arXiv subjects

Eduardo Ahedo

Publications and source records attributed to Eduardo Ahedo.

9 recordsLinked to original sources

arXiv2026

Azimuthal mode decomposition Particle in Cell algorithm for cylindrical plasma sources

An efficient Particle-in-Cell numerical approach to perform full-dimensional kinetic simulations of low temperature plasmas is presented. Taking advantage of the cylindrical geometry of most plasma sources, a Fourier mode decomposition of the fields is carried out in the azimuthal ($θ$) direction up to a chosen maximum number of modes $N_m$. Macroparticles are pushed in all $D$ dimensions and weighed, for each mode $m$, onto a $(D-1)$ dimensional grid. The computation of the electric field for each mode is independent and reduces to solving $(N_m+1)$ $(D-1)$ dimensional Poisson problems. The approach brings spectral accuracy in the azimuthal direction, while the computational cost is comparable to that of a simulation with $(D-1)$ dimensions. We verify this approach against a planar test case based on a Penning discharge, widely used for benchmarking and validation purposes in the low-temperature plasma community. Our approach allows us to reduce the 2D problem into a collection of coupled 1D problems and to naturally perform spectral analysis of the different azimuthal modes, recovering the contribution of each mode to radial transport, with a computational time saving of one order of magnitude with respect to state of the art 2D particle-in-cell codes.

physics.plasm-ph↗

arXiv2026

Analysis of collisional and facility effects in a magnetic nozzle plasma expansion

An axisymmetric, quasineutral three-fluid model is proposed to study the plasma expansion in a magnetic nozzle under the presence of neutrals coming either from the plasma source or as an homogeneous background. As a difference with other models, electron cooling in the plume is achieved by treating the electron energy flux as mainly convective and without the need to postulate any anomalous resistivity. Solutions are presented for the electron high-magnetization limit, in which the electron main magnitudes can be integrated along magnetic lines. Ionization, elastic and charge-exchange collisions with neutrals do not change the main qualitative features of the plasma expansion, known from previous collisionless models. Ionization enhances the plasma flow in the nozzle, and leads to additional electron cooling, which decreases the electric potential fall along the nozzle. The efficiency of the nozzle is quantified in terms of the gain of magnetic thrust and the plume divergence angle. Two types of boundary conditions are discussed for the electron flow: local current ambipolarity conditions at the nozzle throat and global current-free conditions at the outer boundary (i.e., metallic vacuum chamber walls). These last ones are shown to be physically more reliable: they introduce the influence of the chamber walls on the plasma expansion by shaping the ambipolar electric field; they permit the extrapolation to undisturbed free space conditions; and they approximate better experimental trends with the background pressure.

physics.plasm-ph↗

arXiv2025

Benchmark for two-dimensional large scale coherent structures in partially magnetized ExB plasmas -- Community collaboration & lessons learned

Low-temperature plasmas are essential to both fundamental scientific research and critical industrial applications. As in many areas of science, numerical simulations have become a vital tool for uncovering new physical phenomena and guiding technological development. Code benchmarking remains crucial for verifying implementations and evaluating performance. This work continues the Landmark benchmark initiative, a series specifically designed to support the verification of low-temperature plasma codes. In this study, seventeen simulation codes from a collaborative community of nineteen international institutions modeled a partially magnetized ExB Penning discharge. The emergence of large scale coherent structures, or rotating plasma spokes, endows this configuration with an enormous range of time scales, making it particularly challenging to simulate. The codes showed excellent agreement on the rotation frequency of the spoke as well as key plasma properties, including time-averaged ion density, plasma potential, and electron temperature profiles. Achieving this level of agreement came with challenges, and we share lessons learned on how to conduct future benchmarking campaigns. Comparing code implementations, computational hardware, and simulation runtimes also revealed interesting trends, which are summarized with the aim of guiding future plasma simulation software development.

physics.plasm-ph↗

arXiv2024

Lower-Hybrid Drift Instabilities in a magnetic nozzle

Magnetic nozzles are a key component of electrodeless plasma thrusters, acting as their main acceleration stage. Non-stationary phenomena common to the entire range of $E \times B$ devices, such as oscillations and instabilities, are likely to exist in the magnetic nozzle, according to the mounting experimental evidence. These mechanisms could lead to anomalous cross-field transport, either enhancing the plasma plume divergence or favoring electron detachment. In this work we present a local linear analysis of fluid instabilities relevant for said devices, expanding on previous works with the addition of plasma inhomogeneities in the direction parallel to the magnetic field, with a rigorous inclusion of the effects of magnetic curvature, finite Larmor radius and $3$D wave propagation, allowing for a general formulation of drift-driven instabilities in partially magnetized plasmas. Instability conditions are first studied analytically, and then applied to simulation data of a helicon plasma thruster. Finally, the effect of instabilities on wave-driven cross-field electron transport is assessed by means of quasi-linear analysis. This study predicts the onset of essentially-azimuthal instabilities in the $1$ kHz--$1$ MHz range, in qualitative agreement with some of the available experimental data, and highlights the importance of including parallel inhomogeneities in the formulation of the dispersion relation of an $E \times B$ plasma, as these gradients may drive instabilities even in the absence of axial propagation. Lastly, quasi-linear analysis suggests that the induced cross-field transport acts to smooth out the zeroth-order drifts which cause the plasma to destabilize in the first place.

