S/CB@NC). The Li2S/CB@NC cathode yields an exceptionally high initial capacity of 1020 mAh/g based on Li2S mass at 0.1 C with stable Coulombic efficiency of 99.7% over 200 cycles. Also, cycling performance shows the capacity decay per cycle as small as 0.17%. Most importantly, to further understand the materials for battery applications, field emission transmission electron microscopy (FETEM) and elemental mapping tests without exposure to air for Li2S samples in cycled cells are reported. Along with the first ever FETEM and field emission scanning electron microscopy (FESEM) investigations of cycled batteries, Li2S/CB@NC cathode demonstrates the capability of robust core-shell nanostructures for different rates and improved capacity retention, revealing Li2S/CB@NC designed here as an outstanding system for high-performance lithium-sulfur batteries.

A neutron diagnostic for high current deuterium beams.

PubMed

Rebai, M; Cavenago, M; Croci, G; Dalla Palma, M; Gervasini, G; Ghezzi, F; Grosso, G; Murtas, F; Pasqualotto, R; Cippo, E Perelli; Tardocchi, M; Tollin, M; Gorini, G

2012-02-01

A neutron diagnostic for high current deuterium beams is proposed for installation on the spectral shear interferometry for direct electric field reconstruction (SPIDER, Source for Production of Ion of Deuterium Extracted from RF plasma) test beam facility. The proposed detection system is called Close-contact Neutron Emission Surface Mapping (CNESM). The diagnostic aims at providing the map of the neutron emission on the beam dump surface by placing a detector in close contact, right behind the dump. CNESM uses gas electron multiplier detectors equipped with a cathode that also serves as neutron-proton converter foil. The cathode is made of a thin polythene film and an aluminium film; it is designed for detection of neutrons of energy >2.2 MeV with an incidence angle < 45°. CNESM was designed on the basis of simulations of the different steps from the deuteron beam interaction with the beam dump to the neutron detection in the nGEM. Neutron scattering was simulated with the MCNPX code. CNESM on SPIDER is a first step towards the application of this diagnostic technique to the MITICA beam test facility, where it will be used to resolve the horizontal profile of the beam intensity.

A neutron diagnostic for high current deuterium beams

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rebai, M.; Perelli Cippo, E.; Cavenago, M.

2012-02-15

A neutron diagnostic for high current deuterium beams is proposed for installation on the spectral shear interferometry for direct electric field reconstruction (SPIDER, Source for Production of Ion of Deuterium Extracted from RF plasma) test beam facility. The proposed detection system is called Close-contact Neutron Emission Surface Mapping (CNESM). The diagnostic aims at providing the map of the neutron emission on the beam dump surface by placing a detector in close contact, right behind the dump. CNESM uses gas electron multiplier detectors equipped with a cathode that also serves as neutron-proton converter foil. The cathode is made of a thinmore » polythene film and an aluminium film; it is designed for detection of neutrons of energy >2.2 MeV with an incidence angle < 45 deg. CNESM was designed on the basis of simulations of the different steps from the deuteron beam interaction with the beam dump to the neutron detection in the nGEM. Neutron scattering was simulated with the MCNPX code. CNESM on SPIDER is a first step towards the application of this diagnostic technique to the MITICA beam test facility, where it will be used to resolve the horizontal profile of the beam intensity.« less

Observation of Quartz Cathode-Luminescence in a Low Pressure Plasma Discharge

NASA Technical Reports Server (NTRS)

Foster, John E.

2004-01-01

Intense, steady-state cathode-luminescence has been observed from exposure of quartz powder to a low pressure rf-excited argon plasma discharge. The emission spectra (400 to 850 nm) associated with the powder luminescence were documented as a function of bias voltage using a spectrometer. The emission was broad-band, essentially washing out the line spectra features of the argon plasma discharge.

Development of all-solid-state flash x-ray generator with photoconductive semiconductor switches.

PubMed

Xun, Ma; Jianjun, Deng; Hongwei, Liu; Jianqiang, Yuan; Jinfeng, Liu; Bing, Wei; Yanling, Qing; Wenhui, Han; Lingyun, Wang; Pin, Jiang; Hongtao, Li

2014-09-01

A compact, low-jitter, and high repetitive rate all-solid-state flash x-ray generator making use of photo conductive semiconductor switches was developed recently for the diagnostic purpose of some hydrokinetical experiments. The generator consisted of twelve stages of Blumlein pulse forming networks, and an industrial cold cathode diode was used to generate intense x-ray radiations with photon energy up to 220 keV. Test experiments showed that the generator could produce >1 kA electron beam currents and x-ray pulses with ~40 ns duration under 100 Hz repetitive rates at least (limited by the triggering laser on hand), also found was that the delay time of the cathode explosive emission is crucial to the energy transfer efficiency of the whole system. In addition, factors affecting the diode impedance, how the switching synchronization and diode impedance determining the allowable operation voltage were discussed.

Absolute continuum intensity diagnostics of a novel large coaxial gridded hollow cathode argon plasma

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gao, Ruilin; Yuan, Chengxun, E-mail: yuancx@hit.edu.cn, E-mail: zhouzx@hit.edu.cn; Jia, Jieshu

2016-08-15

This paper reports a novel coaxial gridded hollow discharge during operation at low pressure (20 Pa–80 Pa) in an argon atmosphere. A homogeneous hollow discharge was observed under different conditions, and the excitation mechanism and the discharge parameters for the hollow cathode plasma were examined at length. An optical emission spectrometry (OES) method, with a special focus on absolute continuum intensity method, was employed to measure the plasma parameters. The Langmuir probe measurement (LPM) was used to verify the OES results. Both provided electron density values (n{sub e}) in the order of 10{sup 16} m{sup −3} for different plasma settings. Taken together, themore » results show that the OES method is an effective approach to diagnosing the similar plasma, especially when the LPM is hardly operated.« less