Electron Beam Injection Research Articles

PEA System Modeling and Signal Processing for Measurement of Volume Charge Distributions in Thin Dielectric Films

This paper discusses our effort to develop advanced pulsed electroacoustic (PEA) measurement system capabilities that incorporate: 1) improved signal processing tools for increased signal/noise ratios and 2) integrated PEA modeling tools. In addition, we emphasize the state-of-the-art system electronic components, integrated environmental controls, and sensor improvements required to achieve high spatial resolution while maintaining reasonable temporal resolution for both ambient and in vacuo measurements of thin dielectrics charged using electron beam injection, which is most applicable for spacecraft charging tests. PEA measurement systems provide an important tool to investigate the spatial extent and dynamic evolution of embedded charge distributions in thin dielectric materials. This knowledge has important applications in spacecraft industries, as well as for semiconductors, high-power electronic devices, high-voltage dc power cable insulation, and high-energy and plasma physics apparatus. The emphasis of this paper is on improved signal processing methods and integrated PEA modeling tools.

Resonant excitation of whistler waves by a helical electron beam

AbstractChorus‐like whistler mode waves that are known to play a fundamental role in driving radiation belt dynamics are excited on the Large Plasma Device by the injection of a helical electron beam into a cold plasma. The mode structure of the excited whistler wave is identified using a phase correlation technique showing that the waves are excited through a combination of Landau resonance, cyclotron resonance, and anomalous cyclotron resonance. The dominant wave mode excited through cyclotron resonance is quasi‐parallel propagating, whereas wave modes excited through Landau resonance and anomalous cyclotron resonance propagate at oblique angles that are close to the resonance cone. An analysis of the linear wave growth rates captures the major observations in the experiment. The results have important implications for the generation process of whistler waves in the Earth's inner magnetosphere.

Плазменно-пучковый супергетеродинный лазер на свободных электронах с Н-убитронной накачкой с неосевой инжекцией электронного пучка

Плазменно-пучковый супергетеродинный лазер на свободных электронах с Н-убитронной накачкой с неосевой инжекцией электронного пучка

Many-body manifestation of interaction-free measurement: The Elitzur-Vaidman bomb

We consider an implementation of the Elitzur-Vaidman bomb experiment in a DC-biased electronic Mach-Zehnder interferometer with a leakage port on one of its arms playing the role of a "lousy bom". Many-body correlations tend to screen out manifestations of interaction-free measurement. Analyzing the correlations between the current at the interformeter's drains and at the leakage port, we identify the limit where the originally proposed single-particle effect is recovered. Specifically, we find that in the regime of sufficiently diluted injected electron beam and short measurement times, effects of quantum mechanical wave-particle duality emerge in the cross-current correlations.

Electron beam manipulation, injection and acceleration in plasma wakefield accelerators by optically generated plasma density spikes

We discuss considerations regarding a novel and robust scheme for optically triggered electron bunch generation in plasma wakefield accelerators [1]. In this technique, a transversely propagating focused laser pulse ignites a quasi-stationary plasma column before the arrival of the plasma wake. This localized plasma density enhancement or optical “plasma torch” distorts the blowout during the arrival of the electron drive bunch and modifies the electron trajectories, resulting in controlled injection. By changing the gas density, and the laser pulse parameters such as beam waist and intensity, and by moving the focal point of the laser pulse, the shape of the plasma torch, and therefore the generated trailing beam, can be tuned easily. The proposed method is much more flexible and faster in generating gas density transitions when compared to hydrodynamics-based methods, and it accommodates experimentalists needs as it is a purely optical process and straightforward to implement.

Asymmetric valley-resolved beam splitting and incident modes in slanted graphene junctions

Electron injection into a graphene sheet through a slanted armchair graphene nanoribbon (AGNR) is investigated. An incident mode, or subband, in the AGNR is valley-unpolarized. Our attention is on the valley-resolved nature of the injected electron beams and its connection to the incident mode. It is known for a normal injection that an incident mode will split symmetrically into two valley-resolved beams of equal intensity. We show, in contrast, that slanted injections result in asymmetric valley-resolved beam splitting. The most asymmetric beam splitting cases, when one of the valley-resolved beams has basically disappeared, are found and the condition derived. This is shown not due to trigonal warping because it holds even in the low incident energy regime, as long as collimation allows. These most asymmetric beam splitting cases occur at energies within an energy interval near and include the subband edge of an incident mode. The physical picture is best illustrated by a projection of the slanted AGNR subband states onto that of the 2D graphene sheet. It follows that the disappearing of a valley-resolved beam coincides with the situation that the group velocities of the projected states in the corresponding valley are in backward directions.

