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Abstract: Material processing using nano-technology is now advancing towards a more precise and controllable “smart” stage and plasma systems with high performance are being required for advanced thermal processing. One such unique plasma generator, a high speed plasma accelerator is capable of generating high energy plasma flows of required composition within a large range of plasma parameters. Another gas tunnel type plasma system also exhibits high energy density and high efficiency. Its application to the plasma spraying of ceramics proved that the characteristics of these ceramic coatings are superior to conventional ones. Various types of plasma accelerators are described here with emphasis on a MagnetoPlasma Compressor of Compact Geometry (MPC-CG) which was used to investigate plasma flow interaction with solid silicon surfaces. Different types of submicron structure were obtained due to the compression plasma flow action? The plasma produced by a gas tunnel type plasma source was used for the surface modification of Titanium, TiN films being formed in a relatively short time of 5 s. Plasma sprayed ZrO2/Al2O3 coatings were also investigated, and the results showed that the ZrO2/Al2O3 composite system has the possibility for the development of high functionally graded thermal barrier coating (TBC), which exhibits excellent mechanical properties and oxidation resistance. [ABSTRACT FROM AUTHOR]

Using the ellipsoidal cavity model, the quasi-monoenergetic electron output beam in laser-plasma interaction is described. By the cavity regime the quality of electron beam is improved in comparison with those generated from other methods such as periodic plasma wave field, spheroidal cavity regime and plasma channel guided acceleration. Trajectory of electron motion is described as hyperbolic, parabolic or elliptic paths. We find that the self-generated electron bunch has a smaller energy width and more effective gain in energy spectrum. Initial condition for the ellipsoidal cavity is determined by laser-plasma parameters. The electron trajectory is influenced by its position, energy and cavity electrostatic potential. [ABSTRACT FROM AUTHOR]

We briefly summarize the contributions presented during the working group 5 (WG5) sessions, dedicated to high-gradient plasma structures and ground-breaking electron beam diagnostics. [ABSTRACT FROM AUTHOR]

Abstract: A pipelining algorithm to overcome the limitation on scaling quasi-static particle-in-cell models of relativistic beams in plasmas to a very large number of processors is described. The pipelining algorithm uses multiple groups of processors and optimizes the job allocation on the processors in parallel computing. The algorithm is implemented on the quasi-static code QuickPIC and is shown to scale to over 103 processors and increased the scale and speed by two orders of magnitude over the non-pipelined model. The new approach opens the door to performing full scale 3D simulations of future plasma wakefield accelerators or full lifetime models of beam interaction with electron clouds in circular accelerators such as the Large Hadron Collider (LHC) at CERN. [Copyright &y& Elsevier]

Abstract: The damage threshold and damage mechanisms of divertor armor materials, i.e. CFC and tungsten, were studied under the impact of ITER relevant ELM-like loads. These experiments were carried out in a Quasi-Stationary Plasma Accelerator applying repetitive pulses of 500μs up to 100 cycles. CFC showed preferential erosion of the PAN fiber-bundles above 0.6MJ/m2 and cracking of pitch fiber-bundles. Tungsten showed cracking already at 0.2MJ/m2 and melting at flat surfaces above 1MJ/m2. Cracks in tungsten were identified as primary and secondary cracks which all propagated in the vertical direction, which was considered to be less critical. At an energy density of 1.5MJ/m2, the melt-layer completely covered the surface and bridged the castellation slots. [Copyright &y& Elsevier]

In this work, we introduce a new ellipsoid model to describe bubble acceleration of electrons and discuss the required conditions of forming it. We have found that the electron trajectory is strongly related to background electron energy and cavity potential ratio. In the ellipsoid cavity regime, the quality of the electron beam is improved in contrast to other methods, such as that using periodic plasma wakefield, spherical cavity regime, and plasma channel guided acceleration. The trajectory of the electron motion can be described as hyperbola, parabola, or ellipsoid path. It is influenced by the position and energy of the electrons and the electrostatic potential of the cavity. In the experimental part of this work, a 20 TW power and 30 fs laser pulse was focused on a pulsed He gas jet. We have focused the laser pulse in the best matched point above the nozzle gas to obtain a stable ellipsoid bubble. The finding of the optimum points will be described in analytical details. [ABSTRACT FROM AUTHOR]

This paper reports the results of numerical studies of axisymmetric flows in a coaxial plasma accelerator in the presence of a longitudinal magnetic field. The calculations were performed using a two-dimensional two-fluid magnetohydrodynamic model taking into account the Hall effect and the conductivity tensor of the medium. The numerical experiments confirmed the main features of the plasmadynamic processes found previously using analytical and one-fluid models and made it possible to study plasma flows near the electrodes. [ABSTRACT FROM AUTHOR]

