Abstract Details
Abstracts
Author: Aaron Tran
Requested Type: Poster
Submitted: 2025-03-13 22:07:34
Co-authors: S. J. Frank, A. Y. Le, A. J. Stanier, B. A. Wetherton, J. Egedal, D. A. Endrizzi, R. W. Harvey, Y. V. Petrov, T. M. Qian, K. Sanwalka, J. Viola, C. B. Forest, E. G. Zweibel
Contact Info:
University of Wisconsin–Madison
1150 University Ave
Madison, WI 53706
United States
Abstract Text:
The Wisconsin High-temperature superconductor Axisymmetric Mirror (WHAM) experiment's beam-ion plasma may induce drift-cyclotron loss-cone (DCLC) instability: a coupled ion Bernstein / drift wave excited by the plasma’s radial density gradient and loss-cone velocity distribution. We present 3D plasma simulations, using the kinetic-ion/fluid-electron code Hybrid-VPIC, of various WHAM configurations with sloshing (45 deg. pitch angle) ion distributions from the collisional Fokker-Planck code CQL3D-m as an initial condition. Edge-localized electrostatic waves grow and saturate in ~1–10 μs with ω ~ 1–2× the ion cyclotron frequency. Wave properties can be explained by linear theory of DCLC in a planar slab. DCLC scatters ions to a marginally-stable distribution with a filled loss cone and hence gas-dynamic rather than classical-mirror confinement. Sloshing ions can trap cool (low-energy) ions in an electrostatic potential well to help stabilize DCLC, but DCLC itself does not scatter sloshing beam-ions into said well. Instead, cool ions must come from external sources such as charge-exchange collisions with a low-density neutral population. Manually adding cool ~1 keV ions to the plasma edge improves beam-ion confinement several-fold in our simulations. I will also briefly comment on (i) other ways to stabilize DCLC, (ii) how DCLC fits into a broader landscape of instabilities in mirrors, and (iii) the effect of externally-driven shear flows.
Characterization: 1.0
Comments: