Low-voltage Beam Research Articles

The effect of a constant electric field in an undisturbed plasma on the stability of the electron beam–gas discharge collisional plasma system

This work is devoted to the study of a fast non-relativistic electron beam–gas discharge plasma system within the framework of the kinetic theory of stability. The influence of a constant electric field, collinear beam velocity, on the stability of the system in an undisturbed plasma is studied. It is shown that even a relatively small electric field, which does not significantly affect the energy of the electron beam, can lead to significant changes in the parameters of harmonic disturbances propagating in the electron beam–plasma system in the region of its instability. It was found that the reason for such changes is the drift of plasma electrons, which, as a consequence, leads to a change in the frequency of disturbances in the coordinate system associated with the plasma due to the Doppler effect. The results obtained are demonstrated by calculations based on the kinetic theory of perturbation parameters in a low-voltage beam discharge in rare gases, which is used in the development of plasma electronics devices. The effect of electron-atomic collisions on the stability of the electron beam–plasma system is investigated and compared with the results of other authors' works.

An Overview of Multibeam Klystron Technology

The multibeam klystron (MBK) is a compact high-power microwave vacuum electronic device that features low beam voltage, high efficiency, wide bandwidth, and low volume and weight. Since the 1960s, high-performance broadband MBKs have been developed that cover the entire microwave frequency band with relative instantaneous bandwidths <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$&gt;$</tex-math> </inline-formula> 15%, peak power <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$&gt;$</tex-math> </inline-formula> 1 MW, average power up to 40 kW, and efficiencies <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$&gt;$</tex-math> </inline-formula> 40%. In recent years, driven by the needs of high-energy particle accelerators, ultra high frequency (UHF) and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\textit{L}$</tex-math> </inline-formula> -band MBKs with peak powers of more than 20 MW and efficiencies of nearly 80% are being developed. This article presents an overview of the development of broadband MBKs used in microwave electronic systems, such as radar and communication, and high-power MBKs used in the RF systems of particle accelerators. It also introduces the latest progress and development trends in MBKs leading to higher frequency, output power, bandwidth, efficiency, and lifetime.

Kinetic theory of nonrelativistic electron beam–inhomogeneous plasma system instability

On the basis of kinetic theory, the stability of an electron beam interacting with inhomogeneous plasma is investigated at Knudsen numbers of the order of 1. The theory has been tested on the example of a low-voltage beam discharge in a rear gas. It is shown that in the case of an inhomogeneous plasma even if the attenuation of a beam is neglected, several perturbations can propagate simultaneously at the same frequency, but with different phase and group velocities and increments. The case of a linear dependence of the plasma density on the coordinate is investigated in detail. In this case, there are two solutions: n- and p-waves, only the n-wave having a physical meaning. It is found that an increase in the plasma density gradient leads to a decrease in the increment and an increase in the phase and group velocities of propagation of perturbations with a frequency of the order of plasma frequency. A system with a growing plasma density along the beam direction is more stable than that with a constant density. For a significant change in the growth rate of the disturbance, the relative gradient of plasma density by an amount of about 10% at the wavelength is sufficient. All the observed features of the perturbation parameters depending on the plasma density gradient are physically interpreted. The calculations are confirmed by experimental data.

Low-voltage extraction characteristics of ion beams and space potential measurements on ECRIS

We have been using an electron cyclotron resonance ion source (ECRIS) for ion beam production, and it is desirable to construct a universal ECRIS that can produce ions with a wide range of mass/charge ratios, e.g. from several to several thousand. We investigated the characteristics of ions with high mass/charge ratios, e.g., iron endohedral fullerenes production, which requires low voltage beam extraction. We investigated the characteristics of the ion beam extraction at low extraction voltage. It is found that the beam current almost obeyed the Child-Langmuir law for various ion species. The space potential of the plasma in the ion source can be obtained from the relation between the extraction voltage and the square of the magnetic field strength of the dipole magnet. It is found that space potential values are larger with large charge state of ions, in low gas pressure condition and in high microwave incident power. At the same time, the plasma space potential was measured by using a Langmuir probe and compared with the ion beam method. It is found that same trend is confirmed with probe method.

Dispersion effect on phase focusing of monochromatic waves in a low voltage beam discharge in rare gases. Kinetic theory

The work is devoted to the development of the kinetic theory of phase focusing in a low-voltage beam discharge in rare gases at the Knudsen numbers for electron transport of order of 1, taking into account dispersion during the propagation of perturbations. It is shown that the dispersion leads to a significant increase in the phase focusing length. Taking into account the dependence of the electron beam intensity on the distance to the cathode, the simultaneous formation of several regions of negative charge (points of phase foci) corresponding to waves with the same frequency and different propagation increments and velocities is found. The phenomenon of locking electrons in a potential well between two simultaneously formed phase foci is discovered. The results of our calculations of the minimum phase focusing length describe well the known experimental data on the length of anomalous beam relaxation in a low-voltage beam discharge for He at the Knudsen numbers for electron transfer of the order of 1.

