Showing papers on "Plasma channel published in 2013"
TL;DR: In this article, a simple fluid model of the discharge of a non-equilibrium plasma column can be generated by discharge pulses in a helium jet surrounded by atmospheric-pressure air, and the authors show that the plasma jet is very similar to a cathode streamer (ionization wave) guided by the helium jet.
Abstract: It has been demonstrated experimentally that a non-equilibrium plasma column can be generated by discharge pulses in a helium jet surrounded by atmospheric-pressure air. The ?plasma jet? can be longer than 10?cm and fast imaging shows that most of the light emitted by the plasma jet is produced in a small ?plasma bullet? that propagates along the helium jet at speeds of several tens of km?s?1. With the help of a simple fluid model of the discharge, we show that the plasma jet is very similar to a cathode streamer (ionization wave) guided by the helium jet. We discuss the properties of the helium streamer and of the plasma channel behind the streamer head as a function of parameters such as electrode geometry, voltage pulse waveform and preionization density. The model can reproduce qualitatively and explain most of the features observed experimentally.
329 citations
TL;DR: In this paper, the ABAQUS code finite element software has been used to simulate the temperature distribution on the surface of workpiece and tool during a single discharge in the electrical discharge machining process.
Abstract: In the present study, the temperature distribution on the surface of workpiece and tool during a single discharge in the electrical discharge machining process has been simulated using ABAQUS code finite element software. The temperature dependency of material properties and the expanding of plasma channel radius with time have been employed in the simulation stage. The profile of temperature distribution has been utilized to calculate the dimensions of discharge crater. Based on the results of FEM and the experimental observations, a numerical analysis has been developed assessing the contribution of input-parameters on the efficiency of plasma channel in removing the molten material from molten puddles on the surfaces of workpiece and tool at the end of each discharge. The results show that the increase in the pulse current and pulse on-time have converse effects on the plasma flushing efficiency, as it increases by the prior one and decreases by the latter one. Later, the introduced formulas for plasma flushing efficiency based on regression model were utilized to predict the cardinal parameter of recast layer thickness on the electrodes which demands expensive empirical tests to be obtained.
122 citations
TL;DR: In this article, the authors present a model to study the streamer-to-leader transition process and to obtain its scaling with ambient air density, in agreement with similarity laws for Joule heating in a streamer channel.
Abstract: [1] In this paper we present modeling studies of air heating by electrical discharges in a wide range of pressures. The developed model is capable of quantifying the different contributions for heating of air at the particle level and rigorously accounts for the vibration-dissociation-vibration coupling. The model is validated by calculating the breakdown times of short air gaps and comparing to available experimental data. Detailed discussion on the role of electron detachment in the development of the thermal-ionizational instability that triggers the spark development in short air gaps is presented. The dynamics of fast heating by quenching of excited electronic states is discussed and the scaling of its main channels with ambient air density is quantified. The developed model is employed to study the streamer-to-leader transition process and to obtain its scaling with ambient air density. Streamer-to-leader transition is the name given to a sequence of events occurring in a thin plasma channel through which a relatively strong current is forced through, culminating in heating of ambient gas and increase of the electrical conductivity of the channel. This process occurs during the inception of leaders (from sharp metallic structures, from hydrometeors inside the thundercloud, or in virgin air) and during their propagation (at the leader head or during the growth of a space leader). The development of a thermal-ionizational instability that culminates in the leader formation and propagation is characterized by a change in air ionization mechanism from electron impact to associative ionization and by contraction of the plasma channel. The introduced methodology for estimation of leader speeds shows that the propagation of a leader is limited by the air heating of every newly formed leader section. It is demonstrated that the streamer-to-leader transition time has an inverse-squared dependence on the ambient air density at near-ground pressures, in agreement with similarity laws for Joule heating in a streamer channel. Model results indicate that a deviation from this similarity scaling occurs at very low air densities, where the rate of electronic power deposition is balanced by the channel expansion, and air heating from quenching of excited electronic states is very inefficient. These findings place a limit on the maximum altitude at which a hot and highly conducting lightning leader channel can be formed in the Earth’s atmosphere, result which is important for understating of the gigantic jet (GJ) discharges between thundercloud tops and the lower ionosphere. Simulations of leader speeds at GJ altitudes demonstrate that initial speeds of GJs are consistent with the leader propagation mechanism. The simulation of a GJ, escaping upward from a thundercloud top, shows that the lengthening of the leader streamer zone, in a medium of exponentially decreasing air density, determines the existence of an altitude at which the streamer zones of GJs become so long that they dynamically extend (jump) all the way to the ionosphere.
