Group Member: Ian Ellis
I am studying the wakes of charged particles passing through plasmas in 3D. The analytic theory describing the wake was derived back in 1987, but only during the past few years have computers become powerful enough to compute the solution at multiple points in space in 3D and perform particle simulations to compare the results with. I wrote a program to calculate and plot the wake using the analytic solution and am performing particle simulations for comparison purposes using UCLA's particle-in-cell code BEPS and Lawrence Livermore National Lab's particle-particle particle-mesh code ddcMD.
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|Image 1. The conceptual layout of the process used in the particle-in-cell (PIC) algorithm. PIC uses a mesh to calculate the fields to achieve greater computational efficiency than calculating pair-wise interactions between particles directly.||Image 2. The conceptual layout of the process used in the particle-particle particle-mesh (PPPM) algorithm. PPPM calculates long-range forces like PIC, but then takes into account pair-wise interactions within a certain cutoff sphere, allowing the method to accurately model collisions.|
|Image 3. A plot of the electrostatic potential, showing the wake produced by an electron in a BEPS simulation. The simulation was 3D, so I've plotted a slice containing the path of the electron. The test electron starts at x=128 λDe and z=64 λDe and travels with a constant velocity of 5 vth in the +z direction. It is at x=128 λDe and z=214 λDe at the current time.||Image 4. A plot of the electrostatic potential from the simulation shown in Image 3 at a later time.|
|Image 5. The electrostatic potential along the trajectory of a particle traveling at 3 vth||Image 6. A plot of the electrostatic potential, showing the wake produced by an electron in a ddcMD simulation. The simulation was 3D, so I've plotted a slice containing the path of the electron. The test electron starts at x=64 λDe and z=32 λDe and travels at a constant speed of 5 vth in the +z direction. It is at x=64 λDe and z=52 λDe at the current time. The “bubbles” that appear in the plot indicate electrons that have undergone large-angle c ollisions, and appear due to a differencing technique we use during data analysis.|
This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344 and by the University of California, Los Angeles under Grant DE-FG52-09NA29552.