arXiv subjects

Johan Lundberg

Publications and source records attributed to Johan Lundberg.

4 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↗

arXiv2023

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↗

arXiv2017

GAMBIT: The Global and Modular Beyond-the-Standard-Model Inference Tool

We describe the open-source global fitting package GAMBIT: the Global And Modular Beyond-the-Standard-Model Inference Tool. GAMBIT combines extensive calculations of observables and likelihoods in particle and astroparticle physics with a hierarchical model database, advanced tools for automatically building analyses of essentially any model, a flexible and powerful system for interfacing to external codes, a suite of different statistical methods and parameter scanning algorithms, and a host of other utilities designed to make scans faster, safer and more easily-extendible than in the past. Here we give a detailed description of the framework, its design and motivation, and the current models and other specific components presently implemented in GAMBIT. Accompanying papers deal with individual modules and present first GAMBIT results. GAMBIT can be downloaded from gambit.hepforge.org.

hep-ph↗

arXiv2004

WIMP diffusion in the solar system including solar depletion and its effect on Earth capture rates

Weakly Interacting Massive Particles (WIMPs) can be captured by the Earth, where they eventually sink to the core, annihilate and produce e.g. neutrinos that can be searched for with neutrino telescopes. The Earth is believed to capture WIMPs not dominantly from the Milky Way halo directly, but instead from a distribution of WIMPs that have diffused around in the solar system due to gravitational interactions with the planets in the solar system. Recently, doubts have been raised about the lifetime of these WIMP orbits due to solar capture. We here investigate this issue by detailed numerical simulations. Compared to earlier estimates, we find that the WIMP velocity distribution is significantly suppressed below about 70 km/s which results in a suppression of the capture rates mainly for heavier WIMPs (above ~100 GeV). At 1 TeV and above the reduction is almost a factor of 10. We apply these results to the case where the WIMP is a supersymmetric neutralino and find that, within the Minimal Supersymmetric Standard Model (MSSM), the annihilation rates, and thus the neutrino fluxes, are reduced even more than the capture rates. At high masses (above ~1 TeV), the suppression is almost two orders of magnitude. This suppression will make the detection of neutrinos from heavy WIMP annihilations in the Earth much harder compared to earlier estimates.

astro-ph↗