Focusing Electrode Research Articles

Beam Test of a Novel CNT Cathode-Based Electron Gun Assembled in a TWT

A magnetic-focused X-band traveling wave tube (TWT) based on carbon nanotube (CNT) cathode is presented. The CNT TWT has a simple structure of the electron gun, consisting of a CNT emitter electrode and a ring-shaped anode, with no metallic mesh extracting electrode, nor electrostatic focusing electrode. The field emission electrons are extracted directly by the ring-shaped anode, while the electron beam focusing is realized by an extra magnetic field. Apart from the CNT electron gun, the TWT mainly has a high-frequency interaction circuit and a collector. All these components are totally immersed in a uniform axial magnetic field, and thus, electrons are confined by the Lorentz force during their traveling process from the cathode surface toward the collector. The fabricated CNT TWT was tested in a superconducting system providing a uniform axial magnetic field. The dc mode testing showed about 86% of the emission electrons can reach collector, which is better than a common gate-controlled CNT electron gun.

Design and beam dynamics of a Transmission Electron Microscope electron gun assembly

We present the design and beam dynamics analysis of a Transmission Electron Microscope illumination system. A LaB6 emitter is used as a cathode/source with an emissive surface area of diameter 50 μm generating fixed emission current of 5 mA which is biased by −300 V with Wehnelt electrode. The gun is comprised of five electrostatic lenses in-between the focusing and anode electrodes to accelerate and focus the beam with integrated energy of 160 keV in the post anode region with diameter around 228 μm. Finally, the beam is focused using the condensed electro-magnetic lenses of field strengths 183 mT and 331 mT, respectively to spot size 1.8 μm in the post-lens position. The obtained focal spots are largely symmetric along the two transverse directions. The illumination system geometry offers full beam collimation control. The study provides a theoretical basis for the structure and optics design of the Transmission Electron Microscope.

Direct Analysis of Carbonyl Compounds by Mass Spectrometry with Double-Region Atmospheric Pressure Chemical Ionization.

Direct analysis of highly reactive volatile species such as the aliphatic aldehydes as vital biomarkers remains a great challenge due to difficulties in the sample pretreatment. To address such a challenge, we herein report the development of a novel double-region atmospheric pressure chemical ionization mass spectrometry (DRAPCI-MS) method. The DRAPCI source implements a separated structural design that uses a focus electrode to divide the discharge and ionization region to reduce sample fragmentation in the ionization process. Counterflow introduction (CFI) configuration was adopted in the DRAPCI source to reduce background noise, while ion transmission efficiency was optimized through simulating the voltage of the focus electrode and the ion trajectory of the ion source. The limits of detection (LODs) of four carbonyl compounds cyclohexanone, hexanal, heptanal, and octanal by DRAPCI-MS were between 0.1 and 3 μg·m-3, approximately two to eight times lower than those by atmospheric pressure chemical ionization mass spectrometry. Additionally, the DRAPCI-MS method carried out effective in situ analyses of the volatile components in expired milk and the exhaled breath of smokers, demonstrating the DRAPCI-MS as a practical tool to analyze complex mixtures. The DRAPCI-MS method provides a rapid, sensitive, and high-throughput technique in the real-time analysis of gaseous small-molecule compounds.

Design of a Hollow-Beam Electron Optics System With Control Focus Electrodes

The design of a hollow electron beam (HEB) electron optics system for a 10-kW Ka-band extended interaction klystron is presented. To lower the maximum cathode current density and realize the fast switch of the current emission, an HEB with two focus electrodes (FEs) is chosen, which attains to a high area compression ratio of over 100. A 25-kV, 2.5-A beam is produced by a curved spherical segment cathode with the area of 0.321 cm2 and an average beam loading of 8 A/cm2, namely, the high area compression ratio is necessary to reduce the cathode emission current density. The HEB with an area compression ratio of 105 can propagate 40 mm long with good laminarity confined by a 0.7-T uniform magnetic field. The beam current can be quickly shut off when the voltages of the FEs are biased to −4100 V. The results were simulated with two simulation codes: EGUN and OPERA 3-D. A sensitivity analysis with respect to critical parameters such as the displacement of FE1 and FE2 in the radial direction is provided. The simulation results of OPERA 3-D/SCALA and EGUN show an excellent agreement.

