Publications de Trach-Minh Tran

Chattez avec Graph Search

Posez n’importe quelle question sur les cours, conférences, exercices, recherches, actualités, etc. de l’EPFL ou essayez les exemples de questions ci-dessous.

AVERTISSEMENT : Le chatbot Graph n'est pas programmé pour fournir des réponses explicites ou catégoriques à vos questions. Il transforme plutôt vos questions en demandes API qui sont distribuées aux différents services informatiques officiellement administrés par l'EPFL. Son but est uniquement de collecter et de recommander des références pertinentes à des contenus que vous pouvez explorer pour vous aider à répondre à vos questions.

Linearized operators describing inter-species and like-species collisions have been discretized and implemented in the gyrokinetic Particle-In-Cell (PIC) code ORB5 [S. Jolliet, Comp. Phys. Comm. 177, 409 ( 2007)] based on the delta-f approach. Simulation r ...

The parallel velocity distribution function of the weakly relativistic electron beam of a quasi-optical gyrotron has been determined by measuring the Doppler-shifted Electron Cyclotron Emission (ECE) at an angle theta=15 degrees with respect to the external magnetic de-field. Due to the Doppler shift, the frequency of the spontaneous cyclotron emission at the fundamental (nu(0) = 100 GHz) is upshifted to 140 GHz. A broadening of the spectrum up to 10 GHz [full width at half maximium (FWHM)] was measured. Th

The parasitic oscillation of the TE21-degrees gyrotron backward wave (gyro BW) mode is observed in a low-Q, 8 GHz TE011-degrees gyrotron. Although at low power (P(BW) < 5 kW), the oscillation of the gyro BW mode, simultaneously with the gyrotron mode, results in a maximum TE011-degrees mode efficiency of less than 0.25. The parasitic oscillation is suppressed by operating the gyrotron with a negative magnetic field gradient along the electron beam, which allows the maximum efficiency to reach 0.40 and the o

A two-dimensional PIC code aimed at the investigation of electron-cyclotron beam instabilities in gyrotrons and their effects on the beam quality is presented, The code is based on recently developed techniques for handling charge conservation and open boundaries and uses an electromagnetic field which is decomposed in its transverse magnetic (TM) and electric (TE) components, The code has been implemented on the massively parallel computer CRAY T3D, but can also be run on a single processor of the CRAY Y-M

Global gyrokinetic particle simulations have been used to search tokamak configurations which are stable again st the ion-temperature-gradient - driven (ITG) modes commonly held responsible for the core anomalous ion heat transport. The stable configuratio ...

The particle-in-cell code ORB5 is a global gyrokinetic turbulence simulation code in tokamak geometry. It has been developed at CRPP, Lausanne, Switzerland, with major contributions from IPP, Garching, Germany, and IPP, Greifswald, Germany, under a long-st ...

Electron beam instabilities occurring in a gyrotron electron beam can induce an energy spread which might significantly deteriorate the gyrotron efficiency. Three types of instabilities are considered to explain the important discrepancy found between the theoretical and experimental efficiency in the case of quasi-optical gyrotrons (QOG): the electron cyclotron maser instability (ECMI), the electrostatic Bernstein instability (BI) and the Langmuir instability (LI). When the magnetic field gradient in drift

Turbulent transport dynamics and level are investigated with the 5D gyrokinetic global code GYSELA, modelling the Ion Temperature Gradient instability with adiabatic electrons. The heat transport exhibits large scale events, propagating radially in both directions at velocities of the order of the diamagnetic velocity. The effective diffusivity is in agreement with that reported in other gyrokinetic codes such as ORB5. Transition from Bohm to gyroBohm scaling is observed on the turbulence correlation length

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

A new three-dimensional code, VENUS+delta f, for neoclassical transport calculations in nonaxisymmetric toroidal systems is presented. Numerical drift orbits from the original VENUS code and the delta f method developed for tokamak transport calculations a ...

In global gyrokinetic simulations it takes a long time for the turbulence to reach a quasisteady state, and quantitative predictions about the quasisteady state turbulence have been difficult to obtain computationally. In particular, global particle-in-cel ...

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.

