Cold Cathode Electron Gun Research Articles

A Picosecond Pulsed Cold-Cathode Electron Gun for Ultrafast Electron Characterization and High-Frequency Radiation Source Applications

A Picosecond Pulsed Cold-Cathode Electron Gun for Ultrafast Electron Characterization and High-Frequency Radiation Source Applications

Investigation of Spindt Cold Cathode Electron Guns for Terahertz Traveling Wave Tubes

In this work, a Spindt cold cathode electron gun with a PPM (periodic permanent magnet) focusing system for a terahertz TWT (traveling wave tube) was designed and simulated based on the Pierce electron gun structure. More specifically, a new 3D (three dimensional) emission model was used, where the cathode radius of the electron gun was 1 mm and the cathode current was 30 mA, with an emitting half angle of about 28°. It was demonstrated that the electron beam was well focused with an electron beam radius of 0.3 mm and a filling ratio of 0.5 when the maximum value of the PPM field along with the axis was 0.122T. According to the simulation results, a planar cold cathode electron gun was developed. Measurements demonstrated that the I/V characteristics of the cold cathode gun were consistent with that of a cold cathode, revealing that the electrons emitted from the cathode are not intercepted when passing through the electron gun.

Achieving High Current Stability of Gated Carbon Nanotube Cold Cathode Electron Source Using IGBT Modulation for X-ray Source Application.

The cold cathode X-ray source has potential application in the field of radiotherapy, which requires a stable dose. In this study, a gated carbon nanotube cold cathode electron gun with high current stability was developed by using Insulated Gate Bipolar Transistor (IGBT) modulation, and its application in X-ray source was explored. Carbon nanotube (CNTs) films were prepared directly on stainless steel substrate by chemical vapor deposition and assembled with control gate and focus electrodes to form an electron gun. A maximum cathode current of 200 μA and approximately 53% transmission rate was achieved. An IGBT was used to modulate and stabilize the cathode current. High stable cathode current with fluctuation less than 0.5% has been obtained for 50 min continuous operation. The electron gun was used in a transmission target X-ray source and a stable X-ray dose rate was obtained. Our study demonstrates the feasibility of achieving high current stability from a gated carbon nanotube cold cathode electron source using IGBT modulation for X-ray source application.

A Carbon-Nanotube Cold-Cathode Reflex Klystron Oscillator: Fabrication @ X-Band and Returning Electron Beam Realization

This paper presents the design and fabrication of a reflex klystron oscillator based on a carbon nanotube (CNT) cold-cathode. An X-band klystron oscillator structure is assembled with a CNT cold-cathode electron gun with an electrostatic focusing, a re-entrant cavity as anode, and a repeller. The electron gun adopts a convex CNT film emitter as the cathode. A re-entrant cavity resonating at 8.376 GHz is fabricated. The study mainly focuses on the returning electron beam in the klystron oscillator structure. The experimental results of variations of the anode current and returning electron beam amplitude with repeller voltage are presented. It is demonstrated that a higher extracting voltage of the cold-cathode has an important influence on the returning electron beam. To decelerate electron velocity from the extracting voltage, increasing negative focusing voltage and focusing electrode height in the electron gun can improve the returning electron beam characteristics.

Theoretical study of extended interaction frequency‐locking oscillator based on carbon nanotube cold cathodes

An extended interaction frequency-locking oscillator based on carbon nanotube (CNT) cold cathode is proposed to overcome locked-frequency limits of the conventional oscillator. Compared with the conventional oscillators, the oscillation frequency is locked by a modulation electron beam, which can be obtained in a field emission CNT cold cathode electron gun. The frequency-locking signal does not enter the high-frequency (HF) system but imposes an additional HF electric field on the cathode surface by a microstrip structure, which consumes considerably less power to lock the oscillation frequency. A ladder structure extended interaction oscillator operating in 2π mode is numerically investigated by three-dimensional Particle-In-Cell simulation code. By analysing the impacts of different frequency-locking power on the locked ranges, the results show that the average output power of 30.6 W is achieved at 35.11 GHz when the frequency-locking power consumption is 460 mW. The 3-dB bandwidth of a frequency-locking region reaches 100 MHz.

A truncated-cone carbon nanotube cold-cathode electron gun

A concurrently high beam current and high current density carbon nanotube (CNT) cold cathode electron gun is herein developed. A radial electron source has been realized, formed from CNTs synthesized directly on the side walls of a stainless steel truncated-cone electron gun. Experimental results evidenced a 35 kV/50 mA electron beam can achieve a beam transparency of nearly 100% through the use of double anodes and crossed electric and magnetic fields. A maximum beam current density of 3.5 A/cm2 was achieved. These results demonstrate the potential impact of coupling novel cold cathode gun architectures and emerging nanomaterials and their collective role in augmenting the performance of incumbent electron gun technologies, alongside allowing for the realization new types of field emission vacuum electron radiation sources.

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

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.

