Publications by Trach-Minh Tran

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The three-dimensional (3-D) VMEC code has been modified to model an energetic species with a variant of a Bi-Maxwellian distribution function that satisfies the constraint B . del F-h = 0, and the 3-D TERPSICHORE stability code has been extended to investi ...

Important steps towards the understanding of turbulent transport have been made with the development of the gyrokinetic framework for describing turbulence and with the emergence of numerical codes able to solve the set of gyrokinetic equations. This paper ...

The implementation of linearized operators describing inter- and like-species collisions in the global gyrokinetic particle-in-cell code ORB5 [ S. Jolliet, Comput. Phys. Commun. 177, 409 (2007) ] is presented. A neoclassical axisymmetric equilibrium with s ...

In the tokamak scrape-off layer (SOL) the magnetic field lines are open, channeling particles and heat onto plasma facing components, and constraining their lifetime. Therefore, safe operation of future fusion reactors requires an understanding of SOL plasma dynamics. Recently, we have gained deep insights into the tokamak SOL dynamics by means of massively-parallel fluid electromagnetic turbulence simulations carried out with the Global Braginskii Solver (GBS) code. GBS is currently capable of performing f

A global plasma turbulence simulation code, ORB5, is presented. It solves the gyrokinetic electrostatic equations including zonal flows in axisymmetric magnetic geometry. The present version of the code assumes a Boltzmann electron response on magnetic sur ...

It is now widely believed that low frequency turbulence developing from smallscale instabilities is responsible for the phenomenon of anomalous transport generally observed in magnetic confinement fusion experiments. The microinstabilities are driven by gradients of equilibrium density, ion and electron temperatures and magnetic field strength. Gyrokinetic theory is based on the Vlasov-Maxwell equations and, consistent with the ordering, averages out the fast particle gyromotion, reducing the phase space fr

The problem of mode competition in cylindrical cavity gyrotrons is considered. The normalized variable equations are used to calculate the oscillation regions of possible operating modes in the energy-velocity-pitch-angle plane. The analysis is self-consistent and includes the effect of changing beam current, pitch angle, and energy during the startup phase. The time evolution of beam parameters during startup is computed for several types of startup methods and used to determine the oscillating cavity mode

Flux-driven global gyrokinetic codes are now mature enough to make predictions in terms of turbulence and transport in tokamak plasmas. Some of the recent breakthroughs of three such codes, namely GYSELA, ORB5 and XGC1, are reported and compared wherever a ...

A global nonlinear simulation code for the time evolution of ion-temperature-gradient-driven modes in theta-pinch geometry as a first approximation to the stellarator Wendelstein 7-X (W7-X) [Grieger , Proceedings of the 13th International Conference on Plasma Physics and Controlled Nuclear Fusion Research, Washington, DC, 1990 (International Atomic Energy Agency, Vienna, 1991), Vol. 3, p. 525] has been developed. A deltaf particle-in-cell (PIC) method is used to solve the coupled system of gyrokinetic equat

The theoretical study of plasma turbulence is of central importance to fusion research. Experimental evidence indicates that the confinement time results mainly from the turbulent transport of energy, the magnitude of which depends on the turbulent state r ...

Computer aided design of powerful gyrotrons for electron cyclotron resonance heating and current drive of fusion plasmas requires adequate physical models and efficient software packages for analysis, comparison and optimization of their electron-optical s ...

The mutual interactions of ion temperature gradient (ITG) driven modes, zonal flows and geodesic acoustic modes (GAM) in tokamak plasmas are investigated using a global nonlinear gyrokinetic formulation with totally unconstrained evolution of temperature g ...

In this work, a Fourier solver [B.F. McMillan, S. Jolliet, A. Bottino, P. Angelino, T.M. Tran, L Villard, Comp. Phys. Commun. 181 (2010) 7151 is implemented in the global Eulerian gyrokinetic code GT5D [Y. Idomura, H. Urano, N. Aiba, S. Tokuda, Nucl. Fusio ...

