I will present results of the first self-consistent reacting multi-fluid simulations of magnetic reconnection in a partially ionized plasma, where the ionized and neutral fluids are treated as coupled but distinct. Partially ionized plasma environments where release of magnetic energy and topological reconfiguration of magnetic fields via magnetic reconnection is known or conjectured to take place range from highly collisional, e.g. interstellar medium and lower solar chromosphere with ionization fraction below 0.1%, to weakly collisional, e.g. in the upper solar chromosphere with ionization fraction of 1%-10%. Different plasma processes, such as ionization and recombination, ion neutral interaction via charge-exchange collisions, Hall currents, and radiative losses can become the dominant factors in determining the reconnection rate and the structure of the reconnection region in different parameter regimes. The HiFi multi-fluid modeling framework has been used to implement all of the above processes in a single self-consistent model and to perform 2D simulations of magnetic reconnection under a variety of plasma conditions. In particular, as shown in the adjacent image, we observe the formation of previously predicted non-LTE current layers and explore the associated onset of the secondary plasmoid instability.

Lithium has a number of great advantages in fusion devices:  low recycling, disruption and edge-localized mode suppression, increased confinement time etc.  In particular, the low-recycling means that the temperature at the edge of the fusion device can remain very high since no cold hydrogen from the wall returns. A hot edge means that fusion can occur throughout the cross-section of the device, so the device can be much smaller. Smaller is cheaper, so fusion as an energy source may indeed be feasible. Of course the problem is that lithium melts at such a low temperature, most people have thought it could not be used in a high-heat-flux environment – like an actual fusion energy device. Our work at Illinois has also shown that upward of 20 MW/m2 heat fluxes can be removed from a divertor plate using lithium-infused metal trenches (LiMIT) without significant evaporation. In this scheme the lithium creates a self-driven flow across the divertor plate utilizing the Thermo-Electric magnetohydrodynamic force.  The divertor heat stripe hits LiMIT causing the top of the region with the lithium flow to get hotter than the regions below it.  This causes a thermo-electric current in the lithium that goes in the vertical direction.  Since the magnetic field is in the toroidal direction there will be a force on the lithium in the radial direction along the trenches.  Even without active cooling, the temperature gradient will still be established during the shot due to thermal inertia.  What makes this approach attractive is that it is self limiting.  The hotter it gets, the faster the lithium flows, which in turn cools the structure.  With no heat flux the lithium is stationary.   We have demonstrated this effect in the Solid/Liquid Divertor Experiment (SLiDE) device at Illinois and in the the HT-7 tokamak in China. Experiments are planned in Europe and at the Princeton Plasma Physics Laboratory.

Flux ropes form basic building blocks for magnetic dynamics, are analogues of macroscopic magnetic field lines, and are irreducibly three dimensional (3D).

We have used the Reconnection Scaling Experiment (RSX) to study flux ropes, and have found many new features involving unexpected 3D dynamics, kink instability driven reconnection, non linearly stable but kinking flux ropes, large flows, and shear flow induced magnetic fields. For example the onset threshold for external kink instability depends upon boundary conditions that can be adjusted between line tied and free. These two boundary conditions could correspond to CME eruption flux ropes that are anchored ("line tied") at one end to solar coronal holes while the other end remains "free" to drift as magnetic clouds in the solar system. The dynamics of two flux ropes form a fairly simple 3D system that allowed the first identification of how a plasma instability (in this case the kink) initiated magnetic reconnection. When there is significant guide magnetic field, flux ropes bounce off each other much of the time instead of merging and reconnecting. As we assemble large 3D experimental data sets for density, temperature, pressure, magnetic field, and current density we observe local violations of MHD, and strongly sheared flow and fields. We show data where magnetic field is generated from sheared electron fluid flow. Movies from 3D experimental data also show that MHD forces fail to balance, i.e. JxB - grad P_e does not vanish at the 30% level, and we evaluate some candidates for the missing physics. We intend to model these 3D data with a PIC code (VPIC), 2 fluid code (HiFi) and possibly other hybrid approaches, and solicit collaborators.

