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

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

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, Damien Fasel, Joaquim Loizu Cisquella, Severino Antonioni, Jérémy Genoud, Steve Couturier, 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, Guillaume Michel Le Bars, Francesco Romano

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

Global fluid simulation of plasma turbulence in stellarators with the GBS code

Joaquim Loizu Cisquella, Paolo Ricci, António João Caeiro Heitor Coelho

The implementation of three-dimensional magnetic fields, such as the ones of stellarators, in the GBS code (Ricci et al 2012 Plasma Phys. Control. Fusion54 124047; Giacomin et al 2022 J. Comput. Phys.464 111294) is presented, and simulation results are dis ...

IOP Publishing Ltd2024

Parallel flows as a key component to interpret Super-X divertor experiments

Basil Duval, Holger Reimerdes, Joaquim Loizu Cisquella, Christian Gabriel Theiler, Curdin Tobias Wüthrich, Olivier Claude Martin Février, Garance Hélène Salomé Durr-Legoupil-Nicoud, Davide Galassi, Lorenzo Martinelli, Sophie Danielle Angelica Gorno, Claudia Colandrea, Guang-Yu Sun, Luke Simons, Artur Perek

The Super-X Divertor (SXD) is an alternative divertor configuration leveraging total flux expansion at the Outer Strike Point (OSP). While the extended 2-Point Model (2PM) predicts facilitated detachment access and control in the SXD configuration, these a ...

IOP Publishing Ltd2024

Simplified and Flexible Coils for Stellarators using Single-Stage Optimization

Joaquim Loizu Cisquella

Single-stage optimization, also known as combined plasma-coil algorithms or direct coil optimization, has recently emerged as a possible method to expedite the design of stellarator devices by including, in a single step, confinement, stability, and engine ...

2024

First self-consistent simulations of trapped electron clouds in a gyrotron gun and comparison with experiments

Stefano Alberti, Jean-Philippe Hogge, Joaquim Loizu Cisquella, Ioannis Pagonakis, Jérémy Genoud, Francesco Romano

We report on the initial validation of the novel code FENNECS, which simulates the spontaneous formation of trapped electron clouds in coaxial geometries with strong externally applied azimuthal flows and in the presence of a residual neutral gas. For this ...

American Institute of Physics (AIP)2023

Validation of GBS plasma turbulence simulation of the TJ-K stellarator

Joaquim Loizu Cisquella, Paolo Ricci

We present a validation of a three-dimensional, two-fluid simulation of plasma turbulence in the TJ-K stellarator, a low temperature plasma experiment ideally suited for turbulence measurements. The simulation is carried out by the GBS code, recently adapt ...

IOP Publishing Ltd2023

Structure of pressure-gradient-driven current singularity in ideal magnetohydrodynamic equilibrium

Joaquim Loizu Cisquella

Singular currents typically appear on rational surfaces in non-axisymmetric ideal magnetohydrodynamic (MHD) equilibria with a continuum of nested flux surfaces and a continuous rotational transition. These currents have two components: a surface current (D ...

2023

Nonlinear saturation of resistive tearing modes in a cylindrical tokamak with and without solving the dynamics

Joaquim Loizu Cisquella

We show that the saturation of resistive tearing modes in a cylindrical tokamak, as well as the corresponding island width, can be directly calculated with a magnetohydrodynamics (MHD) equilibrium code without solving the dynamics and without considering r ...

Cambridge University Press2023

On the relationship between the multi-region relaxed variational principle and resistive inner-layer theory

Joaquim Loizu Cisquella, Ankit Kumar

We show that the variational energy principle of the multi-region relaxed magnetohydrodynamic (MRxMHD) model can be used to predict finite-pressure linear tearing instabilities. In this model, the plasma volume is sliced into sub-volumes separated by 'idea ...

2023

Erratum: Structure of pressure-gradient-driven current singularity in ideal magnetohydrodynamic equilibrium (vol 65, 034008, 2023)

Joaquim Loizu Cisquella, Yao Zhou

Iop Publishing Ltd2023

Equilibrium β-limits dependence on bootstrap current in classical stellarators

Jonathan Graves, Joaquim Loizu Cisquella, Antoine Baillod

While it is important to design stellarators with high magnetohydrodynamic stability β-limit, it is also crucial to ensure that good magnetic surfaces exist in a large range of β values. As β increases, pressure-driven currents perturb the vacuum magnetic ...

Cambridge University Press2023