Theoretical Research on a Multibeam-Modulated Electron Gun Based on Carbon Nanotube Cold Cathodes

Multi-beam modulation in a carbon nanotube (CNT) cold cathode electron gun is herein investigated in order to develop miniaturized and fully integrated vacuum electron devices. By exposing the electron source to a millimeter-wave signal, the steady-state field emission current density is efficiently modulated by the incident high-frequency (HF) electric field. Our simulation results of this multibeam electron gun show that the field emission current density can be efficiently modulated by different incident frequency millimeter waves. We find that the modulation depth is increased by enhancing the HF input power and anode operation voltage. The modulation frequency and phase of each electron beam can be controlled using a single millimeter-wave source and by simply adjusting the lateral distance between adjacent CNT cold cathodes.

A Gridded High-Compression-Ratio Carbon Nanotube Cold Cathode Electron Gun

In order to develop field emission cold cathode radiation source devices, a gridded carbon nanotube (CNT) cold cathode electron gun is theoretically and experimentally investigated in this letter. The planar grid and annular CNT cold cathode are used and optimal parameters of a high-compression-ratio electron gun are obtained by particle in cell simulation software. A 4-mA/10-kV annular electron beam with an average radius of 1.75 mm is achieved based on a permanent magnet in the experiment. The area compression ratio of electron beam is $\sim 10.$

Theoretical research on electron beam modulation in a field-emission cold cathode electron gun

In order to develop miniaturized and integrated electron vacuum devices, the electron beam modulation in a field-emission (FE) electron gun based on carbon nanotubes is researched. By feeding a high-frequency field between the cathode and the anode, the steady FE electron beam can be modulated in the electron gun. The optimal structure of the electron gun is discovered using 3D electromagnetism simulation software, and the FE electron gun is simulated by PIC simulation software. The results show that a broadband (74–114 GHz) modulation can be achieved by the electron gun with a rhombus channel, and the modulation amplitude of the beam current increases with the increases in the input power and the electrostatic field.

Pulse shaping for optimal energy deposition with a cold cathode electron gun for surface treatment

A pulse-forming network is added in the discharge circuit of a cold-cathode electron gun that gives rise to an improved shape of the pulse, making it closer to the ideal square pulse needed for optimal energy deposition in material surface treatments. It is shown that the circuit can be very accurately designed by means of simulations using empirical equations for the nonlinear response of the gun. Due to the particular nonlinear behavior of the current-voltage in these guns, and the strong nonlinear self-focusing of the beam, the adequate shaping of the temporal profile of the discharge becomes relevant to the efficiency of the system. The effect of using a new discharge circuit for a glow-discharge pulsed electron gun for materials processing is analyzed, showing an almost two-fold improvement in the efficiency of the system regarding the fraction of the energy not wasted in long pulse tails.

Numerical modeling of materials processing applications of a pulsed cold cathode electron gun

A numerical study of the application of a pulsed cold cathode electron gun to materials processing is performed. A simple semiempirical model of the discharge is used, together with backscattering and energy deposition profiles obtained by a Monte Carlo technique, in order to evaluate the energy source term inside the material. The numerical computation of the heat equation with the calculated source term is performed in order to obtain useful information on melting and vaporization thresholds, melted radius and depth, and on the dependence of these variables on processing parameters such as operating pressure, initial voltage of the discharge and cathode–sample distance. Numerical results for stainless steel are presented, which demonstrate the need for several modifications of the experimental design in order to achieve a better efficiency.

A simple model of a glow discharge electron beam for materials processing

A simple semiempirical model of the electron beam generated by a pulsed cold cathode electron gun has been developed. The model describes analytically the observed self-focusing of the discharge and predicts the dynamical variation of the focal distance, in good agreement with experiments. This effect plays a major role in the determination of the effective duration of the energy pulse. The model was used to conduct simple calculations of energy thresholds for melting of solid materials, giving helpful insight on ranges of operation of this kind of electron gun for its application to material processing. A comparison with available experimental data for Mg/sub 70/Zn/sub 30/ samples is given.

A correlation of CL emissions from Penrith sandstone with elemental distributions obtained by simultaneous SEM-CL and EDS analysis

Most industrial and academic geologists are familiar with the beautiful red and orange cathodoluminescence colours produced by carbonate minerals in an optical microscope with a cold cathode electron gun attached. The cement stratigraphies interpreted from colour photographs have been widely used to determine the post depositional processes which have modified sedimentary rock textures.However to study quartzose materials high electron densities and kV's are necessary to stimulate sufficient emission. A scanning electron microscope with an optical collection system and monochromator provides an adequate tool and gives the advantage of providing secondary and backscattered electron imaging as well as elemental analysis and distribution mapping via standard EDS/WDS facilities.It has been known that the incorporation of many elements modify the characteristics of the CL emissions from geological materials. They do this by taking up positions between the valence and conduction band thus providing sites to assist in the recombination of electron hole pairs.