physics.plasm-ph↗

arXiv2024

Effect of injection conditions on the non-linear behavior of the ECDI and related turbulent transport

The electron-cyclotron drift instability (ECDI) has been proposed as one of the main actors behind the anomalous transport of electrons in Hall plasmas. In this work, we revisit the classical theory of this instability [Forslund et al., Phys. Rev. Lett. 25, 1266 (1970)] and perform two-dimensional kinetic simulations under several conditions to analyze the non-linear behavior and the induced transport. Fully-periodic simulations, with conditions faithful to the linear theory are analyzed first. In agreement with existing literature, they show the growth of ECDI modes, ion-wave trapping vortexes and an induced cross-field electron current in early simulation times. However, in contrast with similar works, non-linear saturation is observed and the plasma tends, in the long term, to a new equilibrium with mild oscillations and mild anomalous current. This evolution is consistent to what can be expected from energy conservation. The quenching of the oscillations seem to be highly related with the distortion of ion vortexes in phase space after a long-term interaction with the electrostatic wave. This result suggests that sustained oscillations and turbulent current could thrive if ions are renewed by, e.g., removing and injecting particles through axial boundaries instead of applying periodicity.This second type of simulations shows that injection conditions highly impact the late simulation behavior of ECDI oscillations, where we identify several regimes depending on the value of the ion residence time compared to the characteristic saturation time in the fully periodic case. The intermediate regime, where these two times are close, is the only one providing sustained oscillations and electron transport.

physics.plasm-ph↗

arXiv2024

A study of an air-breathing electrodeless plasma thruster discharge

Plasma chemistry of main air components is implemented in a hybrid 2D axisymmetric simulation code to assess the air-breathing concept in an electrodeless plasma thruster. Relevant electron-heavy species collisions for diatomic molecules are included: rotational and vibrational excitation, dissociation and dissociative ionization. Plasma-wall interaction giving rise to associative recombination of atomic species into molecular species is included too. As reference, the plasma thruster is operated with Xe, at a power of 300W and a mass flow of 1mg/s. Simulations are run by injecting 1mg/s of N$_2$ and O independently for powers between 100 and 3000W. The performances and trends of plasma response for these propellants are similar to Xe, but displaced to powers between 1250 and 2000W. At optimum power, the thrust efficiency for N$_2$ and O surpasses that of Xe, due to the excess of re-ionization for Xe. Performances of 50/50 mixtures of N$_2$/O, which are a realistic composition in the ionosphere, are found to be linear combinations of the performances of each propellant. Performances using O$_2$, which could be generated from associative recombination of O at the intake, are very similar to those of the atomic oxygen.

physics.plasm-ph↗

arXiv2023

Analysis of a cusped helicon plasma thruster discharge

A compact helicon plasma thruster that features a cusp in its internal magnetic field is analyzed with experiments and simulations. A compensated Langmuir probe and a Faraday cup are used in the former, while a hybrid PIC/fluid transport model combined with a frequency-domain electromagnetic field model are used in the latter. Measurements serve to tune the anomalous transport parameters of the model and overall show the same trends as the numerical results, including a secondary peak of electron temperature downstream in the magnetic nozzle, where electron cyclotron resonance conditions for the 13.56 MHz excitation frequency are met. The cusp plays a central role in determining the plasma losses to the walls and the profile of electron temperature, which in turn defines the excitation and ionization losses. While losses to the rear wall are reduced, losses to the lateral wall are increased, which, together with the low production efficiency, limit the performance of the device. Shorter chamber lengths and optimization of antenna and cusp location are suggested as potential ways to improve performance.

physics.plasm-ph↗

arXiv2022

Kinetic Electron Cooling in Magnetic Nozzles: Experiments and Modeling

As long-distance space travel requires propulsion systems with greater operational flexibility and lifetimes, there is a growing interest in electrodeless plasma thrusters that offer the opportunity of improved scalability, larger throttleability, running on different propellants, and limit device erosion. The majority of electrodeless designs rely on a magnetic nozzle (MN) for the acceleration of the plasma, which has the advantage of utilizing the expanding electrons to neutralize the ion beam without the additional installation of a cathode. The plasma expansion in the MN is nearly collisionless, and a fluid description of electrons requires a non-trivial closure relation. Kinetic electron effects, and in particular electron cooling, play a crucial role in various physical phenomena such as energy balance, ion acceleration, and particle detachment. Based on the experimental and theoretical studies conducted in recognition of this importance, the fundamental physics of the electron cooling mechanism revealed in MNs and magnetically expanding plasma are reviewed. Especially, recent approaches from the kinetic point of view are discussed, and our perspective on the future challenges of electron cooling and the relevant physical subject of MN is presented.

physics.plasm-ph↗

arXiv2020

Perspectives on Physics of ExB Discharges Relevant to Plasma Propulsion and Similar Technologies

This paper provides perspectives on recent progress in the understanding of the physics of devices where the external magnetic field is applied perpendicularly to the discharge current. This configuration generates a strong electric field, which acts to accelerates ions. The many applications of this set up include generation of thrust for spacecraft propulsion and the separation of species in plasma mass separation devices. These ExB plasmas are subject to plasma-wall interaction effects as well as various micro and macro instabilities, and in many devices, we observe the emergence of anomalous transport. This perspective presents the current understanding of the physics of these phenomena, state-of-the-art computational results, identifies critical questions, and suggests directions for future research

physics.plasm-ph↗