
August 30th, Wed. 3:30PM
ERF 1207, Large Conference Room

John Finn, Tibbar Plasma
Technologies and LANL
Meshfree Analysis of Particle Methods for Plasma Kinetic Theory
We reconsider a meshfree approach to
plasma kinetic theory, specialized to 1D electrostatic
plasmas. This method uses kernel density estimation for
the charge density and a related Green's function method,
from Gauss's law, for the electric field. The kernel
K(xy) represents the the charge distribution within each
macroparticle, both for computing the electric field E(x)
and for using E(x) to compute the force on each
macroparticle. This method has good conservation
properties, conserving momentum and energy
exactly. Similarly, the continuity equation is satisfied
exactly, and this VlasovGauss system is exactly
equivalent to the VlasovAmpere and the VlasovPoisson
systems. The use of the same kernel above leads to a
symmetric and positive definite kernel, the correlation of
the original kernel with itself, and allows an analog of
the kernel trick in Machine Learning: a single positive
definite kernel can be subsituted for this correlation. We
show how the use of a nonpositive definite kernel can
lead to a numerical instability. This analysis uncovers a
connection between kernels used for density estimation and
the positive definite (reproducing) kernels. This analysis
is useful for analyzing PIC codes, which do have a mesh,
and for constructing meshfree codes. For the latter, I
will discuss ways to deal with the major drawback of
meshfree codes, the N^2 scaling, where N is the number of
particles. These include lowdiscrepancy sampling and a
Fourier formulation. 
September 6th, Wed. 3:30PM
ERF 1207, Large Conference Room

Open

September 13th, Wed. 3:30PM
ERF 1207, Large Conference Room

Open

September 20th, Wed. 3:30PM
ERF 1207, Large Conference Room

Open

September 27th, Wed. 3:30PM
ERF 1207, Large Conference Room

Open

October 4th, Wed. 3:30PM
ERF 1207, Large Conference Room

Sarah Conley, Princeton University
Characterizing the FieldParticle Correlation
Signatures of Electron Landau Damping
A longstanding goal in the heliophysics
community is to understand the mechanisms that dissipate
turbulent energy and energize particles in weakly
collisional plasmas like the solar wind. One of these
dissipation mechanisms is Landau damping, but the extent
to which it and other mechanisms contribute remains
unclear due to the inherent difficulty in observing and
simulating the small length scales and fast time scales
involved. However, evidence for electron Landau damping
has been found in situ near 1 AU using the fieldparticle
correlation (FPC) technique. Motivated by this
observation, we apply the FPC technique to gyrokinetic
simulations of strong plasma turbulence in the dissipation
range at varying plasmabeta in order to develop a more
thorough understanding of how to identify signatures of
electron Landau damping throughout the heliosphere.

October 11th, Wed. 3:30PM
ERF 1207, Large Conference Room

Harry Arnold, APL
PIC simulations of overstretched ion scale current
sheets applicable to the magnetotail
Onset of reconnection in Earth's magnetotail
requires the current sheet thickness to be of the order of the ion
thermal gyroradius or smaller. However, existing isotropic plasma
models cannot explain the formation of such thin sheets at distances
where the Xlines are typically observed. Here we reproduce such thin
and long sheets in particleincell simulations using a new model of
their equilibria with weakly anisotropic ion species assuming
quasiadiabatic ion dynamics, which substantially modifies the current
density. It is found that anisotropy/agyrotropy contributions to the
force balance in such equilibria are comparable to the pressure
gradient in spite of weak ion anisotropy. New equilibria whose current
distributions are substantially overstretched compared to the magnetic
field lines are found to be stable in spite of the fact that they are
substantially longer than isotropic sheets with similar thickness.

October 18th, Wed. 3:30PM ERF
1207, Large Conference Room

Vadim Uritsky, Catholic University
Selfsimilar Outflows at the Source of the Fast Solar
Wind: A Smoking Gun of Turbulent Coronal Reconnection?
I present recent results of a quantitative
analysis of structured plasma outflows above a polar
coronal hole observed by the Atmospheric Imaging Assembly
(AIA) on board the Solar Dynamics Observatory (SDO)
spacecraft. In a 6 hr interval of continuous highcadence
SDO/AIA images, more than 2300 episodes of smallscale
plasma flows in the polar corona were identified. The mean
upward flow speed measured by the surfing transform
technique is estimated to be 122 +/ 34 km/s, which is
comparable to the local sound speed. The typical
recurrence period of the flow episodes is 1030 minutes,
and the mean duration and transverse size of each episode
are about 35 minutes and 34 Mm, respectively. The
largest identifiable episodes last for tens of minutes and
reach widths up to 40 Mm. The results show, for the first
time, that the polar coronalhole outflows obey a family
of powerlaw probability distributions which could be
indicative of an impulsive interchange magnetic
reconnection driven by a turbulent photosphere. The
estimated occurrence rate of the detected selfsimilar
coronal outflows is sufficient for them to make a dominant
contribution to the fastwind mass and energy fluxes and
to account for the wind's smallscale structure.

