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We present a new particle-merging algorithm for the particle-in-cell method. Based on the concept of the Voronoi diagram, the algorithm partitions the phase space into smaller subsets, which consist of only particles that are in close proximity in the phase space to each other. We show the performance of our algorithm in the case of the two-stream instability and the magnetic shower., 11 figures

With the emergence of the CAN (Coherent Amplification Network) laser technology, a new scheme for direct particle acceleration in periodic plasma structures has been proposed. By using our full electromagnetic relativistic particle-in-cell (PIC) simulation code equipped with ionisation module, we simulate the laser fields dynamics in the periodic structures of different materials. We study how the dynamic ionization influences the field structure.

The novel PIC/fluid hybrid plasma simulation code H-VLPL3D is introduced. In addition to the particle-in-cell algorithm, it uses a new numerical fluid scheme for wake field simulations. Specially designed for the accurate simulation of very long wake fields, this scheme is capable of simulating ∼1000 plasma oscillations of the wake. A comprehensive description of the discretization schemes is given, and we demonstrate the code's correctness and its order of accuracy. Also, its superior efficiency in the plasma wake field acceleration (PWFA) regime is shown.

Electron acceleration in the laser-plasma bubble appeared to be the most successful regime of laser wake field acceleration in the last decade. The laser technology became mature enough to generate short and relativistically intense pulses required to reach the bubble regime naturally delivering quasi-monoenergetic bunches of relativistic electrons. The upcoming laser technology projects are promising short pulses with many times more energy than the existing ones. The natural question is how will the bubble regime scale with the available laser energy. We present here a parametric study of laser-plasma acceleration in the bubble regime using full three dimensional particle-in-cell simulations and compare numerical results with the analytical scalings from the relativistic laser-plasma similarity theory.

2nd European Advanced Accelerator Concepts Workshop, EAAC2015, La Biodola, Isola d'Elba, Italy, 13 Sep 2015 - 19 Sep 2015 ; Nuclear instruments & methods in physics research / A 829, 3 - 16(2016). doi:10.1016/j.nima.2015.12.050, This paper describes the conceptual steps in reaching the design of the AWAKE experiment currently under construction at CERN. We start with an introduction to plasma wakefield acceleration and the motivation for using proton drivers. We then describe the self-modulation instability – a key to an early realization of the concept. This is then followed by the historical development of the experimental design, where the critical issues that arose and their solutions are described. We conclude with the design of the experiment as it is being realized at CERN and some words on the future outlook. A summary of the AWAKE design and construction status as presented in this conference is given in Gschwendtner et al., Published by North-Holland Publ. Co., Amsterdam

When a long proton bunch propagates in plasma, it is subject to the self-modulational instability. The radius of the proton bunch is modulated at the background plasma wavelength. The wake field is then resonantly excited. The amplitude of the wake is growing exponentially up to a saturation level that can reach a significant fraction of the wave breaking limit. The phase velocity of the wake is defined not only by the driver velocity, but also by the own instability dynamics. At the linear stage of the instability, the phase velocity is decreased that allows to inject low energy electrons in the wake. At the saturation phase, the wake phase velocity becomes close to that of the drvier. Side injection of particles at the right position in plasma may help to improve the maximum energy gain and the quality of acceleration. The wake's phase velocity can be controlled by smooth density gradients. The modulations of the proton bunch can be diagnosed by a transverse coherent transition radiation.

We discuss the level of natural shot noise in a proton bunch-driven plasma accelerator. The required seeding for the plasma wake field must be larger than the cumulative shot noise. This is the necessary condition for the axial symmetry of the generated wake and the acceleration quality. We develop an analytical theory of the noise field and compare it with multi-dimensional simulations. It appears that the natural noise wake field generated in plasma by the available at CERN super-protons-synchrotron (SPS) bunches is very low, at the level of a few 10 kV/m. This fortunate fact eases the requirements on the seed. Our three dimensional simulations show that even a few tens MeV electron bunch precursor of a very moderate intensity is sufficient to seed the proton bunch self-modulation in plasma., Comment: 5 pages, 5 figures

It is demonstrated that the performance of the self-modulated proton driver plasma wakefield accelerator (SM-PDPWA) is strongly affected by the reduced phase velocity of the plasma wave. Using analytical theory and particle-in-cell simulations, we show that the reduction is largest during the linear stage of self-modulation. As the instability nonlinearly saturates, the phase velocity approaches that of the driver. The deleterious effects of the wake's dynamics on the maximum energy gain of accelerated electrons can be avoided using side-injections of electrons, or by controlling the wake's phase velocity by smooth plasma density gradients.

In this paper we present a new three dimensional (3D) full electromagnetic relativistic hybrid plasma code H-VLPL (hybrid virtual laser plasma laboratory). The full kinetic particle-in-cell (PIC) method is used to simulate low density hot plasmas while the hydrodynamic model applies to the high density cold background plasma. To simulate the linear electromagnetic response of the high density plasma, we use a newly developed form of an exponential integrator method. It allows us to simulate plasmas of arbitrary densities using large time steps. The model reproduces the plasma dispersion and gives correct spatial scales like the plasma skin depth even for large grid cell sizes. We test the hybrid model validity by applying it to some physical examples.

International audience; We analyze in detail the ground-state structure of model systems of athermal star polymers with an additional, tunable attraction that may result from dispersion or depletion forces. To perform a free, unbiased search in the space spanned by the crystal parameters, we employ genetic algorithms, which are enhanced with respect to previous versions in their ability to find stable structures that occupy very narrow basins of attraction in the energy landscape. Application of this method brings about a very large variety of ground states for star polymers with attractions, in particular for the case of intermediate functionalities and strong, short-range attractive forces.

New acceleration technology is mandatory for the future elucidation of fundamental particles and their interactions. A promising approach is to exploit the properties of plasmas. Past research has focused on creating large-amplitude plasma waves by injecting an intense laser pulse or an electron bunch into the plasma. However, the maximum energy gain of electrons accelerated in a single plasma stage is limited by the energy of the driver. Proton bunches are the most promising drivers of wakefields to accelerate electrons to the TeV energy scale in a single stage. An experimental program at CERN -- the AWAKE experiment -- has been launched to study in detail the important physical processes and to demonstrate the power of proton-driven plasma wakefield acceleration. Here we review the physical principles and some experimental considerations for a future proton-driven plasma wakefield accelerator., 12 pages, 5 figures, submitted to Plasma Phys. Control. Fusion special edition for LPAW 2013. Small updates after comments from Journal referees

Energy flux transport of a finite high current relativistic electron beam with the Gaussian profile in both the transverse and axial directions in a dense collisional background plasma is studied by means of three-dimensional particle-in-cell simulations. Simulation results reveal the development of a needle-like super-filament formation in both homogeneous as well as inhomogeneous collisional background plasmas. However, in the case of an inhomogeneous background plasma, the beam suffers severe filamentation due to the lower plasma density encountered in the early stage, and only the head of the super-filament survives and travels further inside the plasma. This may not be desirable for the fast ignition fusion scheme.