A new generation of laser wakefield accelerators, supported by the extremeaccelerating fields generated in the interaction of PW-Class lasers andunderdense targets, promises the production of high quality electron beams inshort distances for multiple applications. Achieving this goal will relyheavily on numerical modeling for further understanding of the underlyingphysics and identification of optimal regimes, but large scale modeling ofthese scenarios is computationally heavy and requires efficient use ofstate-of-the-art Petascale supercomputing systems. We discuss the maindifficulties involved in running these simulations and the new developmentsimplemented in the OSIRIS framework to address these issues, ranging frommulti-dimensional dynamic load balancing and hybrid distributed / shared memoryparallelism to the vectorization of the PIC algorithm. We present the resultsof the OASCR Joule Metric program on the issue of large scale modeling of LWFA,demonstrating speedups of over 1 order of magnitude on the same hardware.Finally, scalability to over $\sim 10^6$ cores, and sustained performance over$\sim 2$ PFlops is demonstrated, opening the way for large scale modeling oflaser wakefield accelerator scenarios.
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