arXiv subjects

Katarina Bendtz

Publications and source records attributed to Katarina Bendtz.

3 recordsLinked to original sources

arXiv2025

Novatron: Equilibrium and Stability

The Novatron is a fusion concept characterized by its axisymmetric mirror-cusp magnetic topology. The magnetic field exhibits good curvature and a high mirror ratio. Plasma equilibrium profiles for the Novatron are obtained by solving an axisymmetric guiding-center anisotropic boundary-value problem. These profiles are then analyzed with respect to several MHD stability criteria, including the mirror, firehose, and interchange conditions. A generalized Rosenbluth and Longmire MHD interchange criterion, where anisotropic pressure variations along flux tubes are allowed for, is subsequently employed for determining stable MHD equilibria. Additionally, a corresponding CGL double adiabatic interchange criterion is investigated for obtaining stable equilibria in the collisionless limit, both theoretically and numerically using the large scale Hybrid Particle-In-Cell code WarpX.

physics.plasm-ph↗

arXiv2024

Introducing the Novatron, a novel mirror fusion concept

A new magnetic mirror-cusp concept is described - the Novatron - with the potential to confine compact and stable fusion plasmas. Traditionally, the major challenges for open field line designs include MHD interchange modes, drift cyclotron loss-cone (DCLC) modes, neoclassical transport, and axial losses of particles and energy. The novel magnetic field configuration features favorable curvature throughout the plasma region, suppressing interchange modes. Moreover, the Novatron is designed to be self-stabilized against DCLC modes by allowing for a large plasma to Larmor radius ratio. The vacuum magnetic field geometry is axisymmetric, mitigating neoclassical transport. The Novatron features a high mirror ratio, providing strong magnetic confinement and suppressed axial losses. This paper describes the fundamental magnetic field topology and outlines the design of the magnet system. MHD interchange stability of anisotropic low-\b{eta} equilibria is demonstrated by derivation of two novel criteria, based on anisotropic ideal MHD and the Chew-Goldberger-Low model, and numerical computation in Novatron geometry. The Novatron design is also placed into a historic context by summarizing challenges faced by both previous and more current mirror/cusp concepts.

physics.plasm-ph↗

arXiv2022

Look Twice: A Generalist Computational Model Predicts Return Fixations across Tasks and Species

Primates constantly explore their surroundings via saccadic eye movements that bring different parts of an image into high resolution. In addition to exploring new regions in the visual field, primates also make frequent return fixations, revisiting previously foveated locations. We systematically studied a total of 44,328 return fixations out of 217,440 fixations. Return fixations were ubiquitous across different behavioral tasks, in monkeys and humans, both when subjects viewed static images and when subjects performed natural behaviors. Return fixations locations were consistent across subjects, tended to occur within short temporal offsets, and typically followed a 180-degree turn in saccadic direction. To understand the origin of return fixations, we propose a proof-of-principle, biologically-inspired and image-computable neural network model. The model combines five key modules: an image feature extractor, bottom-up saliency cues, task-relevant visual features, finite inhibition-of-return, and saccade size constraints. Even though there are no free parameters that are fine-tuned for each specific task, species, or condition, the model produces fixation sequences resembling the universal properties of return fixations. These results provide initial steps towards a mechanistic understanding of the trade-off between rapid foveal recognition and the need to scrutinize previous fixation locations.

cs.CV↗