Nonlinear and self-consistent single-mode formulation for TM-mode gyrotrons.

This work develops a nonlinear and self-consistent framework for the single-mode simulation of TM-mode gyrotrons. Unlike TE modes, a nonlinear TM wave equation is derived by considering the additional axial modulation on the electron beam due to the interaction with the axial electric field. Together with the electrons' equations of motion, particle tracing simulation is conducted to model TM-mode oscillation. For a uniform structure, the electron-beam efficiency of the TM_{11}-mode gyrotron at the W band can achieve 30% over broad parameter space. Its beam-current, beam-voltage, and pitch-factor tuning properties are investigated under different magnetic fields. By optimizing the interaction structure of the proposed gyrotron backward-wave oscillator (gyro-BWO), the maximum interaction efficiency is higher than 30% with a frequency tuning range of more than 6 GHz at the pitch factor of 1.5. The peak efficiency can remain high of 32% at low beam voltage (10 kV) and low magnetic field (32.8 kG), indicating additional operating conditions. These special features may facilitate the development of low-cost and compact gyrotron systems and show great potential in the applications for TM-mode gyro-BWOs.

Beam-Plasma Stabilizer for the New Type of Nuclear Power Energy Systems

In this paper the electrokinetic characteristics of helium low-voltage beam discharge plasma in operating conditions of a three-electrode device with a hot cathode are studied. A method and a device are proposed to ensure effective voltage stabilization in a range up to 110 V by controlling the electron velocity distribution function using the plasma channel external boundaries.

Effect of Electron Energy Distribution Function in Plasma and Energy Dispersion of Electron Beam on the Stability of a Low-Voltage Beam Discharge

Effect of Electron Energy Distribution Function in Plasma and Energy Dispersion of Electron Beam on the Stability of a Low-Voltage Beam Discharge

Kinetic theory of monochromatic waves bunching in a low-voltage beam discharge in rare gases

The kinetic theory of phase focusing, that is bunching in a low-voltage beam discharge in rare gases (LVBD) during the propagation of longitudinal electrostatic oscillations at the Knudsen numbers of the order of unity have developed. The anomalous relaxation of the almost monoenergetic electron beam in momentum and energy is described for the case when this process cannot be explained by electron–atom collisions. The paper has shown the important role of electrons that have the beam energy and isotropic directional distribution, which is formed as a result of elastic collisions between the beam electrons and atoms. The dependence of the anomalous relaxation length on parameters of the LVBD in rare gases is studied.The developed theory makes it possible to quantitatively interpret experimental data on the LVBD under conditions when the electron mean free path is of the order of the interelectrode gap. According to these data, regardless of the density of the charged particles in the LVBD plasma in rare gases, five Langmuir plasma wavelengths fit along the length of the anomalous relaxation of the electron beam. The study of the electron beam dynamics laws in a plasma is important for the development of plasma-electrical devices, where the beam discharge is applied, namely: widely used all-movable stabilizers, sources of intense electromagnetic radiation, controlled elements of electronic circuits, plasma chemical reactors, etc.

Влияние вида функции распределения электронов в плазме и дисперсии по энергии электронного пучка на устойчивость низковольтного пучкового разряда

Within the framework of the kinetic approach, the conditions for the loss of stability of a low-voltage beam discharge in inert gases (LVBD) are studied depending on the temperature of the electron beam, the dispersion of the electron beam velocity in the direction of the discharge axis, and the form of the electron energy distribution function (EEDF). Regimes are considered when the interelectrode distance is on the order of the electron mean free path relative to elastic collisions with inert gas atoms. It is shown that the beam temperature Tb, determined in the LVBD by the cathode temperature not exceeding 1500 K, and the dispersion of the beam electron energy, which in the LVBD can be significantly higher than kTb and reaches 1 - 2 eV, have little effect on the conditions for the loss of stability of the LVBD and the magnitude of the growth rate of disturbance amplification at frequencies up to plasma It was found that the form of the EEDF monotonically decreasing with increasing electron energy also does not affect the parameters of the perturbations propagating in the LVBD at the beam energy much higher than the average electron energy in the plasma. The results obtained are applicable not only to LVBD, but also to other types of self-sustained beam discharges.

