Plasma Physics Seminar
  Spring 2017 Schedule  
February 3, Friday 2PM
ERF 1207, Large Conference Room
Prof. Troy Carter, UCLA
Electromagnetic turbulence and transport in increased-beta LAPD plasmas
February 8, Wednesday 4PM
ERF 1207, Large Conference Room

February 15, Wednesday 4PM
ERF 1207, Large Conference Room

February 22, Wednesday 4PM
ERF 1207, Large Conference Room
Dr. Alfred Mallet, University of New Hampshire
Intermittency and Anisotropy in Alfvenic Turbulence

On length scales larger than the ion gyroradius, the turbulence in a plasma with a strong mean magnetic field may be modelled using the equations of reduced magnetohydrodynamics, which describe the evolution of Alfvenic fluctuations propagating up and down the magnetic field. This (strongly nonlinear) turbulence is (i) anisotropic with respect to the direction of the local mean magnetic field - a steeper spectral index (for example) in the parallel direction compared to the perpendicular. (ii) "aligned" - vector fluctuations in the fields in the perpendicular plane point in the same direction to within a small angle. (iii) highly intermittent - the shape of the probability distributions of many (but not all!) turbulent quantities depends on scale in a non-trivial way. I will discuss the work we have performed connecting these phenomena, and the resulting statistical model for the Alfvenic turbulence we have developed.
March 1, Wednesday 4PM
ERF 1207, Large Conference Room

March 8, Wednesday 4PM
ERF 1207, Large Conference Room
External Review

March 15, Wednesday 4PM
ERF 1207, Large Conference Room
Prof. Ben Maruca, University of Delaware
Thermalization of Solar-Wind Ions via Coulomb Collisions

The solar wind consists of hot, magnetized plasma that supersonically streams from the solar corona into deep space. The ions therein are rarely in thermal equilibrium because Coulomb collisions, through which particles exchange energy, act in the solar wind on timescales comparable to those of its expansion. Even the two most abundant ion-species, protons (ionized hydrogen) and alpha-particles (fully ionized helium), rarely have equal temperatures. In-situ observations from the Wind spacecraft's Faraday cups reveal that, at 1 AU from the Sun, values of the alpha-proton temperature-ratio have a complex, bimodal distribution. To better understand this, a theoretical model was developed to account for collisional and expansion effects and was then applied to the observations to backtrack them from 1 AU to the corona. Remarkably, the extrapolated alpha-proton temperature-ratios show a simple, monomodal distribution. Thus, the bimodality observed in the 1-AU distribution may simply result from the incomplete thermalization of protons and alpha-particles. This result suggests that the relative heating of different ion species in the corona may be more uniform than previously believed.
March 22, Wednesday 4PM
ERF 1207, Large Conference Room
Spring Break - No Seminar

March 29, Wednesday 4PM
ERF 1207, Large Conference Room
Eric Shi, Princeton University
Gyrokinetic continuum simulations of turbulence in open-field-line plasmas

The scrape off layer (SOL) of a tokamak is an edge region in which plasma flows freely along open magnetic field lines towards a material surface, where plasma losses are mediated by a Debye sheath. It is important to develop numerical codes to study the SOL because an accurate prediction for the SOL heat-flux-channel width in ITER is necessary to address major concerns regarding damage to plasma-facing components by the exhaust power. While the use of sophisticated gyrokinetic particle-in-cell and continuum codes for studies in the tokamak core region has become widespread, major code extensions or new codes are required to handle the additional challenges of the edge region. In this talk, I will present results from my thesis work on developing a gyrokinetic continuum code for the simulation of plasma turbulence in a model SOL. I will discuss details about our numerical approach, which is based on discontinuous Galerkin methods, and gyrokinetic sheath model boundary conditions. I will show results from our simulations of turbulence in the Large Plasma Device at UCLA, including the suppression of turbulence by applied flow shear, and results from our recent work in modeling a NSTX-like SOL to investigate turbulent heat-flux spreading.
April 5, Wednesday 4PM
ERF 1207, Large Conference Room
Dr. Colin Komar, NASA/Catholic University
Electron Drift Resonance in the MHD-coupled Comprehensive Inner Magnetosphere Ionosphere model

Encircling Earth are two donut-shaped structures called the radiation belts, which contain vast quantities of electrons and ions. The outer radiation belt exists between 3 and 7 Earth radii, consisting primarily of electrons traveling between 20% and 99.5% the speed of light. The dynamics of the electrons in this region of space are important to understand as orbiting telecommunication satellites are continuously bathed in relativistic electron radiation. Relativistic electrons in the outer radiation belt are highly dynamic and respond to interplanetary solar wind structures interacting with the Earth's magnetic field. A known mechanism of electron radial transport and energization resulting from the drift-resonant interaction with ultra-low frequency (ULF) waves.

