We present a hybrid quantum-classical electrostatic Particle-in-Cell (PIC) method, where the electrostatic field Poisson solver is implemented on a quantum computer simulator using a hybrid classical-quantum Neural Network (HNN) using data-driven and physics-informed learning approaches. The HNN is trained on classical PIC simulation results and executed via a PennyLane quantum simulator. The remaining computational steps, including particle motion and field interpolation, are performed on a classical system. To evaluate the accuracy and computational cost of this hybrid approach, we test the hybrid quantum-classical electrostatic PIC against the two-stream instability, a standard benchmark in plasma physics. Our results show that the quantum Poisson solver achieves comparable accuracy to classical methods. It also provides insights into the feasibility of using quantum computing and HNNs for plasma simulations. We also discuss the computational overhead associated with current quantum computer simulators, showing the challenges and potential advantages of hybrid quantum-classical numerical methods.

Efficient simulation of complex plasma dynamics is crucial for advancing fusion energy research. Particle-in-Cell (PIC) Monte Carlo (MC) simulations provide insights into plasma behavior, including turbulence and confinement, which are essential for optimizing fusion reactor performance. Transitioning to exascale simulations introduces significant challenges, with traditional file input/output (I/O) inefficiencies remaining a key bottleneck. This work advances BIT1, an electrostatic PIC MC code, by improving the particle mover with OpenMP task-based parallelism, integrating openPMD’s streaming API, and enabling in-memory data streaming with the ADIOS2 Sustainable Staging Transport (SST) engine to enhance I/O performance, computational efficiency, and system storage utilization. We employ profiling tools such as gprof, perf, IPM and Darshan, which provide insights into computation, communication, and I/O operations. We implement time-dependent data checkpointing with the openPMD API enabling seamless data movement and in-situ visualization for real-time analysis without interrupting the simulation. We demonstrate improvements in simulation runtime, data accessibility and real-time insights by comparing traditional file I/O with the ADIOS2 BP4 and SST backends. The proposed hybrid BIT1 openPMD SST enhancement introduces a new paradigm for real-time scientific discovery in plasma simulations, enabling faster insights and more efficient use of exascale computing resources.

As fusion energy devices advance, plasma simulations play a critical role in fusion reactor design. Particle-in-Cell Monte Carlo simulations are essential for modelling plasma-material interactions and analysing power load distributions on tokamak divertors. Previous work introduced hybrid parallelization in BIT1 using MPI and OpenMP/OpenACC for shared-memory and multicore CPU processing. In this extended work, we integrate MPI with OpenMP and OpenACC, focusing on asynchronous multi-GPU programming with OpenMP Target Tasks using the "nowait" and "depend" clauses, and OpenACC Parallel with the "async(n)" clause. Our results show significant performance improvements: 16 MPI ranks plus OpenMP threads reduced simulation runtime by 53% on a petascale EuroHPC supercomputer, while the OpenACC multicore implementation achieved a 58% reduction compared to the MPI-only version. Scaling to 64 MPI ranks, OpenACC outperformed OpenMP, achieving a 24% improvement in the particle mover function. On the HPE Cray EX supercomputer, OpenMP and OpenACC consistently reduced simulation times, with a 37% reduction at 100 nodes. Results from MareNostrum 5, a pre-exascale EuroHPC supercomputer, highlight OpenACC's effectiveness, with the "async(n)" configuration delivering notable performance gains. However, OpenMP asynchronous configurations outperform OpenACC at larger node counts, particularly for extreme scaling runs. As BIT1 scales asynchronously to 128 GPUs, OpenMP asynchronous multi-GPU configurations outperformed OpenACC in runtime, demonstrating superior scalability, which continues up to 400 GPUs, further improving runtime. Speedup and parallel efficiency (PE) studies reveal OpenMP asynchronous multi-GPU achieving an 8.77x speedup (54.81% PE) and OpenACC achieving an 8.14x speedup (50.87% PE) on MareNostrum 5, surpassing the CPU-only version. At higher node counts, PE declined across all implementations due to communication and synchronization costs. However, the asynchronous multi-GPU versions maintained better PE, demonstrating the benefits of asynchronous multi-GPU execution in reducing scalability bottlenecks. While the CPU-only implementation is faster in some cases, OpenMP's asynchronous multi-GPU approach delivers better GPU performance through asynchronous data transfer and task dependencies, ensuring data consistency and avoiding race conditions. Using NVIDIA Nsight tools, we confirmed BIT1's overall efficiency for large-scale plasma simulations, leveraging current and future exascale supercomputing infrastructures. Asynchronous data transfers and dedicated GPU assignments to MPI ranks enhance performance, with OpenMP’s asynchronous multi-GPU implementation utilizing OpenMP Target Tasks with "nowait" and "depend" clauses outperforming other configurations. This makes OpenMP the preferred application programming interface when performance portability, high throughput, and efficient GPU utilization are critical. This enables BIT1 to fully exploit modern supercomputing architectures, advancing fusion energy research. MareNostrum 5 brings us closer to achieving exascale performance.

