USC Progress Report: 3D EMPIC Simulations of Whistler Turbulence I. Modeling Nonlinear Evolution of Whistler Turbulence: Local Simulation II. Modeling Whistler Wave/Turbulence Propagation: Toward a Global Simulation Model Joseph Wang, Ouliang Chang Department of Astronautical Engineering University of Southern California Acknowledgement: S. Peter Gary, Los Alamos National Lab Guru Ganguli, Naval Research Lab
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USC Progress Report: 3D EMPIC Simulations of Whistler Turbulence I. Modeling Nonlinear Evolution of Whistler Turbulence: Local Simulation II. Modeling.
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USC Progress Report: 3D EMPIC Simulations of Whistler Turbulence
I. Modeling Nonlinear Evolution of Whistler Turbulence: Local Simulation
II. Modeling Whistler Wave/Turbulence Propagation: Toward a Global Simulation Model
Joseph Wang, Ouliang ChangDepartment of Astronautical Engineering
University of Southern California
Acknowledgement:S. Peter Gary, Los Alamos National Lab
Guru Ganguli, Naval Research Lab
Summary of Recent WorkSummary of Recent Work
• Extension of previous study on ring-beam induced instabilities • Cross comparison/validation: EMPIC simulations of lower hybrid
wave/instability vs. Winske’s hybrid ES simulation
• 3D EMPIC simulations of whistler turbulence evolution
• Development of a global EMPIC simulation of whistler wave/turbulence propagation
This talk
I. I. Modeling Nonlinear Evolution of Whistler Turbulence: Local Simulation
IntroductionIntroduction• Two recent studies on the evolution of whistler turbulence:
• Saito et al (2008), Gary et al (2010):
• 2D EMPIC simulation showed the evolution is dominated by forward cascade from long to short wavelengths
• Ganguli et al (2010):
• Whistler turbulence is fundamentally a 3-D phenomena
• Pseudo-3D EMPIC simulation which includes the
effect showed that the evolution is dominated by inverse cascade from short to long wavelengths.
2-D simulations may not allow the development of important nonlinear wave-wave processes
0)( Bnk
Objective:
To perform 3D EMPIC simulations of whistler turbulence and to investigate the “forward cascade vs inverse cascade” issue in a fully 3D setup
Previous Work [Ganguli et al., 2010]Previous Work [Ganguli et al., 2010]pseudo-3D; pseudo-3D; whistler instability launched by a ring beamwhistler instability launched by a ring beam
X
Y
Z
oB
config.) (Saito0θ al. et
oB
06θ
. 0θ 06θ
Ongoing WorkOngoing Workfully 3D; fully 3D; whistler instability launched by a prescribed spectrum of whistlerswhistler instability launched by a prescribed spectrum of whistlers
z (Bo, ||)
xy
• Initial simulations focus on 3D vs. 2D using the Satio-Gary initial condition
• Larger simulations to determine whether the forward cascade or the inverse cascade is going to “win” are currently running
Due to computer limitations: this talk addresses the intermediate questions:1) How does the 3D forward cascade compare against the 2D forward cascade 2) Is there an inverse cascade in a fully 3D setup of Saito-Gary initial condition
Computational Challenge to Perform a Fully 3D EMPIC Computational Challenge to Perform a Fully 3D EMPIC Simulation of Whistler TurbulenceSimulation of Whistler Turbulence
• Simulation Parameters to extend Saito et al (2008) 2D setup to full 3DMemory Requirement Estimation: 8TBParticle per Cell: ~64 particles per cell per speciesCell resolution: dx= dy=1 Debye length=0.1c/omega_peDomain size: 1024X1024X1024>109
Total # of particles: >128X109
Computing Time Estimation on USC HPC: >35 days on 256 nodes dt=0.05*(omega_pe) -1 CPU Time/particle/step: ~2.75E-7sTotal CPU time for 20000 steps (447Ωce
-1): : >8770 day
• USC High Performance Computing Center Parallel Supercomputer:typical node: quad-core/dual processortypical memory each node: 12-16GBtheoretical peak speed: 83.29teraflops on 1460nodesprocessor availability: <256 node for each run
Parallel Simulation Code DevelopmentParallel Simulation Code Development
• Code development, optimization, and validation completed• Implementation using hybrid MPI+OpenMP
• New particle sorting algorithm to enhance data locality and speed up the computation
• Various initial loading of whistler waves for pre-conditioned simulation
• Code Validation against pervious simulations
Simulation SetupSimulation Setup
• Initial condition:
• Initial waves:
where
• 2D configuration: 42 models calculated from S. Peter Gary’s dispersion solver
On a 2D grid containing the background magnetic field, lay out 42 modes with k_|| and k_perp calculated from dispersion solver.Put the appropriate amount of magnetic energy in each component for each mode based on dispersion solver. Each mode should have the same total magnetic energy density, by assumption.Use Faraday's Law to get the appropriate amount of electric field energy in each component for each mode.Use Ampere's Law to compute the components of the fluctuating electron velocities for each mode, which is imposed as a perturbation of the average velocity of the electron velocity distribution.