97 citations
TL;DR: This work demonstrates for the first time, that applicability of the Zweifach-Fung bifurcation law can be extended to dimensions much higher than the suspended particle size and shows nearly 100 % separations in microchannels which are much easier to fabricate than previously designed devices.
Abstract: In recent years, microfluidic chips have proven ideal tools for biochemical analysis, which, however, demands a unique and compatible plasma separation scheme. Various research groups have established continuous flow separation methods in microfluidic devices; however, they have worked with relatively small dimension microchannels (similar to the blood cell diameter). The present work demonstrates separation of plasma by utilizing the hydrodynamic separation techniques in microchannels with size of the order of mm. The separation process exploits the phenomenon, which is very similar to that of plasma skimming explained under Zweifach-Fung bifurcation law. The present experiments demonstrates for, the first time, that applicability of the Zweifach-Fung bifurcation law can be extended to dimensions much higher than the suspended particle size. The T-microchannel device (comprising perpendicularly connected blood and plasma channels) were micro-fabricated using conventional PDMS micro-molding techniques. Three variables (feed hematocrit, main channel width, and flow rate distributions) were identified as the important parameters which define the device’s efficiency for the blood plasma separation. A plasma separation efficiency of 99.7 % was achieved at a high flow ratio. Novel concepts of 2-stage or multiple plasma channel designs are also proposed to yield high separation efficiency with undiluted blood. The possible underlying principle causing plasma separation (viz. aggregation and shear thinning) are investigated in detail as part of this work. The results are significant because they show nearly 100 % separations in microchannels which are much easier to fabricate than previously designed devices.
54 citations
TL;DR: In this paper, the evolution of the electron energy distribution function in a plasma channel in a xenon plasma at atmospheric pressure created by radiation of a KrF femtosecond laser has been considered.
Abstract: The evolution of the electron energy distribution function in a plasma channel in a xenon plasma at atmospheric pressure created by radiation of a KrF femtosecond laser has been considered. It has been shown that, owing to the existence of the Ramsauer minimum in the transport scattering cross section, such a channel can be used to amplify electromagnetic waves up to the terahertz frequency range at relaxation times of the energy spectrum of ∼10−7 s. The gain factor has been calculated as a function of the time and radiation frequency.
44 citations
TL;DR: In this article, a method of creating plasma channels with controllable depth and transverse profile for the guiding of short, high power laser pulses for efficient electron acceleration is proposed, where the hydrogen-filled capillary discharge waveguide is modified by a ns-scale laser pulse, which heats the electrons near the capillary axis.
Abstract: A method of creating plasma channels with controllable depth and transverse profile for the guiding of short, high power laser pulses for efficient electron acceleration is proposed. The plasma channel produced by the hydrogen-filled capillary discharge waveguide is modified by a ns-scale laser pulse, which heats the electrons near the capillary axis. This interaction creates a deeper plasma channel within the capillary discharge that evolves on a ns-time scale, allowing laser beams with smaller spot sizes than would otherwise be possible in the unmodified capillary discharge.
42 citations
TL;DR: In this paper, a near-hollow channel is proposed to provide independent control over the focusing and accelerating forces in a plasma accelerator, where the low density in the channel contributes to the focusing forces, while the accelerating fields are determined by the high density in channel walls.
Abstract: A near-hollow plasma channel, where the plasma density in the channel is much less than the plasma density in the walls, is proposed to provide independent control over the focusing and accelerating forces in a plasma accelerator. In this geometry the low density in the channel contributes to the focusing forces, while the accelerating fields are determined by the high density in the channel walls. The channel also provides guiding for intense laser pulses used for wakefield excitation. Both electron and positron beams can be accelerated in a nearly symmetric fashion. Near-hollow plasma channels can effectively mitigate emittance growth due to Coulomb scattering for high-energy physics applications.
