Publications by Umar Sheikh | EPFL Graph Search

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

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

2018

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

Sliding Surface Based Schemes for the Tokamak a Configuration Variable

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

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

Pedestal Structure and Energy Confinement Studies on TCV

Olivier Sauter, Basil Duval, Patrick Blanchard, Benoît Labit, Christian Gabriel Theiler, Antoine Pierre Emmanuel Alexis Merle, Umar Sheikh, Cedric Kar-Wai Tsui

High external gas injection rates are foreseen for future devices to reduce divertor heat loads and this can influence pedestal stability. Fusion yield has been estimated to vary as strongly as

{T}_{e,{\rm{ped}}}^{2}

so an understanding of the underlying ...

2018

Results from recent detachment experiments in alternative divertor configurations on TCV

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

Divertor detachment is explored on the TCV tokamak in alternative magnetic geometries. Starting from typical TCV single-null shapes, the poloidal flux expansion at the outer strikepoint is varied by a factor of 10 to investigate the X-divertor characterist ...

2017

Spectroscopic investigations of divertor detachment in TCV

Basil Duval, Holger Reimerdes, Benoît Labit, Christian Gabriel Theiler, Umar Sheikh, Nicola Vianello, Federico Nespoli, 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 ...

2017

Understanding and suppressing the near scrape-off layer heat flux feature in inboard-limited plasmas in TCV

Ivo Furno, Paolo Ricci, Holger Reimerdes, Benoît Labit, Christian Gabriel Theiler, Umar Sheikh, Richard Pitts, Jan Horacek, Federico Nespoli, Federico David Halpern, Cedric Kar-Wai Tsui, Kevin Henricus Annemarie Verhaegh, Roberto Maurizio

In inboard-limited plasmas, the scrape-off layer (SOL) shows two regions: the near SOL, extending a few mm from the last closed flux surface (LCFS), characterized by a steep gradient of the parallel heat flux radial profile, and a far SOL, typically some c ...

International Atomic Energy Agency2017

TCV divertor upgrade for alternative magnetic configurations

Ambrogio Fasoli, Basil Duval, Stefano Coda, Yves Martin, Pierluigi Bruzzone, Jean-Marc Moret, Stefano Alberti, Duccio Testa, Patrick Blanchard, Holger Reimerdes, Benoît Labit, Christian Gabriel Theiler, René Chavan, Umar Sheikh, Davide Uglietti, Matthieu Toussaint, Marco Wischmeier, Nicola Vianello

The Swiss Plasma Center (SPC) is planning a divertor upgrade for the TCV tokamak. The upgrade aims at extending the research of conventional and alternative divertor configurations to operational scenarios and divertor regimes of greater relevance for a fu ...

2017

Detachment evolution on the TCV tokamak

Basil Duval, Holger Reimerdes, Benoît Labit, Christian Gabriel Theiler, Umar Sheikh, Marco Wischmeier, Cedric Kar-Wai Tsui, Kevin Henricus Annemarie Verhaegh, Wouter Vijvers

Divertor detachment in the TCV tokamak has been investigated through experiments and modelling. Density ramp experiments were carried out in ohmic heated L-mode pulses with the ion del B drift directed away from the primary X-point, similar to previous stu ...

2017

Experimental Studies of the Snowflake Divertor in TCV

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

To address the risk that, in a fusion reactor, the conventional single-null divertor (SND) configuration may not be able to handle the power exhaust, alternative divertor configurations, such as the Snowflake divertor (SFD), are investigated in TCV. The ex ...

Elsevier Science Bv2017

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

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

Sliding Surface Based Schemes for the Tokamak a Configuration Variable

Pedestal Structure and Energy Confinement Studies on TCV

Results from recent detachment experiments in alternative divertor configurations on TCV

Spectroscopic investigations of divertor detachment in TCV

Understanding and suppressing the near scrape-off layer heat flux feature in inboard-limited plasmas in TCV

TCV divertor upgrade for alternative magnetic configurations

Detachment evolution on the TCV tokamak

Experimental Studies of the Snowflake Divertor in TCV

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

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

Sliding Surface Based Schemes for the Tokamak a Configuration Variable

Results from recent detachment experiments in alternative divertor configurations on TCV

Spectroscopic investigations of divertor detachment in TCV

Detachment evolution on the TCV tokamak

Experimental Studies of the Snowflake Divertor in TCV

Understanding and suppressing the near scrape-off layer heat flux feature in inboard-limited plasmas in TCV

Pedestal Structure and Energy Confinement Studies on TCV

TCV divertor upgrade for alternative magnetic configurations