Quantitative material analysis using secondary electron energy spectromicroscopy

This paper demonstrates how secondary electron energy spectroscopy (SEES) performed inside a scanning electron microscope (SEM) can be used to map sample atomic number and acquire bulk valence band density of states (DOS) information at low primary beam voltages. The technique uses an electron energy analyser attachment to detect small changes in the shape of the scattered secondary electron (SE) spectrum and extract out fine structure features from it. Close agreement between experimental and theoretical bulk valance band DOS distributions was obtained for six different test samples, where the normalised root mean square deviation ranged from 2.7 to 6.7%. High accuracy levels of this kind do not appear to have been reported before. The results presented in this paper point towards SEES becoming a quantitative material analysis companion tool for low voltage scanning electron microscopy (LVSEM) and providing new applications for Scanning Auger Microscopy (SAM) instruments.

Reflective Gyrotron Backward-Wave Oscillator With Piecewise Frequency Tunability

The gyrotron backward-wave oscillators (gyro-BWOs) feature a continuous frequency tunability in a single transverse mode, while the step-tunable gyrotrons are famous for their ultrawide frequency hopping between various transverse modes. This study proposed a reflective gyro-BWO with a piecewise-continuous and wide tunability. The frequency is tunable in one transverse mode and can be switched to another by changing the applied magnetic field or/and the beam voltage. Meanwhile, the high-order axial modes (HOAMs) inside a cavity with a low-Q factor could broaden the bandwidth of each transverse mode. The interaction structure is optimized for the TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">22</sub> and TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">02</sub> modes that serve as the principal operating modes. The adjacent TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">51</sub> and TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">61</sub> modes could be excited to broaden the overall tuning range by adjusting the operating parameters. The measured magnetic tunings show a wide bandwidth of 36 GHz from 182 GHz at 6.6 Tup to 218 GHz at 8.0 T, which agrees with the numerical simulation predicted from the Computer Simulation Technology (CST). Besides, the measured voltage tunings exhibit a bandwidth of 2 GHz for the TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">02</sub> mode with a low-beam voltage from 12 to 19 kV. This study demonstrated that the reflective gyro-BWO could generate piecewise frequency tuning in four transverse modes and will be an excellent, moderate-power, terahertz source for many applications.

Simultaneous generation of several waves in a rare gas low-voltage beam discharge

The instability of a low-voltage beam discharge in rare gases is studied using He as an example. Attenuation of an electron beam due to collisions of electrons with atoms is taken into account when the electron mean free path is of the order of the inter-electrode distance. It was found that amplification of several waves with different increments and different speeds is possible with the loss of stability. In the case of a linear decrease in the beam intensity, two waves are generated. The wave having a smaller gain increment propagates at a higher speed. The indicated phenomenon is characteristic not only for a low-voltage beam discharge in rare gases, but also for any “cold high-energy electron beam—plasma” system when collisions of beam electrons with atoms should be taken into account.

A Novel Chevron-Shape Double-Staggered Grating Waveguide Slow Wave Structure for Terahertz Traveling Wave Tubes

A novel slow wave structure (SWS), called the chevron-shaped double-staggered grating waveguide structure, is proposed for traveling wave tube (TWT) amplifier for the terahertz (THz) region. The potential of this SWS is that it provides higher interaction impedance and has low phase velocity; thus, higher output power can be expected at a lower beam voltage. The electromagnetic characteristics and particle-in-cell (PIC) large-signal simulations were performed with CST Microwave Studio software. The SWS was optimized for the central frequency of 200 GHz, which synchronizes with a beam voltage of 18.8 kV in the second spatial harmonic ( ${2}\pi -{3}\pi $ ). A sheet electron beam with a current density of ${133}~\text {A/cm}^{{2}}$ was used to excite the structure, which interacts with the longitudinal electric field component to provide gain. The reflection coefficient at the port interface is less than −15 dB over the frequency range 181–220 GHz, and a small-signal gain of 30.98 dB is achieved for a tube length of 60 mm.

Kinetic theory of low-voltage beam discharge instability in rare gases

The kinetic theory of a low-voltage beam discharge instability in He is developed in the conditions, when the distance between electrodes is of the order of electron–atom collision length and the density of electrons in a primary beam is up to ten percent of the plasma density. The dispersion equation and its numerical and analytical solutions are obtained. The stability loss of this discharge is described in the framework of the problem with initial and boundary conditions. A significant dispersion is found in the propagation of harmonic disturbances in this system. On the basis of the developed theory, the areas of applicability of the hydrodynamic approach to the consideration of the system “cold electron beam - cold plasma” are elucidated. The theory significantly expands the range of parameters of the electron beam–plasma system, where a quantitative description of the spatial and temporal dynamics of wave propagation in such a system is possible. In the well-known special cases, such as a “weak electron beam - cold plasma,” the results obtained coincide with the data of other authors.

