Publications de Minh Quang Tran

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The TCV tokamak (R = 0.88 in, a < 0.25 in, BT < 1.54 T) is equipped with six 0.5 MW gyrotron sources operating at 82.7 GHz for second harmonic X mode ECH. By distributing the ECCD current sources over the discharge cross section, fully driven stationary plasmas with I-p = 210 kA, n(e0) = 2 x 10(19) m(-3), T-e0 approximate to 4 keV, were obtained for the full discharge duration of 2 s. Highly peaked electron temperature profiles with T-e0 up to 12 keV were obtained in central counter-current drive scenarios

The operating space of the TCV tokamak has been extended to higher elongation, kappa = 2.8, and higher normalized current, I-N = I-p/aB = 3.6MA/mT, than were previously attainable. This has been achieved by optimizing the parameters of the vertical position control system and by optimizing the plasma shape. Experimental current and beta limits were found to be consistent with ideal MHD stability calculations, using measured plasma shapes and profiles. The sawtooth period was measured as a function of elonga

The TCV tokamak (B-T < 1.5 T, R approximate to 0.88 m, a < 0.25 m) has produced a wide variety of plasma configurations, both diverted and limited, with elongations kappa(a), ranging from 0.9 to 2.58, triangularities delta(a) from -0.7 to 1 as well as discharges with nearly rectangular cross sections. Plasma currents of 1 MA have been obtained in elongated discharges (kappa(a) approximate to 2.3). Ohmic discharges with delta(a) < 0 have smaller sawteeth and higher levels of MHD mode activity than plasmas wi

In the frame of development of the ITER electron cyclotron wave (ECW) system, a two MW CW coaxial cavity gyrotron will be developed during the Sixth Framework Program (2003-2006). Such development relies on the availability of a test stand capable of providing the electrical energy and cooling capacity. This test stand will possibly be used, in a later stage, for the component test of the ITER ECW system. This paper will first present the main parameters of this new coaxial gyrotron. Then we describe the te

The onset of chaotic ion dynamics in electrostatic waves is investigated in a linear magnetized plasma. The existence of a threshold for heating in agreement with the predictions of single particle Hamiltonian theories and the fast time scale for velocity space diffusion are observed in the experiment. Measurements of test-particle dynamics indicate an exponential separation of initially close ion trajectories for amplitudes above the heating threshold. Ion orbits in the different wave-particle interaction

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

Basic wave-particle interaction dynamics from linear to chaotic regimes is experimentally studied on a frequency tunable gyrotron generating THz radiation in continuous mode (200W) at 263GHz which will be used for dynamic nuclear polarization nuclear magnetic resonance spectroscopy applications. In the studied system, the nonlinear dynamics associated to the waveparticle interaction is dominated by longitudinal mode competition of a given transverse TEm;p cavity-mode. This study covers a wide range of contr

The linear relativistic theory of electron cyclotron wave propagation predicts partial absorption of the extraordinary mode at the third electron cyclotron harmonic for typical parameters of present day tokamak plasmas. Since the waves are not totally damped, a quantitative confirmation of such predictions is important to establish this particular resonance scheme firmly for plasma heating and current drive. Specific experiments have been performed on Tore Supra, to measure the optical thickness of the thir

During the first two years of operation, the TCV tokamak has produced a large variety of plasma shapes and magnetic configurations, with 1.0 less than or equal to B-tor less than or equal to 1.46T, I-p less than or equal to 800kA, kappa less than or equal to 2.05, -0.7 less than or equal to delta less than or equal to 1. A new shape control algorithm, based on a finite element reconstruction of the plasma current in real time, has been implemented. Vertical growth rates up to 1000 s(-1) have been stabilized

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 future fusion reactor will use deuterium and tritium as fuel. The former is found in abundance in seawater, while the latter is not available naturally due to its short lifetime. Present developments in the context of fusion propose generating tritium in ...

