Showing papers on "Plasma channel published in 2023"

Experimental Demonstration of Laser Guiding and Wakefield Acceleration in a Curved Plasma Channel.

Abstract: Curved plasma channels have been proposed to guide intense lasers for various applications, such as x-ray laser emission, compact synchrotron radiation, and multistage laser wakefield acceleration [e.g. J. Luo et al., Phys. Rev. Lett. 120, 154801 (2018)PRLTAO0031-900710.1103/PhysRevLett.120.154801]. Here, a carefully designed experiment shows evidences of intense laser guidance and wakefield acceleration in a centimeter-scale curved plasma channel. Both experiments and simulations indicate that when the channel curvature radius is gradually increased and the laser incidence offset is optimized, the transverse oscillation of the laser beam can be mitigated, and the stably guided laser pulse excites wakefields and accelerates electrons along the curved plasma channel to a maximum energy of 0.7 GeV. Our results also show that such a channel exhibits good potential for seamless multistage laser wakefield acceleration.

Study on radial uniformity of large aperture capacitively coupled plasma

Abstract: We simulated a large-aperture capacitively coupled plasma (CCP) using a two-dimensional fluid model, and explored the effects of radio frequency, electrode power, and gas pressure on the period-averaged electron density and electron temperature. The influence and control ability of various discharge parameters on the plasma uniformity are analyzed, which provides reference for the selection of plasma process parameters.

Stress wave analysis of high voltage pulse discharge rock fragmentation based on plasma channel impedance model

Abstract: High voltage pulse discharge (HVPD) rock fragmentation controls the plasma channel to form inside the rock by adjusting the electrical parameters, electrode type, etc. In this paper, a HVPD rock fragmentation test platform was built and the test waveforms were measured. Considering the effects of temperature, channel expansion and electromagnetic radiation, the impedance model of the plasma channel in the rock was established. The parameters and initial values of the model were determined by an iterative computational process. The model calculation results can reasonably characterize the development of plasma channel in rock and estimate the shock wave characteristics. Based on the plasma channel impedance model, the temporal and spatial distribution characteristics of the radial stress and tangential stress in the rock were calculated, and the rock fragmentation effect of the HVPD was analyzed.

Generation of tunable terahertz radiation by a laser pulse propagating in a magnetized plasma channel

Abstract: A study of the generation of terahertz (THz) radiation by propagation of a circularly polarized laser pulse in a parabolic plasma channel is presented. The laser–plasma system is embedded in a uniform axial magnetic field. Transverse electric and magnetic wakefields are evaluated using a perturbation scheme and quasi-static approximation. Nonlinear plasma electron velocities arise along the longitudinal and transverse directions as a result of interaction with the laser pulse. This results in the generation of an electromagnetic wave oscillating at THz frequency. The frequency of the obtained THz radiation can be controlled using the plasma channel parameters and can be tuned by varying the transverse position of observation. The THz radiation amplitude is enhanced in the presence of the parabolic channel compared to the homogeneous plasma configuration. The possibility of obtaining a tunable range of THz frequencies is presented. The analytical results have been validated using three-dimensional particle-in-cell simulations.

Generation of Large-Bandwidth High-Power X-Ray Free-Electron-Laser Pulses Using a Hollow-Channel Plasma

Abstract: Large-bandwidth x-ray free-electron-laser (XFEL) facilities are desirable scientific tools in various fields, such as molecular structural dynamics and spectroscopy diagnosis. Various methods are proposed to broaden the FEL spectra. Here, a method is proposed to generate high-power XFEL radiation of tunable spectral bandwidth using plasma wakefield acceleration. An ultrabroad bandwidth is achieved by chirping the electron beam in a hollow-channel plasma without noticeable slice-beam-quality degradation. A dedicated beamline can match the beams with a large energy chirp in the undulators almost without beam loss. Numerical simulations demonstrate that a relative spectral bandwidth (full width) of up to 24% can be obtained with optimized beam and plasma parameters.