41 citations
TL;DR: In this paper, a method of creating plasma channels with controllable depth and transverse profile for the guiding of short, high power laser pulses for efficient electron acceleration is proposed, where the hydrogen-filled capillary discharge waveguide is modified by a ns-scale laser pulse, which heats the electrons near the capillary axis.
Abstract: A method of creating plasma channels with controllable depth and transverse profile for the guiding of short, high power laser pulses for efficient electron acceleration is proposed. The plasma channel produced by the hydrogen-filled capillary discharge waveguide is modified by a ns-scale laser pulse, which heats the electrons near the capillary axis. This interaction creates a deeper plasma channel within the capillary discharge that evolves on a ns-time scale, allowing laser beams with smaller spot sizes than would otherwise be possible in the unmodified capillary discharge.
37 citations
TL;DR: In this article, the authors analyzed the optical spectra of a drive laser exiting a channel guided laser-plasma accelerator (LPA) to infer the magnitude of the excited wakefields.
Abstract: Optical spectra of a drive laser exiting a channel guided laser-plasma accelerator (LPA) are analyzed through experiments and simulations to infer the magnitude of the excited wakefields. The experiments are performed at sufficiently low intensity levels and plasma densities to avoid electron beam generation via self-trapping. Spectral redshifting of the laser light is studied as an indicator of the efficiency of laser energy transfer into the plasma through the generation of coherent plasma wakefields. Influences of input laser energy, plasma density, temporal and spatial laser profiles, and laser focal location in a plasma channel are analyzed. Energy transfer is found to be sensitive to details of laser pulse shape and focal location. The experimental conditions for these critical parameters are modeled and included in particle-in-cell simulations. Simulations reproduce the redshift of the laser within uncertainties of the experiments and produce an estimate of the wake amplitudes in the experiments as a function of amount of redshift. The results support the practical use of laser redshifting to quantify the longitudinally averaged accelerating field that a particle would experience in an LPA powered below the self-trapping limit.
35 citations
TL;DR: In this paper, the filamentation of IR and UV laser pulses has been studied numerically and experimentally for different initial beam focusing geometries, and linear electron density profiles along the plasma channel of filaments have been obtained.
Abstract: The filamentation of IR and UV laser pulses has been studied numerically and experimentally for different initial beam focusing geometries, and linear electron density profiles along the plasma channel of filaments have been obtained. The results demonstrate that changes in laser beam focusing have a stronger effect on filament and plasma channel parameters for UV radiation than for IR radiation. Focusing causes individual high fluence regions produced by refocusing to merge to form a continuous extended filament with a continuous plasma channel.
33 citations
TL;DR: In this article, a deformable mirror was used to control the plasma channel length by introducing a spherical aberration into the initial transverse spatial distribution of a femtosecond laser pulse.
Abstract: Filamentation of focused UV and IR femtosecond laser pulses and plasma channel formation governed by variable wavefront distortions was experimentally and numerically studied. A deformable mirror was used to control the plasma channel length by introducing a spherical aberration into the initial transverse spatial distribution of a femtosecond laser pulse. An at least double increase of the plasma channel length was observed with increasing deformation of the mirror. Numerical calculations show that the hat-like phase shape of the aberration ensures that the energy of the initial laser pulse remains confined for a longer distance within the limited transverse size of the filament.
TL;DR: In this paper, a near-hollow channel is proposed to provide independent control over the focusing and accelerating forces in a plasma accelerator, where the low density in the channel contributes to the focusing forces, while the accelerating fields are determined by the high density in channel walls.
Abstract: A near-hollow plasma channel, where the plasma density in the channel is much less than the plasma density in the walls, is proposed to provide independent control over the focusing and accelerating forces in a plasma accelerator. In this geometry the low density in the channel contributes to the focusing forces, while the accelerating fields are determined by the high density in the channel walls. The channel also provides guiding for intense laser pulses used for wakefield excitation. In certain regimes, both electron and positron beams can be accelerated and focused in a nearly symmetric fashion. Near-hollow plasma channels can effectively mitigate emittance growth due to Coulomb scattering for high-energy physics applications.
