Home

Person

Umar Sheikh

About
Privacy
Disclaimer

Graph Chatbot

Related publications (74)

Page 2 of 4

Observation of magnetic islands in tokamak plasmas during the suppression of edge-localized modes

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

In tokamaks, a leading platform for fusion energy, periodic filamentary plasma eruptions known as edge-localized modes occur in plasmas with high-energy confinement and steep pressure profiles at the plasma edge. These edge-localized modes could damage the ...

2024

Enhanced confinement in diverted negative-triangularity L-mode plasmas in TCV

Olivier Sauter, Stefano Coda, Alessandro Pau, Benoît Labit, Laurie Porte, Antoine Pierre Emmanuel Alexis Merle, Umar Sheikh, Cedric Kar-Wai Tsui, Alessandro Marinoni, Matteo Vallar, Filippo Bagnato

The favorable confinement properties of negative-triangularity (NT) tokamak configurations were discovered in the TCV tokamak in the late 1990s and were documented over the two following decades, through investigations of predominantly electron-heated plas ...

2022

A control oriented strategy of disruption prediction to avoid the configuration collapse of tokamak reactors

Olivier Sauter, Ambrogio Fasoli, Henri Weisen, Duccio Testa, Patrick Blanchard, Federico Alberto Alfredo Felici, Umar Sheikh, Alessandro Pau, Davide Galassi, Cristian Sommariva, Paulo Giovane Paschoali Pereira Puglia, Mike Machielsen, Gino Marceca, Eduardo José Lascas Neto

The objective of thermonuclear fusion consists of producing electricity from the coalescence of light nuclei in high temperature plasmas. The most promising route to fusion envisages the confinement of such plasmas with magnetic fields, whose most studied ...

Nature Research2024

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

Olivier Sauter, Stefano Coda, Basil Duval, Timothy Goodman, Benoît Labit, Laurie Porte, Federico Alberto Alfredo Felici, Antoine Pierre Emmanuel Alexis Merle, Umar Sheikh, Simon Van Mulders, Alessandro Pau, Mengdi Kong, Cristian Sommariva

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

Spectroscopic investigations of divertor detachment in TCV

Basil Duval, Holger Reimerdes, Benoît Labit, Nicola Vianello, Federico Nespoli, Christian Gabriel Theiler, Umar Sheikh, Cedric Kar-Wai Tsui, Kevin Henricus Annemarie Verhaegh, Wouter Vijvers, Roberto Maurizio, Claudio Marini

The aim of this work is to provide an understanding of detachment at TCV with emphasis on analysis of the Balmer line emission. A new Divertor Spectroscopy System has been developed for this purpose. Further development of Balmer line analysis techniques h ...

Elsevier2017

3D radiated power analysis of JET SPI discharges using the Emis3D forward modeling tool

Umar Sheikh

Precise values for radiated energy in tokamak disruption experiments are needed to validate disruption mitigation techniques for burning plasma tokamaks like ITER and SPARC. Control room analysis of radiated power (P rad) on JET assumes axisymmetry, since ...

IOP Publishing Ltd2024

Spurious radiated power signal following massive material injections in JET and the effect of neutral gas pressure on resistive bolometers

Umar Sheikh

Massive material injections in the JET tokamak have been observed to substantially affect resistive bolometer measurements, resulting in a spurious radiated power signal proportional to the quantity injected and reaching up to 8 MW. These bolometers are ca ...

2024

Runaway electron beam control

Stefano Coda, Basil Duval, Umar Sheikh, Cristian Galperti, Joan Decker, Diego Carnevale, Filippo Bagnato, Georgios Pappas

Post-disruption runaway electron (RE) beams in tokamaks with large current can cause deep melting of the vessel and are one of the major concerns for ITER operations. Consequently, a considerable effort is provided by the scientific community in order to t ...

IOP PUBLISHING LTD2019

The X-Point radiating regime at ASDEX Upgrade and TCV

Holger Reimerdes, Christian Gabriel Theiler, Marco Wischmeier, Umar Sheikh, Artur Perek

Future fusion reactors require a safe, steady-state divertor operation. With deep divertor detachment, which is typically induced by impurity seeding, the radiation concentrates in a small region at the X-point or on closed flux surfaces above the X-point. ...

Elsevier2023

Experimental investigation of the radial structure of energetic particle driven GAM in TCV

Duccio Testa, Alexander Karpushov, Mario Ludovico Podesta, Umar Sheikh, Luke Simons, Jesús Poley Sanjuán, Anton Jansen Van Vuuren

High amplitude energetic particle geodesic acoustic mode (EGAM) oscillations driven by Neutral Beam (NBI) injected in the direction counter to the toroidal plasma current are observed in the TCV tokamak. The modes appear at frequencies close to the geodesi ...

IOP Publishing Ltd2025

Resonant interaction between runaway electrons and the toroidal magnetic field ripple in TCV

Umar Sheikh, Artur Perek, Carl Mathias Paul Hoppe

This work explains the anomalously high runaway electron (RE) pitch angles inferred in the flat-top of dedicated Tokamak a Configuration Variable (TCV) experiments. Kinetic modelling shows that the resonant interaction between the gyromotion of the electro ...