Laser–Plasma Wake Velocity Control by Multi-Mode Beatwave Excitation in a Channel

Abstract: The phase velocity of a laser-driven wakefield can be efficiently controlled in a plasma channel. A beatwave of two long laser pulses is used. The frequency difference between these two laser pulses equals the local plasma frequency, so that the slow resonant excitation of the plasma wave is possible. Because the driver energy is spread over many plasma periods, the interference pattern can run with an arbitrary velocity along the channel and generate the wakefield with the same phase velocity. This velocity is defined by the channel radius and the structure of laser transverse modes excited in the channel. The wake velocity can be matched exactly to the witness velocity. This can be the vacuum speed of light for ultra-relativistic witnesses, or subluminal velocities for low-energy, weakly relativistic witnesses such as muons.

An improved resistance model of positive subsonic plasma channels in water

Abstract: The subsonic plasma channel and water can be regarded as series resistors in the pre-breakdown stage of sub-millisecond pulsed discharge in conductive water. An improved resistance model of the positive subsonic plasma channel is proposed. The gap resistance and the morphology of the bubble cluster and the plasma channel inside it are obtained from the electrical measurement and optical observation, respectively. The resistance of the plasma channel in the strong-ionization stage is calculated using the small-current arc resistance model. The improved model of the water resistance is established by analyzing the relationship between its equivalent cross-sectional area and its length in an uneven electric field. The resistance of the plasma channel in the weak-ionization stage is calculated. The resistance, voltage, and energy in the gap are analyzed based on the improved resistance model. The plasma channel's resistance is far less than the water resistance. The low voltage drop in the plasma channel leads to a high electric potential in the plasma channel's head, which is conducive to the plasma channel's development. 97% of the total energy in the pre-breakdown stage is consumed by the water resistor. The improved resistance model is helpful to supplement the development mechanism of the sub-millisecond pulsed discharge in water.

Flow modelling and gas heating inside a profiling channel of an electric arc plasma torch

Abstract: This paper presents a theor. model for the numerical anal. of the acceleration and heating of a gas by an elec. arc in a profiling channel with a diffuser anode. The thermal parameters and transport coeffs. of helium were detd. and the approximative expression for their calcn. in a broad range of temp. (0,3-100) kK and pressures are proposed. The calcn. and study of the effect of the thermal nonequil. plasma on the characteristics of the cylindrical arc were carried out. The results of the calcns. were compared with exptl. data and calcns. obtained from an equil. plasma model. [on SciFinder (R)]

Study on gas spark discharge plasma diagnosed by laser interferometric technology

Abstract: Laser interferometric technology is an important means for diagnosing plasmas due to its high temporal and spatial resolution. In this work, an air switch discharge plasma was diagnosed by a Mach-Zehnder laser interferometer with a wavelength of 532 nm. The air switch discharge plasma was generated between two needle-type Cu electrodes. Three dimensional electron density profiles of the air switch discharge plasma were deduced by numerical processing the interferograms containing plasma phase information obtained from experiments, revealing the formation and evolution processes of the arc channel of the air switch between the electrodes. At the start of the discharge, a large number of electrons were generated at the cathode, and then accelerated to the anode under the action of the electric field. During motion, neutral gas was ionized, and a cylindrical arc channel formed rapidly. A large pressure gradient was generated due to the dense plasma in the arc channel, so the dense plasma began to expand and push the surrounding air, forming a shock wave. The experimental results indicated that laser interferometric technology is an effective way to study air switch discharge plasmas.