*DOE Fusion Energy Sciences DE-AC52-06NA25396, NASA Geospace NNHIOA044I, Basic

Magnetic reconnection transforms magnetic field energy into particle kinetic energy; it may be the mechanism for accelerating particles to high enough energies to emit energetic synchrotron radiation, which is observed in various astrophysical objects, including pulsars, active Galactic nuclei, and gamma-ray bursts. Using 2D particle-in-cell simulations of relativistic, radiating, pair plasma reconnection, this work demonstrates that reconnection accelerates particles, bunching and focusing the most energetic particles into a narrow beam that wiggles in the plane of the reconnection layer. This beaming leads to brief, intense flares of high-energy photons when the beam crosses the line of sight. A newly-developed PIC code, which includes the radiation reaction, has recently shed new light (so to speak) on the picture of relativistic reconnection under strong synchrotron cooling. The most energetic particles feel very little radiative losses while they are accelerated in a straight line deep inside the layer where the electric field exceeds the magnetic field. Eventually, the particles get kicked out of the layer and subsequently radiate >160 MeV synchrotron radiation, which would be impossible to explain with ideal MHD-based models of particle acceleration. This result is essential in understanding the origin of >100 MeV gamma-ray flares observed in the Crab Nebula.

Recent advances in imaging present tantalizing prospects for diagnosing fluctuations in laboratory plasmas. Commercially available cameras now allow recording of large arrays of simultaneous data points on relevant time scales. In this talk, I will present the status of our ongoing study of imaging-based plasma turbulence measurements in the Controlled Shear Decorrelation Experiment (CSDX) at the University of California, San Diego. CSDX is a linear machine producing dense plasmas relevant to the tokamak edge (T_e ~ 3 eV, n_e ~ 10^13/cc). Electrostatic fluctuations are measured with Langmuir probes in concert with visible-light imaging over a range of plasma parameters. Comparisons between probe and imaging data constrain operational limits for both diagnostics. Drift like modes are observed and characterized using an image correlation technique. Time-resolved velocity fields are obtained using a pattern-matching algorithm, allowing access to flow dynamics across the plasma radius. Current work includes measurements of wave dispersion, velocity profiles, and probe/imaging relationships.

Collimated, relativistic outflows (jets) have been extensively observed to originate from supermassive black holes in the centers of galaxies. When the jet flow is moving close to our line of sight (the so called "blazar"), it results in an extremely bright, broadband and variable source of electromagnetic radiation. The mechanisms responsible for the energetic particles behind the jet emission remain poorly understood. The recent observations of powerful, minute timescale flares from  several blazars pose serious challenges to theoretical models for the blazar emission. The fast flaring requires compact regions in the jet that boost their emission towards the observer at an extreme Doppler factor of delta~50, while for TeV photons to avoid annihilation with softer radiation at the source, the flares must originate far from the black hole (at multi light-year distance). In this talk, I will introduce the magnetic reconnection model for the blazar flaring. Focusing on the inherently time-dependent aspects of the process of magnetic reconnection, I argue that, for the physical conditions prevailing in blazar jets, the reconnection layer fragments leading to the formation a large number of plasmoids. Occasionally a plasmoid grows to become a large, ``monster'' plasmoid.  I show that radiation emitted from the reconnection event can account for  the observed ``envelope'' of ~day-long blazar activity while radiation from monster plasmoids can power the fastest observed TeV flares. The model is applied to several blazars with observed fast flaring. The inferred distance of the dissipation ("blazar") zone is R~1-3 light years. The required magnetization of the jet at this distance is sigma=B^2/4 pi rho c^2~ a few.

