arXiv subjects

Seth Dorfman

Publications and source records attributed to Seth Dorfman.

8 recordsLinked to original sources

arXiv2026

The FLARE Facility

The Facility for Laboratory Reconnection Experiments (FLARE) has been constructed to study magnetic reconnection in multiple X-line regimes relevant to space, astrophysical, and fusion plasmas. Building upon the successful design of the Magnetic Reconnection Experiment (MRX), FLARE features a larger physical volume, stronger magnetic fields, and an independent ohmic heating drive to significantly extend the accessible parameter space, targeting Lundquist numbers up to S ~ 10^5 and normalized system sizes up to \lambda ~ 10^3. This paper details the facility's core engineering components, including the primary vacuum vessel, internal flux cores, highly segmented external coil systems, modular capacitor banks, and the safety interlock and control architecture. An initial diagnostic suite is presented, comprising high-resolution 2D magnetic probe arrays, triple Langmuir probes, a fully fiber-coupled interferometer, ion Doppler spectroscopy, and fast camera imaging. Initial operations demonstrate the device's experimental flexibility and reliability, successfully executing symmetric push-pull reconnection, spheromak merging, and asymmetric downstream configurations. Currently operating within "Stage 2.5" with S ~ 2,500 and \lambda ~ 60 for anti-parallel reconnection, FLARE provides immediate access to the multiple X-line regimes. Planned hardware upgrades, advanced diagnostic additions, and integration with fully kinetic simulations will further expand its capabilities as it transitions into a collaborative user facility for the broader plasma science community.

physics.plasm-ph↗

arXiv2026

Particle-in-Cell Simulation of the Parametric Decay Instability of Alfv\'en Waves with Absorbing Boundary Conditions

The Alfv\'en wave parametric decay instability (PDI) facilitates energy transfer, plasma heating, and turbulence generation in space, astrophysical, and fusion plasmas. Most simulation studies of Alfv\'en wave PDI have focused on kinetic ions under periodic boundary conditions. Here, we present fully kinetic one-dimensional simulations (perpendicular wave-vector $k_\perp=0$) of the Alfv\'en wave PDI at low plasma beta using absorbing boundary conditions for the waves to understand the energy partition in an open system. For $\beta=5\times 10^{-4}$ and a normalized wave amplitude $\frac{\delta B}{B_0}=0.01$, nearly 92\% of the pump wave energy is transferred to the backward-propagating child Alfv\'en wave, and the remaining energy is partitioned between electrons ($\sim 1$-$2\%$) and ions ($\sim 6$-$7\%$). In the parameter regime considered, the ion and electron heating appears only when the PDI has sufficiently developed, and their rates are approximately twice the linear PDI growth rate, which roughly corresponds to the quadratic dependence of energy on the fluctuation amplitude. Furthermore, we find a qualitative agreement between theoretical and numerical growth rates over a range of plasma and wave parameters. This work establishes critical steps for future extension to finite $k_\perp$ waves in high dimensions, where stronger electron heating may be induced.

physics.plasm-ph↗

arXiv2025

A novel scheme for measuring the growth of Alfven wave parametric decay instability using counter-propagating waves

The parametric decay instability (PDI) of Alfven waves -- where a pump Alfven wave decays into a backward-propagating child Alfven wave and a forward ion acoustic wave -- is a fundamental nonlinear wave-wave interaction and holds significant implications for space and laboratory plasmas. However, to date there has been no direct experimental measurement of PDI. Here, we propose a novel and experimentally viable scheme to quantify the growth of Alfven wave PDI on a linear device using a large pump Alfven wave and a small counter-propagating seed Alfven wave, with the seed wave frequency tuned to match the backward Alfven wave generated by standard PDI. Using hybrid simulations, we show that energy transfer from the pump to the seed reduces the latter's spatial damping. By comparing seed wave amplitudes with and without the pump wave, this damping reduction can be used as a direct and reliable proxy for PDI growth. The method is validated in our simulations across a range of plasma and wave parameters and agrees well with theoretical predictions. Notably, the scheme exhibits no threshold for PDI excitation and is, in principle, readily implementable under current laboratory conditions. This scheme is a critical step toward solving the challenge of experimentally accessing Alfven wave PDI and provides an elegant method that may be used to validate fundamental theories of parametric instabilities in controlled laboratory settings.

physics.plasm-ph↗

arXiv2024

Effects of wave damping and finite perpendicular scale on three-dimensional Alfven wave parametric decay in low-beta plasmas

