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Stationary and unstable pulsating flows of ionizing hydrogen in the channel of a quasi-stationary plasma accelerator are considered. Numerical studies of two-dimensional axisymmetric flows are carried out based on the modified magnetogasdynamic (MGD) equations in the approximation of local thermodynamic equilibrium, taking into account electrical conductivity, thermal conductivity, and radiation transport. The generalization of the calculation results led to the formulation of the empirical condition for the stationarity of two-dimensional flows of an ionizing gas. [ABSTRACT FROM AUTHOR]

In this paper, we consider the acceleration of plasma fluxes in crossed electromagnetic fields. The possible technical approach to a prospective plasma accelerator is discussed. A simple hydrodynamic model describing the dynamics of the plasma ring in these fields is proposed. Based on this model, the estimations of basic characteristics for the accelerated flux are calculated for typical experimental conditions.

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. [ABSTRACT FROM AUTHOR]

In this paper, the electron acceleration by plasma wave in IFEL mechanism in the presence of a quadruple magnetic field and ion channel guiding effects has been investigated both analytically and numerically. The results illustrate that the increasing of the quadruple wiggler amplitude and wavelength up to an optimum value has considerable effects on the electron acceleration and its relativistic dynamics in laser ion channel. It was found that in the presence the optimum values of quadruple wiggler amplitude and wavelength, the electron energy gain increases more than 90% than that obtained in the absence of the wiggler. Moreover, the numerical simulations reveal that if the electrons are thrown with higher initial kinetic energy into the wiggler field, they can longer remain in the acceleration phase of the plasma wave and gain more energy from the wave. Therefore, it turns out that, in a laser-plasma accelerator, the electron acceleration and its relativistic dynamics can be tuned by the wiggler field strength, wiggler wavelength, and initial kinetic energy of electrons. The favorable results of studies in this field can be promising for the new generation of the laser-plasma accelerators based on the wiggler structures.

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.

Studies were performed on the possibility of using the coaxial plasma jet accelerator to facilitate breakdown and the plasma current start-up in the Globus-M2 and KTM tokamaks. The results of experiments on the jet injection into the Globus-M2 tokamak with a magnetic field of 0.7 T showed that the discharge current rise began 1–2 ms earlier than it did in experiments using gas puffing and inductive breakdown of the working gas. In this case, the breakdown voltage decreased approximately 2 times. The results of experiments on plasma jet injection through the equatorial diagnostic duct into the KTM tokamak with a magnetic field of 0.9 T showed that the gas breakdown occurred up to 6 ms earlier than the breakdown initiated using the inductive method. In this case, the loop voltage decreases approximately 1.5 times. In almost all shots using the accelerator, the gas breakdown occurred, while in its absence, sometimes the gas breakdown could not be obtained. [ABSTRACT FROM AUTHOR]

The electron energy dependence of a scintillating screen (Lanex Fast) was studied with sub-nanosecond electron beams ranging from 106 MeV to 1522 MeV at the Lawrence Berkeley National Laboratory Advanced Light Source (ALS) synchrotron booster accelerator. The sensitivity of the Lanex Fast decreased by 1percent per 100 MeV increase of the energy. The linear response of the screen against the charge was verified with charge density and intensity up to 160 pC/mm2 and 0.4 pC/ps/mm2, respectively. For electron beams from the laser plasma accelerator, a comprehensive study of charge diagnostics has been performed using a Lanex screen, an integrating current transformer, and an activation based measurement. The charge measured by each diagnostic was found to be within +/-10 percent.

Injection of plasma flow generated by a quasi-stationary plasma accelerator into a region with a magnetic field created by a series of ring current-carrying conductors forming a solenoid is considered. Numerical studies are carried out based on the set of magnetogasdynamic (MGD) equations represented in terms of the vector potential of the magnetic field, taking into account electrical conductivity, thermal conductivity, and radiation transport, provided that the plasma accelerator and ring conductors are located on the same axis. It is shown that small currents in ring conductors create a magnetic field inside the solenoid, which does not significantly affect the main stream, while simultaneously isolating it from the current coils as a result of the formation of a rarefied plasma layer separating the high-speed flow of dense plasma. Calculations of the MGD problem also show that the plasma flow within the solenoid is not accompanied by an increase in the temperature of the medium. [ABSTRACT FROM AUTHOR]

