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Umar Sheikh

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Publications associées (80)

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

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

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

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

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

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

Overview of ASDEX upgrade results in view of ITER and DEMO

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

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

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

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

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

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

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

The X-Point radiating regime at ASDEX Upgrade and TCV

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

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

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

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, Sophie Danielle Angelica Gorno, Claudia Colandrea, 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

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

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

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

RADCAM-A radiation camera system combining foil bolometers, AXUV diodes, and filtered soft x-ray diodes

Basil Duval, Umar Sheikh, Luke Simons

Measurements of radiated power are critical for characterizing and optimizing tokamak performance. The RADCAM system, comprising arrays of foil bolometers, Absolute eXtreme UltraViolet (AXUV), and filtered soft x-ray diodes, has been constructed to provide ...

2022

Full conversion from ohmic to runaway electron driven current via massive gas injection in the TCV tokamak

Patrick Blanchard, Basil Duval, Olivier Sauter, Stefano Coda, Benoît Labit, Joan Decker, Umar Sheikh, Cristian Galperti, Gergely Papp

Full conversion from ohmic to runaway electron (RE) driven current was observed in the tokamak a configuration variable (TCV) following massive injection of neon through a disruption mitigation valve into a low-density limited circular plasma. Following a ...

IOP Publishing Ltd2022

Improved heat and particle flux mitigation in high core confinement, baffled, alternative divertor configurations in the TCV tokamak

Patrick Blanchard, Basil Duval, Holger Reimerdes, Benoît Labit, Christian Gabriel Theiler, Hugo De Oliveira, Umar Sheikh, Filippo Bagnato, Matteo Vallar, Sophie Danielle Angelica Gorno, Claudia Colandrea, Harshita Raj, Artur Perek

Nitrogen seeded detachment has been achieved in the tokamak a configuration variable (TCV) in alternative divertor configurations (ADCs), namely X-divertor and X-point target, with and without baffles in H-mode plasmas with high core confinement. Both ADCs ...

IOP Publishing Ltd2022

Evidence on the effects of main-chamber neutrals on density shoulder broadening

Basil Duval, Holger Reimerdes, Christian Gabriel Theiler, Cedric Kar-Wai Tsui, Umar Sheikh, Marcelo Baquero Ruiz, Nicola Vianello, Mirko Wensing, Sophie Danielle Angelica Gorno, Artur Perek

Evidence that density shoulder broadening is dependent on high main-chamber neutral density is presented. Shoulder broadening does notoccur when the sources for main-chamber neutrals are minimized using divertor baffles and wide gaps to the first wall (sim ...

2022

Overview of the TCV tokamak experimental programme

Patrick Blanchard, Stephan Brunner, Stefano Alberti, Basil Duval, Ambrogio Fasoli, Timothy Goodman, Xavier Llobet, Yves Martin, Jean-Marc Moret, Olivier Sauter, Henri Weisen, Ivo Furno, Holger Reimerdes, Jean-Philippe Hogge, Jan Horacek, Alexander Karpushov, Laurie Porte, Yanis Andrebe, Jonathan Graves, Duccio Testa, Benoît Labit, Joaquim Loizu Cisquella, Paolo Ricci, Christian Gabriel Theiler, Federico Alberto Alfredo Felici, Miguel Filipe Silva Füglister, Antoine Pierre Emmanuel Alexis Merle, Oulfa Chellaï, Curdin Tobias Wüthrich, Joan Decker, Cedric Kar-Wai Tsui, Pedro Andres Molina Cabrera, Matteo Fontana, Umar Sheikh, Cristian Galperti, Marcelo Baquero Ruiz, Dahye Choi, Aylwin Iantchenko, Mengdi Kong, Roberto Maurizio, Francesco Carpanese, , , , , , , , , , , , , , , , , , , , , , ,

Shattered pellet injection experiments at JET in support of the ITER disruption mitigation system design

Umar Sheikh

A series of experiments have been executed at JET to assess the efficacy of the newly installed shattered pellet injection (SPI) system in mitigating the effects of disruptions. Issues, important for the ITER disruption mitigation system, such as thermal l ...

IOP Publishing Ltd2022

Upgrade of the neutral beam heating system on the TCV tokamak - second high energy neutral beam

Basil Duval, Damien Fasel, Ambrogio Fasoli, Pierre Lavanchy, Blaise Marlétaz, Yves Martin, Holger Reimerdes, Stefano Coda, Ugo Siravo, Alexander Karpushov, Jérémie Dubray, Frédéric Dolizy, Rémy Jacquier, Matthieu Toussaint, Umar Sheikh, Marcelo Baquero Ruiz, Filippo Bagnato, Lorenzo Martinelli, Matteo Vallar, Claudia Colandrea, Dmytry Mykytchuk, Jesús Poley Sanjuán

The TCV tokamak continues to leverage its unique shaping capabilities, flexible heating systems and modern control system to provide a stepladder approach for extrapolations of experimental results from different ma-chines to ITER and DEMO. TCV's configura ...

ELSEVIER SCIENCE SA2022

Overview of JET results for optimising ITER operation

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

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

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

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

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

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

Basil Duval, Holger Reimerdes, Benoît Labit, 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

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

Basil Duval, Joan Decker, Umar Sheikh, Gergely Papp, 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

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Ajay Chandrarajan Jayalekshmi

Mirko Wensing

Lorenzo Stipani

Federico Pesamosca

Olivier Claude Martin Février

Anna Ngoc Minh Trang Vu

Arsène Stéphane Tema Biwole

Lorenzo Martinelli

Jean Arthur Cazabonne

Alessandro Pau

Matteo Vallar

Sophie Danielle Angelica Gorno

The tokamak a configuration variable (TCV) continues to leverage its unique shaping capabilities, flexible heating systems and modern control system to address critical issues in preparation for ITER and a fusion power plant. For the 2019-20 campaign its c ...

IOP Publishing Ltd2022