Within the range of plasma shapes and plasma currents investigated, the electron confinement time, Tau_E increases with density, elongation and negative triangularity (-0.4

A steady-state, fully noninductive plasma current has been sustained for the first time in a tokamak using electron cyclotron current drive only. In this discharge, 123 kA of current have been sustained for the entire gyrotron pulse duration of 2 s. Careful distribution across the plasma miner radius of the power deposited from three 0.5-MW gyrotrons was essential for reaching steady-state conditions. With central current drive, up to 153 kA of current have been fully replaced transiently for 100 ms. The no

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

The development of high power CW gyrotrons for ECRH heating of fusion relevant plasmas has been in progress for several years in a joint collaboration between different European research institutes and an industrial partner. Two development are on going, aiming, respectively, towards a 0.51-MW-210-s gyrotron at 118 GHz for the tokamaks TCV of CRPP (2 s pulse length) and Tore Supra of CEA (210 s pulse length), and towards a 1 MW-CW gyrotron at 140 GHz for the stellarator W7-X under construction in Greifswald

A review of the two key technologies for the electron cyclotron wave (ECW) system, the gyrotron source and the window, is presented. In both fields, significant progress has been made to meet the requirements of the heating and current drive systems planned for devices such as W7-X or ITER, namely 1 MW-CW (continuous wave) in the frequency range 140-170 GHz. Gyrotrons in this performance range have been tested in long pulse operation (many seconds). With the use of a diamond window, extremely long pulse (mu

The EU is working towards providing 2 MW, coaxial-cavity, CW, 170 GHz gyrotrons for ITER. Their design is based on results from an experimental pre-prototype tube in operation at FZK for several years, having a pulse length of several milliseconds. The fir ...

The Tokamak Configuration Variable (TCV) tokamak (R = 0.88 m, a < 0.25 m, B < 1.54 T) programme is based on flexible plasma shaping and heating for studies of confinement, transport, control and power exhaust. Recent advances in fully sustained off-axis electron cyclotron current drive (ECCD) scenarios have allowed the creation of plasmas with high bootstrap fraction, steady-state reversed central shear and an electron internal transport barrier. High elongation plasmas, kappa = 2.5, are produced at low nor

The presence of an electron beam in a quasioptical gyrotron cavity alters the structure of the fields from that of the empty cavity. A computer code has been written that calculates this alteration for either an electron beam or a thin dielectric tube placed in the cavity. Experiments measuring the quality factor of such a cavity were performed for the case of a dielectric tube and the results agree with the predictions of the code. Simulations of the case of an electron beam indicate that self-consistent e

The European Union is working toward providing 2-MW, coaxial-cavity, continuous-wave (cw) 170-GHz gyrotrons for ITER. Their design is based on results,from an experimental preprototype tube having a pulse length of several milliseconds, in operation at For ...

Minh Quang Tran

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Overview of TCV results

Stability and energy confinement of highly elongated plasmas in TCV

Effect of plasma shape on confinement and MHD behaviour in TCV

Design study of a test stand for ITER gyrotron

Study of Wave Particle Interaction from the Linear Regime to Dynamical Chaos in a Magnetized Plasma

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

Experimental study from linear to chaotic regimes on a terahertz-frequency gyrotron oscillator

Measurement of the optical depth at the third electron cyclotron harmonic in tore supra

Recent Results from the Tcv Tokamak

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

Availability of lithium in the context of future D-T fusion reactors

Preliminary Confinement Studies during ECRH in TCV

Steady-state fully noninductive current driven by electron cyclotron waves in a magnetically confined plasma

Electron beam instabilities in gyrotron beam tunnels

European high-power CW gyrotron development for ECRH systems

Status of electron cyclotron wave technology

First experimental results from the EU 2 MW coaxial cavity ITER gyrotron prototype

An overview of results from the TCV tokamak

Studies of Self-Consistent-Field Structure in a Quasi-Optical Gyrotron

First experimental results from the European Union 2 MW coaxial cavity ITER gyrotron prototype