Global electromagnetic gyrokinetic simulations show the existence of near threshold conditions, for both a high-n Kinetic Ballooning Mode (KBM) and an intermediate-n kinetic version of Peeling-Ballooning Mode (PBM). The KBM and the PBM have been used to constrain the EPED model [1]. Global gyrokinetic simulations show that the H-mode pedestal, just prior to the onset of the Edge Localized Mode (ELM), is very near the KBM threshold. Two DIII-D experimental discharges are studied, one reporting KBM features in fluctuation measurements [2]. Simulations find that in addition to the high-n KBM, an intermediate-n electromagnetic mode is unstable. This kinetic version of the PBM has phase velocity in the electron diamagnetic direction, but otherwise has features similar to the MHD PBM. When the magnetic shear is reduced in a narrow region near the steep pressure gradient, the intermediate-n kinetic PBM'' is stabilized, while the high-n KBM becomes the most unstable mode. Global simulation results of the KBM compare favorably with flux tube simulations. The KBM transitions to an unstable electrostatic ion mode as the plasma beta is reduced. The intermediate-n "kinetic peeling ballooning mode'' is sensitive to the q-profile and only seen in global electromagnetic simulations. Collisions increase the KBM critical beta and growth rate. These results indicate that an improved pedestal model should include, in detail, any corrections to the bootstrap current, and any other equilibrium effects that might reduce the local magnetic shear. The bootstrap current may flatten the q-profile in the steep gradient region[3]. Simulations are carried out using the global electromagnetic GEM code, including kinetic electrons, electron-ion collisions and the effects of realistic magnetic geometry, including the MHD kink term. In addition to global linear analysis, nonlinear simulations will be reported showing that, while the equilibrium radial electric field has a weak effect on the linear growth rate, it has a larger stabilizing effect nonlinearly.

[1] P. Snyder, et al., Phys. Plasmas 16 056118 (2009).

[2] Z. Yan, et al., Phys. Plasmas 18 056117 (2011).

[3] J. Callen, et al. Nucl. Fusion 50 064004 (2010).

A plasma in which the inter-particle spacing approaches the thermal de Broglie wavelength must be subject to statistical effects due to Pauli exclusion. Also, many familiar plasma phenomena could be modified on such length scales because of the Heisenberg uncertainty principle. The question of how to model quantum effects in plasmas pushes the envelope of our knowledge of plasma physics and applies the well-established principles of quantum mechanics in a novel context. We will discuss potential quantum effects in plasmas and the possibility of real systems exhibiting these effects, followed by an overview of how to model such plasmas. In addition, a mean-field quantum kinetic model will be applied to the case of unmagnetized Fermi-Dirac equilibrium plasmas with arbitrary degree of degeneracy. Linear dispersion relations for electrostatic waves, including Landau damping, will be derived and analyzed. We will conclude with a discussion of possible future directions within this area of research.

The physics capabilities of modern gyrokinetic microstability codes, e.g. GEM, GYRO, and GS2, are now so extensive that they can be expected to predict energy and particle transport in tokamaks. Therefore, they are being validated by comparing their results with transport measurements in existing devices. However, as a prerequisite, they must be verified, i.e., demonstrate that they correctly solve the underlying gyrokinetic-Maxwell equations. Because of the complexity of actual tokamak plasmas, this cannot be accomplished using purely analytic approaches. Instead, verification must rely on benchmarking (comparing different code results for identical plasmas and physics) - the premise being that all the codes would not produce the same erroneous results. We will present benchmarking exercises for a low-power DIII-D discharge and a high-power Alcator C-Mod discharge at the mid-radius of the plasma, both omitting and including equilibrium ExB flow shear. This benchmarking includes magnetic fluctuations, plasma shaping, kinetic electrons, collisions, and one impurity. In addition, we compare linear results among the three codes for the steep-gradient edge region of a DIII-D plasma. These three disparate plasmas and radial locations serve to test the codes over a broad range of plasma parameters.

The turbulent cross helicity (velocity--magnetic-field correlation in turbulence) coupled with the large-scale vortical motion leads to the turbulent electromotive force aligned with the mean vortical motion. This is called the cross-helicity effect in magnetic-field induction, and is in remarkable contrast with the well-known helicity or alpha effect, where the induced electromotive force is aligned with the mean magnetic field. The cross-helicity effects have been investigated in several astro/geophysical and fusion plasma phenomena. Some interesting features of the cross-helicity effects will be presented with special reference to the turbulent magnetic reconnection. It is stressed that the combination of the transport enhancement and suppression due to turbulence plays an important role in magnetic reconnection.

Reconnection is a process of intense localised phenomena. Particularly active are the regions of transition between fresh plasma with unreconnected field lines and processed plasma embedded in reconnected field lines. These regions are characterised by a plurality of possible drivers of instability: flows, shears, anisotropies. We will review the results obtained by the MMS theory team at colorado in collaboration with the center of plasma astrophysics (CPA) at the KU Leuven in Belgium. We will identify several instances of waves and instabilities measured in simulations and try to discuss possible causes. The format will be truly seminarial, open to discussion and suggestion from the attendees.

