arXiv subjects

Brenno De Lucca

Publications and source records attributed to Brenno De Lucca.

4 recordsLinked to original sources

arXiv2026

Implicit-Explicit time integration scheme with Physics-based preconditioning for two-fluid tokamak boundary simulations

In this work, a globally stiffly accurate Implicit-Explicit (IMEX) Runge-Kutta scheme is developed and implemented in the GBS code [Ricci et al., Plasma Phys. Control. Fusion, 2012], for two-fluid plasma turbulence simulations. The stiffest phenomena, governed by shear Alfvén waves and parallel diffusion, are treated implicitly, while the remaining non-stiff terms are advanced explicitly. This splitting enables time steps well beyond the Courant-Friedrichs-Lewy limit, without incurring the full computational cost of a globally implicit formulation. To efficiently solve the implicit subsystem at each time step, a three-dimensional physics-based preconditioner, inspired by techniques developed in the magnetohydrodynamic (MHD) context, is used. The resulting framework is verified through the method of manufactured solutions and exhibits both algorithmic and parallel scalability. Significant advantages in numerical stability and computational efficiency are demonstrated with respect to an adaptive explicit Runge-Kutta scheme.

physics.plasm-ph↗

arXiv2026

The L-H transition in tokamaks: power threshold, density minimum and toroidal-field asymmetry

The physical mechanism underlying the L--H transition in tokamaks has remained an open problem for over forty years. We present three-dimensional flux-driven two-fluid simulations in a diverted geometry that exhibit a confinement transition at lower power in the favourable toroidal-field configuration. The simulations show that electromagnetic drift-wave turbulence spontaneously generates a sheared $\bm{E}\times \bm{B}$ flow responsible for transport suppression. The toroidal-field-direction asymmetry arises from time-reversal symmetry breaking by finite collisionality, as demonstrated by a quasilinear calculation of the turbulent momentum flux. First-principles scaling laws are derived for the L--H power threshold in both density branches, the density minimum, and the minimum power, all matching or surpassing existing empirical scalings.

physics.plasm-ph↗

arXiv2026

Conservative formulation of the drift-reduced fluid plasma model

A conservative formulation of the drift-reduced fluid plasma model is constructed by analytically inverting the implicit relation defining the polarisation velocity as a function of the time-derivative of the electric field. The obtained model satisfies exact conservation laws for energy, mass, charge and momentum, in arbitrary magnetic geometry, also when electromagnetic fluctuations are included.

physics.plasm-ph↗

arXiv2024

Constructing nested coordinates inside strongly shaped toroids using an action principle

A new approach for constructing polar-like boundary-conforming coordinates inside a toroid with strongly shaped cross-sections is presented. A coordinate mapping is obtained through a variational approach, which involves identifying extremal points of a proposed action in the mapping space from [0, 2π] x [0, 2π] x [0, 1] to a toroidal domain in R3. This approach employs an action built on the squared Jacobian and radial length. Extensive testing is conducted on general toroidal boundaries using a global Fourier-Zernike basis via action minimization. The results demonstrate successful coordinate construction capable of accurately describing strongly shaped toroidal domains. The coordinate construction is successfully applied to the computation of 3D MHD equilibria in the GVEC code where the use of traditional coordinate construction by interpolation from the boundary failed.

physics.plasm-ph↗