For the guarantee of the long-distance transport of the bunches of China Initiative Accelerator Driven System (CIADS), a new scheme is proposed that extra magnetic field is used in the accelerator-target coupling section before the windowless target to minimize the self-modulation (SM) mechanism. Particle-in-cell simulations are carried out to study the influence of the solenoidal magnetic field on the self-modulation mechanism when long proton bunches move in the background plasmas. The long proton bunches used in the simulations are similar to these in the linear accelerator of CIADS. It is found that the presence of the solenoidal magnetic field will significantly inhibit the self-modulation process. For the strong magnetic field, the longitudinal separation and transverse focusing of the long bunches disappear. We attribute these phenomena to the reason that the strong solenoidal magnetic field restricts the transverse movement of plasma electrons. Thus, there are not enough electrons around the bunch to compensate the space charge effect. Moreover, without transverse current, the longitudinal pinched effect disappears, and the long bunch can not be separated into small pulses anymore. [ABSTRACT FROM AUTHOR]

Properties of compressible flows in the quasi‐stationary plasma accelerator have been studied in the presence of an additional longitudinal magnetic field and the arising rotation of plasma flow. Numerical study was carried out within the framework of two‐dimensional magnetic hydrodynamics (MHD) model of the axisymmetric plasma flows taking into account the finite conductivity of medium and radiation transport. Dynamics of compressible plasma flows is accompanied by the MHD dynamo effect or generation of magnetic field on a conical shock wave forming at the outlet from the accelerator. [ABSTRACT FROM AUTHOR]

The paper presents new generation plasma optical devices based on the electrostatic plasma lens configuration that opens a novel attractive possibility for effective high-tech practical applications. Original approaches to use of plasma accelerators with closed electron drift and open walls for the creation of a cost-effective low-maintenance plasma lens with positive space charge and possible application for low-cost, low-energy rocket engine are described. The preliminary experimental, theoretical and simulation results are presented. It is noted that the presented plasma devices are attractive for many different applications in the state-of-the-art vacuum-plasma processing.

A classical model of radiation reaction for the betatron oscillation of an electron in a plasma wakefield accelerator is presented. The maximum energy of the electron due to the longitudinal radiation reaction is found, and the betatron oscillation damping due to both the longitudinal and transverse radiation reaction effects is analyzed. Both theoretical and numerical solutions are shown with good agreements. The regime that the quantum radiation takes effect is also discussed. This model is important for designing future plasma based super accelerators or colliders.

Abstract On the wake of the results obtained so far at the SPARC_LAB test-facility at the Laboratori Nazionali di Frascati (Italy), we are currently investigating the possibility to design and build a new multi-disciplinary user-facility, equipped with a soft X-ray Free Electron Laser (FEL) driven by a ∼ 1 GeV high brightness linac based on plasma accelerator modules. This design study is performed in synergy with the EuPRAXIA design study. In this paper we report about the recent progresses in the on going design study of the new facility. [ABSTRACT FROM AUTHOR]

Structural changes in the surface layer of target samples made of double forged tungsten were investigated after successive pulsed plasma irradiation thereof using different irradiation facilities such as plasma focus (PF), plasma gun (PG), and plasma accelerator (PA). The irradiation modes simulated hard conditions occurring under the action of thermonuclear plasma on the material in modern tokamaks in such extreme situations as plasma disruption, vertical displacement, and edge localized mode effects (ELMs). Hydrogen and deuterium were used as working gases. Double forged tungsten (DFW) samples were irradiated using PF facilities (PF-6 and PF-1000U) with a subsequent irradiation using PG or PA, as well as another sequence consisting in the initial irradiation using PA and a subsequent irradiation using PF-6 at the final stage. The DFW samples in the experiments were positioned normal to the incident energy flux. The following irradiation modes were used. The PF-1000U facility provides a power density of the deuterium plasma flux onto the target surface qpl = 109-1010 W/cm2, pulse duration τpl = 50-100 ns, power density of the of fast ion beam (with energy Ei > 100 keV) qfi = 1011-1012 W/cm2, pulse duration τfi = 10-50 ns. The PF-6 facility provides qpl = 109-1010 W/cm2, τpl = 50 ns, qfi = 1010-1011 W/cm2, τfi = 10-50 ns. The PG facility provides energy density Q = 0.8 MJ/m2, density of hydrogen plasma q ≈ 5 × 106 W/cm2, pulse duration τ = 15 μs. The PA facility provides Q = 0.75 MJ/m2, power density of deuterium plasma q = 3.6 × 105 W/cm2, τ = 0.25 ms. General features and peculiarities inherent in tungsten damage and changes in the structural state thereof under the action of energy flows in the hard mode of preliminary irradiation in PF facilities with subsequent radiation exposure in softer modes implemented in PG and PA facilities are considered. It is shown that, in the irradiation modes under investigation, the character of material degradation depends not only on the magnitude and duration of the single energy pulses generated by a testing facility but also on the number of energy pulses. The depth of the apparent damaged layer, wherein the crippling of the material occurs, is about 200 μm in almost all the studied irradiation modes, the damage being of thermal and shock-wave nature. [ABSTRACT FROM AUTHOR]

