Engineering topics

Bellan, Paul M.

Publications and source records attributed to Bellan, Paul M..

10 records

DOE OSTI2021

How Hall electric fields intrinsically chaotize and heat ions during collisionless magnetic reconnection

The origin of extreme and anomalous ion heating during magnetic reconnection has been a longstanding mystery. It is shown in this paper that, at the core of the process, the stochastic heating mechanism is responsible for this energization. The in-plane Hall electric fields that intrinsically develop during collisionless reconnection not only accelerate ions, but also thermalize them by inducing chaotic motion. The mechanism explains various observed features of ion heating, e.g., its relation to the guide field strength and the ion mass-to-charge ratio.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2020

Caltech Lab Experiments and the Insights They Provide Into Solar Corona Phenomena

A comprehensive overview of two decades of Caltech experiments relevant to solar corona physics is presented. The extent to which the experiments scale to the solar corona, the basic configurations and operation, and the importance of the magnetic force J × B common to all the experiments is discussed. Summaries are given of the various configurations used, the main observations, and interpretations of these observations, including new models developed to provide these interpretations. Topics include observations and explanations for flux rope self-collimation, axial flows along flux ropes, eruption of arched flux ropes, strapping magnetic fields that inhibit eruption, the torus instability, and effects such as X-ray emission of a kink-driven secondary Rayleigh-Taylor instability.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2020

3D Numerical Simulation of Kink-driven Rayleigh–Taylor Instability Leading to Fast Magnetic Reconnection

Fast magnetic reconnection involving non-MHD microscale physics is thought to underlie both solar eruptions and laboratory plasma current disruptions. While there is extensive research on both the MHD macroscale physics and the non-MHD microscale physics, the process by which large-scale MHD couples to the microscale physics is not well understood. An MHD instability cascade from a kink to a secondary Rayleigh–Taylor instability in the Caltech astrophysical jet laboratory experiment provides new insights into this coupling and motivates a 3D numerical simulation of this transition from large to small scale. A critical finding from the simulation is that the axial magnetic field inside the current-carrying dense plasma must exceed the field outside. In addition, the simulation verifies a theoretical prediction and experimental observation that, depending on the strength of the effective gravity produced by the primary kink instability, the secondary instability can be Rayleigh–Taylor or mini-kink. Finally, it is shown that the kink-driven Rayleigh–Taylor instability generates a localized electric field sufficiently strong to accelerate electrons to very high energy.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2020

Determination of a macro- to micro-scale progression leading to a magnetized plasma disruption

We report here the observations of a plasma jet evolving through a macro- to micro-scale progression sequence. This leads to a fast magnetic reconnection that results in the jet breaking off from its originating electrode and forming a force-free state. A sausage-like pinching occurs first and squeezes an initially fat, short magnetized jet so that it becomes thin. The thin jet then becomes kink unstable. The lengthening of the jet by the kinking thins the jet even more since the kink is an incompressible instability. When the jet radius becomes comparable to the ion-skin depth, Hall and electron inertial physics become important and establish the environment for a fast magnetic reconnection. This fast reconnection occurs, disrupting the jet and establishing a force-free state. X-ray bursts and whistler waves, evidence of a magnetic reconnection, are observed when the plasma jet breaks off from the electrode. This experimentally confirmed sequence of successive thinning from pinching followed by kinking is reproduced in a three-dimensional ideal Magnetohydrodynamic (MHD) numerical simulation. The results of the experiment and the numerical simulation, together demonstrate a viable path from macro-scale MHD physics to micro-scale non-MHD physics where fast reconnection occurs.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2019

The electron canonical battery effect in magnetic reconnection: Completion of the electron canonical vorticity framework

A widespread practice in studying magnetic reconnection is to examine the electron momentum equation. Here, we present an alternative, ab initio framework that examines the motion of the electron canonical vorticity, which is the curl of the electron canonical momentum. The competition between just two terms—the convective term and the electron canonical battery term—determines the dynamics of electron canonical vorticity and equivalently the electron physics down to first principles. To demonstrate the power of this approach, the growth, saturation, stability, and morphology of the electron diffusion region are explained within the electron canonical vorticity framework. The framework provides a clear distinction between reconnection models where the frozen-in property of the magnetic field is violated by electron inertia and by pressure tensor effects such as electron viscosity.