Shear Alfven wave parametric decay instability (PDI) provides a potential path toward significant wave dissipation and plasma heating. However, fundamental questions regarding how PDI is excited in a realistic three-dimensional (3D) open system and how critically the finite perpendicular wave scale--as found in both laboratory and space plasmas--affects the excitation remain poorly understood. Here, we present the first 3D, open-boundary, hybrid kinetic-fluid simulations of kinetic Alfven wave PDI in low-beta plasmas. Key findings are that the PDI excitation is strongly limited by the wave damping present, including electron-ion collisional damping (represented by a constant resistivity) and geometrical attenuation associated with the finite-scale Alfven wave, and ion Landau damping of the child acoustic wave. The perpendicular wave scale alone, however, plays no discernible role: waves of different perpendicular scales exhibit similar instability growth as long as the magnitude of the parallel ponderomotive force remains unchanged. These findings are corroborated by theoretical analysis and estimates. The new understanding of 3D kinetic Alfvén wave PDI physics is essential for laboratory study of the basic plasma process and may also help evaluate the relevance/role of PDI in low-beta space plasmas.

physics.plasm-ph↗

arXiv2023

Nonlinear dynamics of small-scale Alfvén waves

We study the nonlinear evolution of very oblique small-scale Alfvén waves with $k_\perp d_i\gtrsim 1$. At these scales, the waves become significantly compressive, unlike in MHD, due to the Hall term in the equations. We demonstrate that when frequencies are small compared to the ion gyrofrequency and amplitudes small compared to unity, no new nonlinear interaction appears due to the Hall term alone at the lowest non-trivial order, even when $k_\perp d_i \sim 1$. However, at the second non-trivial order, we discover that the Hall physics leads to a slow but resonant nonlinear interaction between co-propagating Alfvén waves, an inherently 3D effect. Including the effects of finite temperature, finite frequency, and electron inertia, the two-fluid Alfvén wave also becomes dispersive once one or more of $k_\perp ρ_s$, $k_\perp d_e$, or $k_\parallel d_i$ becomes significant: for oblique waves at low $β$ as studied here, this can be at a much smaller scale than $d_i$. We show that the timescale for one-dimensional steepening of two-fluid Alfven waves is only significant at these smaller dispersive scales, and also derive an expression for the amplitude of driven harmonics of a primary wave. Importantly, both new effects are absent in gyrokinetics and other commonly used reduced two-fluid models. Our calculations have relevance for the interpretation of laboratory Alfvén wave experiments, as well as shedding light on the physics of turbulence in the solar corona and inner solar wind, where the dominant nonlinear interaction between counter-propagating waves is suppressed, allowing these new effects to become important.

physics.plasm-ph↗

arXiv2022

Hybrid simulation of Alfvén wave parametric decay instability in a laboratory relevant plasma

Large-amplitude Alfvén waves are subject to parametric decays which can have important consequences in space, astrophysical, and fusion plasmas. Though the Alfvén wave parametric decay instability was predicted decades ago, observational evidence is limited, stimulating considerable interest in laboratory demonstration of the instability and associated numerical modeling. Here, we report novel hybrid simulation of the Alfvén wave parametric decay instability in a laboratory relevant plasma (based on the Large Plasma Device), using realistic wave injection and wave-plasma parameters. Considering only collisionless damping, we identify the threshold Alfvén wave amplitudes and frequencies required for triggering the instability in the bounded plasma. These threshold behaviors are corroborated by simple theoretical considerations. Other effects not included in the present model such as finite transverse scale and ion-neutral collision are briefly discussed. These hybrid simulations demonstrate a promising tool for investigating laboratory Alfvén wave dynamics that can provide guidance for future laboratory demonstration of the parametric decay instability.

physics.plasm-ph↗

arXiv2021

Parametric decay of Alfvénic wave packets in nonperiodic low-beta plasmas

The parametric decay of finite-size Alfvén waves in nonperiodic low-beta plasmas is investigated using one-dimensional hybrid simulations. Compared with the usual small periodic system, a wave packet in a large system under the absorption boundary condition shows different decay dynamics, including reduced energy transfer and localized density cavitation and ion heating. The resulting Alfvén wave dynamics are influenced by several factors of the instability including the growth rate, central wave frequency, and unstable bandwidth. A final steady state of the wave packet may be achieved when the instability does not have enough time to develop within the residual packet, and the packet size shows well-defined scaling dependencies on the growth rate, wave amplitude, and plasma beta. Under the proper conditions enhanced secondary decay can also be excited in the form of a narrow, amplified wavepacket. These results may help interpret laboratory and spacecraft observations of Alfvén waves, and refine our understanding of associated energy transport and ion heating.

physics.plasm-ph↗

arXiv2014

Analysis of Magnetic Fields in Inertial Alfven Wave Collisions

Turbulence in astrophysical and space plasmas is dominated by the nonlinear interaction of counterpropagating Alfven waves. Most Alfven wave turbulence theories have been based on ideal plasma models, such as incompressible MHD, for Alfven waves at large scales. However, in the inertial Alfven wave regime (vA > vthe), relevant to magnetospheric plasmas, how the turbulent nonlinear interactions are modified by the dispersive nature of the waves remains to be explored. Here we present the first laboratory evidence of the nonlinear interaction in the inertial regime. A comparison is made with the theory for MHD Alfven waves.

astro-ph.SR↗