Publications by Stefano Alberti

Chat with Graph Search

Ask any question about EPFL courses, lectures, exercises, research, news, etc. or try the example questions below.

DISCLAIMER: The Graph Chatbot is not programmed to provide explicit or categorical answers to your questions. Rather, it transforms your questions into API requests that are distributed across the various IT services officially administered by EPFL. Its purpose is solely to collect and recommend relevant references to content that you can explore to help you answer your questions.

In noninductively driven discharges, 0.9 MW second harmonic (X2) off-axis co-electron cyclotron current drive deposition is combined with 0.45 MW X2 central heating to create an electron internal transport barrier (eITB) in steady plasma conditions resulting in a 1.6-fold increase of the confinement time (tau(Ee)) over ITER-98L-mode scaling. The eITB is associated with a reversed shear current profile enhanced by a large bootstrap current fraction (up to 80%) and is sustained for up to 10 current redistribu

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 ...

Sawtooth inversion radii and profile peaking factors of a large variety of ohmic and ECH heated L mode plasmas, including, elongations up to 2.6 and triangularities between -0.5 and 0.75, have been investigated in the TCV tokamak. In ohmic plasmas, normalized inversion radii and electron temperature profile peaking factors (corrected for sawtoothing effects) depend solely on the parameter (j)/q(0)j(0), irrespective of plasma shape. With ECH this parameter remains the main scaling parameter. Density profiles

Recently developed self-consistent models for beam-wave interaction simulations of a gyrotron oscillator have been extended to study spurious backward-wave instabilities in smooth-wall circular symmetric beam ducts. Starting from a purely metallic case, th ...

The first series tube of the gyrotrons for the 10-MW electron cyclotron resonance heating system of the stellarator W7-X was tested at Forschungszentrum Karlsruhe (FZK) and yielded a total output power of 0.98 MW, with an,efficiency of 31% (without a singl ...

The self-consistent simulation of the electron beam interaction was performed in the presence of a lossy dielectric layer in the smooth-wall beam duct of a gyrotron oscillator. For this purpose, the linear and spectral code TWANGlinspec was extended. In th ...

Experimental start-up results of a 118 GHz TE(22,6) gyrotron are presented and compared with theory. The theoretical excitation regimes of competing modes are computed in the energy-velocity-pitch-angle plane. The start-up paths through the plane are determined by the time evolution of the beam parameters during the start-up phase and are seen to determine the cavity oscillating mode. Experimental results show that competition between the TE(22,6) and TE-(19,7) modes can be completely eliminated by using th

The development of high-power gyrotrons (118 GHz, 140 GHz) in continuous-wave (CW) operation for heating nuclear fusion plasmas has been in progress for several years in a joint collaboration between different European research institutes and industrial partners. The 140-GHz gyrotron being under development for the installation at the W7-X stellarator now under construction at the IPP Greifswald, Germany, operates in the TE28,8 mode and is equipped with a diode type magnetron injection electron gun, an impr

Fully noninductive, steady-state electron cyclotron current drive (ECCD) has been demonstrated for the first time in experiments carried out in the tokamak a configuration variable (TCV) [O. Sauter , Phys. Rev. Lett. 84, 3322 (2000)]. By appropriately distributing six 0.45 MW ECCD sources over the discharge cross section, fully noninductive, stable, and stationary plasmas with I-p up to 210 kA were obtained for the full discharge duration of 1.9 s, corresponding to more than 900 energy confinement times and

The future EC systems will consist of several gyrotron sources providing MW-level millimeter wave power at a frequency around or above 170 GHz. The development of matched loads is necessary to test the new sources, the components for the transmission lines ...

The European 1 MW, 170 GHz industrial CW prototype gyrotron has been designed within EGYC (European GYrotron Consortium) in collaboration with the industrial partner Thales Electron Devices (TED) and under the coordination of Fusion for Energy (F4E). This ...

Extensive simulations are performed to investigate effects of electron cyclotron instabilities on the gyrotron beam quality, using two-dimensional axisymmetric particle-in-cell (PIG) codes. Both electrostatic and electromagnetic models, as well as realistic geometries of the gyrotron, are considered. It is found that a large beam density can lead to an electrostatic-instability-induced energy spread which substantially degrades the gyrotron efficiency. (C) 1997 American institute of Physics.

