Publications by Umar Sheikh | EPFL Graph Search

Milestone in predicting core plasma turbulence: successful multi-channel validation of the gyrokinetic code GENE

Olivier Sauter, Basil Duval, Stefano Coda, Timothy Goodman, Benoît Labit, Alessandro Pau, Federico Alberto Alfredo Felici, Cristian Sommariva, Laurie Porte, Antoine Pierre Emmanuel Alexis Merle

On the basis of several recent breakthroughs in fusion research, many activities have been launched around the world to develop fusion power plants on the fastest possible time scale. In this context, high-fidelity simulations of the plasma behavior on lar ...

2025

An upper pressure limit for low-Z benign termination of runaway electron beams in TCV

Basil Duval, Stefano Coda, Holger Reimerdes, Joan Decker, Umar Sheikh, Luke Simons, Claudia Colandrea

We present a model for the particle balance in the post-disruption runaway electron plateau phase of a tokamak discharge. The model is constructed with the help of, and applied to, experimental data from TCV discharges investigating the so-called 'low-Z be ...

IOP Publishing Ltd2025

X-point radiation: From discovery to potential application in a future reactor

Holger Reimerdes, Christian Gabriel Theiler, Umar Sheikh, Olivier Claude Martin Février

Power exhaust is a crucial issue for future fusion reactors. Divertor detachment and the required power dissipation fractions of about 95% are foreseen to be achieved by impurity seeding. In a tokamak, at high seeding levels the radiation often concentrate ...

Elsevier2025

Multi-device Analysis of Energy Loss Duration and Pellet Penetration with Implications for Shattered Pellet Injection in Iter

Umar Sheikh

A robust disruption mitigation system (DMS) requires accurate characterization of key disruption timescales, one of the most notable being the thermal quench (TQ). Recent modeling of shattered pellet injection (SPI) into ITER plasmas, using JOREK and INDEX ...

IOP Publishing Ltd2025

Nonlinear excitation of energetic particle driven geodesic acoustic mode by resonance overlap with Alfvén instability in ASDEX Upgrade

Olivier Sauter, Basil Duval, Stefano Coda, Timothy Goodman, Benoît Labit, Alessandro Pau, Federico Alberto Alfredo Felici, Cristian Sommariva, Laurie Porte, Antoine Pierre Emmanuel Alexis Merle

The Alfvén instability nonlinearly excited the energetic-particle-driven geodesic acoustic mode on the ASDEX-Upgrade tokamak, as demonstrated experimentally. The mechanism of the energetic-particle-driven geodesic acoustic mode excitation and the mode nonl ...

Nature Research2025

Radiated Energy Fraction of Spi-induced Disruptions at Asdex Upgrade

Umar Sheikh

Future large tokamaks will operate at high plasma currents and high stored plasma energies. To ensure machine protection in case of a sudden loss of plasma confinement (major disruption), a large fraction of the magnetic and thermal energy must be radiated ...

IOP Publishing Ltd2025

Impact of impurity seeding on shattered pellet injection mitigations on the Joint European Torus

Umar Sheikh, Mengdi Kong

Plasma disruptions present a significant challenge to the viability of fusion energy production in tokamak reactors. Among disruption mitigation techniques, shattered pellet injection (SPI) has emerged as a promising approach. The results presented in this ...

IOP Publishing Ltd2025

Effect of energetic ions on edge-localized modes in tokamak plasmas

Olivier Sauter, Stefano Coda, Timothy Goodman, Jean-Marc Moret, Duccio Testa, Patrick Blanchard, Holger Reimerdes, Benoît Labit, Christian Gabriel Theiler, Federico Alberto Alfredo Felici

The most efficient and promising operational regime for the International Thermonuclear Experimental Reactor tokamak is the high-confinement mode. In this regime, however, periodic relaxations of the plasma edge can occur. These edge-localized modes pose a ...

2025

Progress in Pedestal and Edge Physics: Chapter 3 of the Special Issue: on the Path to Tokamak Burning Plasma Operation

Benoît Labit, Umar Sheikh

This paper describes the extensive progress that has been made in the understanding of tokamak pedestal physics since the 2007 publication of 'Progress in the ITER Physics Basis' (Ikeda 2007 Nucl. Fusion 47 E01-S500). It serves as Chapter 3 of the 2025 Nuc ...

IOP Publishing Ltd2025

Thermal energy mitigation and toroidal peaking effects in JET disruptions

Umar Sheikh

Previous investigations on JET suggest half or less of plasma stored thermal energy Wth is radiated (frad,th≲0.5) using either massive gas injection (MGI) or shattered pellet injection (SPI) disruption mitigation. We investigate whether the apparent incomp ...

AIP Publishing2025