Plasma Physics Seminar
 
   
  Spring 2024 Schedule  
 
January 24th, Wed. 3:30PM
ERF 1207, Large Conference Room
Open


January 31st, Wed. 3:30PM
ERF 1207, Large Conference Room
Open


February 7th, Wed. 3:30PM
ERF 1207, Large Conference Room
Open


February 14th, Wed. 3:30PM
ERF 1207, Large Conference Room
Dave Gates, Thea Energy
Thea Energy: Reinventing the stellarator

Thea Energy (formerly Princeton Stellarators, Inc.) is a new stellarator fusion company that is focused on the use of an entirely new way of building the stellarator coil system using only non- interlocking planar coils - which we refer to as the all-planar coil stellarator. The coil set includes hundreds of small, individually controllable coils, allowing for an unprecedented degree of configurability and controllability. Initial work has focused on demonstrating viable techniques to optimize this new configuration, both the plasma and the coil set. As an initial use case, we propose a beam-target deuterium-deuterium stellarator neutron source at ~1/2 the linear dimensions of a fusion pilot plant based on the same concept. We present the concepts behind the all-planar coil stellarator as well as the methods we have developed to perform the field coil optimization. We also discuss the compatibility of the concept with reliability, accessibility, maintenance, and inspectability as well as the ability to incorporate a blanket. Additionally we will present initial studies of blanket design for the stellarator neutron source.
February 21st, Wed. 3:30PM
ERF 1207, Large Conference Room
Open


February 28th, Wed. 3:30PM
ERF 1207, Large Conference Room
Henry Freund, University of Maryland
The State of the Art in Free-Electron Laser Simulations

Free-electron Lasers have come a long way since the concept was first proposed by Hans Motz in 1950. Early FELs relied on the available accelerator/gun technology and were largely confined to operation in the IR and longer wavelength regimes. However, the development of laser-driven photocathodes permitted the production of extremely low emittance electron beams in RF linacs and has enabled the development of x-ray FELs, which are now under construction around the world. The fundamental theory explaining the operation of FELs was quickly developed and simulations, starting with one-dimensional formulations, were extended to include complete three-dimensional models. Two distinct simulation paths have been followed. One integrates the full 3D Lorentz force equations for the particles and uses a modal superposition for the fields. Another uses a wiggler-averaged orbit analysis in which only two equations are integrated; specifically, for the particle phase and energy. One- or two-dimensional field solvers are typically used with the wiggler-averaged formulations. In this seminar, I will discuss the basic physics of FELs and then go on to discuss the nonlinear simulation codes that are in use. Examples showing the level of agreement between the non-wiggler-averaged formulation and experiments will be presented.
March 6th, Wed. 3:30PM
ERF 1207, Large Conference Room
Open


March 13th, Wed. 3:30PM
ERF 1207, Large Conference Room
Andy Inglis, GSFC
Quasi-periodic pulsations in solar flares

Quasi-periodic pulsations (QPPs) are a regularly observed phenomenon during both the impulsive and decay phases of solar flare emission. They have been observed and studied over a wide range of wavelengths for more than 50 years. QPPs are crucial to understand because they are signatures of fundamental physical processes that occur during solar flare energy release, including magnetic reconnection, particle acceleration, and magnetohydrodynamic (MHD) wave generation. However, disambiguation of different explanations of QPPs remains elusive. In this talk, we explore the history of observations of QPPs, the different possible physical mechanisms and how to disambiguate them, the statistical picture of QPPs, as well as recent developments and future needs in determining the nature of this phenomenon.
March 20th, Wed. 3:30PM
ERF 1207, Large Conference Room
UMD Spring Break


March 27th, Wed. 3:30PM
ERF 1207, Large Conference Room
Sijie Yu, NJIT
Long-Lasting Aurora-like Radio Emission Above a Sunspot and Implications for Solar-Stellar Connection

Planetary radio aurorae are typically characterized by highly polarized, intense radio bursts. These emissions are generally attributed to electron cyclotron maser (ECM) emission from energetic electrons in regions with converging magnetic fields, such as planetary polar areas. Similar radio emissions have been observed in magnetically active low-mass stars and brown dwarfs, often prompting analogous interpretations. In this talk, we detail our observations of long-lasting solar radio bursts with high brightness temperature, wide bandwidth, and high circular polarization fraction akin to these auroral and exo-auroral radio emissions, albeit two to three orders of magnitude weaker than those on certain low-mass stars. Notably, long-lasting radio emissions originate above a sunspot with a strong, converging magnetic field. Our spatial, spectral, and temporal analysis suggest that the morphology and frequency dispersion of the source align with ECM emissions, likely driven by energetic electrons from recurring nearby solar flares. These observations provide new insights into the nature of intense solar radio bursts and suggest a potential model for understanding aurora-like radio emissions in other flare stars with significant starspots.
April 3rd, Wed. 3:30PM
ERF 1207, Large Conference Room
Jimmy Juno, PPPL
Novel parallel-kinetic perpendicular-moment model for magnetized plasmas