We present a fully-global linear gyrokinetic simulation code (GYGLES) aimed at describing the unstable spectrum of the ion-temperature-gradient modes in toroidal geometry. We formulate the Particle-In-Cell method with finite elements defined in magnetic coordinates, which provides excellent numerical convergence properties. The poloidal mode structure corresponding to k(parallel to) = 0 is extracted without approximation from the equations, which reduces drastically the numerical resolution needed. The code

A two-dimensional PIC code aimed at the investigation of electron-cyclotron beam instabilities in gyrotrons and their effects on the beam quality is presented. The code is based on recently developed techniques for handling charge conservation and open boundaries. It has been implemented on the massively parallel computer CRAY T3D. First results show an electromagnetic backward-wave instability periodically growing and decaying to energy levels close to those obtained from the electrostatic Bernstein wave i

The gyrotron system for ECH and burn control on ITER requires at least 50MW of RF power at frequencies near 170GHz operating in CW. To meet these requirements, high efficiency gyrotron tubes with greater than or equal to 1MW power output capability are necessary, as well as simple coupling to either a quasi-optical or waveguide transmission line. The paper reports the feasibility study on the design of an ITER-relevant gyrotron oscillator at 170GHz, 1MW CW employing a diode electron gun, an advanced interna

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

Fluctuating quantities in magnetic confinement geometries often inherit a strong anisotropy along the field lines. One technique for describing these structures is the use of a certain set of Fourier components on the tori of nested flux surfaces. We descr ...

The direct sparse matrix solver is based on a domain decomposition technique to achieve data and work parallelization. Geometries that have long and thin structures are specially efficiently tractable with this solver, provided that they can be decomposed mainly in one direction. Due to the separation of the algorithm into a factorization stage and a solution stage, time-dependent problems with a constant coefficient matrix are particularly well suited for this solver. The parallelization performances obtai

Recent experiments on a 100 GHz quasioptical gyrotron have shown that for a large resonator setup [Phys. Fluids B 2, 1654 (1990)] the observed frequency up-shift between the starting current and a current of 10 A corresponds to a shift of 4-5 longitudinal modes. In this Letter it is shown that the interpretation of this frequency up-shift should involve the current-dependent electron beam voltage depression in the beam tunnel and interaction region for both the single-mode and multimode time evolution codes

Nonlinear electrostatic global gyrokinetic simulations of collisionless ion temperature gradient (ITG) turbulence and ExB zonal flows in axisymmetric toroidal plasmas are examined for different choices of the initial distribution function. Using a local Ma ...

Trach-Minh Tran

Chattez avec Graph Search

Global collisional gyrokinetic simulations of ITG microturbulence starting from a neoclassical equilibrium

Measurement of the parallel velocity distribution function of the electron beam in a quasi-optical gyrotron by Electron Cyclotron Emission

Parasitic Oscillation in and Suppression of a Gyrotron Backward-Wave Mode in a Low-Q 8 Ghz Gyrotron

G2DEM: A parallel two-dimensional electromagnetic PIC code for the study of electron-cyclotron instabilities of relativistic electron beams in cylindrical cavities

Stabilization of ion-temperature-gradient-driven tokamak modes by magnetic-field gradient reversal

Global Nonlinear Electromagnetic Simulations of Tokamak Turbulence

Electron beam instabilities in gyrotron beam tunnels

Global gyrokinetic simulations of rho* and nu* scalings of turbulent transport

Startup Methods for Single-Mode Gyrotron Operation

Venus plus delta f: A bootstrap current calculation module for 3-D configurations

Long global gyrokinetic simulations: Source terms and particle noise control

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

Finite element approach to global gyrokinetic Particle-In-Cell simulations using magnetic coordinates

Effects of electron-cyclotron instabilities on gyrotron beam quality

Feasibility Study of the Eu Home Team on a 170ghz 1mw Cw Gyrotron for Ech on Iter

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

Rapid Fourier space solution of linear partial differential equations in toroidal magnetic confinement geometries

A direct parallel sparse matrix solver

Dc Space-Charge-Induced Frequency up-Shift in a Quasi-Optical Gyrotron

On the definition of a kinetic equilibrium in global gyrokinetic simulations