In this work, we have studied the effect of the dielectric material on the properties of the modes in a smooth metallic gyrotron beam tunnel partially filled with a lossy dielectric material. Two kinds of modes have been identified, one located inside the ...

Intense electron cyclotron resonance heating (ECRH) and electron cyclotron current drive (ECCD) are employed on the Tokamak a Configuration Variable (TCV) both in second- and third-harmonic X-mode (X2 and X3). The plasma behaviour under such conditions is ...

Generation of a swing electron cyclotron current drive (swing ECCD), i.e. driving alternated, symmetric, positive or negative local ECCD, during a single discharge and at constant total input EC power, was performed at the Tokamak a Configuration Variable ...

During the ongoing pre-concept phase (2014 - 2020) for a possible future European DEMOnstration Fusion Power Plant (DEMO) the activities within EUROfusion WP HCD EC Gyrotron R&D and Advanced Developments are focusing on options for near-term solutions, and ...

A significant effort has recently been initiated at ETHZ for the development of high frequency, high power, frequency-agile gyrotrons for DNP-NMR spectroscopy. In this context an in house cavity interaction code is under development. In this paper, some de ...

In the frame of the TCV Tokamak upgrade, two 84/126 GHz/2 s dual frequency gyrotrons designed by SPC and KIT and manufactured by THALES will be added to the existing EC-System. The first unit has been delivered to EPFL-SPC and tested. In the commissioning ...

In the foreseen upgrade of the Tokamak-a-Configuration-Variable (TCV) it is planned to add 3MW of additional RF power (3rd harmonic X-mode, X3, top-launch) to the present Electron Cyclotron (EC) system. With the upgrade of the EC-system, bringing the total EC power in X3-mode to 4.5MW, and the installation of 1 MW of neutral beam injection, a new avenue will be opened allowing the extensive study of H-mode physics in TCV. The envisaged new gyrotrons (lMW, 126GHz) are based on a minimum redesign of the 140 G

The development of high power gyrotrons in continuous wave (CW) operation for heating of plasmas used in nuclear fusion research has been in progress for several years in a joint collaboration between different European research institutes and industrial partners. A recent R&D program aims at the development of 140 GHz gyrotrons with an output power of 1 MW in CW operation for the 10 MW ECRH system of the new stellarator plasma physics experiment Wendelstein 7-X at IPP Greifswald, Germany. The work is perfo

Stefano Alberti

Chat with Graph Search

Recent results from the electron cyclotron heated plasmas in Tokamak à Configuration Variable (TCV)

Overview of the TCV tokamak experimental programme

Shape dependence of sawtooth inversion radii and profile peaking factors in TCV L mode plasmas

Linear studies of spurious backward-wave instabilities in a dielectric-loaded smooth-wall gyrotron beam ducts

EU megawatt-class 140-GHz CW gyrotron

Modeling of parasitic oscillations in smooth-wall circular symmetric dielectric-loaded gyrotron beam ducts

Startup Methods for Single-Mode Gyrotron Operation

Development of a 140-GHz 1-MW continuous wave gyrotron for the W7-X stellarator

Steady-state fully noninductive operation with electron cyclotron current drive and current profile control in the tokamak a configuration variable (TCV)

Tests and developments of a long-pulse high-power 170 GHz absorbing matched load

Report of recent experiments with the European 1 MW, 170 GHz CW and SP prototype gyrotrons for ITER

Particle-in-cell (PIC) simulations of beam instabilities in gyrotrons

The Effect of the Lossy Material on the Modes in a Smooth Metallic Dielectric Loaded Gyrotron Beam Tunnel

Plasma dynamics with second and third-harmonic ECRH and access to quasi-stationary ELM-free H-mode on TCV

Modulation of electron transport during Swing ECCD discharges in TCV

Towards Advanced Fusion Gyrotrons: 2018 Update on Activities within EUROfusion

Development of Kilowatt THz Gyrotrons for Pulsed Dynamic Nuclear Polarization - Cavity Design Code Phaedra -

Megawatt power generation of the dual-frequency gyrotron for TCV at 84 and 126 GHz, in long pulses

Millimeter Wave System Upgrades On TCV: Additional X3 Power And Fast ECE Polarizers

Development of a 140 GHz, 1 MW, continuous wave gyrotron for the W7-X stellarator