Publications de Umar Sheikh | EPFL Graph Search

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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 ...

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 ...

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 ...

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 ...

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 ...

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 ...

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 ...

The aim of this paper is to present a signal processing algorithm that, applied to the raw Locked Mode signal, allows us to obtain a disruption indicator in principle exploitable on different tokamaks. A common definition of such an indicator for different ...

A robust disruption mitigation system (DMS) requires accurate characterization of key disruption timescales, one of the most notable being the thermal quench (TQ). Recent modeling of shattered pellet injection (SPI) into ITER plasmas, using JOREK and INDEX ...

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 ...

In ASDEX Upgrade, the propagation of cold pulses induced by type-I edge localized modes (ELMs) is studied using electron cyclotron emission measurements, in a dataset of plasmas with moderate triangularity. It is found that the edge safety factor or the pl ...

Plasma disruptions present a significant challenge to the viability of fusion energy production in tokamak reactors. Among disruption mitigation techniques, shattered pellet injection (SPI) has emerged as a promising approach. The results presented in this ...

This paper describes the extensive progress that has been made in the understanding of tokamak pedestal physics since the 2007 publication of 'Progress in the ITER Physics Basis' (Ikeda 2007 Nucl. Fusion 47 E01-S500). It serves as Chapter 3 of the 2025 Nuc ...

The pre-thermal quench (pre-TQ) dynamics of a pure deuterium ( D 2 ) shattered pellet injection (SPI) into a 3 MA / 7 MJ JET H-mode plasma is studied via 3D non-linear MHD modelling with the JOREK code. The interpretative modelling captures the overall evo ...

We present a model for the particle balance in the post-disruption runaway electron plateau phase of a tokamak discharge. The model is constructed with the help of, and applied to, experimental data from TCV discharges investigating the so-called 'low-Z be ...

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 ...

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 ...

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 ...

A new set of carbon tiles, neutral beam heating optics and gas baffles were installed on TCV during thebaffled divertor upgrade in early 2019. The installation of the baffles allows a deconvolution of the roles ofmain chamber and divertor neutral pressure ...

Umar Sheikh

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

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

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

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

Runaway electron synchrotron radiation in a vertically translated plasma

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

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

A locked mode indicator for disruption prediction on JET and ASDEX upgrade

Multi-device Analysis of Energy Loss Duration and Pellet Penetration with Implications for Shattered Pellet Injection in Iter

Overview of the TCV tokamak experimental programme

ELM-induced cold pulse propagation in ASDEX Upgrade

Impact of impurity seeding on shattered pellet injection mitigations on the Joint European Torus

Progress in Pedestal and Edge Physics: Chapter 3 of the Special Issue: on the Path to Tokamak Burning Plasma Operation

Interpretative 3D MHD modelling of deuterium SPI into a JET H-mode plasma

An upper pressure limit for low-Z benign termination of runaway electron beams in TCV

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

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

Expulsion of runaway electrons using ECRH in the TCV tokamak

Impact of the new TCV baffled divertor upgrade on pedestal structure and performance

Spectrally Filtered Imaging and Vacuum Ultraviolet Spectroscopy of Preheated Models in X2 (Sept, 10.2514/1.J056021, 2017)