arXiv subjects

Evdokiya G. Kostadinova

Publications and source records attributed to Evdokiya G. Kostadinova.

4 recordsLinked to original sources

arXiv2026

Spacecraft heat shield study in the DIII-D tokamak

We report a new experimental platform developed at the DIII-D National Fusion Facility to investigate carbon ablation and spallation under extreme heat fluxes relevant to fusion plasma-facing components and high-enthalpy atmospheric entry. Carbon samples were exposed to parallel heat fluxes of $30$--$40~\mathrm{MW\,m^{-2}}$ in the scrape-off layer using two complementary approaches: stationary carbon rods inserted near the divertor strike point and slow-launch carbon pellets injected vertically into the edge and core plasma. Pellets penetrating the core experienced heat fluxes approximately an order of magnitude higher. The conditions reproduce key aspects of the shock-layer environment encountered by the Galileo probe during entry into Jupiter's atmosphere. Fast visible imaging, divertor spectroscopy, infrared thermography, CO$_2$ interferometry, and post-exposure profilometry provided measurements of ablation rates, surface recession, and temperature evolution. Measured mass-loss rates of $(1$--$3)\times10^{-2}~\mathrm{g\,cm^{-2}\,s^{-1}}$ agree with semi-empirical aerospace ablation models, while wedge-shaped rods exhibited greater ablation than cylindrical and concave samples. UEDGE-DUSTT simulations incorporating parallel plasma flows, ${\bf j}\times{\bf B}$ forces, and ablation-cloud shielding reproduce the measured pellet trajectories and ablation timescales. These results establish tokamak plasma as a high-heat-flux environment for validating carbon ablation models and studying material response and impurity dynamics in reactor-relevant divertor plasmas.

physics.plasm-ph↗

arXiv2025

Anisotropic anomalous diffusion and nonequilibrium in microgravity dusty plasma. Part Two: Spectral Analysis

Anisotropic anomalous dust diffusion in microgravity dusty plasma is investigated using experimental data from the Plasmakristall-4 (PK-4) facility on board the International Space Station. The PK-4 experiment uses video cameras to track individual dust particles, which allows for the collection of large amounts of statistical information on the dust particle positions and velocities. In Part One of this paper, these statistics were used to quantify anomalous dust diffusion caused by anisotropies in the plasma-mediated dust-dust interactions in PK-4. Here we use scaling relations to convert statistical parameters extracted from data into input parameters for a Hamiltonian spectral model. The kinetic energy term of the Hamiltonian (modeling anomalous diffusion) is informed from the dust displacement distribution functions, while the potential energy term (modeling stochasticity) is informed from fluctuations in the dust positions. The spectrum of energy states for each Hamiltonian is studied to assess probability for extended states (i.e., a continuous portion of the spectrum). The spectral model shows that the combination of nonlocality and stochasticity leads to high probability for transport at certain scales in Hilbert space, which coincide with the characteristic spatial scales of dust particle jumps observed in the experiments. Lastly, we discuss how this spectral approach is generalizable to many complex systems, such as electron transport in 2D materials where statistical models are not feasible.

physics.plasm-ph↗

arXiv2021

Design and Testing of Dimes Carbon Ablation Rods in the DIII-D Tokamak

We present the design of ATJ graphite rods developed for ablation experiments under high heat flux (up to 50 MW/m2) in the lower divertor of the DIII-D tokamak [1], a magnetic plasma confinement device. This work is motivated by the need to test ablation models relevant to carbon-based thermal shields used in high-speed spacecraft atmospheric entries, where the heat fluxes encountered can be comparable to those achieved in the DIII-D divertor plasma. Several different designs for the flow-facing side of the rod are analyzed, including "sharp nose," "blunt," and "concave". The last shape is studied for its potential to lower heat fluxes at the rod surface by increased radiation from trapped neutrals and reduced parallel plasma pressure. We also analyze the possibility of applying a thin (approximately 30 microns) layer of silicon carbide (SiC) to the exposed part of several carbon ablation rods to benchmark its erosion calculations and lifetime predictions. Such calculations are of interest as SiC represents a promising material for both thermal protection systems (TPS) and a fusion plasma-facing material (PFM). Preliminary results from the DIII-D rod ablation experiments are also discussed.

physics.plasm-ph↗

arXiv2018

Self-diffusion in two-dimensional quasi-magnetized rotating dusty plasmas

The self-diffusion phenomenon in a two-dimensional dusty plasma at extremely strong (effective) magnetic fields is studied experimentally and by means of molecular dynamics simulations. In the experiment the high magnetic field is introduced by rotating the particle cloud and observing the particle trajectories in a co-rotating frame, which allows reaching effective magnetic fields up to 3000 Tesla. The experimental results confirm the predictions of the simulations: (i) super-diffusive behavior is found at intermediate time-scales and (ii) the dependence of the self-diffusion coefficient on the magnetic field is well reproduced.

physics.plasm-ph↗