Luca Comisso

Luca Comisso
Columbia University | CU · Department of Astronomy and Astrophysics

PhD

About

51
Publications
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1,070
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Introduction
I work at Columbia University on problems related to laboratory, space, and astrophysical plasmas. I am interested in a wide variety of topics of central importance in modern plasma physics and astrophysics such as plasma turbulence, magnetic reconnection, energetic particles, physics of stellar coronae and winds, plasma confinement and control, computational physics, connections between laboratory, space and astrophysical plasmas.

Publications

Publications (51)
Article
Full-text available
A general theory of the onset and development of the plasmoid instability is formulated by means of a principle of least time. The scaling relations for the final aspect ratio, transition time to rapid onset, growth rate, and number of plasmoids are derived, and shown to depend on the initial perturbation amplitude $({\hat w}_0)$, the characteristi...
Article
Full-text available
Due to its ubiquitous presence, turbulence is often invoked to explain the origin of nonthermal particles in astrophysical sources of high-energy emission. With particle-in-cell simulations, we study decaying turbulence in magnetically-dominated (or equivalently, "relativistic") pair plasmas. We find that the generation of a power-law particle ener...
Article
Full-text available
Magnetized turbulence and magnetic reconnection are often invoked to explain the nonthermal emission observed from a wide variety of astrophysical sources. By means of fully-kinetic 2D and 3D particle-in-cell simulations, we investigate the interplay between turbulence and reconnection in generating nonthermal particles in magnetically-dominated (o...
Article
Full-text available
The ideal magnetohydrodynamic theorem on the conservation of the magnetic connections between plasma elements is extended to non-ideal relativistic plasmas in curved spacetime. The existence of generalized magnetofluid connections that are preserved by the plasma dynamics is formalized by means of a covariant connection equation that includes diffe...
Article
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Spinning black holes store rotational energy that can be extracted. When a black hole is immersed in an externally supplied magnetic field, reconnection of magnetic field lines within the ergosphere can generate negative energy (relative to infinity) particles that fall into the black hole event horizon while the other accelerated particles escape...
Preprint
Full-text available
Collisionless, magnetized turbulence offers a promising framework for the generation of non-thermal high-energy particles in various astrophysical sites. Yet, the detailed mechanism that governs particle acceleration has remained subject to debate. By means of 2D and 3D PIC, as well as 3D (incompressible) magnetohydrodynamic (MHD) simulations, we t...
Preprint
Full-text available
Non-collisional current sheets that form during the nonlinear development of magnetic reconnection are characterized by a small thickness, of the order of the electron skin depth. They can become unstable to the formation of plasmoids, which allows the magnetic reconnection process to reach high reconnection rates. However, no work has so far inves...
Article
The plasmoid formation in collisionless plasmas, where magnetic reconnection within turbulence may take place driven by the electron inertia, is analyzed. We find a complex situation in which, due to the presence of strong velocity shears, the typical plasmoid formation, observed to influence the energy cascade in the magnetohydrodynamic context, h...
Article
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Nature’s most powerful high-energy sources are capable of accelerating particles to high energy and radiating it away on extremely short timescales, even shorter than the light crossing time of the system. It is yet unclear what physical processes can produce such an efficient acceleration, despite the copious radiative losses. By means of radiativ...
Article
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Synchrotron emission from astrophysical nonthermal sources usually assumes that the emitting particles are isotropic. By means of large-scale two- and three-dimensional particle-in-cell simulations, we demonstrate that the dissipation of magnetically dominated ($\sigma_0\gg1$) turbulence in pair plasmas leads to strongly anisotropic particle distri...
Article
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Analytic scaling relations are derived for a phenomenological model of the plasmoid instability in an evolving current sheet, including the effects of reconnection outflow. Two scenarios are considered, where the plasmoid instability can be triggered either by an injected initial perturbation or by the natural noise of the system (here referred to...
Article
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We outline a model of the Crab Pulsar Wind Nebula with two different populations of synchrotron emitting particles, arising from two different acceleration mechanisms: (i) Component-I due to Fermi-I acceleration at the equatorial portion of the termination shock, with particle spectral index p I ≈ 2.2 above the injection break corresponding to γ wi...
Article
We analytically explore the effects of the gravitational electromotive force on magnetic reconnection around Schwarzschild black holes through a generalized general-relativistic magnetohydrodynamic model that retains two-fluid effects. It is shown that the gravitational electromotive force can couple to collisionless two-fluid effects and drive mag...
Article
Full-text available
The plasmoid instability in evolving current sheets has been widely studied due to its effects on the disruption of current sheets, the formation of plasmoids, and the resultant fast magnetic reconnection. In this Letter, we study the role of the plasmoid instability in two-dimensional magnetohydrodynamic (MHD) turbulence by means of high-resolutio...
Article
Full-text available
This paper addresses one aspect of the problem of the suppression of tearing mode magnetic islands by electron cyclotron current drive (ECCD) injection, formulating the problem as the converse of a forced reconnection problem. New physical conditions are discussed which should be considered in the technical approach towards a robust control strateg...
Article
Full-text available