Status of the proton and electron transfer lines for the AWAKE Experiment at CERN

The AWAKE project at CERN is planned to study proton driven plasma wakefield acceleration with an externally injected electron beam. Therefore two transfer lines are being designed in order to provide the proton beam from the SPS and the electron beam from an RF gun to the plasma cell. The commissioning of the proton line will take place in 2016 for the first phase of the experiment, which is focused on the self-modulation of a 12cm long proton bunch in the plasma. The electron line will be added for the second phase of AWAKE in 2017, when the wakefield will be probed with an electron beam of 10–20MeV/c. The challenge for these transfer lines lies in the parallel operation of the proton, electron and laser beam used to ionize the plasma and seed the self-modulation. These beams, of different characteristics, need to be synchronized and positioned for optimized injection conditions into the wakefield. This task requires great flexibility in the transfer line optics. The status of these designs will be presented in this paper.

Modification of thin oxide films of MOS structure by high-field injection and irradiation

We have investigated processes of modification and changing of the charge state of MOS structures having a multilayer gate dielectric based on a thermal SiO2 film doped with phosphorus under conditions of different modes of high-field electron injection and an electron irradiation. We have determined that negative charge, accumulating in the phosphosilicate glass (PSG) ultra thin film of the MOS structures having the two-layer gate dielectric SiO2-PSG under conditions of both high-field tunneling injection of electrons and electron beam, could be used for a modification of devices having the same structure (e.g. correction of threshold voltage, increase of charge stability and breakdown voltage of MOS structure). We have shown that when thickness of PSG film increased, a raising of the electron traps density occurred, but the value of the cross-section of electron traps was the same. It was established that in order to obtain MOS structures with high thermal stability, one has to anneal them at 200° C after performing irradiation treatment.

Improved Design of a Multistage Axial Vircator With Reflectors for Enhanced Performances

The basic design of an axial virtual cathode oscillator (vircator) with axial extraction operating in TM01 mode is modified by introducing thin conducting disks, also called reflectors, into the cylindrical waveguide. The operation principal of this novel type of device relies on the formation of a series of virtual cathodes, located at the center of adjacent quasi-cavities. The behavior of this new type of multistage vircator is numerically investigated using CST Particle Studio 3-D particle-in-cell code. Progressively decreasing the radii of the reflectors installed upstream in the tube allows the mitigation of spurious modes. Tapering the radii of the reflectors turns out to be crucial in focusing the electron beam on axis in the downstream region and maximizing the TM01 power conversion efficiency. This novel architecture enables a five-reflector vircator operating with an injected electron beam of 508-kV mean voltage and 19-kA mean current to deliver up to 2-GW mean power sustained only by the TM01 mode in the S-band with a power conversion efficiency close to 21%.

Matching strategies for a plasma booster

This paper presents a theoretical study of a matching strategy for the laser-plasma wakefield accelerator where the injected electron beam is produced by an external source. The matching is achieved after an initial focusing using conventional beam optics, combining a linear tapering of plasma density and the increasing non linearity of the plasma wake due to the focusing of the laser driver. Both effects contribute in increasing the focusing strength from an initial relatively low value, to the considerably higher value present in the flat top plasma profile, where acceleration takes place. The same procedure is exploited to match the beam from plasma to vacuum once acceleration has occurred. Beam loading plays a crucial role both at the very beginning and end of the whole process. In the last stage, two more effects take place: a partial emittance compensation, reducing emittance value by a sizable amount, and a reduction of the energy spread, due to the relevant beam loading operating when the laser is defocused.

