Publications de Minh Quang Tran

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Fusion power is the most significant prospects in the long-term future of energy in the sense that it composes a potentially clean, cheap, and unlimited power source that would substitute the widespread traditional nonrenewable energies, reducing the geogr ...

Fusion power may be seen as the energy of the future in the sense that it composes a potentially clean, cheap and unlimited power source that would reduce the worldwide dependency on non-renewable energies. Nevertheless, while nowadays the fusion reaction ...

A modulated high frequency wave is used to remotely excite low frequency oscillations in a linear, strongly magnetized plasma column. An electromagnetic wave is launched as an extraordinary mode across the plasma by an external waveguide in the upper-hybrid frequency regime f almost-equal-to f(UH) almost-equal-to f(ce) almost-equal-to 8 GHz, with P less-than-or-equal-to 2 W. By frequency modulating (at f(FM) almost-equal-to 1-60 kHz, with f(ci) congruent-to 30 kHz) the pump wave, the resonant layer is swept

In the first part of this paper, the status of the 140-GHz continuously operated gyrotrons with an output power of I MW for the stellarator Wendelstein 7-X will be described. With the first series tube, an output power of 1000 kW has been achieved in short ...

The fluid equations for an electron beam are used to calculate the equilibrium velocity and density profiles, limiting current and space-charge wave properties of an annular beam undergoing magnetic compression in a gyrotron beam tunnel. Both non-relativistic and relativistic equations are derived. The beam tunnel may have a conventional smooth wall or an absorbing dielectric-loaded wall. Small values of magnetic compression are seen to have large effect on the profiles and the current limit of a given tunn

Gyrotrons at high frequency with high-output power are mainly developed for microwave heating and current drive in plasmas for thermonuclear fusion. For the stellarator Wendelstein 7-X, now under construction at IPP Greifswald, Germany, a 10-MW electron-cyclotron-resonance-heating (ECRH) system is foreseen. A 1-MW 140-GHz gyrotron with synthetic diamond window for continuous wave operation and with a single stage depressed collector for energy recovery and improvement of efficiency has been designed, constr

This paper presents experimental results on the accessibility and the properties of plasmas with improved confinement in TCV. First, the H-mode threshold power is measured in Ohmic plasmas. Above an Ohmic threshold density, the threshold power increases with the density. A lower threshold density is found when additional electron cyclotron heating (ECH) is applied. At these low densities, the threshold power increases dramatically with decreasing density. Only a small fraction of the wide operational domain

On the Tokamak a Configuration Variable (TCV), electron internal transport barriers (eITBs) can be formed during a gradual evolution from a centrally peaked to a hollow current profile while all external actuators are held constant. The formation occurs ra ...

Experiments with high-power electron cyclotron heating (ECH) and current drive (ECCD) in the TCV tokamak are discussed. Power up to 2.7 MW from six gyrotrons is delivered to the tokamak at the second-harmonic frequency (82.7 GHz) in X-mode. The power is transmitted to the plasma by six independent launchers, each equipped with steerable mirrors that allow a wide variety of injection angles in both the poloidal and toroidal directions. Fully non-inductive operation of the tokamak has been achieved in steady

Electron cyclotron resonance heating (ECRH) experiments at 39 GHz with power levels similar to those of Ohmic heating have been conducted in the TCA tokamak, in either the X-mode or the O-mode. ECRH was observed to be more efficiently absorbed in low density and low q(a) discharges. At low density the central electron temperature increased by a factor of two over Ohmic values and the stored energy increased by 40% when up to 80% of the plasma energy was supplied by ECRH. During low density ECRH operation, t

The physics of tokamak plasmas, in which electrons are heated by electron cyclotron heating (ECH) and whose current is driven by electron cyclotron current drive (ECCD), is investigated in this paper together with applications on tokamak A configuration variable (TCV) using modifications of the pressure and current profiles to improve the operational regimes. In order to explain the experimentally determined current drive efficiency and hard x-ray and electron cyclotron emission measurements, it is shown th

