arXiv subjects

T. Waltenspiel

Publications and source records attributed to T. Waltenspiel.

4 recordsLinked to original sources

arXiv2026

Efficient ion re-acceleration in laboratory-produced interpenetrating collisionless shocks

Although the origin of cosmic rays (CRs) remains an open question, collisionless magnetized shock waves are widely regarded as key sites for particle acceleration. Recent theories further suggest that shock-shock collisions in stellar clusters could provide the additional acceleration needed to explain the observed high-energy CR spectrum. Here, we investigate this hypothesis through a laser-based experiment that creates magnetized plasma conditions similar to astrophysical environments. Our results demonstrate that interpenetrating collisionless shocks can significantly boost the energy of ambient protons previously energized by the individual shocks, while also improving the overall acceleration efficiency. Numerical kinetic simulations corroborate these findings, revealing that protons are reaccelerated via their bouncing motion in the convective electric fields of the colliding magnetized flows. By allowing to highly energize ambient protons, our novel colliding-shock platform opens the prospect to test the long-discussed mechanism of diffusive shock acceleration in a controlled laboratory setting.

physics.plasm-ph↗

arXiv2026

Laboratory evidence of electron pressure anisotropy driving plasmoid mediated magnetic reconnection

Plasmoid-driven magnetic reconnection in elongated current sheets is suspected to be an ubiquitous phenomenon in space and astrophysical plasmas, but the mechanisms driving its onset and dynamics are still debated. Deciphering the physical mechanisms dominating the destabilization and fragmentation of the current sheet, as well as its evolution, would have a wide impact into our understanding of the induced plasma turbulence and particle acceleration. Here, by coupling 3D hybrid simulations with laser-driven experiments that involve counterflowing high-energy-density magnetized plasmas with a long aspect ratio of their contact layer, we show that electron pressure anisotropy is the driving factor of the growth rate of the tearing instability, and will sustain the reconnection process even without classical resistivity. Dissipative mechanisms, such as resistivity and isotropization, are further found to stabilize the sheet to varying degrees, thus modifying plasmoid formation. By identifying the roles of pressure anisotropy, dissipation, and large-scale geometry, our work lays the groundwork for the evaluation of plasmoid-driven reconnection impact on the dynamics of laboratory and astrophysical plasmas.

physics.plasm-ph↗

arXiv2026

Investigation of Laser Plasma Instabilities driven by Coupled High-Power Laser Beams in Magnetized Underdense Plasmas

Stimulated Brillouin and Raman scattering (SBS and SRS) are instabilities that affect the propagation of high-power lasers in plasmas. The latter is further affected by Cross-Talk (CT) effects when multiple laser beams are simultaneously propagated in the plasma, as found in the schemes proposed for inertial confinement fusion (ICF). Here we develop a new theoretical model that allows us to evaluate the impact of CT on SBS and SRS in low-density plasmas. As supported by experiments, we demonstrate that CT can lead to a reduction of both SBS and SRS, due to the destabilization of the individually triggered instabilities. We further demonstrate that this destabilization effect is accelerated by applying an externally magnetic field to the plasma, which is also beneficial for the hydrodynamics or fuel heating of ICF. By shedding new light on the promising scheme of magnetized ICF, our findings thus offer beneficial prospects for ICF.

physics.plasm-ph↗

arXiv2024

Saturation of the compression of two interacting magnetic flux tubes evidenced in the laboratory

Interactions between magnetic fields advected by matter play a fundamental role in the Universe at a diverse range of scales. A crucial role these interactions play is in making turbulent fields highly anisotropic, leading to observed ordered fields. These in turn, are important evolutionary factors for all the systems within and around. Despite scant evidence, due to the difficulty in measuring even near-Earth events, the magnetic field compression factor in these interactions, measured at very varied scales, is limited to a few. However, compressing matter in which a magnetic field is embedded, results in compression up to several thousands. Here we show, using laboratory experiments and matching three-dimensional hybrid simulations, that there is indeed a very effective saturation of the compression when two independent parallel-oriented magnetic fields regions encounter one another due to plasma advection. We found that the observed saturation is linked to a build-up of the magnetic pressure, which decelerates and redirects the inflows at their encounter point, thereby stopping further compression. Moreover, the growth of an electric field, induced by the incoming flows and the magnetic field, acts in redirecting the inflows transversely, further hampering field compression.

physics.plasm-ph↗