arXiv subjects

A. Scarabosio

Publications and source records attributed to A. Scarabosio.

3 recordsLinked to original sources

arXiv2026

Langmuir probe and infrared thermography measurements of wide and narrow heat flux profiles in the ST40 tokamak

Very narrow heat flux profiles have been observed on ST40 with decay lengths in the near scrape-off-layer (SOL) of $\lambda_{q,near}<$~1~mm in H-mode plasmas. Measurements from divertor Langmuir probes are compared with an infrared (IR) thermography system for upper-single null diverted plasmas in L-mode and ELM-free H-mode. SOL current to the grounded divertor targets is measured from the Langmuir probes with profiles exhibiting a similar exponential decay to $\lambda_{q,near}$ suggesting the near SOL heat flux is related to enhanced electron current to the divertor. Inclusion of electron current contributions to the heat flux transmission coefficient is crucial in capturing similar narrow profiles to those from the IR thermography system. Ongoing upgrades to ST40 will enable more investigations on SOL power decay lengths on inboard and outboard targets in double and single null configurations.

physics.plasm-ph↗

arXiv2024

Inferring the scrape-off layer heat flux width in a divertor with a low degree of axisymmetry

Plasma facing components (PFCs) in the next generation of tokamak devices will operate in challenging environments, with heat loads predicted to exceed 10 MWm$^{-2}$. The magnitude of these heat loads is set by the width of the channel, the "scrape-off layer" (SOL), into which heat is exhausted, and can be characterised by an e-folding length scale for the decay of heat flux across the channel. It is expected this channel will narrow as tokamaks move towards reactor relevant conditions. Understanding the processes involved in setting the SOL heat flux width is imperative to be able to predict the heat loads PFCs must handle in future devices. Measurements of the SOL width are performed on the high-field spherical tokamak, ST40, using a newly commissioned infrared thermography system. With its high on-axis toroidal magnetic field ($\geq$1.5 T) ST40 is uniquely positioned to investigate the influence of toroidal field on the heat flux width in spherical tokamaks, whilst also extending measurements of the SOL width in spherical tokamaks to increased poloidal field ($\geq$0.3 T). Due to the divertor on ST40 having a low degree of axisymmetry, it is necessary for a set of radial measurements of the heat flux to be taken across the divertor, made possible using an automated toolchain that fully incorporates its 3D geometry. These radial profiles are combined with the magnetic topology of the plasma to infer the width of the SOL, with both single and double exponential profiles of heat flux observed. A reduction in the heat flux is observed toroidally across part of the divertor, with preliminary investigations indicating that partial shadowing occurs, resulting from the separation between magnetic field lines and trailing edges upstream of the observed region becoming comparable to the ion gyro-radius.

physics.plasm-ph↗

arXiv2021

Radiation and Scattering of EM Waves in Large Plasmas Around Objects in Hypersonic Flight

Hypersonic flight regime is conventionally defined for Mach larger than 5; in these conditions, the flying object becomes enveloped in a plasma. This plasma is densest in thin surface layers, but in typical situations of interest it impacts electromagnetic wave propagation in an electrically large volume. We address this problem with a hybrid approach. We employ Equivalence Theorem to separate the inhomogeneous plasma region from the surrounding free space via an equivalent (Huygens) surface, and the Eikonal approximation to Maxwell equations in the large inhomogeneous region for obtaining equivalent currents on the separating surface. Then, we obtain the scattered field via (exact) free space radiation of these surface equivalent currents. The method is extensively tested against reference results and then applied to a real-life re-entry vehicle with full 3D plasma computed via Computational Fluid Dynamic (CFD) simulations. We address both scattering (RCS) from the entire vehicle and radiation from the on-board antennas. From our results, significant radio link path losses can be associated with plasma spatial variations (gradients) and collisional losses, to an extent that matches well the usually perceived blackout in crossing layers in cutoff. Furthermore, we find good agreement with existing literature concerning significant alterations of the radar response (RCS) due to the plasma envelope.

physics.comp-ph↗