An injection scheme is proposed to realize electron trapping in sub-relativistic plasma wakefield accelerators. A laser under oblique angle of incidence ionizes a dopant gas in plasma and ponderomotively accelerates the released electrons into the direction of wake propagation. This process enables electron trapping in the wakefield even for a wakefield potential below the trapping threshold. We study the scheme theoretically and by means of particle-in-cell (PIC) simulations to demonstrate high-quality beam formation and acceleration with sub-micrometer normalized emittances and sub-percent uncorrelated energy spreads.

Plasma accelerators (Esary et al 2009 Rev. Mod. Phys. 81 1229) are a potentially important source of high energy, low emittance electron beams with high peak currents generated within a relatively short distance. As such, they may have an important application in the driving of coherent light sources such as the Free Electron Laser (FEL) which operate into the x-ray region (McNeil and Thompson 2010 Nat. Photon. 4 814–21). While novel plasma photocathodes (Hidding et al 2012 Phys. Rev. Lett. 108 035001) may offer orders of magnitude improvement to the normalized emittance and brightness of electron beams compared to Radio Frequency-driven accelerators, a substantial challenge is the energy spread and chirp of beams, which can make FEL operation impossible. In this paper it is shown that such an energy-chirped, ultrahigh brightness electron beam, with dynamically evolving current profile due to ballistic bunching at moderate energies, can generate significant coherent radiation output via the process of Coherent Spontaneous Emission (CSE) (Campbell and McNeil 2012 Proc. FEL2012 ( Nara, Japan )). While this CSE is seen to cause some FEL-induced electron bunching at the radiation wavelength, the dynamic evolution of the energy chirped pulse dampens out any high-gain FEL interaction. This work may offer the prospect of a future plasma driven FEL operating in the high-gain Self Amplified CSE mode.

The effects of a correlated linear energy/velocity chirp in the electron beam in the free electron laser (FEL), and how to compensate for its effects by using an appropriate taper (or reverse-taper) of the undulator magnetic field, is well known. The theory, as described thus far, ignores velocity dispersion from the chirp in the undulator, taking the limit of a 'small' chirp. In the following, the physics of compensating for chirp in the beam is revisited, including the effects of velocity dispersion, or beam compression or decompression, in the undulator. It is found that the limit of negligible velocity dispersion in the undulator is different from that previously identified as the small chirp limit, and is more significant than previously considered. The velocity dispersion requires a taper which is nonlinear to properly compensate for the effects of the detuning, and also results in a varying peak current (end thus a varying gain length) over the length of the undulator. The results may be especially significant for plasma driven FELs and low energy linac driven FEL test facilities. [ABSTRACT FROM AUTHOR]

The pulse source for plasma-accelerators supply operates under the conditions of nonlinear growth of load inductance, which complicates the matching of the source and the load. This article presents experimental studies of the use of both traditional pulse-energy sources based on capacitive storage and alternative ones based on explosive magnetic generators (EMG). It is shown that the EMG with the special device of the current-pulse formation more effectively matches with such a plasma load as the pulse plasma-accelerator (PPA). This device allows a wide range to manage the current-pulse formation in a variable load and, consequently, to optimize the operation of the power source for the specific plasma load. A mathematical model describing the principle of operation of this device in EMG on inductive load was developed. The key adjustable parameters are the current into the load, the residual inductance of the EMG, and the sample time of the specified inductance and the final current in the load. The device was successfully tested in experiments with the operation on both one and two accelerators connected in parallel. In the experiments, the optimal mode of device operation was found in which the total energy inputted to a pair of accelerators in one pulse reached 0.55 MJ, and the maximum current reached about 3.5 MA. A comparison with the results of experiments performed with capacitive sources of the same level of stored energy is given. The experiments confirmed not only the principal possibility of using EMG with a special device of current-pulse formation for operation with plasma loads in the MJ energy range but also showed the advantages of its application with specific types of plasma load.

