Publications by Joaquim Loizu Cisquella

Turnstile flux as a measure for chaotic transport in magnetic confinement fusion devices

We analyze a measure for the degree of chaos in the magnetic fields of magnetic confinement fusion reactors by calculating the lobe fluxes of turnstiles - a method developed for characterizing transport into and out of resonance zones in Hamiltonian dynami ...

2025

Measurements of radial neutral density profiles from Balmer-α emission in Wendelstein 7-X

Joaquim Loizu Cisquella, Mike Machielsen

Radial neutral density profiles are estimated from measurements of passive Hα emission in the Wendelstein 7-X stellarator. To parametrize the generally three-dimensional distribution with a low number of degrees of freedom, the neutral density is reduced t ...

2025

Electron trapping in gyrotron electron guns: Validation of the FENNECS code with the T-REX experiment

Timothy Goodman, Stefano Alberti, Jean-Philippe Hogge, Joaquim Loizu Cisquella, Mario Ludovico Podesta, Jérémy Genoud, Falk Hans Braunmüller, Francesco Romano, Guillaume Michel Le Bars

Gyrotrons are essential devices for the development of nuclear fusion, but their design and reliable operation still present numerous challenges. In particular, certain gyrotrons encounter issues related to trapped electron clouds in the magnetron injectio ...

AIP Publishing2025

Efficient single-stage optimization of islands in finite-β stellarator equilibria

Joaquim Loizu Cisquella

We present single-stage optimization of islands in finite- β stellarator equilibria. Stellarator optimization is traditionally performed as a two-stage process; in the first stage, an optimal equilibrium is calculated that balances a set of competing const ...

American Institute of Physics (AIP)2025

Sawtooth crash in tokamak as a sequence of multi-region relaxed MHD equilibria

Joaquim Loizu Cisquella

This study examines the sawtooth crash phenomenon in tokamak plasmas by modeling it as a sequence of multi-region relaxed magnetohydrodynamic (MRxMHD) equilibria. Using the stepped-pressure equilibrium code, we constructed a series of equilibria representi ...

2025

Design and First Tests of the Trapped Electrons Experiment T-REX

Stefano Alberti, Joaquim Loizu Cisquella, Damien Fasel, Jérémy Genoud, Steve Couturier, Severino Antonioni, Francesco Romano

Gyrotrons are essential for electron cyclotron resonance heating (ECRH) in fusion reactors, making efficient operation crucial for advancing fusion energy. Past experiments revealed instability issues due to trapped electrons in the magnetron injection gun ...

AIP Publishing2024

Constructing nested coordinates inside strongly shaped toroids using an action principle

Joaquim Loizu Cisquella

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 pr ...

Cambridge University Press2024

Direct prediction of saturated neoclassical tearing modes in slab using an equilibrium approach

Jonathan Graves, Joaquim Loizu Cisquella

We demonstrate for the first time that the nonlinear saturation of neoclassical tearing modes (NTMs) can be found directly using a variational principle based on Taylor relaxation, without needing to simulate the intermediate, resistivity-dependent dynamic ...

IOP Publishing2024

Overview of the first Wendelstein 7-X long pulse campaign with fully water-cooled plasma facing components

Joaquim Loizu Cisquella, Mike Machielsen

After a long device enhancement phase, scientific operation resumed in 2022. The main new device components are the water cooling of all plasma facing components and the new water-cooled high heat flux divertor units. Water cooling allowed for the first lo ...

IOP Publishing Ltd2024

FENNECS: a novel particle-in-cell code for simulating the formation of magnetized non-neutral plasmas trapped by electrodes of complex geometries

Stefano Alberti, Jean-Philippe Hogge, Joaquim Loizu Cisquella, Jérémy Genoud, Francesco Romano, Guillaume Michel Le Bars

This paper presents the new 2D electrostatic particle -in -cell code FENNECS developed to study the formation of magnetized non -neutral plasmas in geometries with azimuthal symmetry. This code has been developed in the domain of gyrotron electron gun desi ...

2024