Magnetohydrodynamic turbulence and magnetic reconnection are ubiquitous in astrophysical environments. In most situations, these processes do not occur in isolation, but interact with each other. This renders a comprehensive theory of these processes highly challenging. Here, we propose a theory of magnetohydrodynamic turbulence driven at large sca...
Article
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Magnetic reconnection in curved spacetime is studied by adopting a general relativistic magnetohydrodynamic model that retains collisionless effects for both electron-ion and pair plasmas. A simple generalization of the standard Sweet-Parker model allows us to obtain the first order effects of the gravitational field of a rotating black hole. It is...
Article
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The Principle of Maximum Entropy, a powerful and general method for inferring the distribution function given a set of constraints, is applied to deduce the overall distribution of 3D plasmoids (flux ropes/tubes) for systems where resistive MHD is applicable and large numbers of plasmoids are produced. The analysis is undertaken for the 3D case, wi...
Article
Full-text available
The ideal MHD theorem on the conservation of the magnetic connections between plasma elements is generalized to relativistic plasmas in curved spacetime. The connections between plasma elements, which are established by a covariant connection equation, display a particularly complex structure in curved spacetime. Nevertheless, it is shown that thes...
Presentation
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Invited talk on the general theory of the plasmid instability.
Article
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The disruptive collapse of the current sustained equilibrium of a tokamak is perhaps the single most serious obstacle on the path toward controlled thermonuclear fusion. The current disruption is generally too fast to be identified early enough and tamed efficiently, and may be associated with a variety of initial perturbing events. However, a comm...
Article
Full-text available
The plasmoid instability has revolutionized our understanding of magnetic reconnection in astrophysical environments. By preventing the formation of highly elongated reconnection layers, it is crucial in enabling the rapid energy conversion rates that are characteristic of many astrophysical phenomena. Most of the previous studies have focused on S...
Article
Full-text available
The scaling of plasmoid instability maximum linear growth rate with respect to Lundquist number $S$ in a Sweet-Parker current sheet, $\gamma_{max}\sim S^{1/4}$, indicates that at high $S$, the current sheet will break apart before it approaches the Sweet-Parker width. Therefore, a proper description for the onset of the plasmoid instability must in...
Presentation
Full-text available
Invited seminar on relativistic magnetic reconnection
Article
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A new formulation of the plasma resistivity that stems from the collisional momentum-transfer rate between electrons and ions is presented. The resistivity computed herein is shown to depend not only on the temperature and density but also on all other polynomial velocity-space moments of the distribution function, such as the pressure tensor and h...
Article
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The magnetic reconnection process is analyzed for relativistic magnetohydrodynamical plasmas around rotating black holes. A simple generalization of the Sweet-Parker model is used as a first approximation to the problem. The reconnection rate, as well as other important properties of the reconnection layer, have been calculated taking into account...
Article
This paper reviews key aspects of the problem of magnetic islands control by electron cyclotron current drive in fusion devices. On the basis of the ordering of the basic spatial and time scales of the magnetic reconnection physics, we present the established results, highlighting some of the open issues posed by the small-scale structures that typ...
Article
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Numerical simulations have consistently shown that the reconnection rate in certain collisionless regimes can be fast, of the order of $0.1 v_A B_u$, where $v_A$ and $B_u$ are the Alfvén speed and the reconnecting magnetic field upstream of the ion diffusion region. This particular value has been reported in myriad numerical simulations under dispa...
Article
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An important problem in plasma physics is the lack of an accurate and complete description of Coulomb collisions in associated fluid models. To shed light on the problem, this Letter introduces an integral identity involving the multivariate Hermite tensor polynomials and presents a method for computing exact expressions for the fluid moments of th...
Article
Full-text available
The plasmoid instability in visco-resistive current sheets is analyzed in both the linear and nonlinear regimes. The linear growth rate and the wavenumber are found to scale as $S^{1/4} (1+P_m)^{-5/8}$ and $S^{3/8} (1+P_m)^{-3/16}$ with respect to the Lundquist number $S$ and the magnetic Prandtl number $P_m$. Furthermore, the linear layer width is...
Article
Full-text available
We extend the magnetic connection theorem of ideal magnetohydrodynamics to nonideal relativistic pair plasmas. Adopting a generalized Ohm's law, we prove the existence of generalized magnetofluid connections that are preserved by the plasma dynamics. We show that these connections are related to a general antisymmetric tensor that unifies the elect...
Article
Full-text available
Recent progress in the understanding of how externally driven magnetic reconnection evolves is organized in terms of parameter space diagrams. These diagrams are constructed using four pivotal dimensionless parameters: the Lundquist number S, the magnetic Prandtl number P_m, the amplitude of the boundary perturbation \hat \Psi_0, and the perturbati...
Article
Full-text available
A fundamental problem of forced magnetic reconnection has been solved taking into account the plasmoid instability of thin reconnecting current sheets. In this problem, the reconnection is driven by a small amplitude boundary perturbation in a tearing-stable slab plasma equilibrium. It is shown that the evolution of the magnetic reconnection proces...
Article