We present theoretical and numerical studies of matching sub-femtosecond space-charge-dominated electron bunch into the Laser-plasma Wake Field Accelerator (LWFA) foreseen at the SINBAD facility. The longitudinal space-charge (SC) effect induced growths of the energy spread and longitudinal phase-space chirp are major issues in the matching section, which will result in bunch elongation, emittance growth and spot size dilution. In addition, the transverse SC effect would lead to a mismatch of the beam optics if it were not compensated for. Start-to-end simulations and preliminary optimizations were carried out in order to understand the achievable beam parameters at the entrance of the plasma accelerator. [ABSTRACT FROM AUTHOR]

Zinc oxide is well-known semiconductor material having good electrical, optical and catalytic properties. This paper shows the results on synthesis of hexagonal zinc oxide with single-crystalline particle structure using the system based on coaxial magnetoplasma accelerator. The synthesis is implemented during one short cycle (up to 10 −3 s) of plasma accelerator work. X-ray diffractometry analysis allow us to confirm that the product consists of only hexagonal zinc oxide with lattice parameters a = b = 3.24970 Å, c = 5.20270 Å. This result is in a good agreement with EDAX data, which show the presence only Zn and O elements in the final product. SEM, TEM and HRTEM methods are used to investigate the particles morphology. It is found that the product consists of single-crystalline hexagonal particles of zinc oxide and electron diffraction from particles also confirmed the zinc oxide structure. The particle sizes are up to 350 nm but the most of the particles (85%) are less than 150 nm. [ABSTRACT FROM AUTHOR]

The ultrafine iron oxide powders were successfully synthesized using the plasma dynamic synthesis method, based on the use of a coaxial magnetoplasma accelerator with the iron electrode system. The synthesis was implemented in the high-speed iron-containing plasma jet, flowing into the space of the sealed chamber, filled with the gaseous mixture of oxygen and argon at different ratios. The XRD investigations showed that the synthesized products were heterophase and consisted of three main phases such as magnetite Fe 3 O 4 , hematite α-Fe 2 O 3 and ε-Fe 2 O 3 . The SEM data confirmed the presence of three particle types: the hollow spheroids with sizes about hundreds of micrometers (magnetite), the particles with sizes up to 100 μm from the porous material of sintered submicron particles (hematite), and nanoscale particles (ε-phase). We found that at the higher oxygen concentration the content of ε-Fe 2 O 3 is increased up to ~50% at the same time with decreasing the Fe 3 O 4 phase. The magnetic properties of the products are mainly determined by magnetite characteristics and are significantly reduced with decreasing its content in the powder. In order to investigate the synthesized ε-Fe 2 O 3 on the ability to absorb the electromagnetic radiation in the millimeter wavelength range, we separated the product with the higher ε-phase concentration. The fraction mainly, consisting of ε-Fe 2 O 3 , showed the occurrence of the natural resonance at frequencies of 8.3 GHz and 130 GHz. [ABSTRACT FROM AUTHOR]

This paper continues the series of numerical investigations of self-ionizing gas flows in plasma accelerator channels with an azimuthal magnetic field. The mathematical model is based on the equations of dynamics of a three-component continuous medium consisting of atoms, ions, and electrons; the model is supplemented with the equation of ionization and recombination kinetics within the diffusion approximation with account for photoionization and photorecombination. It also takes into account heat exchange, which in this case is caused by radiative heat conductance. Upon a short history of the issue, the proposed model, numerical methods, and results for steady-state and pulsating flows are described. [ABSTRACT FROM AUTHOR]

The effects of a correlated linear energy/velocity chirp in the electron beam in the free electron laser (FEL), and how to compensate for its effects by using an appropriate taper (or reverse-taper) of the undulator magnetic field, is well known. The theory, as described thus far, ignores velocity dispersion from the chirp in the undulator, taking the limit of a ‘small’ chirp. In the following, the physics of compensating for chirp in the beam is revisited, including the effects of velocity dispersion, or beam compression or decompression, in the undulator. It is found that the limit of negligible velocity dispersion in the undulator is different from that previously identified as the small chirp limit, and is more significant than previously considered. The velocity dispersion requires a taper which is nonlinear to properly compensate for the effects of the detuning, and also results in a varying peak current (end thus a varying gain length) over the length of the undulator. The results may be especially significant for plasma driven FELs and low energy linac driven FEL test facilities.

In this review paper, basic principles of high current plasma accelerators, history and recent state of their investigations in IPP NSC KIPT are briefly described. In such devices an internal magnetic field is created by high current up to several MA in the discharge and it is used for both plasma flow acceleration up to 1000 km/s. Particular attention is paid to the quasi-stationary plasma accelerators (QSPA), where discharge duration exceeds considerable the plasma flight time in acceleration channel. Application of QSPA for plasma-surface interaction studies relevant to thermonuclear reactors, like ITER and DEMO, is discussed. Results on surface modification and improvement of material properties by powerful pulsed plasma processing are described. Potential technological applications for materials treatment are emphasized.

