Publications by Andrei Martynov

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Abandoning the assumption of nested magnetic surfaces in tokamak plasma expands the field of research and opens up new approaches for both theoretical and experimental plasma physics. The computer code KINX for calculations of the ideal MHD stability was d ...

The need of durable and abundant energy sources for future ages stimulates the studies of thermonuclear energy sources, based on hot plasma confinement by magnetic fields. The most developed concept of hot plasma trap is the tokamak, where the plasma confi ...

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

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

Clear observations of early triggering of neo-classical tearing modes by sawteeth with long quiescent periods have motivated recent efforts to control, and in particular destabilize, sawteeth. One successful approach explored in TCV utilizes electron cyclo ...

The paper presents the KINX code for computing linear ideal MHD growth rates and eigenvectors of axisymmetric plasmas surrounded by a vacuum layer and a conducting wall. Plasma equilibrium magnetic surfaces are assumed to be nested either in the whole plasma domain (separatrix at the plasma boundary is possible) or in the domains separated by an internal separatrix (doublet and divertor configurations). The computational domain is decomposed into subdomains with nested flux surfaces. In each subdomain finit

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

In the TCV tokamak the sawtooth period and the sawtooth amplitude are observed to depend strongly on the shape of the poloidal plasma cross section. Systematic scans of plasma elongation and triangularity show small sawteeth with short periods at high elongation or low and negative triangularity, and large sawteeth with long periods at low elongation or high triangularity. Additional central electron cyclotron heating power further amplifies the shape dependence of the sawtooth properties. The sawtooth peri

Current profile tailoring has been performed by application of electron cyclotron heating (ECH) and electron cyclotron current drive, leading to improved energy confinement in the plasma core of the TCV tokamak. The improved confinement is characterized by a substantial enhancement (H-factor) of the global electron energy confinement time relative to the prediction of the RLW scaling law (Rebut P H et al 1989 Proc. 12th Int. Conf. of Plasma Physics and Controlled Fusion Research (Nice, 1988) vol 2 (Vienna:

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

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

The effect of plasma shaping (triangularity and elongation) on sawtooth stability is addressed as well as the technique of current profile broadening using off-axis ECH to enlarge the operational range towards higher elongations. The plasma shape strongly influences the sawtooth period and amplitude. This effect is emphasized by ECH, with the sawtooth period becoming shorter at low triangularity or at high elongation; for these plasma shapes, the pressure profile inside the q = 1 surface remains essentially

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 ideal stability of the internal kink mode is analysed for realistic tokamak geometry. Accurate numerical results demonstrate convergence with Bussac's toroidal solution (Bussac M N, Pellat R Edery D and Soule J L 1975 Phys. Rev. Lett. 35 1638) for inve ...

Recently, an experimental campaign has been launched on TCV with the aim of exploring and extending the limits of the operating space. The vertical position control system has been optimized, with the help of extensive model calculations, in order to allow operation at the lowest possible stability margin. In addition, the growth rate of the axisymmetric instability has been minimized by choosing optimum values for the plasma triangularity and squareness and by operating close to the current limit imposed b

Improved electron energy confinement in tokamak plasmas, related to internal transport barriers, has been linked to nonmonotonic current density profiles. This is difficult to prove experimentally since usually the current profiles evolve continuously and ...

Important ingredients of the advanced-tokamak route to fusion have been explored in depth in the Tokamak a Configuration Variable [F. Hofmann, J. B. Lister, M. Anton , Plasma Phys. Controlled Fusion 36, B277 (1994)] over the past two years. Using a uniquel ...

The effect of plasma elongation kappa on the sawtooth behaviour is studied in ohmically heated TCV plasmas up to values of kappa = 2.8. Above a certain value of kappa, which varies from 2.2 to 2.6 and depends on the current profile, the sawtooth oscillatio ...

Andrei Martynov

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MHD Stability and Energy Principle for Two-Dimensional Equilibria without Assumption of Nested Magnetic Surfaces

Ideal MHD stability of tokamak plasmas with moderate and low aspect ratio

Safety factor profile requirements for electron ITB formation in TCV

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

ECH physics and new operational regimes on TCV

Sawtooth control in fusion plasmas

The KINX ideal MHD stability code for axisymmetric plasmas with separatrix

Overview of TCV results

Stability and energy confinement of highly elongated plasmas in TCV

Effect of triangular and elongated plasma shape on the sawtooth stability

Control of electron internal transport barriers in TCV

An overview of results from the TCV tokamak

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

Plasma shape effects on sawtooth/internal kink stability and plasma shaping using electron cyclotron wave current profile tailoring in TCV

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

The stability of the ideal internal kink mode in realistic tokamak geometry

Extension of the TCV operating space towards higher elongation and higher normalized current

Inductive current density perturbations to probe electron internal transport barriers in tokamaks

High-bootstrap, noninductively sustained electron internal transport barriers in the Tokamak a Configuration Variable

Sawtooth behaviour in highly elongated TCV plasmas