Electrical and Optical Characteristics of Si-Nanoparticle Films Deposited onto Substrates by High-Voltage Electrospraying from Ethanol Sols

The optical and electrical characteristics of films consisting of nanocrystalline silicon (nc-Si) deposited onto substrates by the high-voltage electrospraying of nc-Si sols in ethanol are investigated. It is found that the interaction of ethanol droplets carrying Si nanoparticles with a corona-discharge electric field leads to the polymerization of ethanol and the formation of a polymer layer on the Si-nanoparticle surface. A high-voltage facility for depositing the films using an additional focusing electrode allows one to change the geometry of the electric field and intensity in the region of the ethanol droplet flow. As a result, nc-Si films with qualitatively different properties of the polymer on the nanoparticle surface are formed, specifically, nc-Si_A and nc-Si_B, obtained without a focusing electrode and with it, respectively. Upon annealing at temperatures of up to 400°С, the optical band gap Eg of the nc-Si_A films increases from ~1.9 to ~2.2 eV, while the Eg value of the nc-Si_B films remains constant and amounts to 1.85 eV. The constant Eg value of the nc-Si_B films is explained by the properties of the polymer on the Si-nanoparticle surface and the more effective blocking of oxygen penetration from the surrounding environment upon annealing at temperatures of up to 400°C than in the case of a polymer in nc-Si_A films. The temperature dependences of the dark and photoinduced conductivity of nc-Si_A films are approximated with good accuracy by two activation-type exponential functions and the dark activation energies are ~0.75 and 0.1 eV, respectively. The conductivity of the nc-Si_A films noticeably decreases under irradiation of the samples at wavelengths of 460–470 nm. The temperature dependences of the conductivity of the nc-Si_B films are approximated with good accuracy by exponential functions with activation energies of 0.73 (in the dark) and 0.59 eV (under photoexcitation). In contrast to the case of nc-Si_A films, the photoconductivity of nc-Si_B films grows more than fourfold relative to the dark conductivity under analogous illumination. The nc-Si_B films are photoactive and sandwich-like Al/nc-Si_B/Al structures can generate a voltage. The dark conductivity and photoconductivity of the nc-Si_A films in the voltage range of V > 2 V are determined by the two-center Poole–Frenkel effect; the concentration of the centers affecting the Poole–Frenkel conductivity is ~3 × 1017 cm–3. In nc-Si_B films in the voltage range of 2–5 V, electron transport is determined by space-charge-limited currents and, at high voltages, by the two-center Poole–Frenkel effect. The concentration of traps contributing to the space-charge-limited currents is ~4 × 1016 cm–3. The concentration of Poole–Frenkel centers affecting the conductivity decreases according to the activation law with an activation energy of 0.7 eV from 3 × 1016 to 2 × 1014 cm–3 with a decrease in temperature from 120°C to 40°C.

Prototype 1 MeV X -band linac for aviation cargo inspection

Aviation cargo unit load device (ULD) containers are typically much smaller than standard shipping containers, with a volume of around 1 m3. Standard 3-6 MeV x-ray screening linacs have too much energy to obtain sufficient contrast when inspecting ULDs, hence a lower 1 MeV linac is required. In order to obtain a small physical footprint, which can be adapted to mobile platform applications, a compact design is required, hence X-band radio-frequency technology is the ideal solution. A prototype 1.45 MeV linac cavity optimized for this application has been designed by Lancaster University and Science and Technology Facilities Council (STFC), manufactured by Comeb (Italy) and tested at Daresbury Laboratory using an e2v magnetron, modulator, and electron gun. The cavity is a bi-periodic π/2 structure, with beam-pipe aperture coupling to simplify the manufacture at the expense of shunt impedance, while keeping the transverse size as small as possible. The design, manufacture, and testing of this linac structure is presented. In order to optimize the image it is necessary to be able to modify the energy of the linac. It can be changed by altering the rf power from the magnetron but this also varies the magnetron frequency. By varying the beam current from 0-70 mA the beam energy varied from 1.45 to 1.2 MeV. This allows fast energy variation by altering the focus electrode bias voltage on the electron gun while keeping the dose rate constant by varying the repetition frequency. Varying the beam energy by varying the rf power and by varying the beam current are both studied experimentally. The momentum spread on the electron beam was between 1% and 5% depending on the beam current of 0-70 mA

