arXiv subjects

V. Ospina-Bohórquez

Publications and source records attributed to V. Ospina-Bohórquez.

4 recordsLinked to original sources

arXiv2026

Laser ion acceleration from concave targets by subpicosecond pulses

Laser-driven proton acceleration provides a powerful route for generating ultrashort, high-charge proton beams. Many applications, including secondary neutron sources and inertial fusion, benefit from tight proton beam focusing. Concave targets offer a robust solution, yet the scaling of proton focusing with laser and target parameters remains poorly understood. Here, we present a numerical study of laser-driven proton acceleration and focusing from hemispherical targets using the fully kinetic, relativistic Particle-In-Cell code EPOCH. We focus on the sub-picosecond laser-pulse regime (duration $\lesssim 10^2$ fs), centering on the laser parameters of our recent experiment at the CSU ALEPH laser facility. We investigate the proton acceleration mechanisms, characterize proton focusing, and assess how focal spot parameters scale with laser and target parameters. We identify Target Normal Sheath Acceleration as the dominant mechanism, supplemented by a secondary post-acceleration stage near the geometrical center of the hemisphere. We demonstrate that both the proton focal spot size and focal plane position scale approximately linearly with the hemisphere radius, with the focal plane consistently located downstream of the geometrical center. The opening angle of the concave target mainly affects the proton beam waist. Energy-dependent proton focusing is interpreted as a consequence of the evolving curvature of the accelerating structure, which departs from the target curvature. Evidence for self-similar proton focusing is found in the regime of nearly uniform target irradiation.

physics.plasm-ph↗

arXiv2023

Laser-driven ion and electron acceleration from near-critical density gas targets: towards high-repetition rate operation in the 1 PW, sub-100 fs laser interaction regime

Ion acceleration from gaseous targets driven by relativistic-intensity lasers was demonstrated as early as the late 90s, yet most of the experiments conducted to date have involved picosecond-duration, Nd:glass lasers operating at low repetition rate. Here, we present measurements on the interaction of ultraintense ($\sim 10^{20}\,\rm W\,cm^{-2}$, 1 PW), ultrashort ($\sim 70\,\rm fs$) Ti:Sa laser pulses with near-critical ($\sim 10^{20}\,\rm cm^{-3}$) helium gas jets, a debris-free targetry compatible with high ($\sim 1\,\rm Hz$) repetition rate operation. We provide evidence of $α$ particles being forward accelerated up to $\sim 2.7\,\rm MeV$ energy with a total flux of $\sim 10^{11}\,\rm sr^{-1}$ as integrated over $>0.1 \,\rm MeV$ energies and detected within a $0.5\,\rm mrad$ solid angle. We also report on on-axis emission of relativistic electrons with an exponentially decaying spectrum characterized by a $\sim 10\,\rm MeV$ slope, i.e., five times larger than the standard ponderomotive scaling. The total charge of these electrons with energy above 2 MeV is estimated to be of $\sim 1 \,\rm nC$, corresponding to $\sim 0.1\,\%$ of the laser drive energy. In addition, we observe the formation of a plasma channel, extending longitudinally across the gas density maximum and expanding radially with time. These results are well captured by large-scale particle-in-cell simulations, which reveal that the detected fast ions most likely originate from reflection off the rapidly expanding channel walls. The latter process is predicted to yield ion energies in the MeV range, which compare well with the measurements. Finally, direct laser acceleration is shown to be the dominant mechanism behind the observed electron energization.

physics.plasm-ph↗

arXiv2022

Parametric study on ion acceleration from the interaction of ultra-high intensity laser pulses with near-critical density gas targets

We present a parametric study based on 1-D particle-in-cell (PIC) simulations conducted with the objective of understanding the interaction of intense lasers with near-critical non-uniform density gas targets. Specifically, we aim to find an optimal set of experimental parameters regarding the interaction of a $λ_L$ = 0.8 $μ$m, $I_L =10^{20}$ W/cm$^2$ ($a_0 = 8.8$), $τ_L = 30$ fs laser pulse with a near-critical non-uniform pure nitrogen gas profile produced by a non commercial gas nozzle. The PIC code Calder developed at CEA was used, and both the maximum electron density and the direct laser contribution to ion acceleration were studied. Shock formation was achieved for a peak electron density $n_e$ ranging between 0.35 $n_c$ and 0.7 $n_c$. In this density interval, the survival of a percentage of the laser pulse until the gas density peak, while being strongly absorbed ($>$90$\%$) and creating a hot electron population in the gas up-ramp, is singled out as a necessary condition for shock formation. Moreover, the laser absorption must give rise to a super ponderomotive heating of the target electrons in order to launch an electrostatic shock inside the plasma. The direct laser effect on ion acceleration consists in a strong initial density perturbation that enhances charge separation while the electron pressure gradients are identified as fundamental for shock formation. The production of a controlled and repetitive gas profile as well as the possibility of performing measurements with statistical meaning are highlighted as fundamental for conducting a thorough experimental study.

physics.plasm-ph↗

arXiv2022

A cylindrical implosion platform for the study of highly magnetized plasmas at LMJ

Investigating the potential benefits of the use of magnetic fields in Inertial Confinement Fusion (ICF) experiments has given rise to new experimental platforms like the Magnetized Liner Inertial Fusion (MagLIF) approach at the Z-machine (Sandia National Laboratories), or its laser-driven equivalent at OMEGA (Laboratory for Laser Energetics). Implementing these platforms at MJ-scale laser facilities, such as the Laser MegaJoule (LMJ) or the National Ignition Facility (NIF), is crucial to reaching self-sustained nuclear fusion and enlarges the level of magnetization that can be achieved through a higher compression. In this paper, we present a complete design of an experimental platform for magnetized implosions using cylindrical targets at LMJ. A seed magnetic field is generated along the axis of the cylinder using laser-driven coil targets, minimizing debris and increasing diagnostic access compared with pulsed power field generators. We present a comprehensive simulation study of the initial B-field generated with these coil targets, as well as 2-dimensional extended magneto-hydrodynamics (MHD) simulations showing that a 5T initial B-field is compressed up to 25kT during the implosion. Under these circumstances, the electrons become magnetized, which severely modifies the plasma conditions at stagnation. In particular, in the hot spot the electron temperature is increased (from 1keV to 5keV) while the density is reduced (from 40gcc to 7gcc). We discuss how these changes can be diagnosed using X-ray imaging and spectroscopy, and particle diagnostics. We propose the simultaneous use of two dopants in the fuel (Ar and Kr) to act as spectroscopic tracers. We show that this introduces an effective spatial resolution in the plasma which permits an unambiguous observation of the B-field effects. Additionally, we present a plan for future experiments of this kind at LMJ.

physics.plasm-ph↗