Publications by Umar Sheikh | EPFL Graph Search

Related publications (74)

Disruption thermal load mitigation with shattered pellet injection on the Joint European Torus (JET)

Disruption mitigation remains a critical, unresolved challenge for ITER. To aid in addressing this challenge, a shattered pellet injection (SPI) system was installed on JET and experiments conducted at a range of thermal energy fractions and stored energie ...

IOP Publishing Ltd2021

The effect of the secondary x-point on the scrape-off layer transport in the TCV snowflake minus divertor

Basil Duval, Benoît Labit, Holger Reimerdes, Christian Gabriel Theiler, Cedric Kar-Wai Tsui, Umar Sheikh, Roberto Maurizio

The snowflake (SF) magnetic configuration is investigated as a potential power exhaust solution for a fusion reactor, but also to improve our understanding of divertor physics in general. Unlike a conventional single null (SN), it features an additional ne ...

IOP Publishing Ltd2018

The effect of plasma shaping on high density H-mode SOL profiles and fluctuations in TCV

Nicola Vianello, Benoît Labit, Holger Reimerdes, Christian Gabriel Theiler, Cedric Kar-Wai Tsui, Umar Sheikh, Guang-Yu Sun, Claudia Colandrea, Sophie Danielle Angelica Gorno, Luke Simons

The impact of plasma shaping on the properties of high density H-mode scrape-off layer (SOL) profiles and transport at the outer midplane has been investigated on Tokamaka configuration variable. The experimental dataset has been acquired by evolving the u ...

IOP Publishing Ltd2024

Benign termination of runaway electron beams on ASDEX Upgrade and TCV

Stefano Coda, Basil Duval, Joan Decker, Umar Sheikh, Claudia Colandrea, Luke Simons, Jean Arthur Cazabonne

This paper discusses the development of a benign termination scenario for runaway electron (RE) beams on ASDEX Upgrade and TCV. A systematic study revealed that a low electron density (n e) companion plasma was required to achieve a large MHD instability, ...

Iop Publishing Ltd2024

A Variable Structure Control Scheme Proposal for the Tokamak a Configuration Variable

Olivier Sauter, Ambrogio Fasoli, Stefano Coda, Basil Duval, Henri Weisen, Timothy Goodman, Yves Martin, Yann Camenen, Jan Horacek, Duccio Testa, Marco Wischmeier, Jean-Marc Moret, Ivo Furno, Nicola Vianello, Minh Quang Tran, Patrick Blanchard, Alessandro Pau, Federico Alberto Alfredo Felici, Benoît Labit, Paolo Ricci, Jean-Philippe Hogge, Jonathan Graves, Holger Reimerdes, Laurie Porte, Christian Gabriel Theiler, Alexander Karpushov, Cedric Kar-Wai Tsui, Federico Nespoli, Kevin Henricus Annemarie Verhaegh, Antoine Pierre Emmanuel Alexis Merle, Umar Sheikh, Wouter Vijvers, Xavier Llobet, Christian Schlatter, Yanis Andrebe, Cristian Galperti, Joan Decker, Zhouji Huang, Fabio Riva, Mengdi Kong, Rémy Jacquier, Anna Teplukhina, Roberto Maurizio, Oulfa Chellaï, Francesco Carpanese, Falk Hans Braunmüller, Claudio Marini, Himank Anand, Dahye Choi, Hoang Bao Le, Josef Kamleitner, Joyeeta Sinha, Anton Malygin, Mélanie Preynas, Joshua Nathaniel Hawke

Fusion power is the most significant prospects in the long-term future of energy in the sense that it composes a potentially clean, cheap, and unlimited power source that would substitute the widespread traditional nonrenewable energies, reducing the geogr ...

2019

Overview of JET results for optimising ITER operation

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

The JET 2019-2020 scientific and technological programme exploited the results of years of concerted scientific and engineering work, including the ITER-like wall (ILW: Be wall and W divertor) installed in 2010, improved diagnostic capabilities now fully a ...