Microfluidic based impedance biosensor for pathogens detection in food products.

A MEMS-based impedance biosensor was designed, fabricated, and tested to effectively detect the presence of bacterial cells including E. coli O157:H7 and Salmonellatyphimurium in raw chicken products using detection region made of multiple interdigitated electrode arrays. A positive dielectrophoresis based focusing electrode was used in order to focus and concentrate the bacterial cells at the centerline of the fluidic microchannel and direct them toward the detection microchannel. The biosensor was fabricated using surface micromachining technology on a glass substrate. The results demonstrate that the device can detect Salmonella with concentrations as low as 10 cells/mL in less than 1 h. The device sensitivity was improved by the addition of the focusing electrodes, which increased the signal response by a factor between 6 and 18 times higher than without the use of the focusing electrodes. The biosensor is selective and can detect other types of pathogen by changing the type of the antibody immobilized on the detection electrodes. The device was able to differentiate live from dead bacteria.

Электрические и оптические характеристики пленок из наночастиц Si, нанесенных на подложки высоковольтным электронапылением из золей в этаноле

Abstract The paper describes the results of studying the optical and electrical characteristics of films made of silicon nanoparticles (nc-Si) deposited on substrates by high-voltage electrospray from sols of nc-Si in ethanol. It was found that the interaction of ethanol droplets carrying nc-Si with an electric field of corona discharge leads to polymerization of ethanol and formation of a polymer layer on the nanoparticle surface. The geometry and electric field strength in the flow area of ethanol droplets could be changed by means of the focusing electrode in the high-voltage device. As a result we could make nc-Si films with different kind of polymer layer on Si nanoparicle surface: nc-Si A and nc-Si B (the films deposited without and with focusing electrode, respectively). The optical band gap Eg of nc-Si A films increased from 1.9 to 2.2 eV after annealing at the temperatures from room one to 400◦C in air atmosphere. The Eg of the nc-Si B films was independent on annealing and was 1.85 eV. The constancy of Eg in nc-Si B films is explained by the polymer properties on the Si nanoparticles surface in these films and more effective blocking the penetration of oxygen atoms from the surrounding atmosphere during annealing to temperatures of 400◦C than in the case of the polymer in nc-Si A films. The temperature dependences of the conductivity (dark and photo) of nc-Si A films are approximated with good accuracy by two exponential functions, the dark activation energies of the films being approximately equal to 0.75 and 0.1 eV. The conductivity of nc-Si A films decreased noticeably when illuminated with radiation in the range 460−470 nm The temperature dependences of the conductivity of nc-Si B films with good accuracy is approximated by one-exponential function of the activation type with activation energies of 0.73 (dark) and 0.59 eV (photo). In contrast to the nc-Si A films, the photoconductivity of nc-Si B films increase by more than 4 times with respect to the dark conductivity when the films were illuminated anologically. The nc-Si B films are photoactive, since sandwich-like structures of Al/nc-Si B/Al can generate emf. The dark and photo-conductivity of nc-Si A films in the voltage range > 2V is determined by the two-center Poole−Frenkel effect, the concentration of the centers that determine the character of the Poole−Frenkel conductivity was 3 · 1017 cm−3. In nc-Si B films in the voltage range 2−5V, the electronic transport is determined by space-charge-limited currents (SCLC) and at higher voltages by the two-center Pool−Frenkel conduction. The concentration of traps contributing to SCLC in the films is 4 · 1016 cm−3. The concentration of the Pool−Frenkel centers, decreases from 3 · 1016 to 2 · 1014 cm−3 with decreasing temperature in the range 120−400◦C according to the activation law with an activation energy of 0.7 eV.

