A Multi-Scale Electromagnetic Particle Code with Adaptive Mesh Refinement and Its Parallelization

AbstractSpace plasma phenomena occur in multi-scale processes from the electron scale to the magnetohydrodynamic scale. In order to investigate such multi-scale phenomena including plasma kinetic effects, we started to develop a new electromagnetic Particle-In-Cell (PIC) code with Adaptive Mesh Refinement (AMR) technique. AMR can realize high-resolution calculation saving computer resources by generating and removing hierarchical cells dynamically. In the parallelization, we adopt domain decomposition method and for good locality preserving and dynamical load balancing, we will use the Morton ordered curve. In the PIC method, particle calculation occupies most of the total calculation time. In our AMR-PIC code, time step intervals are also refined. To realize the load balancing between processes in the domain decomposition scheme, it is the most essential to consider the number of particle calculation loops for each cell among all hierarchical levels as a work weight for each processor. Therefore, we calculate the work weights based on the cost of particle calculation and hierarchical levels of each cell. Then we decompose the domain according to the Morton curve and the work weight, so that each processor has approximately the same amount of work. By performing a simple one-dimensional simulation, we confirmed that the dynamic load balancing is achieved and the computation time is reduced by introducing the dynamic domain decomposition scheme

Isotope effects under the influence of global radial electric fields in a helical configuration

Isotope effects under the influence of a radial electric field are examined in a helical magnetic field configuration. We perform global gyrokinetic simulations with additional poloidal rotations to estimate quasi-linear heat flux due to ion temperature gradient mode under the mixing length model. In single-ion-species plasmas, the mass number dependency of heat flux agrees with gyro-Bohm scaling in the absence of a radial electric field. Favorable mass number dependencies violating gyro-Bohm scaling are observed in the presence of a global radial electric field or a heavy hydrogen component in multi-ion-species plasmas. The radial electric field and the heavy hydrogen component affect the heat flux through an increase of wavelength as well as mode stabilization. Poloidal Mach number characterizes the transition from unfavorable to favorable mass number dependency under radial electric fields. While the heat flux is independent of mass number for a given poloidal Mach number, the heat flux decreases for higher mass numbers in a given radial electric field. The heat flux is also independent of average mass number in multi-ion-species plasmas because the heavy hydrogen component effectively enhances the light hydrogen heat flux. The present results are potentially relevant to the violation of gyro-Bohm scaling observed in the recent deuterium experiments in the Large Helical Device

Development of a Gyrokinetic Particle-in-Cell Code for Whole-Volume Modeling of Stellarators

We present initial results in the development of a gyrokinetic particle-in-cell code for the whole-volume modeling of stellarators. This is achieved through two modifications to the X-point Gyrokinetic Code (XGC), originally developed for tokamaks. One is an extension to three-dimensional geometries with an interface to Variational Moments Equilibrium Code (VMEC) data. The other is a connection between core and edge regions that have quite different field-line structures. The VMEC equilibrium is smoothly extended to the edge region by using a virtual casing method. Non-axisymmetric triangular meshes in which triangle nodes follow magnetic field lines in the toroidal direction are generated for field calculation using a finite-element method in the entire region of the extended VMEC equilibrium. These schemes are validated by basic benchmark tests relevant to each part of the calculation cycle, that is, particle push, particle-mesh interpolation, and field solver in a magnetic field equilibrium of Large Helical Device including the edge region. The developed code also demonstrates collisionless damping of geodesic acoustic modes and steady states with residual zonal flow in the core region

PIC Simulation Study of Merging Processes of Two Spheromak-Like Plasmoids

Two different types of merging processes of spheromak-like plasmoids (SPs) without any external guide-field (toroidal) component, which are confined in a rectangular conducting vessel, have been investigated by means of two-dimensional PIC simulation, i.e., counter-helicity merging and co-helicity merging processes. The merging time scale is given by the transit time for ion sound wave to travel from the center of SP in the initial profile to the reconnection point for both cases. Through the counter-helicity SP merging process, toroidal magnetic field energy is effectively converted to thermal energy, while the energy transfer rate is suppressed to lower value for the co-helicity case because most of the toroidal magnetic field energy does not dissipate in the merging process. The reconnection process is impulsive for both cases, and, thus, the released energy is locally distributed around field lines connected to a reconnection point and forms the high temperature region with a spatial structure dependent on Larmor radius and the merging processes

Electron scale magnetic reconnections in laser produced plasmas

Magnetic reconnection is a fundamental process in the universe, in which magnetic field energy is converted into plasma kinetic energy associated with a topological change in the magnetic field. Magnetic reconnections have been extensively investigated in space in the form of solar terrestrial plasmas, and also in laboratories in the form of magnetic confinement plasmas and laser-produced plasmas. Macroscopic features of magnetic reconnections can be well described in the context of magnetohydrodynamics (MHD) across a wide variety of research fields. However, how the kinetic regime of magnetic reconnection should be connected to the macroscopic MHD regime is still an open question. It is generally assumed that electron dynamics play an essential role in the triggering mechanism of magnetic reconnections. In this review, we discuss magnetic reconnections on the electron scale, focusing in particular on laboratory experiments using high-power lasers.Kuramitsu Yasuhiro, Sakai Kentaro, Moritaka Toseo. Electron scale magnetic reconnections in laser produced plasmas. Reviews of Modern Plasma Physics 7, 33–1 (2023); https://doi.org/10.1007/s41614-023-00125-4

Probing vacuum birefringence under a high-intensity laser field with gamma-ray polarimetry at the GeV scale

International audienceProbing vacuum structures deformed by high intense fields is of great interest in general. In the context of quantum electrodynamics (QED), the vacuum exposed by a linearly polarized high-intensity laser field is expected to show birefringence. We consider the combination of a 10 PW laser system to pump the vacuum and 1 GeV photons to probe the birefringent effect. The vacuum birefringence can be measured via the polarization flip of the probe γ-rays which can also be interpreted as phase retardation of probe photons. We provide theoretically how to extract phase retardation of GeV probe photons via pairwise topology of the Bethe-Heitler process in a polarimeter and then evaluate the measurability of the vacuum birefringence via phase retardation given a concrete polarimeter design with a realistic set of laser parameters and achievable pulse statistics