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The concept of magnetic connections is extended to nonideal relativistic magnetohydrodynamical plasmas. Adopting a general set of equations for relativistic magnetohydrodynamics including thermal-inertial, thermal electromotive, Hall and current-inertia effects, we derive a new covariant connection equation showing the existence of generalized magn...
Article
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The formation of plasmoid chains is explored for the first time within the context of the Taylor problem, in which magnetic reconnection is driven by a small amplitude boundary perturbation in a tearing-stable slab plasma equilibrium. Numerical simulations of a magnetohydrodynamical model of the plasma show that for very small plasma resistivity an...
Article
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The magnetic reconnection process is studied in relativistic pair plasmas when the thermal and inertial properties of the magnetohydrodynamical fluid are included. We find that in both Sweet-Parker and Petschek relativistic scenarios there is an increase of the reconnection rate owing to the thermal-inertial effects, both satisfying causality. To c...
Article
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The magnetic island evolution under the action of a current generated externally by electron cyclotron wave beams is studied using a reduced resistive magnetohydrodynamics plasma model. The use of a two-dimensional reconnection model shows novel features of the actual nonlinear evolution as compared to the zero-dimensional model of the generalized...
Article
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The first detailed comparison between gyrokinetic and gyrofluid simulations of collisionless magnetic reconnection has been carried out. Both the linear and nonlinear evolution of the collisionless tearing mode have been analyzed. In the linear regime, we have found a good agreement between the two approaches over the whole spectrum of linearly uns...
Article
Full-text available
The influence of a velocity jet, directed along a magnetic guide field, on the linear evolution of collisionless reconnection is investigated both analytically and numerically. The analysis covers both the small and large Δ′ regimes, with Δ′ indicating the standard tearing stability parameter, and is carried out, in slab geometry, by means of a red...
Article
Full-text available
The stabilization of tearing magnetic islands by means of localized current driven by electron cyclotron waves, requires optimizing the efficiency of the injected helical current. The problem is conventionally addressed using 0-D model of the (generalized) Rutherford equation to find the dependence in terms of the island width, wave beam width and...
Article
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The linear and nonlinear evolution of magnetic reconnection in collisionless high-temperature plasmas with a strong guide field is analyzed on the basis of a two-dimensional gyrofluid model. The linear growth rate of the reconnecting instability is compared to analytical calculations over the whole spectrum of linearly unstable wave numbers. In the...
Article
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The nonlinear evolution of collisionless magnetic reconnection in the presence of a strong guide field is analyzed on the basis of a gyrofluid model for compressible plasmas. It is found that, in a certain regime of plasma parameters, ion gyration contributes to generate two distinctive nonlinear acceleration phases of the growth rate. Furthermore,...
Article
Full-text available
The magnetic island evolution under the action of an externally current generated by electron cyclotron (ECCD) wave beams is studied using a reduced resistive magnetohydrodynamics (RRMHD) plasma model. We found interesting and somewhat unexpected features of the actual nonlinear 2-D evolution of the magnetic perturbation depending on the injection...
Article
Full-text available
Ion Larmor radius effects on collisionless magnetic reconnection in the presence of a guide field are investigated by means of numerical simulations based on a gyrofluid model for compressible plasmas. Compressibility along the magnetic field is seen to favour the distribution of ion guiding center density along the neutral line, rather than along...
Article
Ion temperature plays an important role in collisionless magnetic reconnection, where it can both raise the stability threshold and, once the mode is unstable, accelerate its growth. We have investigated magnetic reconnection with a recently constructed noncanonical Hamiltonian formulation of a four-field electromagnetic gyrofluid model. The new mo...
Article
A four‐field model of magnetic reconnection for tearing modes with m>1 in the neoclassical ordering is studied numerically in its nonlinear evolution, that highlights the effects of diamagnetism and of pressure anisotropy. The effects on growth rates and saturation width are compared with known results.
Article
Full-text available
Time-dependent effects of a radiofrequency driven current on the magnetic island are investigated by applying a new extended magnetohydrodynamics nonlinear model. New basic problems are pointed out, together with results that shed light on crucial questions for the control of neoclassical tearing modes. An interpretation of the numerical results is...
Article
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The design of means to counteract robustly the classical and neoclassical tearing modes in a tokamak by localized injection of an external control current requires an ever growing understanding of the physical process, beyond the Rutherford-type zero-dimensional models. Here a set of extended magnetohydrodynamic nonlinear equations for four continu...
Conference Paper
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The main objective of this work consists in the application of an appropriate set of Extended Magnetohydrodynamics (ExMHD) nonlinear equations for four continuum fields (poloidal magnetic flux ψ , electron pressure e p , ion flow velocity i v , and ion flow vorticity U) to study the response of the reconnecting modes in low collisionality regimes t...
Article
Full-text available
In tokamaks magnetic islands arise from an unstable process of tearing and reconnecting of helical field lines across rational surfaces. After a linear stage the magnetic instability develops through three characteristic nonlinear stages where increasingly complex topological alterations occur in the form of the magnetic islands. The problem of res...

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