TL;DR: In this paper, the beam loading in laser-plasma accelerators using a near-hollow plasma channel is examined in the linear wake regime, and it is shown that by properly shaping and phasing the witness particle beam, high-gradient acceleration can be achieved with high-efficiency, and without induced energy spread or emittance growth.
Abstract: Beam loading in laser-plasma accelerators using a near-hollow plasma channel is examined in the linear wake regime. It is shown that, by properly shaping and phasing the witness particle beam, high-gradient acceleration can be achieved with high-efficiency, and without induced energy spread or emittance growth. Both electron and positron beams can be accelerated in this plasma channel geometry. Matched propagation of electron beams can be achieved by the focusing force provided by the channel density. For positron beams, matched propagation can be achieved in a hollow plasma channel with external focusing. The efficiency of energy transfer from the wake to a witness beam is calculated for single ultra-short bunches and bunch trains.
TL;DR: In this article, a femtosecond double-pulse laser was used to induce air plasma, which can lead to significant increase of the intensity and reproducibility of the optical emission signal compared to femto-single pulse laser.
Abstract: In laser-induced breakdown spectroscopy, a femtosecond double-pulse laser was used to induce air plasma. The plasma spectroscopy was observed to lead to significant increase of the intensity and reproducibility of the optical emission signal compared to femtosecond single-pulse laser. In particular, the optical emission intensity can be optimized by adjusting the delay time of femtosecond double-pulse. An appropriate pulse-to-pulse delay was selected, that was typically about 50 ps. This effect can be especially advantageous in the context of femtosecond laser-induced breakdown spectroscopy, plasma channel, and so on.
TL;DR: In this article, single discharges of electrochemical arc machining are examined and the heat-affected zone is analyzed, and a model is set up to simulate the heat transfer into the workpiece.
Abstract: In this work, single discharges of electrochemical arc machining are examined. The heat-affected zone is analyzed, and a model is set up to simulate the heat transfer into the workpiece. As an input parameter of the simulation, the temperature of the electrochemical arc machining process was determined to be 3,500 K by means of emission spectroscopy. The simulation shows that the diameter of the heat-affected zone is less dependent on discharge duration and heat transfer due to heat flux than on the arc spot diameter. As a result of the investigation, it became clear that varying diameters of the heat-affected zone have to evolve from different diameters of the plasma channel’s arc spot. Understanding the heat distribution into the workpiece in electrochemical arc machining with micro-machining parameters allows the further development of a micro-drilling process for electrically conductive materials based on electrochemical arc machining.
TL;DR: An improved method based on magnetic switch and the results shown that the uniform dielectrics like plastic can be broken down in water is presented, and the feasible mechanism explaining the breakdown of solid is proposed and proved experimentally.
Abstract: Recently, a method utilizing pulsed power technology for disintegration of rocks arouses great interest of many researchers. In this paper, an improved method based on magnetic switch and the results shown that the uniform dielectrics like plastic can be broken down in water is presented, and the feasible mechanism explaining the breakdown of solid is proposed and proved experimentally. A high voltage pulse of 120 kV, rise time 0.2 μs was used to ignite the discharging channel in solids. When the plasma channel is formed in the solid, the resistance of the channel is quiet small; even if a relatively low voltage is applied on the channel on this occasion, it will produce high current to heat the plasma channel rapidly, and eventually disintegrate the solids. The feasibility of promising industrial application in the drilling and demolition of natural and artificial solid materials by the method we presented is verified by the experiment result in the paper.
TL;DR: Two kinds of floating electrode, floating dielectric barrier covered electrode (FDBCE) and floating pin electrode (FPE), which can enhance the performance of plasma jet are reported in this article.
Abstract: Two kinds of floating electrode, floating dielectric barrier covered electrode (FDBCE) and floating pin electrode (FPE), which can enhance the performance of plasma jet are reported. The intense discharge between the floating electrode and power electrode decreased the voltage to trigger the plasma jet substantially. The transition of plasma bullet from ring shape to disk shape in the high helium concentration region happened when the floating electrode was totally inside the powered ring electrode. The enhanced electric field between propagating plasma bullet and ground electrode is the reason for this transition. The double plasma bullets happened when part of the FDBCE was outside the powered ring electrode, which is attributed to the structure and surface charge of FDBCE. As part of the FPE was outside the powered ring electrode, the return stroke resulted in a single intensified plasma channel between FPE and ground electrode.