IOP Publishing Ltd2024

Overview of progress in European medium sized tokamaks towards an integrated plasma-edge/wall solution

Olivier Sauter, Basil Duval, Stefano Coda, Timothy Goodman, Yves Martin, Jean-Marc Moret, Duccio Testa, Patrick Blanchard, Holger Reimerdes, Benoît Labit, Christian Gabriel Theiler, Alessandro Pau, Federico Alberto Alfredo Felici, Cristian Sommariva, Laurie Porte, Alexander Karpushov, Marc Gruber, Antoine Pierre Emmanuel Alexis Merle, Joan Decker, Umar Sheikh, Cristian Galperti, Yanis Andrebe, Richard Pitts, Yann Camenen, Jan Horacek, Roland Behn, Javier García Hernández, Marco Wischmeier, Nicola Vianello, Federico Nespoli, Antonio José Pereira de Figueiredo, Emiliano Fable, Ben McMillan, Cedric Kar-Wai Tsui, Doohyun Kim, Kevin Henricus Annemarie Verhaegh, Wouter Vijvers, Anna Teplukhina, Zhouji Huang, Dávid Wágner, Claudio Marini, Thomas Binderup Jensen, Hoang Bao Le, Himank Anand, Attila Bencze

Integrating the plasma core performance with an edge and scrape-off layer (SOL) that leads to tolerable heat and particle loads on the wall is a major challenge. The new European medium size tokamak task force (EU-MST) coordinates research on ASDEX Upgrade ...

IOP Publishing Ltd2017

H-mode scrape-off layer power width in the TCV tokamak

Basil Duval, Benoît Labit, Holger Reimerdes, Christian Gabriel Theiler, Umar Sheikh, Roberto Maurizio

Obtaining acceptable conditions at the divertor targets of a next-step fusion experiment based on the tokamak concept is expected to be particularly challenging because of the small predicted value of the plasma power exhaust channel width. An increased co ...

IOP Publishing Ltd2021

Runaway electron synchrotron radiation in a vertically translated plasma

Basil Duval, Umar Sheikh, Joan Decker, Artur Perek

Synchrotron radiation observed from runaway electrons (REs) in tokamaks depends upon the position and size of the RE beam, the RE energy and pitch distributions, as well as the location of the observer. We show experimental synchrotron images of a vertical ...

IOP Publishing Ltd2020

PLASMA SHAPE AND FUELING DEPENDENCE ON THE SMALL ELMS REGIME IN TCV AND AUG

Benoît Labit, Antoine Pierre Emmanuel Alexis Merle, Umar Sheikh, Pedro Andres Molina Cabrera, Roberto Maurizio

A series of experiments has been conducted at AUG and TCV to disentangle the role of fueling, plasma triangularity and closeness to a double null (DN) configuration for the onset of the small ELM regime. At AUG, the role of the SOL density has been revisit ...

2018

Progress in disruption prevention for ITER

Olivier Sauter, Alessandro Pau, Francesca Maria Poli, Umar Sheikh, Mengdi Kong, Luc Nicolas Xuan Zeng

Key plasma physics and real-time control elements needed for robustly stable operation of high fusion power discharges in ITER have been demonstrated in recent research worldwide. Recent analysis has identified the current density profile as the main drive ...

IOP Publishing Ltd2019

Tomographic reconstruction of the runaway distribution function in TCV using multispectral synchrotron images

Basil Duval, Joan Decker, Umar Sheikh, Artur Perek

Synchrotron radiation observed in a quiescent Tokamak a Configuration Variable (TCV) runaway discharge is studied using filtered camera images targeting three distinct wavelength intervals. Through the tomographic simultaneous algebraic reconstruction tech ...

IOP Publishing Ltd2021

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

Overview of the EUROfusion Tokamak Exploitation programme in support of ITER and DEMO

Pacôme Henryk Cécil Devleeshouver, Olivier Sauter, Stefano Coda, Basil Duval, Henri Weisen, Timothy Goodman, Duccio Testa, Jean-Marc Moret, Patrick Blanchard, Benoît Labit, Holger Reimerdes, Christian Gabriel Theiler, Federico Alberto Alfredo Felici, Alexander Karpushov, Antoine Pierre Emmanuel Alexis Merle, Umar Sheikh, Simon Van Mulders, Alessandro Pau, Cristian Galperti, Joan Decker, Marcelo Baquero Ruiz, Cedric Kar-Wai Tsui, Mengdi Kong, Matteo Vallar, Olivier Claude Martin Février, Davide Galassi, Guang-Yu Sun, Filippo Bagnato, Paulo Giovane Paschoali Pereira Puglia, Artur Perek, Claudia Colandrea, Sophie Danielle Angelica Gorno, Nicola Offeddu, Luke Simons, Aylwin Iantchenko, Lorenzo Martinelli, Oleg Krutkin, Dmytry Mykytchuk, Jesús Poley Sanjuán, Carl Mathias Paul Hoppe, Benjamin Alexandre Vincent, Umesh Kumar, Garance Hélène Salomé Durr-Legoupil-Nicoud, Massimo Carpita, Jean Arthur Cazabonne, Davide Mancini, Cassandre Ekta Contré, Stefano Marchioni, Samuele Mazzi, Gino Marceca, Renat Karimov, Elena Tonello, Yoeri Renier Johannes Poels, Michele Marin, Martim Zurita, Alessandro Balestri, Anton Jansen Van Vuuren, Francesco Pastore, Mackenzie Peter-Fulford Van Rossem, Emanuel Paul Huett, Nam Axel David Vu, Hari Raj, Antonia Frank, Aleksandr Listopad

Within the 9th European Framework programme, since 2021 EUROfusion is operating five tokamaks under the auspices of a single Task Force called ‘Tokamak Exploitation’. The goal is to benefit from the complementary capabilities of each machine in a coordinat ...

IOP Publishing Ltd2024

Spectrally Filtered Imaging and Vacuum Ultraviolet Spectroscopy of Preheated Models in X2

Pénélope Leyland, Umar Sheikh

This study presents calibrated vacuum ultraviolet spectroscopic measurements and filtered cyanogen violet band images for steel, cold graphite, and preheated graphite models at three reentry-relevant conditions in the X2 Expansion Tube. An analysis of thes ...

2017