IOP Publishing Ltd2022

Sliding Surface Based Schemes for the Tokamak a Configuration Variable

Olivier Sauter, Ambrogio Fasoli, Stefano Coda, Basil Duval, Henri Weisen, Timothy Goodman, Yves Martin, Stefano Alberti, Yann Camenen, Jan Horacek, Duccio Testa, Marco Wischmeier, Jean-Marc Moret, Ivo Furno, Minh Quang Tran, Patrick Blanchard, Alessandro Pau, Federico Alberto Alfredo Felici, Benoît Labit, Paolo Ricci, Jean-Philippe Hogge, Jonathan Graves, Holger Reimerdes, Laurie Porte, Christian Gabriel Theiler, Alexander Karpushov, Bernard Schneider, Federico Nespoli, Kevin Henricus Annemarie Verhaegh, Antoine Pierre Emmanuel Alexis Merle, Umar Sheikh, Wouter Vijvers, Xavier Llobet, Christian Schlatter, Matteo Fontana, Yanis Andrebe, Cristian Galperti, Joan Decker, Cedric Kar-Wai Tsui, Fabio Riva, Mengdi Kong, Nicola Vianello, Rémy Jacquier, Pedro Andres Molina Cabrera, Anna Teplukhina, Zhouji Huang, Roberto Maurizio, Oulfa Chellaï, Francesco Carpanese, Falk Hans Braunmüller, Claudio Marini, Himank Anand, Dahye Choi, Hoang Bao Le, Josef Kamleitner, Miguel Filipe Silva Füglister, Joyeeta Sinha, Anton Malygin, Mélanie Preynas, Joshua Nathaniel Hawke

Fusion power may be seen as the energy of the future in the sense that it composes a potentially clean, cheap and unlimited power source that would reduce the worldwide dependency on non-renewable energies. Nevertheless, while nowadays the fusion reaction ...

IEEE2018

Power exhaust and core-divertor compatibility of the baffled snowflake divertor in TCV

Basil Duval, Holger Reimerdes, Christian Gabriel Theiler, Umar Sheikh, Olivier Claude Martin Février, Claudia Colandrea, Sophie Danielle Angelica Gorno, Luke Simons

A baffled snowflake minus low-field side (SF-LFS) is geometrically-optimised in tokamak a` configuration variable, increasing divertor neutral pressure, to evaluate the roles of divertor closure (comparing with an unbaffled SF-LFS) and magnetic geometry (c ...

2023

Experimental research on the TCV tokamak

Flavio Mauricio Martins E Silva, Vincent Masson, Abhilash Mathews, Olivier Sauter, Ambrogio Fasoli, Stefano Coda, Henri Weisen, Timothy Goodman, Yves Martin, Stefano Alberti, Duccio Testa, Ivo Furno, Patrick Blanchard, Benoît Labit, Jean-Philippe Hogge, Holger Reimerdes, Christian Gabriel Theiler, Federico Alberto Alfredo Felici, Alexander Karpushov, Antoine Pierre Emmanuel Alexis Merle, Umar Sheikh, Simon Van Mulders, Alessandro Pau, Yanis Andrebe, Cristian Galperti, Joan Decker, Jérémy Genoud, Marcelo Baquero Ruiz, Cedric Kar-Wai Tsui, Mengdi Kong, Matteo Vallar, Olivier Claude Martin Février, Davide Galassi, Guang-Yu Sun, Pedro Andres Molina Cabrera, Filippo Bagnato, Artur Perek, Claudia Colandrea, Sophie Danielle Angelica Gorno, Francesco Carpanese, Nicola Offeddu, Luke Simons, Aylwin Iantchenko, Maurizio Giacomin, Lorenzo Martinelli, Oleg Krutkin, Antoine Baillod, Federico Pesamosca, Dmytry Mykytchuk, Jesús Poley Sanjuán, Carl Mathias Paul Hoppe, Hugo De Oliveira, Benjamin Alexandre Vincent, Umesh Kumar, Garance Hélène Salomé Durr-Legoupil-Nicoud, Arsène Stéphane Tema Biwole, Massimo Carpita, Jean Arthur Cazabonne, Yuxuan Wang, Davide Mancini, Cassandre Ekta Contré, Stefano Marchioni, Samuele Mazzi, Reinart Andreas J. Coosemans, Gino Marceca, Renat Karimov, Elena Tonello, Michele Marin, Martim Zurita, Alessandro Balestri, Humberto Torreblanca Quiroz, Francesco Pastore, Daniele Hamm, Mackenzie Peter-Fulford Van Rossem, Emanuel Paul Huett, Nam Axel David Vu, Marta Mariarmanda Pedrini, Cristina Venturini, Hari Raj, Antonia Frank, Silvia Masillo

Tokamak à configuration variable (TCV), recently celebrating 30 years of near-continual operation, continues in its missions to advance outstanding key physics and operational scenario issues for ITER and the design of future power plants such as DEMO. The ...