October 25th, Wed. 3:30PM
ERF 1207, Large Conference Room

Jessie Duncan, GSFC
Characterizing Hot Plasma in Solar Active Regions
with NuSTAR Hard Xray Observations
Solar active regions contain plasma across a
broad range of temperatures, with the thermal distribution
often observed to peak in the few millions of kelvin
(MK). Characterizing this distribution in detail during a
flaring interval can show how energy is released and
transformed over the course of the event. Additionally,
understanding the thermal distribution at nonflaring
times is of interest as we work to determine the
mechanisms that keep the solar corona much hotter than the
photosphere (the "coronal heating problem"). Instruments
observing in different energy (wavelength) ranges are
variably sensitive to emission from plasma at different
temperatures. Hard xray (HXR) observations are uniquely
sensitive to the hightemperature (>5 MK) components of
the corona, which are particularly interesting in
understanding how heating proceeds. The Nuclear
Spectroscopic Telescope ARray (NuSTAR) is a powerful HXR
observatory which makes periodic observations of the
Sun. Via differential emission measure (DEM) analysis, we
can combine NuSTAR's HXR coverage with soft xray and
extreme ultraviolet observations (here, from Hinode/XRT
and SDO/AIA) to estimate the amount of plasma present in a
given source as a function of temperature. In this work,
we present a detailed DEM analysis of an active region
(NOAA designation AR 12671) observed for ~5 hours on 2018
May 29. Over the course of the interval, we show how the
plasma distribution evolves as the region produces several
small microflares and also undergoes quiescent periods
without obvious HXR transients. We discuss results from
this work in tandem with future prospects for gaining
further insight about active region heating using HXR DEM
studies.

November 1st, Wed. 3:30PM
ERF 1207, Large Conference Room

APS DPP meeting

November 8th, Wed. 3:30PM
ERF 1207, Large Conference Room

Open

November 15th, Wed. 3:30PM
ERF 1207, Large Conference Room

Antonio Coelho, Ecole
Polytechnique Federale de Lausanne
Global fluid simulations of plasma turbulence in
stellarators
We present the first 3D, global, twofluid,
fluxdriven simulations of plasma turbulence in stellarators with
different configurations: one with an island divertor; another one
corresponding to the TJK stellarator; and a set of equilibria with
increasing torsion and ellipticity. The simulations were carried out
with the GBS code [1], which solves the twofluid driftreduced
Braginskii equations.
The vacuum magnetic field of the island divertor configuration
corresponds to a 5field period stellarator and was constructed using
the Dommaschk potentials [2]. It was found that the radial particle
and heat transport is mainly driven by a fieldaligned mode with low
poloidal wavenumber, whose origin is investigated theoretically [3].
Transport is observed to be larger on the highfield side of the
device and this is explained by means of a nonlocal linear theory. In
contrast to tokamak simulations and experiments, but in agreement with
edge measurements in W7X [4], radial propagation of coherent
filamentary structures (blobs) is not observed, revealing important
differences between stellarator and tokamak edge transport mechanisms.
We further present the first validation of a simulation of plasma
turbulence in a stellarator configuration against experimental
measurements in the TJK stellarator [5]. The comparison shows that
GBS retrieves the main turbulence properties observed in the device,
namely the fact that transport is dominated by fluctuations with low
poloidal mode number. Finally we present simulations in a set of
equilibria with increasing ellipticitiy and increasing torsion
generated by VMEC. The limit of zero ellipticity and zero torsion
corresponds to a tokamak with circular flux surfaces, allowing to
study edge turbulence in the transition between a tokamak and a
stellarator. The role of ellipticity and torsion as well as of
magnetic shear is discussed.
[1] P. Ricci et al., Plasma Physics and Controlled Fusion 54, 124047 (2012)
[2] W. Dommaschk, Computer Physics Communications 40, 203 (1986)
[3] A. J. Coelho et al, Nuclear Fusion 62, 074004 (2022)
[4] C. Killer et al, Plasma Physics and Controlled Fusion 62, 085003 (2020)
[5] A. J. Coelho et al, Plasma Physics and Controlled Fusion 65, 085018 (2023)

