arXiv subjects

Vicente Valenzuela-Villaseca

Publications and source records attributed to Vicente Valenzuela-Villaseca.

6 recordsLinked to original sources

arXiv2026

Criteria for ion acceleration in laboratory magnetized quasi-perpendicular collisionless shocks: when are 2D simulations enough?

The study of collisionless shocks and their role in cosmic ray acceleration has gained importance through observations and simulations, driving interest in reproducing these conditions in laboratory experiments using high-power lasers. In this work, we examine the role of three-dimensional (3D) effects in ion acceleration in quasi-perpendicular shocks under laboratory-relevant conditions. Using hybrid particle-in-cell simulations (kinetic ions and fluid electrons), we explore how the Alfvénic and sonic Mach numbers, along with plasma beta, influence ion energization, unlocked only in 3D, and establish scaling criteria for when conducting 3D simulations is necessary. Our results show that efficient ion acceleration requires Alfvénic Mach numbers $\geq 25$ and sonic Mach numbers $\geq 13$, with plasma-$β\leq 5$. We theoretically found that, while 2D simulations suffice for current laboratory-accessible shock conditions, 3D effects become crucial for shock velocities exceeding 1000 km/s and experiments sustaining the shock for at least 10 ns. We surveyed previous laboratory experiments on collisionless shocks and found that 3D effects are unimportant under those conditions, implying that 1D and 2D simulations should be enough to model the accelerated ion spectra. However, we do find that the same experiments are realistically close to accessing the regime relevant to 3D effects, an exciting prospect for future laboratory efforts. We propose modifications to past experimental configurations to optimize and control 3D effects on ion acceleration. These proposed experiments could be used to benchmark plasma astrophysics kinetic codes and/or employed as controllable sources of energetic particles.

physics.plasm-ph↗

arXiv2026

Numerical simulations of shock-driven, supersonic interstellar turbulence in colliding three-temperature laboratory plasmas

Shock-driven turbulence is central to astrophysical plasmas in which explosions and compressive driving inject energy through shocks rather than steady stirring. We present three-dimensional, three-temperature (ion, electron, and radiation; 3T) radiation-hydrodynamic simulations of a laboratory platform in which two offset CH mesh targets are irradiated by a $30\,\rm ns$ X-ray pulse. Mesh ablation launches counter-streaming supersonic flows whose vorticity is seeded baroclinically at mesh-cell corners, advected into collimated channels over $\sim15\,\rm ns$, and injected into the outgoing streams before collision. The flows first collide at $t\simeq75\,\rm ns$, forming a shocked turbulent mixing layer that persists for at least $300\,\rm ns$, reaches $\ell_0\simeq4.5\,\rm mm$, and evolves toward an effectively isothermal equation of state with $γ_{\rm eff}\simeq1.1$. After stagnation, $u_0(t)\propto t^{-1.1}$ while $t_0/t_{c_s}\simeq0.2$ remains nearly fixed. Compression and stretching dominate the vorticity budget, and the velocity field relaxes toward a kinetic-energy partition of approximately $70\%$ solenoidal and $30\%$ compressive. The Reynolds stress is strongly anisotropic at the outer scale and remains measurably anisotropic over much of the resolved inertial interval, indicating directional memory of the collision axis and mesh geometry across many scales. The solenoidal strain spectrum implies $\ell_{ν,\rm s}\simeq92\,μ\rm m$, $\ell_0/\ell_{ν,\rm s}\simeq49$, and an effective Reynolds number $\mathrm{Re}\sim2\times10^2$. The density-gradient spectrum is directly tied to the compressive mode spectrum, which evolves independently from the incompressible cascade. Abridged.

physics.plasm-ph↗

arXiv2025

Structure of self-generated magnetic fields in laser-solid interaction from proton tomography