Abstract: Positron sources are a critical system for the future lepton colliders projects. Due to the large beam emittance at the production and the limitation given by the target heating and mechanical stress, the main collider parameters fixing the luminosity are constrained by the sources. In this context also the damping ring design boundary conditions and the final performance are given by the injected positron beam. At present different schemes are being taken into account in order to increase the production and the capture yield of the positron sources, to reduce the impact of the deposited energy in the converter target and to increase the injection efficiency in the damping ring. The final results have a strong impact not only on the collider performance but also on its cost optimization. After a short introduction illustrating their fundamental role, the basic positron source scheme and the performance of the existing sources will be illustrated. The main innovative designs for the future colliders advanced sources will be reviewed and the different developed technologies presented. Finally the positrons-plasma R&D experiments and the futuristic proposals for positron sources will reviewed. [Copyright &y& Elsevier]

A theoretical approach to studying ionizable gas flows with the formation of an ionization front in the plasma accelerator channel is proposed. The study is based on the MHD equations supplemented with the ionization and recombination kinetics equation. As a result, the structure of an ionization front is investigated. [ABSTRACT FROM AUTHOR]

A reliable analytical expression for the potential of plasma waves with phase velocities near the speed of light is derived. The presented spheroid cavity model is more consistent than the previous spherical and ellipsoidal models and it explains the mono-energetic electron trajectory more accurately, especially at the relativistic region. The maximum energy of electrons is calculated and it is shown that the maximum energy of the spheroid model is less than that of the spherical model. The electron energy spectrum is also calculated and it is found that the energy distribution ratio of electrons ΔE/E for the spheroid model under the conditions reported here is half that of the spherical model and it is in good agreement with the experimental value in the same conditions. As a result, the quasi-mono-energetic electron output beam interacting with the laser plasma can be more appropriately described with this model. [ABSTRACT FROM AUTHOR]

A reliable analytical expression for the potential of plasma waves with phase velocities near the speed of light is derived. The presented spheroid cavity model is more consistent than the previous spherical and ellipsoidal model and it explains the mono-energetic electron trajectory more accurately, especially at the relativistic region. As a result, the quasi-mono-energetic electrons output beam interacting with the laser plasma can be more appropriately described with this model. [ABSTRACT FROM AUTHOR]

Abstract: Simulation of laser–plasma accelerator (LPA) experiments is computationally intensive due to the disparate length scales involved. Current experiments extend hundreds of laser wavelengths transversely and many thousands in the propagation direction, making explicit PIC simulations enormously expensive and requiring massively parallel execution in 3D. Simulating the next generation of LPA experiments is expected to increase the computational requirements yet further, by a factor of 1000. We can substantially improve the performance of LPA simulations by modeling the envelope evolution of the laser field rather than the field itself. This allows for much coarser grids, since we need only resolve the plasma wavelength and not the laser wavelength, and therefore larger timesteps can be used. Thus an envelope model can result in savings of several orders of magnitude in computational resources. By propagating the laser envelope in a Galilean frame moving at the speed of light, dispersive errors can be avoided and simulations over long distances become possible. The primary limitation to this envelope model is when the laser pulse develops large frequency shifts, and thus the slowly-varying envelope assumption is no longer valid. Here we describe the model and its implementation, and show rigorous benchmarks for the algorithm, establishing second-order convergence and correct laser group velocity. We also demonstrate simulations of LPA phenomena such as self-focusing and meter-scale acceleration stages using the model. [ABSTRACT FROM AUTHOR]

Abstract: In many experiments plasma guns have been used to study the possibility of lowering the erosion due to disruptions and edge localized modes (ELMs) of great interest for the International Thermonuclear Experimental Reactor (ITER) safe operation. Modification of silicon single crystal surfaces by the action of supersonic compression plasma flow (CPF) generated by magnetoplasma compressor (MPC) has been studied. MPC plasma flow parameters (1 MJ/m2 in 0.1 ms) simulated transient peak thermal loads during Type I ELMs and disruptions. Analysis of the target’s erosion, brittle destruction, melting processes and dust formation has been performed. The layer with some of regular structures (rhombic on the Si (111) and rectangular on Si (100) surface) can be separated from the underlying bulk, being ejected as the blocks from the surface. These surface phenomena are results of specific conditions during CPF interaction with target surface and differential stresses produced in a near surface layer. High plasma flow energy density, large dynamic pressure, thermodynamic parameters gradients and induced magnetic field on treated surfaces cause rapid heating and melting of the surface layer, prolonged existence of the molten layer and fast cooling and recrystallisation, as well as surface fracturing. [ABSTRACT FROM AUTHOR]