A dependence of cutoff proton kinetic energy on laser prepulse duration has been observed. Amplified spontaneous emission pedestal duration is controlled by a fast electrooptic pulse slicer where the rise time is estimated to be 130 ps. We demonstrate a new correlated spectral technique for determining this rise time using a stretched frequency-chirped pulse. [ABSTRACT FROM AUTHOR]

Abstract: A highly efficient, fully parallelized, fully relativistic, three-dimensional particle-in-cell model for simulating plasma and laser wakefield acceleration is described. The model is based on the quasi-static or frozen field approximation, which reduces a fully three-dimensional electromagnetic field solve and particle push to a two-dimensional field solve and particle push. This is done by calculating the plasma wake assuming that the drive beam and/or laser does not evolve during the time it takes for it to pass a plasma particle. The complete electromagnetic fields of the plasma wake and its associated index of refraction are then used to evolve the drive beam and/or laser using very large time steps. This algorithm reduces the computational time by 2–3 orders of magnitude. Comparison between the new algorithm and conventional fully explicit models (OSIRIS) is presented. The agreement is excellent for problems of interest. Direction for future work is also presented. [Copyright &y& Elsevier]

Abstract: This paper presents a two-dimensional computer simulation of the electrical breakdown in an impulse plasma deposition (IPD) accelerator. The spatial and temporal development of the electrical field potential, as well as the electron and ion densities are calculated solving the continuity equations together with the Poisson equation numerically. The pictures of the initial stage of discharges, which were taken with an image converter camera enable to compare the calculation of our model with the experimental results. [Copyright &y& Elsevier]

The results of the development of the high-frequency method in combination with a vacuum arc one for surface coating and surface modifications with pulsed plasma streams are presented. The combined method was applied for deposition of multi-layer coatings with a reduction of droplet formation and decrease of the substrate temperature. It provided metal and dielectric coatings under the substrate temperature ⩽ 200°C. The (TiN–Ti) coatings were deposited onto organic materials and metals. Amorphous and hypocrystalline dielectric films of Al2O3 were obtained. Also, the material surface properties were improved by surface treatment with pulsed plasma streams. This treatment led to melting of the surface layer, introduction of nitrogen into the liquid surface layer and subsequent fast solidification. The formation of modified fine-grained surface layers of 30 μm in depth was observed as a result of a plasma processing. An essential improvement of wear properties of treated samples was obtained. Pulsed plasma processing of FeB or TiAlN coatings has shown that under the plasma treatment intensive mixing of the materials of coating with the material of substrate was achieved. [Copyright &y& Elsevier]

In surface engineering impulse plasma is used in the synthesis and deposition of various materials in the layer form. Within the impulse plasma deposition (IPD) coaxial accelerator plasma is generated in the working gas due to a high-voltage high-current pulse discharge. In the present study the influence of accelerator geometry on the Rayleigh–Taylor instability formation behind the front faces of the electrodes has been analysed both computationally and experimentally. Structure of the plasma in this region is very important for the quality of the coatings produced, thus the presented findings increase the understanding of processes relevant for the IPD technology. [Copyright &y& Elsevier]

An analytic model of steady-state two-dimensional flows in coaxial plasma-accelerator channels in the presence of a longitudinal magnetic field is proposed. The solution of the problem is found in the smooth channel approximation for the MHD equations of an ideal two-component plasma. An example of the developing axisymmetric flows is given and the features of the plasma-dynamic processes are investigated. It is found that the Hall effect and the anode flow zone can be reduced using a longitudinal field and plasma rotation. [ABSTRACT FROM AUTHOR]

A two-dimensional fluid model of snow plow type to simulate the plasma dynamics in a coaxial accelerator is described. The self-consistent model combines the description of the electric circuit with the plasma resistance and inductance, as well as the balance of magnetic and fluid pressures at the contact interface. The applicability of presented model has been proved by comparison of computational results with the high-speed photographs of plasma dynamics in the impulse plasma deposition (IPD) coaxial accelerator. [Copyright &y& Elsevier]

This article presents the results of experimental investigations of compression erosion plasma fluxes of a given composition determined by the material of the internal electrode; the fluxes have been obtained for the first time in air at atmospheric pressure. It is shown that a compression erosion plasma flux possesses marked absorption in the visible spectral region. The basic thermodynamic parameters of these fluxes were determined with the use of a two-channel system of recording plasma radiation. [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. [ABSTRACT FROM AUTHOR]

Abstract: A new technique, named “laser comb”, was tested during the last SPARC run. It is able to produce electron pulse trains with a charge of some hundreds pC, a repetition rate of some terahertz, and a sub-picosecond length. This technique is based on the velocity bunching configuration of the SPARC injector. It can be useful to drive pump and probe free-electron laser experiments, to generate coherent excitation of plasma waves in plasma accelerators, and to produce narrow band terahertz radiation. In this paper, we describe the experimental results achieved so far and provide a comparison with simulations. [Copyright &y& Elsevier]