arXiv subjects

Cary B. Forest

Publications and source records attributed to Cary B. Forest.

6 recordsLinked to original sources

arXiv2026

Experimental Plasma Density Profiles Determined Through Measurements of the Magnetosonic Wave Speed

Information on plasma density in laboratory plasmas is commonly acquired using either Langmuir probes or optical diagnostics. Here, we present an alternative approach, inferring the density profile from magnetic measurements of a plasma wave. In particular, during the process of creating a reconnecting current layer for magnetic reconnection experiments in the Big Red Ball, the reconnection drive first launches a large amplitude fast magnetosonic wave. The propagation of the wavefront is measured with high spatial and temporal resolutions by in situ magnetic diagnostics. Given a known uniform background magnetic field strength and the known dispersion relation of the wave, we here show how the characteristics of the wavefront can be applied to determine the initial plasma density profile.

physics.plasm-ph↗

arXiv2026

Production of Intense Spin-Polarized Beams of Hydrogen Isotopes by Charge Transfer with High Density Raman-Pumped Alkali-Metal Vapors

It should be possible to generate multi-ampere spin-polarized beams of hydrogen isotopes by repeated charge-transfer collisions in highly spin-polarized Cs vapor. Estimates suggest that off-resonant Raman pumping with kW scale narrowband tunable light at 895 nm should be able to produce a 1 m long, 10 cm diameter volume of 80\% polarized Cs vapor. The charge transfer collisions between the Cs and hydrogen result in a high nuclear spin-polarized negative ion beam that can be subsequently accelerated to high energy, neutralized, and be used to heat fusion plasmas with resulting increases in the fusion conversion efficiency.

physics.atom-ph↗

arXiv2025

Application of the Portable Diagnostic Package to the Wisconsin High-temperature-superconducting Axisymmetric Mirror (WHAM)

We present an application of the Portable Diagnostic Package (PDP) on the Wisconsin HTS Axisymmetric Mirror (WHAM), which integrates an optical emission spectroscopy (OES) system and an active Thomson scattering (TS) system. Due to the designed portability of our system, we realized the installation of the PDP OES and TS measurements on WHAM in $\sim$6 months. The OES system facilitates a comprehensive impurity line survey and enables flow measurements through the Doppler effect observed on impurity lines. Notably, plasma rotation profiles were successfully derived from doubly charged carbon lines. In addition, the TS system enabled the first measurements of the electron temperature in commissioning plasmas on WHAM. These successes underscore the diagnostic package's potential for advancing experimental plasma studies.

physics.plasm-ph↗

arXiv2025

Drift-cyclotron loss-cone instability in 3D simulations of a sloshing-ion simple mirror

The kinetic stability of collisionless, sloshing beam-ion (45° pitch angle) plasma is studied in a 3D simple magnetic mirror, mimicking the Wisconsin High-temperature superconductor Axisymmetric Mirror (WHAM) experiment. The collisional Fokker-Planck code CQL3D-m provides a slowing-down beam-ion distribution to initialize the kinetic-ion/fluid-electron code Hybrid-VPIC, which then simulates free plasma decay without external heating or fueling. Over 1-10 $μ$s, drift-cyclotron loss-cone (DCLC) modes grow and saturate in amplitude. DCLC scatters ions to a marginally-stable distribution with gas-dynamic rather than classical-mirror confinement. Sloshing ions can trap cool (low-energy) ions in an electrostatic potential well to 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 improves beam-ion confinement several-fold in Hybrid-VPIC simulations, which qualitatively corroborates prior measurements from real mirror devices with sloshing ions.

physics.plasm-ph↗

arXiv2023

Towards continuum gyrokinetic study of high-field mirrors

High-temperature superconducting (HTS) magnetic mirrors under development exploit strong fields with high mirror ratio to compress loss cones and enhance confinement, and may offer cheaper, more compact fusion power plant candidates. This new class of devices could exhibit largely unexplored interchange and gradient-driven modes. Such instabilities, and methods to stabilize them, can be studied with gyrokinetics given the strong magnetization and prevalence of kinetic effects. Our focus here is to: a) determine if oft-used gyrokinetic models for open field lines produce the electron-confining (Pastukhov) electrostatic potential; b) examine and address challenges faced by gyrokinetic codes in studying HTS mirrors. We show that a one-dimensional limit of said models self-consistently develops a potential qualitatively reaching the analytical Pastukhov level. Additionally, we describe the computational challenges of studying high mirror ratios with open field line gyrokinetic solvers, and offer a force softening method to mitigate small time steps needed for time integration in colossal magnetic field gradients produced by HTS coils, providing a 19X speedup.

physics.plasm-ph↗

arXiv2021

Laminar and Turbulent Plasmoid Ejection in a Laboratory Parker Spiral Current Sheet

Quasi-periodic plasmoid formation at the tip of magnetic streamer structures is observed to occur in experiments on the Big Red Ball as well as in simulations of these experiments performed with the extended-MHD code, NIMROD. This plasmoid formation is found to occur on a characteristic timescale dependent on pressure gradients and magnetic curvature in both experiment and simulation. Single mode, or laminar, plasmoids exist when the pressure gradient is modest, but give way to turbulent plasmoid ejection when the system drive is higher, producing plasmoids of many sizes. However, a critical pressure gradient is also observed, below which plasmoids are never formed. A simple heuristic model of this plasmoid formation process is presented and suggested to be a consequence of a dynamic loss of equilibrium in the high-$β$ region of the helmet streamer. This model is capable of explaining the periodicity of plasmoids observed in the experiment and simulations and produces plasmoid periods of 90 minutes when applied to 2D models of solar streamers with a height of $3R_\odot$. This is consistent with the location and frequency at which periodic plasma blobs have been observed to form by LASCO and SECCHI instruments.

physics.plasm-ph↗