TL;DR: In this article, the influence of driving voltage and frequency on electron heating in geometrically symmetrical dual capacitively coupled radio frequency plasma have been investigated on the basis of the global model, and non-monotonic behavior of dc self bias and plasma heating with increasing high frequency is observed.
Abstract: On the basis of the global model, the influences of driving voltage and frequency on electron heating in geometrically symmetrical dual capacitively coupled radio frequency plasma have been investigated. Consistent with the experimental and simulation results, non-monotonic behavior of dc self bias and plasma heating with increasing high frequency is observed. In addition to the local maxima of plasma parameters for the integer values of the ratio between the frequencies (ξ), ourstudies also predict local maxima for odd integer values of 2ξ as a consequence of the electrical asymmetry effect produced by dual frequency voltage sources.
TL;DR: In this paper, two models determining the electrical conductivity at the vicinity of the electrodes with two different assumptions were used to calculate the flow patterns inside a non-transferred DC arc plasma torch.
Abstract: The hypothesis of local thermal equilibrium (LTE) in thermal plasma has been widely accepted. Most of the simulation models for the arc plasma torch are based on the hypothesis of LTE and its results indicate good validity to mimic the pattern of plasma flow inside a plasma torch. However, according to the LTE hypothesis, electrical conductivity near electrodes is significantly lower because of the low gas temperature. Consequently, it is difficult for electrical current flows to pass between the anode and cathode. Therefore, the key subject for a model concentrating on the LTE assumption is to deal with the low electrical conductivity near the electrodes. In this study, two models determining the electrical conductivity at the vicinity of the electrodes with two different assumptions were used to calculate the flow patterns inside a non-transferred DC arc plasma torch. Gas temperature, velocity, voltage drop, and heat energy of the plasma arc were compared between the two models. The results indicated that the plasma arc inside the plasma torch fluctuates, as simulated by both models. It seems that the model can obtain comparable accuracy with the experimental results if the plasma gas electrical conductivity is determined by nominal electron temperature.
Patent•
12 Apr 2013TL;DR: In this article, the authors present a device for laser nanomachining a sample made of a material having a given transparency band, the device comprising: a focusing module (203, 703) allowing a nondiffracting beam (210, 710) to be generated, along a focusing line generally oriented along the optical axis of the focusing module, from a given incident beam, and second means (202, 702) for emitting at least one second electromagnetic wave (I2) of spectral band comprised in the transparency band of said material, which wave(s) is
Abstract: According to one aspect, the invention relates to a device (1, 2, 3) for laser nanomachining a sample made of a material having a given transparency band, the device comprising: a focusing module (203, 703) allowing a nondiffracting beam (210, 710) to be generated, along a focusing line generally oriented along the optical axis of the focusing module, from a given incident beam; first means (202, 702) for emitting a first light pulse (I1) of spectral band comprised in the transparency band of said material, able to generate in said material, after focusing by said focusing module, a plasma of free charges along said focusing line via multi-photon absorption, thus forming a "plasma channel"; and second means (202, 702) for emitting at least one second electromagnetic wave (I2) of spectral band comprised in the transparency band of said material, which wave(s) is/are intended to be spatially superposed on said plasma channel in order to heat said material via absorption by the free charges of the plasma
21 Aug 2013-Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment
TL;DR: In this paper, the problem of diagnosing a TW/PW class laser with a gas jet or a preexisting particle beam in a plasma channel is discussed. And the problems related to the diagnostic of this kind of beams and the proposed or already realized solutions are discussed.
