Publications by Umesh Kumar | EPFL Graph Search

First measurements of velocity-space resolved intra-ELM fast-ion losses on the TCV tokamak

Ambrogio Fasoli, Basil Duval, Benoît Labit, Alexander Karpushov, Mario Ludovico Podesta, Umesh Kumar, Jesús Poley Sanjuán

Edge Localised Modes (ELMs) induced fast-ion losses have been characterised in the energy, E, and pitch, λ = v ∥ / v , space using a unique Fast Ion Loss Detector (FILD) on the tokamak à configuration variable. The FILD is equipped with a 128 Avalanche Pho ...

2025

Cascades of Parametric Instabilities in the Tokamak Plasma Edge during Electron Cyclotron Resonance Heating

Stefano Coda, Umesh Kumar

We report observations of nonlinear two-plasmon decay instabilities (TPDIs) of a high -power microwave beam, a process similar to half -harmonic generation in optics, during electron cyclotron resonance heating in a tokamak. TPDIs are found to occur regula ...

Amer Physical Soc2024

Experimental research on the TCV tokamak

Olivier Sauter, Ambrogio Fasoli, Stefano Coda, Timothy Goodman, Yves Martin, Stefano Alberti, Ivo Furno, Duccio Testa, Patrick Blanchard, Holger Reimerdes

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

Validation of short-pulse reflectometry turbulence measurements with a synthetic diagnostic

Stefano Coda, Stephan Brunner, Oleg Krutkin, Umesh Kumar, Mackenzie Peter-Fulford Van Rossem, Samuele Mazzi

Experimental measurements of the turbulence amplitude utilizing a short pulse reflectometry method are presented. Two discharges with shaped plasma possessing opposite signs of triangularity are considered and a higher turbulence amplitude is found in the ...

IOP Publishing Ltd2024

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

Olivier Sauter, Basil Duval, Stefano Coda, Timothy Goodman, Jean-Marc Moret, Duccio Testa, Patrick Blanchard, Holger Reimerdes, Benoît Labit, Christian Gabriel Theiler

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

Expulsion of runaway electrons using ECRH in the TCV tokamak

Basil Duval, Stefano Coda, Cristian Sommariva, Laurie Porte, Joan Decker, Umar Sheikh, Luke Simons, Umesh Kumar, Jean Arthur Cazabonne, Arsène Stéphane Tema Biwole

Runaway electrons (REs) are a concern for tokamak fusion reactors from discharge startup to termination. A sudden localized loss of a multi-megaampere RE beam can inflict severe damage to the first wall. Should a disruption occur, the existence of a RE see ...

IOP Publishing Ltd2024

Impact of microwave beam scattering by density fluctuations on the electron-cyclotron power deposition profile in tokamaks

Stefano Coda, Joan Decker, Oleg Krutkin, Umesh Kumar, Jean Arthur Cazabonne

Electron-cyclotron waves are a tool commonly used in tokamaks, in particular to drive current. Their ability to drive current in a very localized manner renders them an optimal tool for MHD mode mitigation. However, such applications require high accuracy ...

IOP Publishing Ltd2024

Utilizing parametric instabilities to diagnose edge density fluctuations in TCV

Stefano Coda, Umesh Kumar

Two-plasmon decay instabilities (TPDIs) are a class of parametric instabilities where a gyrotron beam, polarized in X-mode, decays nonlinearly into two upper hybrid waves at approximately half frequency. Here, we present the design of a simple radiometer t ...

2024

Study of fast-ion-driven toroidal Alfvén eigenmodes impacting on the global confinement in TCV L-mode plasmas

Stefano Coda, Laurent Villard, Stephan Brunner, Justin Richard Ball, Oleg Krutkin, Luke Simons, Umesh Kumar, Baruch Rofman, Jesús Poley Sanjuán, Javier García Hernández

Following recent observations of unstable Toroidal Alfven Eigenmodes (TAEs) in a counter-current Neutral Beam Injection (NBI) scenario developed in TCV, an in-depth analysis of the impact of such modes on the global confinement and performance is carried o ...

2023

Overview of the TCV tokamak experimental programme

Olivier Sauter, Ambrogio Fasoli, Basil Duval, Timothy Goodman, Jonathan Graves, Yves Martin, Jean-Marc Moret, Stefano Alberti, Ivo Furno, Duccio Testa

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