IOP Publishing Ltd2024

Overview of ASDEX upgrade results in view of ITER and DEMO

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

Experiments on ASDEX Upgrade (AUG) in 2021 and 2022 have addressed a number of critical issues for ITER and EU DEMO. A major objective of the AUG programme is to shed light on the underlying physics of confinement, stability, and plasma exhaust in order to ...

IOP Publishing Ltd2024

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

Matthew Paul Goodman, Zhuosheng Huang, Olivier Sauter, Stefano Coda, 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, Yanis Andrebe, Cristian Galperti, Joan Decker, Cedric Kar-Wai Tsui, Mengdi Kong, Olivier Claude Martin Février, Davide Galassi, Cristian Sommariva, Anna Teplukhina, Filippo Bagnato, Roberto Maurizio, Kevin Henricus Annemarie Verhaegh, Mirko Wensing, Francesco Carpanese, Claudio Marini, Aylwin Iantchenko, Dahye Choi, Federico Pesamosca, Hugo Antoine Georges Arnichand, Hugo De Oliveira, Lorenzo Stipani, Joshua Nathaniel Hawke, Nam Axel David Vu

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

Disruption mitigation efficiency and scaling with thermal energy fraction on ASDEX Upgrade

Basil Duval, Umar Sheikh

Disruption mitigation remains a critical and unresolved issue for ITER. Measurement uncertainties preventing quantification of a system's efficacy remains a significant hurdle in producing and validating a viable disruption mitigation system. This study ad ...

IOP Publishing Ltd2020

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

Implementation of low temperature spectrometers for the JET high resolution Thomson scattering diagnostic for disruption plasma measurements

Umar Sheikh

This work presents a system upgrade of the High Resolution Thomson Scattering (HRTS) diagnostic [Pasqualotto et al., Rev. Sci. Instrum. 75, 3891-3893 (2004)] on JET that allows it to measure low temperature (1-500 eV) plasma pre- and post-Thermal quench (T ...

2024

Role of the pedestal position on the pedestal performance in AUG, JET-ILW and TCV and implications for ITER

Stefano Coda, Patrick Blanchard, Benoît Labit, Antoine Pierre Emmanuel Alexis Merle, Umar Sheikh, Pamela Solange Valdés Undurraga, Lenke Horváth

The role of the pedestal position on the pedestal performance has been investigated in AUG, JET-ILW and TCV. When the pedestal is peeling-ballooning (PB) limited, the three machines show a similar behaviour. The outward shift of the pedestal density relati ...

IOP Publishing Ltd2019

Progress from ASDEX Upgrade experiments in preparing the physics basis of ITER operation and DEMO scenario development

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, Cristian Sommariva

An overview of recent results obtained at the tokamak ASDEX Upgrade (AUG) is given. A work flow for predictive profile modelling of AUG discharges was established which is able to reproduce experimental H-mode plasma profiles based on engineering parameter ...

IOP Publishing Ltd2022

MHD modeling of shattered pellet injection in JET

Umar Sheikh

Nonlinear 3D MHD simulations of shattered-pellet injection (SPI) in JET show prototypical SPI-driven disruptions using the M3D-C1 and NIMROD extended-MHD codes. Initially, radiation-driven thermal quenches are accelerated by MHD activity as the pellet cros ...

IOP Publishing Ltd2023

Optical Thickness Measurements of Vacuum Ultraviolet Radiation in the X2 Expansion Tube

Umar Sheikh

Experiments were conducted in the X2 expansion tube to measure vacuum ultraviolet radiation from shock layers representative of reentry conditions at flight equivalent velocities of 10.0 and 12.2 km/s. Cylindrical models of varying lengths were used to mak ...

2016

Overview of T and D-T results in JET with ITER-like wall

Olivier Sauter, Duccio Testa, Benoît Labit, Holger Reimerdes, Umar Sheikh, Alessandro Pau, Matteo Vallar, Olivier Claude Martin Février, Cristian Sommariva, Carl Mathias Paul Hoppe, Cassandre Ekta Contré, Samuele Mazzi, Gino Marceca, Eduardo José Lascas Neto, Mackenzie Peter-Fulford Van Rossem

In 2021 JET exploited its unique capabilities to operate with T and D-T fuel with an ITER-like Be/W wall (JET-ILW). This second major JET D-T campaign (DTE2), after DTE1 in 1997, represented the culmination of a series of JET enhancements-new fusion diagno ...

IOP Publishing Ltd2024

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