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Person# Samuel Lanthaler

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Plasma (physics)

Plasma () is one of four fundamental states of matter, characterized by the presence of a significant portion of charged particles in any combination of ions or electrons. It is the most abundant form

Tritium

Tritium () or hydrogen-3 (symbol T or 3H) is a rare and radioactive isotope of hydrogen with a half-life of about 12 years. The nucleus of tritium (t, sometimes called a triton) contains on

Tokamak

A tokamak (ˈtoʊkəmæk; токамáк) is a device which uses a powerful magnetic field to confine plasma in the shape of a torus. The tokamak is one of several types of magnetic confinement devices being

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Himank Anand, Yanis Andrebe, Otto Asunta, Roland Behn, Attila Bencze, Patrick Blanchard, Alberto Bottino, Yann Camenen, Stefano Coda, Joan Decker, Basil Duval, Emiliano Fable, Ambrogio Fasoli, Jonathan Marc Philippe Faustin, Federico Alberto Alfredo Felici, Davide Galassi, Cristian Galperti, Javier García Hernández, Timothy Goodman, Jonathan Graves, Marc Gruber, Jan Horacek, Zhouji Huang, Thomas Binderup Jensen, Alexander Karpushov, Doohyun Kim, Benoît Labit, Samuel Lanthaler, Hoang Bao Le, Claudio Marini, Yves Martin, Mikhail Maslov, Ben McMillan, Antoine Pierre Emmanuel Alexis Merle, Jean-Marc Moret, Heinz Mueller, Federico Nespoli, Hamish William Patten, Alessandro Pau, Antonio José Pereira de Figueiredo, David Pfefferlé, Richard Pitts, Emanuele Poli, Laurie Porte, Holger Reimerdes, Olivier Sauter, Andrea Scarabosio, Umar Sheikh, Cristian Sommariva, Haomin Sun, Giovanni Tardini, Anna Teplukhina, Christian Gabriel Theiler, Cedric Kar-Wai Tsui, Kevin Henricus Annemarie Verhaegh, Nicola Vianello, Wouter Vijvers, Dávid Wágner, Xiao Wang, Henri Weisen, Dalziel Joseph Wilson, Marco Wischmeier, Liang Yao, Yao Zhou, Hartmut Zohm

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 machines would facilitate the development of portable systems for disruption prediction, which is becoming of increasingly importance for the next tokamak generations. Moreover, the indicator allows us to overcome some intrinsic problems in the diagnostic system such as drift and offset. The behavior of the proposed indicator as disruption predictor, based on crossing optimized thresholds of the signal amplitude, has been analyzed using data of both JET and ASDEX Upgrade experiments. A thorough analysis of the disruption prediction performance shows how the indicator is able to recover some missed and tardy detections of the raw signal. Moreover, it intervenes and corrects premature or even wrong alarms due to, e.g., drifts and/or offsets.

2019The stability of pressure driven modes such as the 1/1 internal kink is known to depend sensitively on a multitude of physical effects such as toroidal rotation, kinetic effects due to thermal and suprathermal particle species and finite Larmor radius effects. Presently available models do not take into account these combined effects in a consistent way. This thesis presents the derivation of a novel kinetic-MHD model utilizing a kinetic pressure closure which incorporates all of these physical mechanisms and can in particular be used to study the interplay of important centrifugal and kinetic effects in strongly rotating plasmas.
The kinetic-MHD model is based on an original derivation of a consistent set of guiding-centre equations allowing for sonic flow. Important higher-order Larmor radius corrections to the guiding-centre coordinates, which are conventionally discarded, are discussed in detail for two applications: The first application concerns neutral beam injection (NBI) heating. It is shown that higher-order (Ba~nos drift) corrections affect the expected resonances of particles with resonant magnetic perturbations (RMP), as well as the estimated NBI driven current in slowing-down simulations in a MAST-like equilibrium by up to 8%. As a second application, the full expression for the gyroviscous contribution to the pressure tensor is obtained from guiding-centre theory. Higher-order guiding-centre corrections are shown to lead to a non-circular Larmor motion of the particle around its guiding-centre which result in off-diagonal components of the pressure tensor. The derived expression for the pressure tensor in terms of the guiding-centre distribution function is used to formulate a consistent linear kinetic-MHD model with kinetic closure for the pressure. The proposed kinetic-MHD model allows for strong flows and includes centrifugal as well as diamagnetic flows. The model also includes a drift-kinetic form of the quasi-neutrality equation, and allows the effects of a parallel electric field on global MHD modes to be studied self-consistently. Pressure closure of the kinetic-MHD model is obtained from a solution of the guiding-centre equations, thus taking into account finite orbit-width effects and particle-wave interactions such as precession resonance. The benefits of the pressure closure approach over an approach following current-closure are discussed. It is shown that due to several convenient cancellations, the pressure closure approach can be based on first-order guiding-centre equations while an equivalent model formulated in terms of current closure would require second-order corrections to be retained. Thus, the benefits and the efficiency of a formulation of kinetic-MHD models with pressure closure over alternative models based on current closure are demonstrated.

Otto Asunta, Patrick Blanchard, Daniele Brunetti, Yann Camenen, Basil Duval, Emiliano Fable, Ambrogio Fasoli, Federico Alberto Alfredo Felici, Davide Galassi, Javier García Hernández, Jonathan Graves, Jan Horacek, Samuel Lanthaler, Yiming Li, Alberto Mariani, Mikhail Maslov, Antoine Pierre Emmanuel Alexis Merle, Federico Nespoli, Hamish William Patten, Alessandro Pau, Antonio José Pereira de Figueiredo, Richard Pitts, Francesca Maria Poli, Olivier Sauter, Cristian Sommariva, Haomin Sun, Kenji Tanaka, Anna Teplukhina, Duccio Testa, Nicola Vianello, Henri Weisen, Marco Wischmeier, Yao Zhou

Developing successful tokamak operation scenarios, as well as confident extrapolation of present-day knowledge requires a rigorous understanding of plasma turbulence, which largely determines the quality of the confinement. In particular, accurate particle transport predictions are essential due to the strong dependence of fusion power or bootstrap current on the particle density details. Here, gyrokinetic turbulence simulations are performed with physics inputs taken from a JET power scan, for which a relatively weak degradation of energy confinement and a significant density peaking is obtained with increasing input power. This way physics parameters that lead to such increase in the density peaking shall be elucidated. While well-known candidates, such as the collisionality, previously found in other studies are also recovered in this study, it is furthermore found that edge E x B shearing may adopt a crucial role by enhancing the inward pinch. These results may indicate that a plasma with rotational shear could develop a stronger density peaking as compared to a non-rotating one, because its inward convection is increased compared to the outward diffusive particle flux as long as this rotation has a significant on E x B flow shear stabilization. The possibly significant implications for future devices, which will exhibit much less torque compared to present day experiments, are discussed.

2019