Low concentration E. coli O157:H7 bacteria sensing using microfluidic MEMS biosensor.

This paper reports the design, fabrication, and testing of a microfluidic MEMS biosensor for rapid sensing of low concentration Escherichia coli O157:H7. It consists of a specially designed focusing and sensing region, which enables the biosensor to detect low concentration of bacterial cells. The focusing region consists of a ramped vertical electrode pair made of electroplated gold along with tilted thin film finger pairs (45°) embedded inside a microchannel. The focusing region generates positive dielectrophoresis force, which moves the cells towards the edges of the tilted thin film electrode fingers, located at the center of the microchannel. The fluidic drag force then carries the focused cells to the sensing region, where three interdigitated electrode arrays (IDEAs) with 30, 20, and 10 pairs, respectively, are embedded inside the microchannel. This technique resulted in highly concentrated samples in the sensing region. The sensing IDEAs are functionalized with the anti-E. coli antibody for specific sensing of E. coli 0157:H7. As E. coli binds to the antibody, it results in an impedance change, which is measured across a wide frequency range of 100 Hz-10 MHz. The biosensor was fabricated on a glass substrate using the SU8 epoxy resist to form the microchannel, gold electroplating to form the vertical focusing electrode pair, a thin gold film to form the sensing electrode, the finger electrodes, traces and bonding pads, and polydimethylsiloxane to seal the device. The microfluidic impedance biosensor was tested with various low concentration bacterial samples and was able to detect bacterial concentration, as low as 39 CFU/ml with a total sensing time of 2 h.

Aligned polyvinylpyrrolidone nanofibers with advanced electrospinning for biomedical applications.

Electrospinning is a highly effective method in order to generate nano-scaled fibers. In conventional electrospinning technique, geometry of nanofibers are mostly random due to the chaotic behavior of polymer jet. Purpose of this study is to produce aligned nanofibers from PVP polymers with advanced electrospinning technique in order to be used in a potential novel sensor applications, tissue regeneration and engineering. In this study, by using finite hollow cylinder focusing electrodes, an external electrostatic field is created. With these electrodes, it is aimed to decrease whipping instability of polymer jet. In addition, it is also investigated that the alignment ratio of nanofibers by using conductive parallel electrodes which placed through jet trajectory. In conclusion, with the effect of electrical field created by cylinder electrodes, radius of the fiber dispersion on the collector was able to be reduced and aligned nanofibers were successfully produced by using electrical field generated from the parallel plates. Radius of the fiber dispersion on the collector is 9.95mm and fiber diameters varied between 800nm and 3μm. Additionally, alignment ratio of the fibers is determined with ImageJ software. These alignment of nanofibers can be used in tissue engineering applications and sensor applications.

Ion Mobility-Mass Spectrometry Using a Dual-Gated 3D Printed Ion Mobility Spectrometer.

Described herein is the development of a 3D-printed drift-tube ion mobility spectrometer (IMS) which operates in the open air and is capable of being coupled to any mass spectrometer. The IMS possesses one electrospray focusing electrode, 31 drift electrodes with 7 mm inner diameters, and 2 ion gates at opposite ends of the IMS, totaling 109 mm in length. The second ion gate was timed with respect to the first ion gate to transmit portions of the separating ion packets to the MS at specified time intervals. By scanning the second ion gate and acquiring mass spectra during each time interval, we reconstructed ion mobility chronograms using mass spectra. Resolving powers of up to 45 were acquired using tetraalkylammonium cations. Separation is also demonstrated for solutions of amphetamines, opioids (fentanyls/fentanils), and bradykinin and angiotensin II. The highest mobility resolving powers were obtained when the injection times of the first and second ion gates were 0.3 and 1.0 ms, respectively. Experiments were performed on both an ion trap and triple quadruple mass analyzer to showcase the adaptability of the plastic IMS. Insights were gained into how ions separate in the open air compared to vacuum conditions with pure gas.