The operating diagram of a low quality factor, 8 GHz TE-degrees-01 gyrotron exhibits oscillations between 6.8 and 7.3 GHz. These oscillations are identified as the backward wave component of the TE-degrees-21 traveling mode. As the resonance condition of this mode depends on the average parallel velocity of the beam electrons (omega-BW approximately-or-equal-to OMEGA-c/gamma-k parallel-to ), the measurement of omega-BW for given OMEGA-c and gamma is used as a diagn

A program environment is presented that enables a co-operative design of high-technology products demanding interdisciplinary computer simulations for their optimisation. The system includes a multi-site, multi-machine, distributed data manager accessible by a data monitor. A client-server concept supports the user of massively parallel machines. The exchange of data between different executable scientific application modules is performed through the data base. Special modules to define the geometry, to dec

A solution to the full two-dimensional eigenvalue problem of electrostatic microinstabilities in a tokamak plasma is presented in the framework of gyrokinetic theory. The approach is the generalization of methods previously developed for a cylindrical system [S. Brunner and J. Vaclavik, Phys. Plasmas 5, 365 (1998)]. By solving the spectral problem in a special Fourier space adapted to the curved geometry, orbit width as well as Larmor radius can be kept to all orders. For a first numerical implementation, a

The design of a diffration grating used as an output coupler for a Fabry-Perot resonator is presented. We then consider the problem of determining the distortion and the cross-polarization of the incident Gaussian beam. Different types of gratings and planes with straight or curvilinear grooves and elliptical, have been designed and built. The output pattern from a resonator using such a grating has been measured experimentally. We found that the elliptical grating generates the least distortion and cross-p

Highly variable flux surface averaged heat fluxes are resolved in gyrokinetic simulations of ion temperature gradient (ITG) turbulence, even in large systems. Radially propagating fronts or avalanches are also seen. Their propagation lengths in gyroradii a ...

First global linear study of electrostatic drift waves in two realistic quasisymmetric configurations, namely the Quasi-Axially symmetric Stellarator with three fields periods (QAS3) [P. Garabian and L. P. Ku, Phys. Plasma 6, 645 (1999)] and the Helically Symmetric eXperiment (HSX) [F. S. B. Anderson , Trans. Fusion Technol. 27, 273 (1995)], are presented. Effects of the shape of the plasma on the growth rate and frequency of the ion temperature gradient (ITG) driven mode are investigated by varying the qua

The investigation of many interesting, complex phenomena in a free-electron laser (FEL) requires the use of numerical computer codes. In this paper we describe the extension of one such code (TDA), which in its original form could only be used to study free-electron laser amplifiers, to include resonator configurations. For convenience of interpretation of results obtained with this code, we have implemented the option of a decomposition of the radiation field into Gauss-Laguerre functions. Also the electro

Trach-Minh Tran

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Stability properties of anisotropic pressure stellarator plasmas with fluid and noninteractive energetic particles

Gyrokinetic simulations of turbulent transport: size scaling and chaotic behaviour

Neoclassical equilibria as starting point for global gyrokinetic microturbulence simulations

Plasma turbulence simulations of the tokamak scrape-off layer

A global collisionless PIC code in magnetic coordinates

First principles based simulations of instabilities and turbulence

Mode Competition and Startup in Cylindrical Cavity Gyrotrons Using High-Order Operating Modes

Predictions on heat transport and plasma rotation from global gyrokinetic simulations

Energy conservation in a nonlinear gyrokinetic particle-in-cell code for ion-temperature-gradient-driven modes in theta-pinch geometry

The role of plasma elongation on turbulent transport in magnetically confined plasmas

Recent evolution of the simulation tools for computer aided design of electron-optical systems for powerful gyrotrons

Effects of plasma current on nonlinear interactions of ITG turbulence, zonal flows and geodesic acoustic modes

Parallel filtering in global gyrokinetic simulations

Velocity Ratio Measurement Using the Frequency of the Gyro Backward-Wave

Problem-solving environment for parallel computers

Global approach to the spectral problem of microinstabilities in tokamak plasmas using a gyrokinetic model

Properties of Diffraction Gratings Used as Output Couplers in a Quasi-Optical Gyrotron

Avalanche-like bursts in global gyrokinetic simulations

Global linear gyrokinetic simulations in quasi-symmetric configurations

Extension of the Free-Electron Laser-Amplifier Code Tda to Resonator Configurations