# Bulletin of the American Physical Society

# 65th Annual Meeting of the APS Division of Plasma Physics

## Monday–Friday, October 30–November 3 2023; Denver, Colorado

### Session JP11: Poster Session IV:

BEAMS: Laser- and beam-plasma interactions

Fundamental: Measurements and analysis in fundamental plasma physics; Plasma Sheaths, Sources, and Shocks

MFE: Turbulence and transport in fusion plasmas; High Field Tokamaks

2:00 PM - 5:00 PM

Tuesday, October 31, 2023

Room: Plaza ABC

### Abstract: JP11.00066 : Finite-particle instability in the gyrokinetic delta-f PIC algorithm*

#### Presenter:

George J Wilkie

(Princeton Plasma Physics Laboratory)

#### Author:

George J Wilkie

(Princeton Plasma Physics Laboratory)

Here a complementary analysis is presented to illuminate the remaining instability studied in Ref. 2: that due to insufficient particles. In this analysis, the mesh is eliminated, but finite-particle effects are maintained. It is found that Fourier modes are linearly coupled to each other via particle weights. The diagonal terms are physical and remain in the limit of infinite particle number, and in this case the physical dispersion relation is recovered. With finite number of particles, off-diagonal coupling terms are nonzero. With sufficiently low number of particles (which can still be quite large for some systems), it is shown that this coupled system is unstable. Properties of this finite-particle instability, implications for more complicated systems, and mitigation methods will be discussed.

[1] Birdsall and Langdon. Plasma Physics via Computer Simulation (2004)

[2] Wilkie and Dorland. PoP 23:052111 (2016)

[3] Sturdevant and Parker. J. Comp. Phys. 305:647 (2016)

[4] McMillan. PoP 27:052106 (2020)

*This work was supported by the United States Department of Energy via contract no. DE-AC02-09CH11466 via the SciDAC Center for High-Fidelity Boundary Plasma Simulation.

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