arXiv subjects

Toseo Moritaka

Publications and source records attributed to Toseo Moritaka.

3 recordsLinked to original sources

arXiv2026

Polarized quantum effects in countable signals from intense laser - electron beam interactions

We investigate the feasibility of precision counting experiments based on laser-electron beam interactions to verify strong-field quantum electrodynamic effects, with particular emphasis on the stochastic nature of photon emission, photon polarization, and spin asymmetry. A precise Monte-Carlo model is developed using photon packets with multi-dimensional phase-space weighting, hierarchical-mesh cumulative distribution functions, and a variable time-step method. This model quantitatively reproduces the highest edge of the photon energy spectrum and the positron yield in the previous SLAC E-144 experiment. The quantized radiation back-reaction determines the highest edge tail and thus the positron yield for higher laser intensities. The spin asymmetry in photon emission and spin flip determines photon polarization in the high-energy tail, while that in pair production can be observed through the large-angle positron scattering. Our simulations predict that these effects depend on the combination of the electron-beam energy and the laser intensity, and that they could be verified in future ELI-NP experiments using sub-GeV electron beams and optical lasers with intensities ~10^22W/cm2.

physics.plasm-ph↗

arXiv2022

Mushroom-instability-driven Magnetic Reconnections in Collisionless Relativistic Jets

We study the kinetic plasma dynamics in collisionless relativistic jets with velocity shear, by carrying out particle-in-cell simulations in the transverse plane of a jet. It is discovered that intermittent magnetic reconnections (MRs) are driven by Mushroom instability (MI), which is an important kinetic-scale plasma instability in the plasma shear-flows with relativistic bulk speed. We refer to this sequence of kinetic plasma phenomena as "MI-driven MR". The MI-driven MRs intermittently occur with moving the location of the reconnection points from the vicinity of the initial velocity-shear surface towards the center of the jet. As a consequence, the number density of high energy electrons, which are accelerated by MI-driven MRs, increases with time in the region inside the initial velocity-shear surface with accompanying the generation and subsequent amplification of magnetic fields by MI. The maximum Lorentz factor of electrons increases with initial bulk Lorentz factor of the jet. A possible relation of MI-driven MR to the bright synchrotron emission in jet-spine of active galactic nucleus jets is also discussed.

astro-ph.HE↗

arXiv2019

Verification of the global gyrokinetic stellarator code XGC-S for linear ion temperature gradient driven modes

XGC (X-point Gyrokinetic Code) is a whole-volume, total-f gyrokinetic particle-in-cell code developed for modelling tokamaks. In recent work, XGC has been extended to model more general 3D toroidal magnetic configurations, such as stellarators. These improvements have resulted in the XGC-S version. In this paper, XGC-S is benchmarked for linear electrostatic ion temperature gradient-driven microinstabilities, which can underlie turbulent transport in stellarators. An initial benchmark of XGC-S in tokamak geometry shows good agreement with the XGC1, ORB5, and global GENE codes. A benchmark between XGC-S and the EUTERPE global gyrokinetic code for stellarators has also been performed, this time in geometry of the optimised stellarator Wendelstein 7-X. Good agreement has been found for the mode number spectrum, mode structure, and growth rate.

physics.plasm-ph↗