November 22nd, Wed. 3:30PM
ERF 1207, Large Conference Room

Technically open, but during
UMD's Thanksgiving recess so extremely unlikely

November 29th, Wed. 3:30PM
ERF 1207, Large Conference Room

Dr. Jason Parisi, PPPL
Bifurcated kineticballooningmode constraints for
tokamak pedestals across aspect ratio and plasma shaping
We find the pedestal widthheight scaling [0]
for multiple tokamaks using a new kinetic ballooningmode (KBM)
gyrokinetic threshold model. At lowaspectratio, we reproduce NSTX's
experimental linear pedestal widthheight scaling for ELMy Hmodes
[2], overcoming previous issues with lowaspectratio pedestal
prediction [3]. We reproduce the square root pedestal widthheight
scaling [0] at regular aspect ratio for previously published DIIID
discharges [4]. Our model uses EFITAI [5] to calculate global
equilibria with selfconsistent bootstrap current and can be applied
to any Hmode equilibria. For ELMy NSTX discharges, kinetic rather
than idealballooning physics is needed to match experimental
data. Combined with peeling ballooning mode (PBM) stability [6,7], our
model will calculate a maximum inter ELM pedestal width and height
based on KBM and nonideal PBM stability. Finally, we predict a
bifurcation in tokamak pedestal width and height scalings that depends
strongly on plasma shaping and aspectratio [8]. This bifurcation
arises from the first and second stability properties of
kineticballooningmodes that yield a wide and narrow pedestal branch,
opening the operating space of accessible pedestal widths and
heights. The wide branch offers potential for edge
localizedmodefree pedestals with a high core pressure.
This
work was supported by US Department of Energy Contract No. DEAC02
09CH11466.
[0] P.B. Snyder et al 2009 Phys. Plasmas 16,
056118
[1] J.F. Parisi et al 2023 arxiv.org/abs/2308.05238
[2] A. Diallo et al 2011 Nucl. Fusion 51 103031
[3] R.J. Groebner et al 2013 Nucl. Fusion 53 093024
[4] W. Guttenfelder et al 2021 Nucl. Fusion 61 056005
[5] S. Kruger et al 2022, PP11.00057, APS DPP Meeting
[6] A. Kleiner et al 2021 Nucl. Fusion 61 064002
[7] A. Kleiner et al 2022 Nucl. Fusion 62 076018
[8] J.F. Parisi et al 2023 In Prep.

December 6th, Wed. 3:30PM
ERF 1207, Large Conference Room

Richard Nies, PPPL
Turbulence saturation via oscillating zonal flows and
grand critical balance
The energy confinement of tokamaks is limited
by turbulent transport, making the understanding of
turbulence saturation crucial. In previous work [1],
tokamak turbulence was modelled using the critical balance
conjecture [2], which posits that the turbulence parallel
and decorrelation timescales are comparable. The theory
does not however predict the radial length scale of the
turbulence  which is required to obtain its saturation
amplitude. Reference [1] made the assumption of
perpendicular spatial isotropy to obtain a solution. We
show using gyrokinetic simulations that the turbulence is
in fact anisotropic in the radial and binormal directions,
and follows the experimentally inferred grand critical
balance [3]. The radial length scale is thus determined by
the balance of the nonlinear, parallel, and magnetic drift
timescales. Grand critical balance requires a revision of
the scalings of [1], e.g. the heat flux scales linearly in
the temperature gradient instead of cubically, which we
show to be satisfied in gyrokinetic simulations using the
GS2 [4], stella [5] and GX [6] codes.
We posit that the validity of grand critical balance is predicated on
the existence of a new oscillating zonal flow mode. We characterise
this mode through a generalised theory of the secondary instability
[7], which considers the growth of zonal flows due to a streamer (the
primary mode) driven by microinstabilities. Our generalised theory
includes the effects of parallel streaming and magnetic drifts, and
describes two new modes, the oscillating toroidal secondary and the
purely growing neoclassical secondary, in addition to the classical
RogersDorland secondary [7]. The latter is found to only be relevant
at large primary amplitudes, above the values seen in gyrokinetic
simulations or expected from grand critical balance. At relevant
primary amplitudes, the zonal flow behaviour is instead governed by
the neoclassical secondary, which relies on the transport of momentum
in banana orbits, and the toroidal secondary, which involves updown
asymmetric fluxes balancing the compressibility of zonal flows induced
by toroidicity. Good agreement is demonstrated between the analytical
theory, gyrokinetic simulations of the secondary, and the zonal flow
behaviour in fully nonlinear simulations.
[1] Barnes, M et al. (2011). Phys. Rev. Lett. 107, 115003
[2] Goldreich, P & Sridhar, S. (1995). ApJ 438, 763
[3] Ghim, Yc. et al. (2013). Phys. Rev. Lett. 110, 145002
[4] Dorland, W et al. (2000). Phys. Rev. Lett. 85, 55795582
[5] Barnes, M et al. (2019). Journal of Computational Physics 391, 365380
[6] Mandell, NR et al. (2022). arXiv:2209.06731
[7] Rogers, BN et al. (2000). Phys. Rev. Lett. 85, 53365339
This work was supported by US Department of Energy Contract No. DEAC0209CH11466.