Abstract: The new frontier in the particle beam accelerator is the so called plasma acceleration. Using the strong electric field inside a plasma it is possible to achieve accelerating gradients in the order of magnitude larger with respect to the actual technologies. Different schemes have been proposed and several already tested, producing beams of energy of several GeV. Mainly two approaches are followed: either the beam is directly produced by the interaction of a TW/PW class laser with a gas jet or a preexisting particle beam is accelerated in a plasma channel. In both cases a precise determination of the emerging beam parameters is mandatory for the fine tuning of the devices. The measurement of these parameters, in particular the emittance, is not trivial, mainly due to the large energy spread and to the tight focusing of these beams or to the background noise produced in the plasma channel. We show the problems related to the diagnostic of this kind of beams and the proposed or already realized solutions.
TL;DR: In this article, a new scheme for accelerating positively charged particles in a plasma wakefield accelerator is proposed, where the proton drive beam propagates in a hollow plasma channel and the beam radius is of order of the channel width, which helps to focus the positively charged witness bunch propagating along the beam axis.
Abstract: A new scheme for accelerating positively charged particles in a plasma wakefield accelerator is proposed. If the proton drive beam propagates in a hollow plasma channel, and the beam radius is of order of the channel width, the space charge force of the driver causes charge separation at the channel wall, which helps to focus the positively charged witness bunch propagating along the beam axis. In the channel, the acceleration buckets for positively charged particles are much larger than in the blowout regime of the uniform plasma, and stable acceleration over long distances is possible. In addition, phasing of the witness with respect to the wave can be tuned by changing the radius of the channel to ensure the acceleration is optimal. Two dimensional simulations suggest that, for proton drivers likely available in future, positively charged particles can be stably accelerated over 1 km with the average acceleration gradient of 1.3 GeV/m.
TL;DR: The electron energy distribution function in the plasma channel produced by a femtosecond laser pulse with a wavelength of 248 nm in atmospheric pressure gases was considered in this article, where conditions were determined whereby this channel may be employed for amplifying electromagnetic waves up to the terahertz frequency range over the energy spectrum relaxation time ∼10{sup -7} s. Gains were calculated as functions of time and radiation frequency.
Abstract: The electron energy distribution function in the plasma channel produced by a femtosecond laser pulse with a wavelength of 248 nm in atmospheric-pressure gases was considered. Conditions were determined whereby this channel may be employed for amplifying electromagnetic waves up to the terahertz frequency range over the energy spectrum relaxation time ∼10{sup -7} s. Gains were calculated as functions of time and radiation frequency. The effect of electron – electron collisions on the rate of relaxation processes in the plasma and on its ability to amplify the electromagnetic radiation was investigated. (interaction of laser radiation with matter)
TL;DR: A novel plasma generator is described that offers large-scale, continuous, non-magnetized plasma with a 30-cm-diameter hollow structure, which provides a path for an electromagnetic wave.
Abstract: A novel plasma generator is described that offers large-scale, continuous, non-magnetized plasma with a 30-cm-diameter hollow structure, which provides a path for an electromagnetic wave. The plasma is excited by a low-pressure glow discharge, with varying electron densities ranging from 10{sup 9} to 2.5 × 10{sup 11} cm{sup −3}. An electromagnetic wave propagation experiment reproduced a continuous radio blackout in UHF-, L-, and S-bands. The results are consistent with theoretical expectations. The proposed method is suitable in simulating a plasma sheath, and in researching communications, navigation, electromagnetic mitigations, and antenna compensation in plasma sheaths.
TL;DR: In this article, the effects of initial and induced chirp on the wake field as well as the laser pulse parameters were investigated, and the group velocity dispersion and nonlinear relativistic effects were taken into account to evaluate the excited wake field in two dimension using source dependent expansion method.
Abstract: The excitation of wake field plasma waves by a short laser pulse propagating through a parabolic plasma channel is studied. The laser pulse is assumed to be initially chirped. In this regard, the effects of initial and induced chirp on the plasma wake field as well as the laser pulse parameters are investigated. The group velocity dispersion and nonlinear relativistic effects were taken into account to evaluate the excited wake field in two dimension using source dependent expansion method. Positive, negative, and un-chirped laser pulses were employed in numerical code to evaluate the effectiveness of the initial chirp on 2-D wake field excitation. Numerical results showed that for laser irradiances exceeding 1018W/cm2, an intense laser pulse with initial positive chirp generates larger wake field compared to negatively and un-chirped pulses.