Many astrophysical plasma systems, from pulsar magnetospheres to the solar wind, are highly magnetized. However, the derivation of large magnetization asymptotic models applicable to this wide variety of plasmas is challenging. Relativistic energies, strong flows, and temperature anisotropies complicate the asymptotics and even if the derivation can be made sufficiently rigorous, the subsequent equations may resist easy discretization via standard numerical methods. I will discuss a recent innovation which addresses these challenges by separating the parallel and perpendicular dynamics starting from the kinetic equation while staying agnostic to the inclusion of effects such as relativity or strong flows. The key component of the derivation lies in a spectral expansion of only the perpendicular degrees of freedom, analogous to spectral methods which have grown in popularity in recent years for gyrokinetics, while retaining the complete dynamics parallel to the magnetic field. We thus leverage our intuition that a magnetized plasma's motion is different parallel and perpendicular to the magnetic field, while allowing for the treatment of complex phase space dynamics parallel to the magnetic field. This approach also naturally couples to Maxwell's equations, allowing easy transitions across energy scales and potentially novel hybrid approaches. A number of benchmarks and tests will be presented to demonstrate the power of this approach.
April 10th, Wed. 3:30PM
ERF 1207, Large Conference Room
Ian DesJardin, UMD
The critical velocity bounds of ion acoustic soliton generation by a charged supersonic grain

Ion acoustic solitons are solitary nonlinear waves observed in space plasmas. They can be generated by a millimeter to centimeter sized conducting grains moving supersonically relative to the ion acoustic velocity through the ionosphere. In this system, soliton generation is an unsteady flow phenomenon, qualitatively like Von Karman vortex shedding. However, instead of propagating in the wake, solitons can propagate upstream. This behavior is predicted to exist in a narrow range of Mach numbers. However, there is tension between experiments and theory, modeled by the forced Korteweg - de Vries equation, as to where the critical transition Mach numbers are. In this talk, we show the results of multifluid simulations to understand the physics of this velocity bound. New theory is created to explain our simulation results. We will also demonstrate some of the higher-order nonlinearities in this system that have until now gone unnoticed. This work has applications to detecting space debris in low Earth orbit via plasma soliton emission.
April 17th, Wed. 3:30PM
ERF 1207, Large Conference Room
Open


April 24th, Wed. 3:30PM
ERF 1207, Large Conference Room
Dylan Kee, GSFC
Developing Generally Applicable Data-Driven and Open Boundary Conditions for Magnetohydrodynamics Simulations

In constructing and analyzing three-dimensional, time-dependent magnetohydrodynamics simulations, it is common for the majority of the effort to be dedicated to the physics of the simulation interior. However, there are a variety of applications where a careful description of the boundary conditions is equally important. This is notably true when a substantial fraction of the plasma, energy, and magnetic field being modeled enter the simulation through one boundary and exit through a different one, as is for instance the case with simulations of the solar atmosphere. In such cases, representing the plasma state directly depends on the way these semi-permeable simulation boundaries are treated. Particularly, it is essential but non-trivial that these boundary conditions be specified in a way that is consistent with the underlying equations of magnetohydrodynamics (MHD), which govern the simulation as a whole.

In this seminar, I discuss so-called characteristics-based boundary conditions which naturally separate information entering the simulation from information leaving the simulation, thereby rendering the problem of appropriately specifying the numerical boundary condition more straightforward by ensuring that the boundary is neither under- nor over-specified at all locations and times. Specifically, I discuss a novel application of such boundary conditions to the problem of data-driving, where the simulation ingests a time-series of observationally inferred plasma properties on a 2D surface, e.g. the solar photosphere, as a direct boundary condition to the simulation. I also discuss the application of characteristics-based methods to general open boundaries where there are few if any a priori constraints.
May 1st, Wed. 3:30PM
ERF 1207, Large Conference Room
M. Hasan Barbhuiya, West Virginia University
Higher-order nonequilibrium term (HORNET): An effective power density quantifying evolution towards or away from local thermodynamic equilibrium

When studying energy conversion in plasma systems, such as space plasma, it is common to compare the power densities of different energy conversion mechanisms. A prominent research area focuses on quantifying energy conversion for such weakly collisional plasmas that are routinely not in local thermodynamic equilibrium (LTE), meaning their local phase space densities can be arbitrarily far from a Maxwellian. We introduce the "higher-order nonequilibrium term" (HORNET) effective power density, which measures the time rate of change of the departure of local phase space densities from LTE. With dimensions of power density, HORNET enables quantitative comparisons with standard power densities, such as the pressure-strain interaction. We compute HORNET using high-resolution particle-in-cell simulations of two plasma phenomena that inherently exhibit non-LTE effects, namely magnetic reconnection and decaying kinetic turbulence in collisionless magnetized plasmas. Comparing HORNET with pressure dilatation, Pi-D, and the divergence of the vector heat flux density (that describe changes to internal energy) reveals that HORNET can be a significant fraction of these other power densities in reconnection and in turbulence, underscoring the importance of capturing the non-LTE evolution in collisionless plasma systems.
May 8th, Wed. 3:30PM
ERF 1207, Large Conference Room
Suying Jin, Princeton University