Acceleration of a Positron Bunch in a Hollow Channel Plasma

Abstract: Plasmas are a compelling medium for particle acceleration owing to their natural ability to sustain electric fields that are orders of magnitude larger than those available in conventional radio-frequency accelerators. Plasmas are also unique amongst accelerator technologies in that they respond differently to beams of opposite charge. The asymmetric response of a plasma to highly-relativistic electron and positron beams arises from the fact that plasmas are composed of light, mobile electrons and heavy, stationary ions. Hollow channel plasma acceleration is a technique for symmetrizing the response of the plasma, such that it works equally well for high-energy electron and positron beams. In the experiment described here, we demonstrate the generation of a positron beam-driven wake in an extended, annular plasma channel, and acceleration of a second trailing witness positron bunch by the wake. The leading bunch excites the plasma wakefield and loses energy to the plasma, while the witness bunch experiences an accelerating field and gains energy, thus providing a proof-of-concept for hollow channel acceleration of positron beams. At a bunch separation of 330 um, the accelerating gradient is 70 MV/m, the transformer ratio is 0.55, and the energy transfer efficiency is 18% for a drive-to-witness beam charge ratio of 5:1.

Streamer Discharge Development in Long Air Gaps

Abstract: Streamer parameters were investigated as a function of the radius of high-voltage electrode (the diameter of the anode was varied from 10 to 200 cm), pulse amplitude and shape. The dependencies of the propagation distance, plasma channel radius, current, velocity of the streamer on the pulse shape and geometry of the electrodes were analyzed. Changes in the pulse amplitude, and voltage rise time do not cause a significant change in the field in the streamer channel, which remains at the level Ech ~ 5 kV/cm in the range from 5 kV to 1000 kV. The length of the streamer propagation essentially depends on the anode radius (through velocity). The field in the channel depends on the electrode radius only at small distances. The pulse rise time has practically no effect on the field in the channel, streamer velocity and propagation distance. The kinetics of ionization and recombination significantly change both the electric field in the channel and the propagation distance of the streamer.

One-Body Capillary Plasma Source for Plasma Accelerator Research at e-LABs

Abstract: We report on the development of a compact, gas-filled capillary plasma source for plasma accelerator applications. The one-body sapphire capillary was created through a diamond machining technique, which enabled a straightforward and efficient manufacturing process. The effectiveness of the capillary as a plasma acceleration source was investigated through laser wakefield acceleration experiments with a helium-filled gas cell, resulting in the production of stable electron beams of 200 MeV. Discharge capillary plasma was generated using a pulsed, high-voltage system for potential use as an active plasma lens. A peak current of 140 A, corresponding to a focusing gradient of 97 T/m, was observed at a voltage of 10 kV. These results demonstrate the potential utility of the developed capillary plasma source in plasma accelerator research using electron beams from a photocathode gun.

Investigations of the fluctuations in the plasmatron with the expansion channel as electrode

Abstract: In many modern plasma-technology units: plasmatrons, circuit breakers, plasma torches, plasma furnaces, most processes are closely connected with some non-steady irregularities or plasma turbulent phenomena. The term "plasma turbulence" may denote a considerably broader spectrum of non-steady random processes than the classical turbulence. The mechanisms of the hydrodynamic classical turbulence in non-electrically conducting gases or perfectly conducting liquids might not be applicable in low temperature plasma flows, especially in plasmas with chemical and ionization reactions and Joule heat release. In this work problems associated with the origin of the turbulence in low temperature strongly collisional plasmas produced in plasmatrons are discussed. The main goals of this discussion are: 1) the experimental investigation of voltage and electric current fluctuations in the plasmatron with the expansion channel as the outlet electrode, 2) the nature of fluctuations and their connection with instabilities in plasmatrons.

Study of the instabilities of plasma channel under electrical discharge in a water

Abstract: It is shown that the growth of the instabilities of the interface between both the plasma channel and liquid causes the change of the characteristics of the pulse discharge in a water. The time dependencies of the spectra of the corrugations are studied for the different type of discharges.