TL;DR: P polarization-independent, electrically tunable/switchable Airy beam based on polymer-stabilized blue phase liquid crystals with wide working temperature range and fast response time through a structure called vertical field driven mode is experimentally demonstrated.
Abstract: Because of their non-diffraction and freely acceleration during propagation, finite energy Airy beams are interesting for application such as optical manipulation, plasma channel generation and optical vortex generation. Especially interesting are tunable/switchable Airy beams, in which the Airy beam tuning by electric field, temperature or optical intensity can be realized. Here we experimentally demonstrate polarization-independent, electrically tunable/switchable Airy beam based on polymer-stabilized blue phase liquid crystals with wide working temperature range and fast response time through a structure called vertical field driven mode.
TL;DR: In this paper, the influence of the electrode system on the emission characteristics of a high-current low-inductance vacuum spark is investigated, and it is shown that the structure and composition of the spark plasma radiating in the X-ray spectral range depend substantially on the geometry and relative position of the electrodes.
Abstract: The influence of the electrode system on the emission characteristics of a high-current low-inductance vacuum spark is investigated. It is shown that the structure and composition of the spark plasma radiating in the X-ray spectral range depend substantially on the geometry and relative position of the electrodes. A mechanism related to the effect of the initial distribution of the electric field in the electrode gap is proposed to explain such a dependence. The conditions in which the radiating plasma forms from the erosion products of one or both electrodes are determined.
Patent•
23 Jun 2013TL;DR: In this paper, a laser-sustained plasma light source includes a plasma bulb containing a working gas flow driven by an electric current sustained within the plasma bulb, which can be stabilized and controlled by control of the voltages present on the each of the electrodes.
Abstract: A laser sustained plasma light source includes a plasma bulb containing a working gas flow driven by an electric current sustained within the plasma bulb. Charged particles are introduced into the working gas of the plasma bulb. An arrangement of electrodes maintained at different voltage levels drive the charged particles through the working gas. The movement of the charged particles within the working gas causes the working gas to flow in the direction of movement of the charged particles by entrainment. The resulting working gas flow increases convection around the plasma and increases laser to plasma interaction. The working gas flow within the plasma bulb can be stabilized and controlled by control of the voltages present on the each of the electrodes. A more stable flow of working gas through the plasma contributes to a more stable plasma shape and position within the plasma bulb.
TL;DR: In this paper, a simple model explaining the origin of anomalous group velocity dispersion in the plasma channel of a filament is suggested, where the authors show that the IR shifted component behaves like a Raman soliton.
Abstract: Complex experimental study of spectral, spatial and temporal behaviors of the IR shifted component observed under filamentation of the collimated femtosecond laser beam (80 GW, 50 fs, 805 nm) in molecular gases showed that this component behaves like a Raman soliton. Namely, it is confined in all domains: (a) it propagates within the filament core, (b) it has a stable duration of 30 fs along the filament, and (c) its spectrum shifts as a whole from 820 to 870 nm on the distance of 2 m from the filament start. A simple model explaining the origin of anomalous group velocity dispersion in the plasma channel of a filament is suggested.
Posted Content•
TL;DR: In this article, a new scheme for accelerating positively charged particles in a plasma wakefield accelerator is proposed, where the proton drive beam propagates in a hollow plasma channel and the beam radius is of order of the channel width, which helps to focus the positively charged witness bunch propagating along the beam axis.
Abstract: A new scheme for accelerating positively charged particles in a plasma wakefield accelerator is proposed. If the proton drive beam propagates in a hollow plasma channel, and the beam radius is of order of the channel width, the space charge force of the driver causes charge separation at the channel wall, which helps to focus the positively charged witness bunch propagating along the beam axis. In the channel, the acceleration buckets for positively charged particles are much larger than in the blowout regime of the uniform plasma, and stable acceleration over long distances is possible. In addition, phasing of the witness with respect to the wave can be tuned by changing the radius of the channel to ensure the acceleration is optimal. Two dimensional simulations suggest that, for proton drivers likely available in future, positively charged particles can be stably accelerated over 1 km with the average acceleration gradient of 1.3 GeV/m.