3-D PIC Numerical Investigations of a Novel Concept of Multistage Axial Vircator for Enhanced Microwave Generation

The enhancement of power conversion efficiency of a classical axial VIRtual CAthode oscillaTOR (vircator) by introducing one or more reflectors beyond the anode in the cylindrical waveguide is numerically investigated. The targeted microwave (MW) output frequency lies in the S-band at around 3 GHz for an operation in TM01 mode. Powered by a 511-kV voltage signal for a duration of 45 ns, the design under consideration operates with an injected electron beam of mean voltage and mean current of around 508 kV and 19 kA, respectively. Full-wave 3-D modeling is performed using well-tested electromagnetic particle-in-cell codes such as Computer Simulation Technology Particle Studio and Magic. Simple rules for designing and installing the reflectors are given. The number of reflectors required to maximize the efficiency is discussed. The power conversion efficiency is shown to be improved over a classical axial vircator design by a factor of 12.8. A maximum mean output power of about 1.26 GW is delivered off-axis in the S-band at around 3 GHz, with an efficiency of nearly 13%. Besides, it is also shown that increasing the number of reflectors allows switching the operation mode from TM01 to TE11 along with a shift of MWfrequency from the S- to the L-band. A five- or six-reflector configuration is predicted to generate MW at both 2.86 and 1.4 GHz with conversion efficiencies ranging from 3.5% to 6.6%. A vircator including seven reflectors is expected to operate in TE11 mode at 1.4 GHz with an efficiency of about 8%.

Sterilization of dielectric containers using a fore-vacuum pressure plasma-cathode electron source

We describe our work on sterilization of 10 ml glass and 60 ml plastic cylindrical containers using a fore-vacuum pressure, plasma-cathode, electron beam source. Beam plasma is formed inside the vessel by injection of a low-energy electron beam at 3 - 6 keV energy and current of 50 mA, at a working gas (air) pressure of 8 Pa. The gas composition was tracked by a quadrupole gas analyzer type RGA-100. As a test biological object for sterilization we used E. coli ATCC 25922 bacteria, the inner surface of each vessel was inoculated with a bacterial suspension. We find a smooth dependence of the degree of sterilization on the total energy density injected into the vessel. The efficacy of sterilization of container inner surfaces using a fore-vacuum pressure, plasma-cathode e-beam source of relatively low energy (a few keV) electrons is thus demonstrated.

Wake potential with exchange-correlation effects in semiconductor quantum plasmas

Using the non-relativistic quantum hydrodynamic model, wake potential has been studied in a magnetized semiconductor quantum plasma in the presence of upper hybrid wave which is excited via externally injected electron beam. The quantum effect contains electron exchange and correlation potential, Fermi degenerate pressure, and Bohm potential. It is found that the contribution of quantum mechanical electron exchange and correlation potential significantly modifies the amplitude and the effective length of the oscillatory wake potential. In the electron-hole plasma systems, electron exchange-correlation effects tend to increase the magnitude of the wake potential and are much effective at the distances of the order of Debye-length. The application of the work in context of the semiconductor plasmas have also been analyzed graphically.

Response of chromospheric lines to different periodic non-thermal electron beams

AbstractSolar flares produce radiations in very broad wavelengths. Spectra can supply us abundant information about the local plasma, such as temperature, density, mass motion and so on. Strong chromospheric lines, like the most studied Hα and Ca II 8542 Å lines are formed under conditions of departures from local thermodynamic equilibrium in the lower atmosphere subject to flare heating. Understanding how these lines are formed is very useful for us to correctly interpret the observations. In this paper, we try to figure out the response of chromospheric lines heated by different periodic non-thermal electron beams. Our results are based on radiative hydrodynamic simulations. We vary the periods of electron beam injection from 1.25 s to 20 s. We compare the response times to different heating parameters. Possible explanations are discussed.

Theoretical analysis and simulation study on a coaxial vircator with enhanced modulation

Based on large-signal theory, a one-dimensional theoretical model of a coaxial vircator is developed to give the microwave gain of the nonlinear beam–wave interaction, and the effect of injected current premodulation on the microwave gain is analysed theoretically. In addition, a coaxial vircator with improved dual-cavity modulation structure, which has the advantage of enhancing the effect of the modulation cavity on the injected electron beam by way of feedback microwaves, is presented. The simulation results are presented to test the validity of the proposed theory, and it can be seen that the system power efficiency can become further strengthened by adjusting the parameters of the microwave feedback channel until the feedback electric field is at the proper phase. Finally, through optimization, a structure capable of generating 7.05 GW average output power and 19.5 % power conversion efficiency at 2.95 GHz operating frequency is obtained.