Large - an innovative plasma torch producing a sheet-shaped plasma jet

Abstract: Conventional plasma torch designs lead to a circular cross-section of the emanating plasma jet. Consequently in surface treatment applications the plasma jet hits the substrate within a limited circular working area. Large scale work-pieces therefore have to be scanned resulting in a time-consuming procedure.
The innovative plasma torch system LARGE is characterized by the arrangement of the anode and the cathode opposite to each other on a common axis with a variable separation. The central body of the torch between the electrodes is divided into several electrically insulated cascade plates, each with a hole to house the arc. The plasma gas is injected perpendicular to the torch axis through an additional hole in each plate. Passing through the arc, the gas is transferred to the plasma state and leaves the torch laterally through a slit as a sheet-shaped plasma jet. Particularly in the case of high gas flows (depending on the plasma gas composition and the arc current), the arc tends to be considerably curved due to viscous forces. This bending can be avoided by a Lorentz force counteracting these viscous forces and resulting from the interaction of the arc current with a superimposed magnetic field generated by permanent magnets.
Shrouding the electrodes with an inert gas and feeding reactive gas mixtures as main plasma gas allow the torch to be used for plasma chemical reactions, too.
The plasma torch LARGE is investigated by electrical and magnetic diagnostics. A numerical simulation of the temperature and velocity fields in a cross-section of the arc chamber is carried out for a better understanding of the experimental results.

Generation of stationary high-density cascade arc plasma and application to plasma windows

Abstract: We have developed indirectly heated hollow cathode electrodes and a cascade arc discharge apparatus with different channel diameters to realize plasma windows (PWs) as virtual vacuum interfaces. A compact arc discharge source with a channel diameter of 3 mm is fabricated to realize windowless vacuum–atmosphere separation. An atmospheric high-density Ar thermal plasma is generated, and a PW that produces 100 kPa and 81 Pa separation is demonstrated. An 8 mm channel diameter arc device is also constructed for application as an alternative differential pump with the separation of low- and high-pressure vacuum chambers, and the production of a high-density He plasma. Pressure differences of 2.5 kPa and 16 Pa between PWs are realized. Moreover, vacuum UV and visible emission spectroscopy reveal the characteristics of expanding plasmas and the plasma parameters.

Femtosecond Laser Fabrication of Curved Plasma Channels with Low Surface Roughness and High Circularity for Multistage Laser-Wakefield Accelerators

Abstract: A multistage laser-wakefield accelerator with curved plasma channels was proposed to accelerate electrons to TeV energy levels. In this condition, the capillary is discharged to produce plasma channels. The channels will be used as waveguides to guide intense lasers to drive wakefields inside the channel. In this work, a curved plasma channel with low surface roughness and high circularity was fabricated by a femtosecond laser ablation method based on response surface methodology. The details of the fabrication and performance of the channel are introduced here. Experiments show that such a channel can be successfully used to guide lasers, and electrons with an energy of 0.7 GeV were achieved.

Comparison of plasma development in a dielectric barrier discharge actuator operated using a constant and sinusoidal applied voltage

Abstract: Simulations of the plasma created by a dielectric barrier discharge actuator operating in pure Nitrogen are presented. The plasma created by a constant applied potential of 1.2 kV is compared to that generated by a sinusoidal applied potential with the same peak to peak potential of 1.2 kV operating at 10 MHz for two cycles. For the constant applied potential the plasma continuously propagates downstream towards the grounded electrode and can be identified by both an area of increased ion density and a high ionization sheath region. For the sinusoidal applied potential the sheath region is observed only during the first half of the cycle and develops at a slower rate than for the instant applied potential case. Furthermore, in the sinusoidal case, the density of free electrons available for ionization in the sheath region is increased at the end of the first cycle, but decreased at the end of the second. The plasma for a sinusoidal applied potential extends further away from the dielectric surface when compared to a constant applied potential case but appears limited in downstream extent by the change in the surface charge developed by the sinusoidal case.