Direct current sputter deposition of titanium nitride controlled in situ by soft x-ray emission spectroscopy

Thin films of TiNx are synthesized by reactive dc sputtering of a titanium cathode in an Ar/N2 gas mixture. The substrates (glass, stainless steel, and silicon) are negatively biased at −200 or −300 V. The composition is monitored in situ by the measurement of the Ti Lα,β, Ti Ll,n, N Kα, and O Kα x-ray line or band intensities. The x-ray emission is induced in the film during the deposition by the high energy secondary electrons (about 4 keV) emitted by the cathode. After deposition, x-ray measurements are also carried out while using a cold cathode electron gun. The oxygen content of the films measured during deposition is low (<1 wt. %). The titanium nitride films appear to become rapidly overstoichiometric (up to TiN1.4) when the nitrogen partial flow rate increases. These overstoichiometric films show an x-ray diffraction pattern corresponding mostly to fcc TiN with the plane (111) oriented parallel to the substrate surface. These results are correlated to the changes of the Ti Lα,β emission band profile which depends drastically on the titanium chemical environment.

Windowless Wide Area Vuv Lamp for Energy Assisted CVD

ABSTRACTA ring shaped cold cathode electron gun provides a large area disc shaped vacuum ultraviolet (VUV) light source up to 20 cm in diameter. The windowless disc plasma is also a source of radical and excited atomic gas species. VUV photons, excited species, and radicals can all assist dissociation of CVD feedstock reactants via volume photo-absorption and sensitized atom-molecule collisions, respectively. In addition, the excited radical flux and VUV impingement on the film may also assist heterogeneous surface reactions and increase surface mobility of absorbed species. Thin films of aluminum nitride, Si3N4, and hydrogenated amorphous silicon have been deposited at temperatures between 100°C - 400°C. The deposited films show significant improvement over other photoassisted CVD processes in the film quality achieved, the substrate temperature required and the maximum deposition rates.

Breakdown Processes in Large-Area Cold-Cathode Vacuum Triodes

Preionization of large-aperture high-pressure dischargepumped gas lasers requires uniform 250 to 500 keV 10 to 100 mA cm-2 electron beams of typically 1 to l0x103 cm2 in area. Impedance collapse due to cathode plasma expansion renders diode electron guns inefficient in this application. Introduction of a control grid limits gun current to low, controllable values until plasma closure of the cathode-grid gap occurs. However, field enhancement at the grid can cause cathode-grid or grid-anode arcs resulting in current runaway. An experimental study of impedance collapse was conducted by measuring element I-V characteristics in a 20x200 cm cold-cathode triode electron gun. Impedance collapse of the gun was dominated by two processes: (1) plasma closure of the cathodegrid gap and (2) grid-anode arcs. Plasma closure rate was ~2x106 cm s-1 independent of configuration or interelectorde potential. Arc thresholds were found to depend (after conditioning) exclusively on local electric field strength at the grid which is, in turn, a function of grid bias and, more importantly, grid geometry. Streamers and arcs were occasionally observed in the cathode-grid region, phenomena deserving of further investigation.

Development of a fast risetime pulsed relativistic electron beam generator for the excitation of shorter wavelength lasers

We have developed a compact and simple high current relativistic electron beam (REB) generator for the excitation of lasers in the shorter wavelength region. This REB generator mainly consists of a Tesla transformer-type high-voltage generator, N2 gas insulated Blumlein-type pulse-forming line and cold-cathode electron gun to generate 800 keV, 12 kA pulsed electron beams with 6 ns current duration and approximately 4 ns current risetime. The design and operational characteristics along with discussions of the excitation capabilities of the gas laser media are presented in this paper.

Propagation of Pulsed Laser Energy Through the Atmosphere

An experimental investigation has been conducted to study pulsed laser energy propagation over long distance through the atmosphere. Typical gain switched pulse of the CO2 cold cathode electron gun laser (160 J, 2.5 /AS) shows an initial high-power spike (5.6 x 108 W, 50 ns FWHM) followed by a high-energy tail (130 J). The laser beam is focused by means of of a 5 X telescope outside the laboratory. Spatial and temporal distributions of intensity and energy density are measured in the breakdown area by burning of thermosensiti ve paper (envelope of the focused laser beam) and by use of calibrated Kalvar film (focal spot). Experimental determination of the air breakdown average threshold (l-2x!08 W/cm2, 3-5 J/cm2) leads to the conclusion that such a phenomenon is initiated on the spike of the pulse by > 4-^m-diam aerosol particles. A particle optical counter is used for in situ measurements of aerosol distribution (axially scattering spectrometer probe, calibrated in the 0.5 ftm <c?<45 iim range), to determine the number in the focal volume.

Design and operational characteristics of a compact relativistic electron beam generator for the excitation of short wavelength lasers

We have designed and constructed a compact and simple high current relativistic electron beam (REB) generator for the excitation of lasers in the short wavelength region. The REB generator mainly consists of Tesla transformer type high-voltage generator, water pulse forming line, cold cathode electron gun and provides the operational characteristics of 250 keV high energy, 15 kA high current and 15 ns pulse width electron beam.