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

In current tokamaks and, in particular, in future larger devices such as ITER, the control of neo-classical tearing modes (NTM) is essential for achieving high performance in terms of the beta limit. A commonly used scheme for NTM stabilization consists in driving a helical current at the resonance surface of interest with electron-cyclotron-current-drive. Depending on the ratio between the magnetic island size and the RF beam width, complete stabilization of the NTM will only be achieved with deep RF power

An over-moded evacuated waveguide line was chosen for use in the transmission system for the proposed JET enhanced performance project (JET-EP) electron cyclotron resonance heating (ECRH) system. A comparison between the quasi-optical, atmospheric waveguide and evacuated waveguide systems was performed for the project with a strong emphasis placed on the technical and financial aspects. The evacuated waveguide line was chosen as the optimal system in light of the above criteria. The system includes six line

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

Confinement in TCV electron cyclotron heated discharges was studied as a function of plasma shape, i.e. as a function of elongation, 1.1 < kappa < 2.15, and triangularity, -0.65 less than or equal to delta less than or equal to 0.55. The electron energy confinement time was found to increase with elongation, owing in part to the increase of plasma current with elongation. The beneficial effect of negative triangularities was most effective at low power and tended to decrease at the higher powers used. The l

Scientific and technical activities on JET focus on the issues likely to affect the ITER design and operation. Our understanding of the ITER reference mode of operation, the ELMy H-mode, has progressed significantly. The extrapolation of ELM size to ITER has been re-evaluated. Neoclassical tearing modes have been shown to be meta-stable in JET, and their beta limits can be raised by destabilization (modification) of sawteeth by ion cyclotron radio frequency heating (ICRH). Alpha simulation experiments with

The TCV tokamak has obtained ohmic H-modes in virtually all diverted plasmas with the ion del B drift directed towards an X-point and in several elongated limiter plasmas. Troyon factors (beta(tor)aB/l(p)) up to 2 and line average densities up to 2.2 x 10(20) m(-3), corresponding to the Greenwald limit, have been obtained in diverted ELM-free H-modes. Quasi-stationary H-modes lasting for the entire current flat top (1.5 s) have been obtained in the presence of regular ELMs. The occurrence and magnitude of E

A comparative study of X- and O-mode high field side launch for electron cyclotron heating (ECH) breakdown and startup of tokamak plasmas has been performed. It is found that X-mode power is not absorbed at the cyclotron resonance but uniquely at the upper hybrid resonance, displaced to the low field side of the cyclotron resonance. O-mode power, however, is absorbed at the cyclotron resonance as well. The displacement of the upper hybrid resonance to the low field side with O-mode launch is significantly s

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

Minh Quang Tran

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A Variable Structure Control Scheme Proposal for the Tokamak a Configuration Variable

Sliding Surface Based Schemes for the Tokamak a Configuration Variable

Ion-Cyclotron Wave Excitation by Double-Resonance Coupling

High-power gyrotron development at Forschungszentrum Karlsruhe for fusion applications

Equilibrium and Space-Charge Wave Analysis of Electron-Beams in Conducting and Absorbing Gyrotron Beam Tunnels

Advanced high-power gyrotrons

Accessibility and properties of ELMy H-mode and ITB plasmas in TCV

Safety factor profile requirements for electron ITB formation in TCV

High-power ECH and fully non-inductive operation with ECCD in the TCV tokamak

Electron-Cyclotron Resonance Heating on the Tca Tokamak

ECH physics and new operational regimes on TCV

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

Power modulation capabilities of the 140 GHz/1 MW gyrotron for the stellarator Wendelstein 7-X

An ITER relevant evacuated waveguide transmission system for the JET-EP ECRH project

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

Energy confinement and MHD activity in shaped TCV plasmas with localized electron cyclotron heating

Overview of JET results

Ohmic H-modes in the TCV tokamak

X-Mode and O-Mode Electron-Cyclotron Heating Breakdown and Startup in Tca

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