Study of discharge characteristics and multi objective optimisation of machining parameters in ultrasonic vibration assisted micro electrical discharge machining

Abstract: Micro-EDM is a non-traditional manufacturing technique that uses the heat energy of the plasma to remove material. When there is a sufficient electric potential between two electrodes, the dielectric in between becomes ionised, resulting in the formation of a plasma channel. The net discharge energy produced is the result of the current and voltage present at the inter-electrode gap (IEG). The current and voltage waveforms obtained from the oscilloscope are used to calculate the discharge energy. A small part of this discharge energy gets converted as plasma temperature, which facilitates material removal in micro-EDM. Because plasma is the only source of heat, its properties must be studied. In the present study, Optical Emission Spectroscopy is used to calculate the temperature of the plasma. This article explores the scope of a hybrid micro EDM process, where an ultrasonic vibration is integrated to the tool electrode. A systematic approach using Response Surface Methodology is employed for modelling and analysis of plasma properties and material removal in micro EDM. Two types of input parameters were chosen: Voltage and pulse on time being the electrical parameters, and Amplitude and Frequency as the vibrational parameters. Dielectric used is deionised water. A single spark experiment was performed on Nitinol Shape Memory Alloy and tool used was of same material. Ultrasonic vibration was provided to the tool using a piezoelectric actuator. It was found that electrical parameters have a significant impact in determining plasma properties and material removal properties. Vibrational parameters play a vital impact in enhancing the crater’s surface features.

Stability of the Modulator in a Plasma-Modulated Plasma Accelerator

Abstract: We explore the regime of operation of the modulator stage of a recently proposed laser-plasma accelerator scheme [Phys. Rev. Lett. 127, 184801 (2021)], dubbed the Plasma-Modulated Plasma Accelerator (P-MoPA). The P-MoPA scheme offers a potential route to high-repetition-rate, GeV-scale plasma accelerators driven by picosecond-duration laser pulses from, for example, kilohertz thin-disk lasers. The first stage of the P-MoPA scheme is a plasma modulator in which a long, high-energy 'drive' pulse is spectrally modulated by co-propagating in a plasma channel with the low-amplitude plasma wave driven by a short, low-energy 'seed' pulse. The spectrally modulated drive pulse is converted to a train of short pulses, by introducing dispersion, which can resonantly drive a large wakefield in a subsequent accelerator stage with the same on-axis plasma density as the modulator. In this paper we derive the 3D analytic theory for the evolution of the drive pulse in the plasma modulator and show that the spectral modulation is independent of transverse coordinate, which is ideal for compression into a pulse train. We then identify a transverse mode instability (TMI), similar to the TMI observed in optical fiber lasers, which sets limits on the energy of the drive pulse for a given set of laser-plasma parameters. We compare this analytic theory with particle-in-cell (PIC) simulations and find that even higher energy drive pulses can be modulated than those demonstrated in the original proposal.

Ecologically pure plasma method rock breaking

Abstract: The results of theoretical, experimental researches and industrial introduction plasma method of hydro-electric-pulse breaking of rocks are stated in the paper. The physical processes which proceed in the plasma channel of the electrical discharge, dynamics of occurrence and development of the plasma channel between electrodes, list of the factors arising in a liquid during plasma electric-pulse processing are described. The hydro-dynamical phenomena in liquids which accompanying the electrical discharge are described.

Mathematical modeling of the temperature field of the arc of a conductive channel taking into account the temperature dependence of thermal conductivity

Abstract: The article is devoted to mathematical modelling of the plasma temperature field taking into account the temperature dependence of thermal conductivity. The channel model was taken as a basis. Neglecting a very small fraction of the energy received by the ions during their acceleration in the longitudinal field, it can be assumed that all the energy taken by the arc discharge from an external source in the arc column passes directly to the plasma electrons. To find the temperature field by the integration method, the equation of thermal conductivity was solved. At the same time, the arc column is considered as a cylindrical continuous conductive rod in which all the supplied electrical energy is diverted due to thermal conductivity to the cooled walls of the discharge tube. The arc itself is represented by two regions: conductive and non-conductive. Based on mathematical modelling, the law of temperature field change in the arc cross-section was obtained. A formula was also derived to determine the effective radius of an electrically conductive channel.