• 3D configuration: 84 modes rotate the plane containing the wave vectors 90 degrees about Bo, and repeat the
above process
Simulation CasesSimulation Cases
• Case 0: code validation. based on Saito et al (2008)
both forward cascade and inverse cascade seem to exist in the 3D Saito-Gary setup; however, which process is going to “win” under realistic magnetospheric parameters remain to be answered
II. II. Modeling Whistler Wave/Turbulence: Toward Global Simulation
IntroductionIntroduction
• All simulation studies on whistler turbulence so far are based on local simulations with periodic BC
• Local simulations do not allow the study of global characteristics of whistler turbulence associated with whistler emission and propagation
Objective:
• To develop a global simulation model for studying anomalous absorption of whistler waves injected by a transmitter
This talk:
• Development and testing of an EMPIC code with absorbing BC for whistler waves
Algorithm: Wave Absorption at Boundary
• Effective damping region
• Outgoing waves at simulation domain boundary are absorbed using a damping region scheme (Umeda, Comp. Phys. Comm., 2001)
• In the damping region, an amplitude damping factor is used to gradually reduce the amplitude (energy) of outgoing waves at each time step and a phase retarding factor is used to gradually reduce the propagation speed of outgoing waves (and plasmas).
Code Testing: 2D Perturbations in Maxwellian Plasma
Initial Condition:
2D sinusoidal wave propagating in X direction. Ey(i,j,k)=Bo*sin(re/20*2*pi); Bz(i,j,k)=Bo*sin(rm/20*2*pi)
re, rm are distance to center point of 2D domain plainwave length: 20cell
Background Plasma:•Background magnetic field in the Z direction•Speed of light c =8•ve_th=1 vi_th=0.125 v_d=0
Domain and Wave Damping Region:
•damping region: 40 cell; Domain size: 280X280X1;
Boundary Condition•Field: Wave absorption•Particle: injection and absorption•Injection: one-sided flux of background distribution
2D Perturbations in Maxwellian Plasma
Bz animation) Oscillating Bz
• 2D Perturbation propagation in X direction
Initial Simulation Results:Whistler Propagation in Open Domain
• 2D open (absorbing) boundary condition, cell size 300*1*512• Open BC in X and Z, periodic BC in Y• Absorbing region size: 100 cells in each side• Background B in Z direction (in simulation plain)
• Magnetic field frequency and wavenumber match the whistler dispersion relation.
• Electric field shows that whistler mode is dominating. Totoal time: t*omega_pe=150
Wave number spectrum at t*omega_pe=50
Summary and Conclusions
• local simulation:– new parallel empic code has been implemented and optimized for
3D simulations of whistler turbulence evolution– First fully 3D EMPIC simulation of whistler turbulence carried out– Initial results (run time: days) showed both forward and inverse
cascade using the Saito-Gary initial condition– Larger scale simulations using more than 109 cells and 1011 particles
(run time: weeks) to resolve the “forward cascade vs. Inverse cascade” issue are ongoing
• global simulation:– new subroutines for wave absorption are developed and tested for
simulation of whistler turbulence associated with whistler emission from a transmitter in open space
– Future work will develop a whistler emission model and study whistler turbulence evolution within the context of emission/ propagation