Large area deposition of ordered nanoparticle layers by electrospray

Mass production of ordered nanostructures with enhanced optical properties such as colloidal crystals for applications such as solar cells or organic light emitted diodes demands low-cost and large-scale manufacturing techniques. In order to enlarge the deposition area of colloidal crystals, this paper presents the results of two different approaches that use the electrospray technique. Areas as large as 25 cm2 have been achieved by using an array of needles, whereas up to 7.5 cm2 areas were achieved by using an additional focusing electrode placed on the same plane as the needle nozzle. COMSOL simulations have been used as a guide for the set up design. The ordered deposition of the nanoparticles has been assessed by reflectance measurements and SEM/FIB observations.

Gain- and Phase-Matched Mini-TWTs

Traveling-wave tubes (TWTs) in broadband power-combining applications should have closely matched gain and phase to achieve high system-level efficiency. A gain- and phase-matched TWT operating over a frequency band of 7.5–18 GHz with a minimum output power of 60 W is currently under production at Teledyne e2v. The tube design is based on an existing mini-TWT that incorporates focus electrode switching gun, phase velocity tapered helix slow wave structure, single-stage depressed collector, subminiature A connector at the input, and threaded Neill–Concelman connector at the output. During development and production stages, a number of devices were manufactured and their performances were matched. In this paper, we have described gain- and phase-matching techniques of such devices. Experimental results of 132 matched devices have been collated that show a gain match within ±3 dB and phase match within ±15°.

Fabrication of ZnO Nanowire Field-Emitter Arrays With Focusing Capability

ZnO nanowire field-emitter arrays (FEAs) show great application potentials in large-area vacuum microelectronics devices. However, the electron divergence is an issue which should be addressed. In this paper, ZnO nanowire FEAs with co-planar focus electrode were designed. A four-mask fabrication process and lift-off process were adopted to achieve the integration of focus electrode. The device demonstrated line-addressing and focusing capability with a spacing of 5 mm between anode and cathode, and the linewidth of field-emission images was reduced from 2.25 to 1.35 mm when the focus voltage changed from 50 to −50 V. Besides, line-shaped emission patterns were observed during focusing process, which was attributed to the emission pattern from the ZnO nanowire and the asymmetrical focusing electrical field.

Performance of a new accelerating-electrode-equipped fast-time-response PMT coupled with fast LGSO

In this study, we measured the performance of a newly developed Hamamatsu Photonics R13478 photomultiplier tube (PMT) and compared the results with those of an existing R9800 PMT. In R13478, an accelerating electrode is placed between the focusing electrode and first dynode for time resolution improvement through reduced transit time jitter. We investigated the time resolution dependence on the supply voltage and time pickoff method for R13478 and R9800 PMTs, each coupled with a 2.9 × 2.9 × 20 mm3 fast LGSO:Ce (0.025 mol%) crystal. In addition, we measured the PMT time resolutions coupled with the crystals in edge and laid positions to determine the effects of the reduced position dependence of transit time in R13478. R13478 exhibited a better time performance than R9800 in various ways. The rise time of R13478 for our experimental setup was 1.54 ns, 100 ps shorter than that of R9800 because of the reduced transit time. Further, R13478 achieved a 169 ps single time resolution at the recommended supply voltage, while this value was 187 ps for R9800. The time resolution of R13478 was also significantly better for a low time pickoff threshold level and a high supplied voltage, which are conditions vulnerable to transit time jitter and noise, respectively. A considerable difference in time resolution was observed for the laid position (R13478: 144 ps; R9800: 167 ps), indicating that the accelerating electrode reduced spatial transit time difference. Overall, we showed the effects of the differentiated characteristics of R13478 PMT compared with R9800 and confirmed its excellent time performance. We suggest use of this device as a photodetector effective for fast timing applications such as time-of-flight positron emission tomography.