Stress wave analysis of high-voltage pulse discharge rock fragmentation based on plasma channel impedance model

Abstract: High-voltage pulse discharge (HVPD) rock fragmentation controls a plasma channel forming inside the rock by adjusting the electrical parameters, electrode type, etc. In this work, an HVPD rock fragmentation test platform was built and the test waveforms were measured. Considering the effects of temperature, channel expansion and electromagnetic radiation, the impedance model of the plasma channel in the rock was established. The parameters and initial values of the model were determined by an iterative computational process. The model calculation results can reasonably characterize the development of the plasma channel in the rock and estimate the shock wave characteristics. Based on the plasma channel impedance model, the temporal and spatial distribution characteristics of the radial stress and tangential stress in the rock were calculated, and the rock fragmentation effect of the HVPD was analyzed.

Simulation of Sub-THz Backward-Wave Oscillators With a Self-Focused Pseudospark-Sourced Sheet Electron Beam

Abstract: The results of simulation of the two previously proposed millimeter-band backward-wave oscillators (BWO) driven by a self-focused pseudospark-sourced sheet electron beams are presented. Plasma focusing makes possible beam transmission through a slow-wave structure (SWS) over distances of the order of several cm while providing effective beam-wave interaction. Two models of beam focusing by plasma in SWS are considered. A simplified approach, in which the electrodynamic structure is pre-filled with fully ionized plasma, allows assessing beam transport with effective beam wave interaction. A more accurate model, in which the plasma is formed as a result of impact ionization of the gas by beam electrons allows simulation of non-stationary processes of plasma channel formation. It describes not only plasma focusing in the interaction region, but also the consequent transport of the spent beam to collector via the plasma channel, which remains intact at the exit of the SWS.

Linearization of an Electron Beam’s Longitudinal Phase Space Using a Hollow-Channel Plasma

Abstract: The removal of undesired beam nonlinear energy chirp (time-energy correlation) or linearization of the beam longitudinal phase space (LPS) is crucial for high-brightness linac-based scientific applications, such as x-ray free-electron lasers. In this paper, we propose that a low-density hollow channel plasma can be used as a near-ideal passive linearizer to significantly linearize the beam LPS and, at the same time, preserve the beam emittance. Physically, the passage of the beam through the hollow plasma channel excites a strong quasicosinoidal longitudinal wakefield that acts to mitigate the beam nonlinear energy chirp by superimposing a reverse chirp on the beam. The theoretical analyses and large-scale three-dimensional start-to-end simulations confirm that the beam longitudinal phase space can be almost completely linearized without noticeable beam emittance growth. Application of such a near-ideal linearizer may significantly improve the performance of numerous accelerator-based applications.

Modeling of the laser-arc plasma torch

Abstract: The aim of this paper is the modeling of a discharge produced by direct action laser-arc plasma torch (LAPT) of linear design, when the focused laser beam passes through the transferred arc along the axis of the plasma-forming channel. The mathematical model of the discharge in such plasma device was constructed on the basis of a system of magnetic-gas dynamic equations in the boundary layer approximation for the plasma and a scalar wave equation in the quasi-optical approximation for the laser beam propagating in it. The results of the computer modeling have shown that for certain ratios of the arc current and the laser beam power the distributions of temperature, current density and velocity of the plasma generated in LAPT differ basically from the corresponding distributions, which are characteristic of the arc plasma torches, while the laser beam is subjected to significant absorption and extra focusing in the plasma. The obtained theoretical results were used in designing of the torch for laser-plasma surfacing and selecting of its operation modes. The experimental examinations of LAPT have proved in general the results of its modeling.

Beam Shaping for the Laser Energy Deposition in Air

Abstract: Controlled laser energy deposition can be very useful for specific applications and can be implemented by varying the shape, size, plasma properties, and controllable transition to the induced plasma breakdown. Advancements in optical technology have made it easier to shape laser beams both in space and in time. In this paper, we have performed a numerical analysis of the formation and evolution of a laser induced plasma when a pre-ionized region, created by a femtosecond laser pulse is heated by a subsequent nanosecond laser pulse of the different intensity distribution at the focus ( Gaussian, flat-top). A quantitative verification of the initial plasma parameters is carried out. A discussion of the effects of beam shaping is presented, including the transition to breakdown, the temporal decay of the formed plasma, the timescales of compression and expansion of the plasma channel.