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Turning the current experimental plasma accelerator state-of-the-art from a promising technology into mainstream scientific tools depends critically on high-performance, high-fidelity modeling of complex processes that develop over a wide range of space and time scales. As part of the U.S. Department of Energy's Exascale Computing Project, a team from Lawrence Berkeley National Laboratory, in collaboration with teams from SLAC National Accelerator Laboratory and Lawrence Livermore National Laboratory, is developing a new plasma accelerator simulation tool that will harness the power of future exascale supercomputers for high-performance modeling of plasma accelerators. We present the various components of the codes such as the new Particle-In-Cell Scalable Application Resource (PICSAR) and the redesigned adaptive mesh refinement library AMReX, which are combined with redesigned elements of the Warp code, in the new WarpX software. The code structure, status, early examples of applications and plans are discussed.

Laser driven plasma accelerators promise much shorter particle accelerators but their development requires detailed simulations that challenge or exceed current capabilities. We report the first direct simulations of stages up to 1 TeV from simulations using a Lorentz boosted calculation frame resulting in a million times speedup, thanks to a frame boost as high as γ = 1300. Effects of the hyperbolic rotation in Minkowski space resulting from the frame boost on the laser propagation in the plasma is shown to be key in the mitigation of a numerical instability that was limiting previous attempts.PACS numbers: 03.30.+p, 52.38.Kd, 29.20.Ej, 52.65.Rr Laser driven plasma waves produce accelerating gradients orders of magnitude greater than standard accelerating structures (which are limited by electrical breakdown) [1,2]. High quality electron beams of energy up-to 1 GeV have been produced in just a few centimeters [3][4][5][6] with 10 GeV stages being planned as modules of a high energy collider [7], and detailed simulations are required to realize the promise of much shorter particle accelerators using this technique [8]. Such simulations challenge or exceed current capabilities, in particular for high energy stages at GeV energies and beyond.The linear theory predicts that for the intense lasers (a > ∼ 1) typically used for acceleration, the laser depletes its energy over approximately the same length L d = λ 3 p /2λ 2 0 over which the particles dephase from the wake, where λ p = πc 2 m/e 2 n e is the plasma wavelength, λ 0 is the laser wavelength, c is the speed of light, and m, e and n e are respectively the electron mass, charge and density in the plasma [1]. As a result of beam dephasing and laser depletion, the maximum bunch energy gain scales approximately as the square of the plasma wavelength and the inverse of the plasma density, which implies that higher energy stages operate with longer plasmas, rending computer simulations more challenging, as the ratio of longest to shortest spatial lengths of interest (plasma length/laser wavelength) rises. As a matter of fact, direct explicit multi-dimensional simulations of 10 GeV stages, which will operate in m-scale plasmas at order 10 17 /cc densities, have been considered until recently beyond the current state of the art [8,9].Recently, first principles Particle-In-Cell modeling of laser-plasma wakefield accelerators using a Lorentz boosted frame of reference [10] have been shown to being sped up by up-to three orders of magnitude in the calculations of stages in the 100 MeV-10 GeV energy range [8,[11][12][13][14][15][16][17][18]. Maximum obtainable speedups calculated using linear theory predict that higher speedups are attainable, in the range of 4-6 orders of magnitude for stages in the energy range of 10 GeV-1 TeV respectively [19,20]. Practical limitations have prevented reaching these speedups, including a violent high frequency numerical instability, limiting the Lorentz boost γ below 100 [8,13,16,19,20].We report for the first time direct explicit s...

Modeling of laser-plasma wakefield accelerators in an optimal frame of reference [J.-L. Vay, Phys. Rev. Lett. 98, 130405 (2007)] allows direct and efficient full-scale modeling of deeply depleted and beam loaded laser-plasma stages of 10 GeV-1 TeV (parameters not computationally accessible otherwise). This verifies the scaling of plasma accelerators to very high energies and accurately models the laser evolution and the accelerated electron beam transverse dynamics and energy spread. Over 4, 5, and 6 orders of magnitude speedup is achieved for the modeling of 10 GeV, 100 GeV, and 1 TeV class stages, respectively. Agreement at the percentage level is demonstrated between simulations using different frames of reference for a 0.1 GeV class stage. Obtaining these speedups and levels of accuracy was permitted by solutions for handling data input (in particular, particle and laser beams injection) and output in a relativistically boosted frame of reference, as well as mitigation of a high-frequency instability that otherwise limits effectiveness.

The equilibrium of an infinitely long, strongly magnetized, non-neutral plasma confined in a Penning-Malmberg trap with an additional mirror coil has been solved analytically [J. Fajans, Phys. Plasmas 10, 1209 (2003)] and shown to exhibit unusual features. Particles not only reflect near the mirror in the low field region, but also may be weakly trapped in part of in the high field region.The plasma satisfies a Boltzmann distribution along field lines; however, the density and the potential vary along field lines. Some other simplifying assumptions were employed in order to analytically characterize the equilibrium; for example the interface region between the low and high field regions was not considered. The earlier results are confirmed in the present study, where two-dimensional particle-in-cell simulations are performed with the Warp code in a more realistic configuration with an arbitrary (but physical) density profile, realistic trap geometry and magnetic field. A range of temperatures and radial plasma sizes are considered. Particle tracking is used to identify populations of trapped and untrapped particles. The present study also shows that it is possible to obtain local equilibria of non-neutral plasmas using a collisionless PIC code, by a scheme that uses the inherent numerical collisionality as a proxy for physical collisions.2