Evaluation of High Energy Density Plasma in Counter‐Facing Plasma Focus Device Driven by Laser‐Triggered Pulse Power System

SUMMARYA laser‐trigger system has been introduced to a pulse power system composed of counter‐facing plasma focus electrodes in order to make high energy density plasma. Lithium plasmas made by a YAG laser ablation were used for both triggering the plasma focus and supplying the source of the high energy density plasma. Also the supply system of plasma source has been improved for stability and repeatability of the device. Operational principle of the device, details of the configuration, and basic characteristics of the triggering system are shown together with possible applications of the device.

Fabrication of a compact glass-sealed x-ray tube with carbon nanotube cold cathode for high-resolution imaging

A glass-sealed x-ray tube with field emission electron sources has been fabricated using carbon nanotubes (CNTs) grown on a silicon substrate by direct current plasma-enhanced chemical vapor deposition. Here, the authors report on the fabrication of CNT-based emitters, the field emission characteristics of these emitters, and the properties of the glass-sealed x-ray tube. The field emission produced a current of 5 mA with an electron transmission rate of 91.1% in a high-vacuum chamber. The glass-sealed x-ray tube had a conventional design and comprised a reflection anode, an evaporation getter, and a vacuum-sealed glass tube without additional focusing electrode requirements for ease of commercialization. Using this x-ray tube, the authors obtained x-ray images of objects, including a human finger and a commercial universal serial bus (USB) flash drive. The x-ray image allowed a 100 μm metal wire to be distinguished in the USB flash drive. The x-ray images were obtained at a dose rate of 1944 mrad/h, which represents a relatively low dose. The grown CNT emitters showed stable field emission after electrical aging. These CNT-based glass-sealed x-ray tubes are expected to become a platform for the fabrication of medical and dental x-ray systems.

Integrated Planar Three-Beam Electron Optics System for 220-GHz Folded Waveguide TWT

An integrated planar three-beam electron optics system is designed for our 220-GHz cascaded folded waveguide TWT. First, a planar three-beam gun is designed based on Pierce theory and Vaughan’s synthesis method with simplification of the focus electrode and the anode to facilitate manufacture and assembly, which is characteristic with 20 kV, ${3} \times {0.1}$ A, and beam radius of 0.1 mm. Simulation results show that the gun model performs well. Next, a uniform magnetic focusing structure used for constraining the three-beam array with adjacent beam separation of 8 mm is designed. Magnetic saturation analysis of the pole piece and structure parameters optimization of the magnets is considered thoroughly, which may guarantee the transport stability of the three-beam array and keep down the volume of the magnet. Simulation results show that the transmission of three-beam array up to 18 mm is 100% with the maximum ripple of 11.2% in the designed focusing structure. And the integrated planar three-beam electron optics system is verified as a stable system with the beam characteristics analyses of matching error, beam voltage fluctuation, and variation of peak ${B}_{z}$ .

Study on Radial Sheet Beam Electron Optical System for Miniature Low-Voltage Traveling-Wave Tube

Angle log-periodic meander line microstrip radial sheet beam traveling-wave tube is one kind of novel minimized vacuum device with low beam voltage. To generate and focus the radial sheet electron beam, a novel radial divergent sheet beam electron optical system, including the tractable radial sheet electron beam gun and miniaturized and feasible radial small tunable periodic cusped magnetic focusing system, is proposed in this paper. The fan-shaped radial sheet beam is emitted from the cylindrical surface cathode, compressed in axial direction, and confined in azimuthal direction by the focusing electrode. Simulation results show that the total emission of the angular radial sheet beam gun is 51.2 mA with the dimensions of $0.26~\text {mm} \times 8$ ° under the voltage of 1.7 kV, and the fan-shaped radial sheet beam can totally pass through the fan-shaped drift tunnel under the magnetic field. The experimental results are good in agreement with the simulation results. The tested angular radial sheet beam transmission efficiency is >90% in an 18.8-mm-length beam tunnel with the fill factor of 50%.

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

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.