Article
In situ discovery of an electrostatic potential, trapping electrons and mediating fast reconnection in the Earth's magnetotail.
Massachusetts Institute of Technology, Plasma Science Fusion Center, Cambridge, Massachusetts 02139, USA.
Physical Review Letters (Impact Factor: 7.73). 02/2005; 94(2):025006. DOI: 10.1103/PhysRevLett.94.025006 Source: PubMed

Article: The incomplete plasma dispersion function: properties and application to waves in bounded plasmas
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ABSTRACT: The incomplete plasma dispersion function is a generalization of the plasma dispersion function in which the defining integral spans a semiinfinite, rather than infinite, domain. It is useful for describing the linear dielectric response and wave dispersion in nonMaxwellian plasmas when the distribution functions can be approximated as Maxwellian over finite, or semiinfinite, intervals in velocity phasespace. A ubiquitous example is the depleted Maxwellian electron distribution found near boundary sheaths or double layers, where the passing interval can be modeled as Maxwellian with a lower temperature than the trapped interval. The depleted Maxwellian is used as an example to demonstrate the utility of using the incomplete plasma dispersion function for calculating modifications to wave dispersion relations.Physics of Plasmas 01/2013; 20(1). · 2.38 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: In the mergingcompression method of plasma startup, two fluxropes with parallel toroidal current are formed around invessel poloidal field coils, before merging to form a spherical tokamak plasma. This startup method, used in the MegaAmpere Spherical Tokamak (MAST), is studied as a high Lundquist number and low plasmabeta magnetic reconnection experiment. In this paper, 2D fluid simulations are presented of this merging process in order to understand the underlying physics, and better interpret the experimental data. These simulations examine the individual and combined effects of tightaspect ratio geometry and twofluid physics on the merging. The ideal selfdriven fluxrope dynamics are coupled to the diffusion layer physics, resulting in a large range of phenomena. For resistive MHD simulations, the fluxropes enter the sloshing regime for normalised resistivity eta < 1.e5. In HallMHD three regimes are found for the qualitative behaviour of the current sheet, depending on the ratio of the current sheet width to the ionsound radius. These are a stable collisional regime, an open Xpoint regime, and an intermediate regime that is highly unstable to tearingtype instabilities. In toroidal axisymmetric geometry, the final state after merging is a MASTlike spherical tokamak with nested fluxsurfaces. It is also shown that the evolution of simulated 1D radial density profiles closely resembles the Thomson scattering electron density measurements in MAST. An intuitive explanation for the origin of the measured density structures is proposed, based upon the results of the toroidal HallMHD simulations.Physics of Plasmas 12/2013; 20(12):122302. · 2.38 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: A linear experiment dedicated to the study of driven magnetic reconnection is presented. The new device (VINETA II) is suitable for investigating both collisional and near collisionless reconnection. Reconnection is achieved by externally driving magnetic field lines towards an Xpoint, inducing a current in the background plasma which consequently modifies the magnetic field topology. Owing to the open field line configuration of the experiment, the current is limited by the axial sheath boundary conditions. A plasma gun is used as an additional electron source in order to counterbalance the charge separation effects and supply the required current. Two drive methods are used in the device. First, an oscillating current through two parallel conductors drive the reconnection. Second, a stationary Xpoint topology is formed by the parallel conductors, and the drive is achieved by an oscillating current through a third conductor. In the first setup, the magnetic field of the axial plasma current dominates the field topology near the Xpoint throughout most of the drive. The second setup allows for the amplitude of the plasma current as well as the motion of the flux to be set independently of the Xpoint topology of the parallel conductors.The Review of scientific instruments 02/2014; 85(2):023501. · 1.52 Impact Factor
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