Surfaces of airless bodies and spacecraft in space are exposed to a variety of charging environments such that a balance of plasma determines the surface charge. Photoelectron emission due to intense solar UV radiation is the dominant charging process on sunlit surfaces, and to first order this results in a positive surface potential, with a photoelectron sheath immediately above the surface. Due to experimental constraints, little laboratory work has been done to characterize this type of plasma. I will present the results of Langmuir probe measurements above both conducting and insulating surfaces in vacuum, and compare some of these measurements with the results from 1D PIC-code simulations to gain a greater understanding of the sheath physics.

Studies of quantum mechanics at intermediate scales between microscopic and mesoscopic regimes have recently focused on the observation of quantum coherent phenomena in optomechanical systems. We demonstrate spectroscopy and thermometry of individual motional modes in a mesoscopic 2D ion array using entanglement-induced decoherence as a method of transduction. Our system is a ~400 µm-diameter planar crystal of several hundred 9Be+ ions exhibiting complex plasma oscillations (i.e. drumhead modes) in the confining potential of a Penning trap. Exploiting precise control over the 9Be+ valence electron spins, we apply a homogeneous spin-dependent optical dipole force to excite arbitrary transverse modes with an effective wavelength approaching the interparticle spacing (~20 µm). Center-of-mass ion plane displacements of ~120 +/- 20 pm are detected via entanglement of spin and motional degrees of freedom.

The four-satellite Magnetospheric MultiScale (MMS) mission, scheduled for launch in 2014, will be able to measure full 3D electron velocity distributions over time intervals as short as 30ms. MMS therefore has the potential of resolving distributions associated with magnetic reconnection in Earth's magnetotail that are effectively local (i.e., for which the motion of the reconnection environment relative to the satellite can be neglected to lowest order). In this talk, I will present the results of implicit-PIC simulations of magnetotail reconnection, with the focus on electron dynamics near the x-point and along branches of the magnetic separatrix. In addition to electron velocity distributions averaged over times resolvable by MMS, the trajectories of selected sets of tagged simulation particles will be presented. These trajectories provide insights into the origin of nonthermal features in the velocity distributions, including the bimodal signatures of (saturated) streaming instabilities that produce electron phase-space holes near the separatrix. Bipolar electric-fields associated with electron holes have been previously observed (e.g., by Cluster) in the vicinity of magnetotail reconnection.

Two sounding rockets were launched in October 2011 into the polar mesosphere, each with a mass analyzer for aerosol particles for the purpose of detecting charged meteor dust. The payloads also carried Faraday rotation antennas and an array of plasma probes for determining electron and ion densities and the payload charging potential. The launches were from the Andøya Rocket Range, Norway.. The 11 October launch was at night (21:50 UT) with the sun below the horizon by about 16 degrees at 100 km altitude and the 13 October launch was in daylight (13:50 UT) with the sun about equally above. Data from both launches show a negative charge layer in the mass range expected for meteoric dust. The nighttime data show negatively charged particles with masses in the range 500 - 2,000 amu, 2,000-8,000 amu, and 8,000 – 20,000 amu, each with density ~300 cm-3. These mass ranges occur together in a layer spanning approximately 77 - 93 km on the upleg and downleg of the flight. Faraday rotation data show that the electron density rises from about 103 cm-3 to about 3 x 104 cm-3 in the same altitude range, hence the dust particles carry only a small fraction of the total charge. The 13 October daytime data show a similar negative charge layer from approximately 80 - 86 km on the upleg and downleg. The ambient electron density in the region of the daytime layer is about half that in the nighttime layer. The daytime data do not show a positively charged layer that would indicate photoelectric charging of the dust.

Equilibrium reconstruction is the process of inferring the parameters characterizing an MHD equilibrium from experimental observations. It is used extensively for axisymmetric plasmas such as those in tokamaks and reversed field pinches, and is the primary basis for reconciling measurements, and assessing plasma stability and transport. For non-axisymmetric plasmas, such as those in stellarators and quasi-helical states of reversed-field pinches, standard axisymmetric equilibrium reconstruction codes based on the Grad-Shafranov equation are inadequate. I will report on progress and results from the V3FIT non-axisymmetric equilibrium reconstruction code.