Study of the impurity composition and effective plasma charge in the GOL-3 facility

Heating and confinement of plasma in a multimirror magnetic configuration have been studied at the GOL-3 facility (Budker Institute of Nuclear Physics, Siberian Branch, Russian Academy of Sciences, Novosibirsk). The experiments are aimed at estimating the densities and charge states of the main impurities in the GOL-3 plasma and determining their contribution to the effective plasma charge. Plasma with a density of ∼1015 cm−3 was heated by a relativistic electron beam (1 MeV, 8 μs, ⩽200 kJ). At the end of electron beam injection, the plasma temperature reached 1 keV. The densities of impurities were determined using VUV and visible spectroscopy, as well as mass spectrometry of the residual vacuum. To determine the effective plasma charge, the experimental data were compared with the results of numerical simulations of the ionization balance of impurities. It is shown that the effective plasma charge calculated with allowance for the contributions from the main impurities does not exceed Zeff = 1.8, which cannot explain the experimentally observed improved confinement of low-density plasma.

Nonlinear Theory of Plasma-Beam Superheterodyne Free Electron Laser of Dopplertron Type with Non-Axial Injection of Electron Beam

We have developed a quadratic nonlinear theory of a plasma-beam superheterodyne free electron laser of dopplertron type with the non-axial injection of an electron beam with respect to the guiding magnetic eld. It is found out that the studied device can work in four di erent modes of operation. We determine the modes that have maximum gain coe cients of electromagnetic signals. It is shown that for all the operating modes the ampli cation factor of an electromagnetic signal is enhanced when the electron beam injection angle is increased.

Introduction of an Electron Beam from a Secondary Emission Magnetron Injection Gun into a Closed Magnetic Trap

The injection of a nonrelativistic electron beam into a toroidal solenoid is considered. A secondary emission magnetron injection gun is proposed as a source of the electron beam. Using the drift approximation, a step value after the first turn of the beam around the solenoid is calculated. For multiturn injection, the beam must not return to the electron gun. Thus, the step value must be large enough by comparison with the gun dimension. Using this condition and the Hull cutoff magnetic field equation, the maximum electrode diameters of the magnetron injection gun are calculated. The maximum gun perveance is calculated using scale theory and experimental data from other authors. Because of the small dimensions of the gun, a concept for a multibeam gun is proposed. As an example, the total current and total power are calculated for two values of the electron beam energy and three operational facilities. In comparison with existing sources for auxiliary plasma heating, a novel approach can provide higher power. The calculated levels of the electric field strength in the gun are several times lower than those achieved in experiments. Prospects for the novel concept for plasma heating and current drive and the problem of gun cooling are discussed. Other possible applications are discussed too.

Observation of spectral composition and polarization of sub-terahertz emission from dense plasma during relativistic electron beam–plasma interaction

The paper presents results of measurements of sub-terahertz electromagnetic emission from magnetized plasma during injection of a powerful relativistic electron beam of microsecond duration in plasma with the density of 3 × 1014 cm−3. It was found that the spectrum of the radiation concentrated in three distinct regions with high level of spectral power density. The first region is located near f1 = 100 GHz; the second one is in the vicinity of 190 GHz, and the third region is in the frequency interval f3 = 280–340 GHz. Polarization vectors of the emission in the first and third regions (f1 and f3) are directed mainly perpendicular to the magnetic field in the plasma. At the same time, the polarization of the radiation in the vicinity of f2 = 190 GHz is parallel to the magnetic field. The most likely mechanism of electromagnetic wave generation in the frequency regions f1 and f2 is the linear conversion of the plasma oscillations into the electromagnetic waves on strong gradients of the plasma density. The third region is situated in the vicinity of second harmonic of electron plasma frequency, and we explain this emission by the coalescence of the upper-hybrid oscillations at high level turbulence in plasma.

The Effect of the Electron-Beam Parameter Spread on Microwave Generation in a Three-Cavity Axial Vircator

The behavior of the generation efficiency and radiation spectrum of a three-cavity axial vircator versus the radius of the injected electron beam, its impedance and energy homogeneity is studied. This paper establishes that for each geometry of a three-cavity resonator, there exist the optimal (maximizing the generation efficiency) values of these parameters and determines the range within which they may vary without losing the efficiency of generation.