25 ENERGY STORAGE↗

DOE OSTI2019

Laboratory Measurement of Large-Amplitude Whistler Pulses Generated by Fast Magnetic Reconnection

Here, we introduce observations of large-amplitude (δB/B~ 0.01) oblique whistler wave pulses generated by a spontaneous, 3-D localized magnetic reconnection event in the Caltech jet experiment. The wave pulses are measured more than 50 ion skin depths from the reconnection location by a tetrahedron array of three-axis B-dot probes that mimic the pyramid flight formations of the Cluster and Magnetospheric Multiscale Mission spacecraft. Measurements of background parameters, wave polarization, and wave dispersion confirm that the pulses are whistler modes. These findings demonstrate that localized impulsive reconnection events can generate large-amplitude, oblique whistler wave pulses that propagate far outside the reconnection region. This offers a new pathway for the generation of magnetospheric whistler pulses and may help explain relativistic particle acceleration in phenomena such as solar flares that incorporate 3-D localized impulsive magnetic reconnection.

3‐D magnetic reconnection↗

DOE OSTI2019

Magnetically Induced Current Piston for Generating Extreme-ultraviolet Fronts in the Solar Corona

Single-pulse, globally propagating coronal fronts, called Extreme-ultraviolet (EUV) waves, were first confirmed in 1995 by the Extreme-ultraviolet Imaging Telescope and every observed EUV wave since has been associated with a coronal mass ejection (CME). The physical mechanism underlying these waves has been debated for two decades with wave or pseudo-wave theories being advocated. We introduce a hybrid model where EUV waves are compressional fronts driven by a reverse electric current layer induced by the time-dependent CME core current. The reverse current layer flows in a direction opposite to the CME core current and is an eddy current layer necessary to maintain magnetic flux conservation above the layer. Repelled by the core current, the reverse current layer accelerates upward so it acts as a piston that drives a compressional perturbation in the coronal regions above. Given a sufficiently fast piston speed, the compressional perturbation becomes a shock that separates from the piston when the piston slows down. Since the model relates the motion of the EUV front to CME properties, the model provides a bound for the core current of an erupting CME. The model is supported and motivated by detailed results from both laboratory experiments and ideal 3D magnetohydrodynamic simulations. Overlaps and differences with other models and spacecraft observations are reported on.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2018

Fast Ion Heating in Transient Collisionless Magnetic Reconnection via an Intrinsic Stochastic Mechanism

Stochastic heating has typically been known to be a powerful ion heating mechanism in the solar wind, atmosphere, and flares. Here, we show that stochastic ion heating is inherent to transient collisionless magnetic reconnection. The explanation exploits the connected nature of electron canonical vorticity to show analytically that the in-plane electric and magnetic fields in a typical reconnection geometry satisfy the condition for stochastic heating of ions. Electron fluid simulations, test ion simulations, and comparisons to experiments all support the existence of this mechanism.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2018

Experimental investigation of the compression and heating of an MHD-driven jet impacting a target cloud

Herein adiabatic compression has been investigated by having an MHD-driven plasma jet impact a gas target cloud. Compression and heating of the jet upon impact were observed and compared to theoretical predictions. Diagnostics for comprehensive measurements included a Thomson scattering system, a fast movie camera, a translatable fiber-coupled interferometer, a monochromator, a visible-light photodiode, and a magnetic probe array. Measurements using these diagnostics provided the time-dependent electron density, electron temperature, continuum emission, line emission, and magnetic field profile. Increases in density and magnetic field and a decrease in jet velocity were observed during the compression. The electron temperature had a complicated time dependence, increasing at first, but then rapidly declining in less than 1 μs which is less than the total compression time. Analysis indicates that this sudden temperature drop is a consequence of radiative loss from hydrogen atoms spontaneously generated via three-body recombination in the high-density compressed plasma. A criterion for how fast compression must be to outrun radiative loss is discussed not only for the Caltech experiment but also for fusion-grade regimes. In addition, the results are analyzed in the context of shocks the effects of which are compared to adiabatic compression.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2018

Reverse Current Model for Coronal Mass Ejection Cavity Formation

In this work, we present a new model for explaining the three-part structure of coronal mass ejections (CMEs). The model proposes that the cavity in a CME forms because a rising electric current in the core prominence induces an oppositely directed electric current in the background plasma; this eddy current is required to satisfy the frozen-in magnetic flux condition in the background plasma. The magnetic force between the inner-core electric current and the oppositely directed induced eddy current propels the background plasma away from the core, creating a cavity and a density pileup at the cavity edge. The cavity radius saturates when an inward restoring force from magnetic and hydrodynamic pressure in the region outside the cavity edge balances the outward magnetic force. The model is supported by (i) laboratory experiments showing the development of a cavity as a result of the repulsion of an induced reverse current by a rising inner-core flux-rope current, (ii) 3D numerical magnetohydrodynamic (MHD) simulations that reproduce the laboratory experiments in quantitative detail, and (iii) an analytic model that describes cavity formation as a result of the plasma containing the induced reverse current being repelled from the inner core. This analytic model offers broad applicability because the predicted cavity widths are relatively independent of both the current injection mechanism and the injection timescale.

79 ASTRONOMY AND ASTROPHYSICS↗