Magnetic reconnection is the driver of explosive phenomena in both laboratory and astrophysical contexts.  Sawtooth crashes in fusion experiments and solar flares are prominent examples of fascinating events where reconnection plays a key role.

Over the past few years, the basic understanding of this fundamental process has undergone profound changes. The validity of the most basic, and widely accepted, reconnection paradigm -- the famous Sweet-Parker (SP) model, which predicts that, in MHD, reconnection is extremely slow, its rate scaling as S^{-1/2}, where S is the Lundquist number of the system has been called into question as it was analytically demonstrated that, for S>>1, SP-like current sheets are violently unstable to the formation of a large number of secondary islands, or plasmoids. Subsequent numerical work has confirmed the validity of the linear theory, and shown that plasmoids quickly grow to become wider than the thickness of the original SP current sheet, thus effectively changing the underlying reconnection geometry. Ensuing numerical work has revealed that the process of plasmoid formation, coalescence and ejection from the sheet drastically modifies the steady state picture assumed by Sweet and Parker, and leads to the unexpected result that MHD reconnection is actually fast (i.e., independent of S). In this talk, we review these recent developments and present a novel theoretical model of MHD reconnection in high Lundquist number plasmas. The results of a detailed numerical study are presented, validating the main predictions of this theory, which we thus suggest as valid replacement of the SP paradigm.

I will discuss drift and Hall effects on tearing modes, island evolution, and relaxation in pinch configurations. An unexpected new result is a drift effect that reduces the growth rate of the tearing mode where the drift is proportional to gradB and poloidal curvature [King et al., Phys. Pl. 2011]. Although computations with the NIMROD code use a non-reduced fluid model, analytics with tearing ordering show this drift is manifest through contributions from ion gyroviscosity. Nonlinear single helicity computations with experimentally-relevant parameters show that the warm-ion gyroviscous effects reduce saturated island widths. In contrast to diamagnetic drift-tearing where the associated pressure-profile gradient is flattened nonlinearly, the gradB and poloidal-curvature profiles are largely unaffected by magnetic islands.

Computations with multiple modes similar to reversed-field pinch discharges show that both MHD and Hall dynamos contribute to relaxation events. The presence of Hall dynamo implies a fluctuation-induced Maxwell stress, and the simulation results show net transport of parallel momentum. The magnitude of force densities from the Maxwell stress and a competing Reynolds stress, and changes in the parallel flow profile are within a factor of 1.5 of measurements [Kuritsyn et al., Phys. Pl. 2009] during a relaxation event in the Madison Symmetric Torus.

The Crab Nebula was formed after the collapse of a star recorded by Chinese astronomers in 1054 AD. The nebula is filled with relativistic electron-positron pairs injected by a powerful pulsar, and radiates at all wavelengths, from radio to very-high energy gamma rays. The gamma-ray space telescopes Agile and Fermi recently detected bright day-long flares above 100 MeV energy photons, presumably of synchrotron origin. This discovery implies that electrons and positrons are accelerated to PeV energies in the nebula, the highest energy particles ever attributed to a specific astrophysical object. The existence of these particles challenges the most established models of particle acceleration. In this talk, I will argue that the flares could be powered by magnetic reconnection in the nebula. Relativistic test-particle simulations show that the particles are naturally focused into a thin fan beam, and accelerated deep inside the reconnection layer. I will show that this scenario provides a viable explanation for the gamma-ray flares in the Crab Nebula.

At the Colorado Center for Lunar Dust and Atmospheric Studies, we are building a 3MV dust accelerator to study dusty plasmas which occur naturally on the lunar surface. Dust accelerators are an important research tool that can be used to study many impact phenomena (i.e., impact generated plasma, ejecta composition), as well as to test instruments that have to withstand the harsh environment of outer space. I will present a summary of science that can be done with a dust accelerator, as well as the tools that can be developed using a dust accelerator, and then discuss the design and performance of the accelerator currently being built here at the University of Colorado.