Achieving net-positive fusion energy and its commercialization requires not only engineering marvels but also state-of-the-art, massively parallel codes that can handle reactor-scale simulations. The GENE-X code is a global continuum gyrokinetic turbulence code designed to predict energy confinement and heat exhaust for future fusion reactors. GENE-X is capable of simulating plasma turbulence from the core region to the wall of a magnetic confinement fusion (MCF) device. Originally written in Fortran 2008, GENE-X leverages MPI+OpenMP for parallel computing. In this paper, we augment the Fortran-based compute operators in GENE-X to a C++-17 layer exposing them to a wide array of C++-compatible tools. Here we focus on offloading the augmented operators to GPUs via directive-based programming models such as OpenACC and OpenMP offload. The performance of GENE-X is comprehensively characterized, e.g., by roofline analysis on a single GPU and scaling analysis on multi-GPUs. The major compute operators achieve significant performance improvements, shifting the bottleneck to inter-GPU communications. We discuss additional opportunities to further enhance the performance, such a.s reducing memory traffic and improving memory utilization efficiency

Particle-in-Cell Monte Carlo simulations on large-scale systems play a fundamental role in understanding the complexities of plasma dynamics in fusion devices. Efficient handling and analysis of vast datasets are essential for advancing these simulations. Previously, we addressed this challenge by integrating openPMD with BIT1, a Particle-in-Cell Monte Carlo code, streamlining data streaming and storage. This integration not only enhanced data management but also improved write throughput and storage efficiency. In this work, we delve deeper into the impact of BIT1 openPMD BP4 instrumentation, monitoring, and in-situ analysis. Utilizing cutting-edge profiling and monitoring tools such as gprof, CrayPat, Cray Apprentice2, IPM, and Darshan, we dissect BIT1’s performance post-integration, shedding light on computation, communication, and I/O operations. Fine-grained instrumentation offers insights into BIT1’s runtime behavior, while immediate monitoring aids in understanding system dynamics and resource utilization patterns, facilitating proactive performance optimization. Advanced visualization techniques further enrich our understanding, enabling the optimization of BIT1 simulation workflows aimed at controlling plasma-material interfaces with improved data analysis and visualization at every checkpoint without causing any interruption to the simulation.

Simulating plasma turbulence in the edge region of a magnetic confinement fusion (MCF) device is crucial for identifying optimal operational scenarios for future fusion energy commercialization. GENE-X, an Eulerian electromagnetic gyrokinetic code, can simulate plasma turbulence throughout an MCF device, including the edge region. This work focuses on characterizing GENE-X's performance, such as the elapsed time during the time integration phase, memory usage, and file I/O. Two cases with different MPI decomposition schemes are analyzed using GENE-X's built-in profiler, along with profiling and monitoring tools such as IPM and Darshan. This study aims to provide a preliminary view of the HPC characteristics of the code to assist in future optimization efforts.

Large-scale HPC simulations of plasma dynamics in fusion devices require efficient parallel I/O to avoid slowing down the simulation and to enable the post-processing of critical information. Such complex simulations lacking parallel I/O capabilities may encounter performance bottlenecks, hindering their effectiveness in data-intensive computing tasks. In this work, we focus on introducing and enhancing the efficiency of parallel I/O operations in Particle-in-Cell Monte Carlo simulations. We first evaluate the scalability of BIT1, a massively-parallel electrostatic PIC MC code, determining its initial write throughput capabilities and performance bottlenecks using an HPC I/O performance monitoring tool, Darshan. We design and develop an adaptor to the openPMD I/O interface that allows us to stream PIC particle and field information to I/O using the BP4 backend, aggressively optimized for I/O efficiency, including the highly efficient ADIOS2 interface. Next, we explore advanced optimization techniques such as data compression, aggregation, and Lustre file striping, achieving write throughput improvements while enhancing data storage efficiency. Finally, we analyze the enhanced high-throughput parallel I/O and storage capabilities achieved through the integration of openPMD with rapid metadata extraction in BP4 format. Our study demonstrates that the integration of openPMD and advanced I/O optimizations significantly enhances BIT1's I/O performance and storage capabilities, successfully introducing high throughput parallel I/O and surpassing the capabilities of traditional file I/O.

Key to the success of developing high-performance applications for present and future heterogeneous supercomputers will be the systematic use of measurement and analysis to understand factors that affect delivered performance in the context of parallelization strategy, heterogeneous programming methodology, data partitioning, and scalable algorithm design. The evolving complexity of future exascale platforms makes it unrealistic for application teams to implement their own tools. Similarly, it is naive to expect available robust performance tools to work effectively out-of-the-box, without integration and specialization in respect to application-specific requirements and knowledge. Vlasiator is a powerful massively parallel code for accurate magnetospheric and solar wind plasma simulations. It is being ported to the LUMI HPC system for advanced modeling of the Earth’s magnetosphere and surrounding solar wind. Building on a preexisting Vlasiator performance API called Phiprof, our work significantly advances the performance measurement and analysis capabilities offered to Vlasiator using the TAU, APEX, and IPM tools. The results presented show in-depth characterization of node-level CPU/GPU and MPI communications performance. We highlight the integration of high-level Phiprof events with detailed performance data to expose opportunities for performance tuning. Our results provide important insights to optimize Vlasiator for the upcoming Exascale machines.

Large-scale plasma simulations are critical for designing and developing next-generation fusion energy devices and modeling industrial plasmas. BIT1 is a massively parallel Particle-in-Cell code designed for specifically studying plasma material interaction in fusion devices. Its most salient characteristic is the inclusion of collision Monte Carlo models for different plasma species. In this work, we characterize single node, multiple nodes, and I/O performances of the BIT1 code in two realistic cases by using several HPC profilers, such as perf, IPM, Extrae/Paraver, and Darshan tools. We find that the BIT1 sorting function on-node performance is the main performance bottleneck. Strong scaling tests show a parallel performance of 77% and 96% on 2,560 MPI ranks for the two test cases. We demonstrate that communication, load imbalance and self-synchronization are important factors impacting the performance of the BIT1 on large-scale runs.