Indicatrix Determination of Electron Elastic Scattering by an Atom Based on Probe Measurements of Distribution Functions of Scattered Electrons in a Low-Voltage Beam Discharge in Inert Gases

In this paper, we propose a method for the experimental determination of an indicatrix of elastic scattering of an electron by an atom based on probe measurements of the distribution function of scattered electrons in the transit mode of a low-voltage beam discharge. We solved the Boltzmann kinetic equation by the method of series expansion according to the number of collisions and experimentally determined the scattered part of the electron distribution function by the method of a planar one-sided probe, which we previously developed for the study of beam discharges. The method was tested in plasma of a low-voltage beam discharge in He. Good agreement was obtained between the experimentally measured indicatrix of elastic scattering of electrons with energy of 30 eV by He atoms and the known data on the differential cross section, including those obtained from beam experiments. It is shown that no a priori data are required for the implementation of the developed method for determining the indicatrix of elastic scattering of an electron beam by atoms.

Starting behaviors of the TM-mode gyrotrons

This work shows the derivations and calculations of the starting behaviors using the Laplace method and the numerical method. Calculated results based on these two methods agree well when dealing with a uniform structure, while the numerical method is advantageous for the non-uniform and practical structure. The applicability of the zero-field and the outgoing-wave boundary conditions at the collector end is discussed. These two boundary conditions agree well when the beam-wave resonant line and the waveguide dispersion curve intercept at the backward-wave region but differ significantly at the forward-wave region. The beam-wave coupling strength of the TM-mode gyrotron is found to be strongly correlated with the starting current, which can be utilized to avoid the potential competition from the transverse electric (TE) modes. The starting current of the TM11 gyrotron exhibits an additional operating condition at the low-beam voltage that may facilitate the development of low-cost and tabletop gyrotron systems. The beam-voltage and magnetic-field tunings are investigated for an open-cavity structure with the numerical method. Interestingly, the TM11 gyrotron as well as the TE01 gyrotron exhibits a similar starting behavior, which warrants the potential applications of the TM-mode gyrotrons.

Определение индикатрисы упругого рассеяния электрона на атоме из зондовых измерений функции распределения рассеянных электронов в низковольтном пучковом разряде в инертных газах

A method for the experimental determination of elastic scattering an electron by an atom indicatrix from probe measurements of the scattered electrons distribution function in the transit mode low voltage beam discharge. The Boltzmann kinetic equation was solved by the expansion method in series by the number of collisions, and the scattered part of the electron distribution function was experimentally determined by the planar one-sided probe method, which was previously developed by the authors for beam discharge studies. The method was tested in a plasma of a low-voltage He beam discharge. A good agreement between the experimentally measured elastic electron scattering indicatrix at an energy of 30 eV and known data on the differential cross section is obtained. It is shown that for the implementation of the developed method for determining the elastic scattering of an electron beam by atoms indicatrix, no a priori data required.

Noncontact diagnostics of remote anisotropic plasmas

A new noncontact method for diagnostics of nonequilibrium plasma that integrates technologies of optical-and-magnetic technique of the Hanley effect and those of probe investigations is proposed. The method mentioned has been experimentally tested in plasmas with cardinally dissimilar structure of the electron velocity distribution function. As a model plasma object the positive column of glow discharge has been studied and as a distant object a short low-voltage beam discharge. The following potentialities of this method were illustrated, viz. in the distant object the complete electron velocity distribution function was determined and the diagram of electron pressure angular anisotropy was constructed. Verification of the method accuracy was carried out using the technique of flat single-sided probe.

Imaging modification of colon carcinoma cells exposed to lipid based nanovectors for drug delivery: a scanning electron microscopy investigation.

The adsorption at cell surfaces and cell internalization of two drug delivery lipid based nanovectors has been investigated by means of Field Emission Scanning Electron Microscopy (FE-SEM) operating at low beam voltage on two different colon carcinoma cell lines, CaCo-2 and CoLo-205, that were compared with the M14 melanoma cell line, as a reference. The cells were incubated with the investigated multifunctional nanovectors, based on liposomes and magnetic micelles loaded with 5-fluorouracil, as a chemotherapeutic agent, and a FE-SEM systematic investigation was performed, enabling a detailed imaging of any morphological changes of the drug exposed cells as a function of time. The results of the FE-SEM investigation were validated by MTS assay and immunofluorescence staining of the Ki-67 protein performed on the investigated cell lines at different times. The two nanoformulations resulted in a comparable effect on CaCo-2 and M14 cell lines, while for CoLo 205 cells, the liposomes provided an cytotoxic activity higher than that observed in the case of the micelles. The study highlighted the high potential of FE-SEM as a valuable complementary technique for imaging and monitoring in time the drug effects on the selected cells exposed to the two different nanoformulations.