arXiv subjects

A. L. Milder

Publications and source records attributed to A. L. Milder.

3 recordsLinked to original sources

arXiv2026

Excitation of the lower-hybrid drift instability in the outflow of electron-only magnetic reconnection

We report experimental evidence for the lower-hybrid drift instability in the current sheet normal direction of electron-only magnetic reconnection. In our laser-driven capacitor-coil experiment, the system size ($\sim$3 ion skin depths) places it in the electron-only regime. Yet, Thomson scattering reveals out-of-plane electron drift oscillations at the local lower-hybrid frequency, with kinetic energy density reaching $\sim$18% of the local magnetic energy density. Linear theory with the measured parameters predicts more than ten e-folding times of growth, indicating that the instability reaches the nonlinear regime within the measurement window. Supported by particle-in-cell simulations, these results demonstrate the importance of ions in the dissipation and energy transfer in electron-only reconnection where their significance has not been previously recognized.

physics.plasm-ph↗

arXiv2026

Differentiable Programming for Plasma Physics: From Diagnostics to Discovery and Design

Differentiable programming, enabled by automatic differentiation (AD), provides a robust framework for gradient-based optimization in computational plasma physics. While optimization is often only used towards design, we demonstrate that it can also be used for discovery and bridging the gap towards multi-scale modeling. We discuss four applications: (1) discovering novel nonlinear plasma phenomena, including a previously unknown superadditive wavepacket interaction regime, by optimizing differentiable kinetic simulations; (2) learning hidden variables that capture spatiotemporally non-local kinetic effects in fluid simulations, enabling hydrodynamic models to reproduce large Knudsen number physics typically requiring kinetic solvers; (3) accelerating Thomson scattering analysis by over $140\times$ while enabling extraction of velocity distribution functions with $\mathcal{O}(10^3)$ parameters; and (4) inverse design of spatiotemporal laser pulses that achieve target far-field behavior where full space-time coupling improves performance by $15\times$ over spatial or temporal optimization alone. These examples illustrate that differentiable programming not only accelerates existing design and inference workflows but enables qualitatively new capabilities, from algorithmic physics discovery to high-dimensional inference and design previously considered intractable.

physics.plasm-ph↗

arXiv2026

Ionization Dynamics in Intense Laser-Produced Plasmas

The ionization dynamic of argon plasma irradiated by an intense laser is investigated to understand transient physics in dynamic systems. This study demonstrates that significant delayed ionization responses and stepwise ionization processes are crucial factors in determining the ionization state of such systems. When an intense laser begins to ionize an initially cold argon plasma, the conditions change rapidly, leading to a delayed response in ionization. Consequently, the dynamics do not reach a steady state, even if the electron temperature and density appear unchanged, particularly when the atomic transition process is not sufficiently rapid compared to the relevant time scales. Furthermore, in this case, numerous highly excited states are created primarily through collisional excitation. Thus, even low-energy photons can predominantly ionize plasmas, challenging the conventional belief that such photon energies insufficient to overcome the binding energy of bound electrons typically contribute less to the ionization. These findings underscore the necessity of incorporating these processes in ionization modeling within radiation hydrodynamic simulations for various laser-plasma experiments.

physics.plasm-ph↗