Strong magnetic fields are naturally self-generated in high-power, laser-solid interactions through the Biermann-battery mechanism. This work experimentally characterizes the 3D location and strength of these fields, rather than path-integrated quantities, through multi-view proton radiography and tomographic inversion on the OMEGA laser. We infer magnetic fields that extend several millimeters off the target surface into the hot, rarefied corona and are sufficient to strongly magnetize the plasma ($Ω_{e}τ_e \gg 1$). The data is used to validate MHD simulations incorporating recent improvements in magnetic transport modeling; we achieve reasonable agreement only with models with re-localization of transport by magnetic fields. This work provides a key demonstration of tomographic inversion in proton radiography, offering a valuable tool for investigating magnetic fields in laser-produced plasmas.

physics.plasm-ph↗

arXiv2025

Reconstruction of 2D line-integrated electron density using angular filter refractometry and a fast marching Eikonal solver

Refraction of an optical probe beam by a plasma can be measured with angular filter refractometry (AFR), which produces an image containing intensity contours that correspond to curves of constant refraction angle. Further analysis is required to reconstruct the underlying line-integrated electron density. Most prior efforts to calculate density from AFR data have been limited to 1D analysis or forward-fitting techniques. In this paper, we detail the use of a fast marching Eikonal solver to directly invert AFR data and obtain the 2D line-integrated electron density. The analysis method is first verified with synthetic data and then applied to laser-driven experiments of single and double plume expansion collected at the OMEGA EP Laser Facility. The calculated densities agree with 1D results and are shown to be consistent with the original AFR measurements via forward modeling. We also discuss how additional measurements could improve the precision of this technique.

physics.plasm-ph↗

arXiv2025

Influence of Conical Wire Array Geometry on Flow and Temperature Profiles Measured via Thomson Scattering and Optical Techniques

Conical wire arrays with different opening angles are used as load of a 400kA, 1kA/ns generator. The differences in opening angle allow the study of the influence of the array geometry on the jet properties. The characterization of the jets is performed using a combination of advanced diagnostic techniques, including moiré schlieren deflectometry, visible self-emission spectroscopy, and optical Thomson scattering. The results reveal that, under the experimental conditions, the plasma jets exhibit electron temperatures ranging from $8$ to $17$ eV, increasing along the axial direction. In contrast, the ion temperature decreases from approximately $35$ eV near the base of the jet to about $20$ eV at higher axial positions. The electron density profile peaks at $\sim 4 \times 10^{18}$ cm$^{-3}$ in the central lower region of the jet and decreases with height exponentially with a characteristic lenght $L_n = $2.86 mm. This behavior is reproducible and independent of the conical array geometry. However, the cone opening angle significantly affect the jet propagation velocity, with larger opening angles producing higher axial velocities ($V_{ϕ=40^\circ} \approx 125\pm3$ km/s, $V_{ϕ=20^\circ} \approx 98\pm5$ km/s), demonstrating that the cone geometry provides effective control over the jet propagation velocity.

physics.plasm-ph↗

arXiv2022

Investigating radiatively driven, magnetised plasmas with a university scale pulsed-power generator

We present first results from a novel experimental platform which is able to access physics relevant to topics including indirect-drive magnetised ICF; laser energy deposition; various topics in atomic physics; and laboratory astrophysics (for example the penetration of B-fields into HED plasmas). This platform uses the X-Rays from a wire array Z-Pinch to irradiate a silicon target, producing an outflow of ablated plasma. The ablated plasma expands into ambient, dynamically significant B-fields (~5 T) which are supported by the current flowing through the Z-Pinch. The outflows have a well-defined (quasi-1D) morphology, enabling the study of fundamental processes typically only available in more complex, integrated schemes. Experiments were fielded on the MAGPIE pulsed-power generator (1.4 MA, 240 ns rise time). On this machine a wire array Z-Pinch produces an X-Ray pulse carrying a total energy of ~15 kJ over ~30 ns. This equates to an average brightness temperature of around 10 eV on-target.

physics.plasm-ph↗