To understand the electron drift-resonant interaction with ULF waves, we perform global simulations using conditions that are known to efficiently generate ULF waves in Earth's magnetic field. This talk will present results from simulations modeling the ring current and radiation belt electron populations in the bounce-averaged, kinetic Comprehensive Inner Magnetosphere-Ionosphere (CIMI) code coupled with the Block Adaptive Tree Solar Wind Roe-type Upwind Scheme (BATS-R-US) global magnetospheric magnetohydrodynamic (MHD) code using an idealized ULF wave solar wind density driver. ULF waves generated with 10 minute periods (1.67 mHz frequency) in the MHD model are characterized and the corresponding energization of electrons and radial transport of electron phase space density is presented. The drift-resonant electron energy is determined in the simulation and is consistent with the resonant energy of electrons within a pure dipole magnetic field. I will discuss the success of such a modeling approach, which enables future studies to further investigate the drift-resonant interaction resulting from other ULF wave sources and to additionally understand the complicated interplay of other wave-particle interactions resulting in global electron dynamics in Earth's radiation belts.
April 12, Wednesday 4PM
ERF 1207, Large Conference Room

April 19, Wednesday 4PM
ERF 1207, Large Conference Room
Dr. Luca Comisso, Princeton Plasma Physics Lab
Plasmoid Instability in General Current Sheets

We present the recent formulation of a general theory of the onset and development of the plasmoid instability [1]. We consider the general problem of a reconnecting current sheet that can evolve in time, rather than assuming a fixed Sweet-Parker current sheet. The new theoretical framework has lead to completely new results, which have shown that previously obtained power laws are insufficient to capture the correct properties of the plasmoid instability. The new scaling laws are shown to depend on the initial perturbation amplitude, the characteristic rate of current sheet evolution, and the Lundquist number. The detailed dynamics of the instability is also elucidated, and shown to comprise of a long period of quiescence followed by sudden growth over a short time scale.

[1] L. Comisso, M. Lingam, Y.-M. Huang, A. Bhattacharjee, Phys. Plasmas 23, 100702 (2016)
April 26, Wednesday 4PM
ERF 1207, Large Conference Room
Dr. Leila Mays, NASA Goddard
SEP Modeling Throughout the Inner Heliosphere Based on the ENLIL Global Heliospheric Model

The Community Coordinated Modeling Center (CCMC, serves as a community access point to space environment models and as a hub for collaborative development. CCMC is making an effort to make SEP models available for research and operational users soon. We are making steps towards offering a system to run SEP models driven by a variety of heliospheric models. Understanding gradual SEP events well enough to forecast their properties at a given location requires a realistic picture of the global background solar wind through which the shocks and SEPs propagate. The global 3D MHD WSA-ENLIL model provides a time-dependent background heliospheric description, into which a spherical shaped CME can be inserted. Heliospheric models provide contextual information of conditions in the heliosphere, including the background solar wind conditions and shock structures, and are used as input to SEP models, providing an essential tool for understanding SEP properties. ENLIL simulates solar wind parameters and additionally one can extract the magnetic topologies of observer-connected magnetic field lines and all plasma and shock properties along those field lines. Multipoint observations help constrain simulations and the modeling provides global context for observations. ENLIL "lúlikelihood/all-clr"ÄĚ forecasting maps provide expected intensity, timing/duration of events at locations throughout the heliosphere with "púpossible SEP affected areas"ÄĚ color-coded based on shock strength. ENLIL simulations also drive SEP models such as the Solar Energetic Particle Model (SEPMOD) (Luhmann et al. 2007, 2010) and the Energetic Particle Radiation Environment Module (EPREM) (Schwadron et al., 2010). SEPMOD injects protons onto a sequence of observer field lines at intensities dependent on the connected shock source strength which are then integrated at the observer to approximate the proton flux. EPREM couples with MHD models such as ENLIL and computes energetic particle distributions based on the focused transport equation along a Lagrangian grid of nodes that propagate out with the solar wind. The coupled SEP models allow us to derive the SEP profiles of different types of events throughout the heliosphere. This presentation will demonstrate case studies of SEP event modeling and solar wind simulations at different observers based on WSA-ENLIL+Cone simulations, and compare them with multipoint observations. In addition, an update on the latest model installations at the CCMC and on CCMC-led community-wide model validation projects will be presented.
May 4, Thursday 4PM
ERF 1207, Large Conference Room
Prof. Tünde Fülöp, Chalmers University of Technology, Sweden
Create and control beams in plasmas

The talk describes recent highlights from the activities of the plasma theory group at the Department of Physics at Chalmers University of Technology in Sweden. These include modelling of runaway electrons, neutral driven plasma flows and laser-plasma interaction.
May 10, Wednesday 4PM
ERF 1207, Large Conference Room
Dr. Chris Crabtree, Naval Research Lab
Nonlinear Whistler Mode Physics: Space and Laboratory Applications

Whistler mode waves are an important electromagnetic emission that are observed in phenomenon called chorus in the radiation belts around magnetized planets. Chorus has a frequency that changes as a function of time due to the nonlinear interaction with resonant electrons. These wave modes are thought to be responsible for the energization of radiation belt particles to relativistic energies and thus are important to understand in detail for space weather applications. Recent experiments in the U.S. Naval Research Lab (NRL) Space Physics Simulation Chamber (SPSC) have been performed with an injected helical energetic electron beam. These experiments show complicated frequency-vs-time characteristics that resemble whistler mode chorus in the radiation belts. In this talk, we will describe the first Bayesian spectral analysis for waveform data from space and laboratory measurement. This synergistic analysis of lab and space data has revealed interesting characteristics of the wave modes previously unseen in the in-situ data. This has also inspired a new self-consistent nonlinear Hamiltonian approach to explain the nonlinear physics of the chorus phenomenon.