Publications de Roland Behn | EPFL Graph Search

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A large variety of shaped tokamak discharges have been created in the Tokamak a Configuration Variable (TCV) with main parameters B-T

Within the range of plasma shapes and plasma currents investigated, the electron confinement time, tau_Ee, increases with safety factor, density and negative triangularity similar to the Ohmic heating case. There is little dependence of tau_Ee on the heating location provided power deposition occurs inside the q=1 surface; as power deposition moves out of the inversion surface, tau_Ee decreases. The power-induced energy confinement degradation exponent (tau_Ee~PaP) is as usual: alpha_P ~-0.5. As a general t

In the Tokamak a Configuration Variable (TCV), the central electron temperature obtained in discharges with counter (CNTR) electron cyclotron current drive (ECCD) is larger than with CO-ECCD or electron cyclotron resonance heating (ECRH) alone. Comparison of experimental results with calculations by the transport code PRETOR [IAEA Technical Conference on Advances in Simulation and Models of Thermonuclear Plasmas. Montreal 142 (International Atomic Energy Agency, Vienna 1992)] indicates that sawtooth stabili

Although ohmic H-modes have long been produced on TCV and the effects of ELMs at the divertor target studied in some detail, no attempt has yet been made to model the scrape-off layer (SOL) in these plasmas. This paper describes details of the first such e ...

An interpretation of non-standard, central MHD events in the TCV tokamak during localized ECRH is presented. It is shown that the non-standard behaviour is a consequence of specific features in the electron temperature profile produced when ECRH power is deposited close to the q = 1 surface and by the advection and mixing of electron thermal energy resulting from a resistive MHD instability.

The unique flexibility of TCV in plasma shaping has been exploited to address different aspects of tokamak physics in which the plasma shape may play a role. This paper summarizes the experiments undertaken in the TCV tokamak ("Tokamak à Configuration Variable") over the last decade in stability and transport and offers a comprehensive and integrated view of the various effects of plasma shape observed. For each of these effects, the relation between experimental results and theoretical predictions is stres

Combined interferometer and polarimeter systems, using a single detecting element per line of sight, are susceptible to perturbation of the interferometric phase when modulation of the polarization vector is applied. This issue has been investigated extensively for the case of a rotating elliptically polarized probing beam, demonstrating that here a perturbation is inevitable. In this article the analogy between this analysis and earlier work is pointed out, and the underlying physics discussed. It will be

Anomalous electron transport is determined by turbulence, which in turn is affected by magnetic shear. A novel application of electron cyclotron current drive (ECCD), aiming at localized shear modulation, has been applied on the TCV tokamak for experiments ...

A 'standard', single null lower diverted discharge has been developed to enable continuous monitoring of the first wall conditions and to characterise the effectiveness and influence of wall conditioning in the TCV tokamak. Measurements over a period encompassing nearly 2000 ohmic discharges of varying configuration and input power show the global confinement time and main plasma impurity concentrations to be good general indicators of the first wall condition, whilst divertor target profiles demonstrate st

The aim of the present work is to provide a better insight on the magnetic shear profile modification in the Switched ECCD experiments. Modelling of the plasma current density is carried on by the ASTRA transport code employed in both predictive and interp ...

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 ...

The energy confinement time of TCV Ohmic, L-mode discharges is observed to depend strongly on the plasma shape, improving slightly with elongation and degrading strongly as triangularity is increased from zero to positive values. The thermal conductivity of these plasmas is found to be independent of the shape. This observation, combined with geometrical effects on the temperature gradient and a degradation with increasing input energy flux, can explain the observed variation in the energy confinement time.

The effects of plasma shape on confinement and sawtooth stability are studied for positive and negative discharge triangularity and for different elongations with 1.5 MW centrally deposited ECH power

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 energy confinement time of TCV ohmic L mode discharges depends strongly on plasma shape. For fixed average current and electron densities, confinement times increase with plasma elongation and decrease with (positive) plasma triangularity. This dependence can be explained by the geometrical effects of flux surface expansion and compression on the temperature gradients together with the effect of power degradation, without the need to invoke a shape dependence of the transport coefficients. A global fact

If vibrationally excited molecules are discretised into individual species and proper account is taken of the toroidal geometry in simulating neutrals, some improvement can be made in simulating the anomalous detachment behaviour seen at the outer target of TCV single-null lower L-mode discharges. This contribution discusses the inclusion of these options into SOLPS5.0 (B2.5/Eirene) simulations of TCV discharges previously modelled with the SOLPS4.0 package, but demonstrates that current physics contained w

In this paper we validate the finite element code RAPLICASOL, which models radiofrequency wave propagation in edge plasmas near ICRF antennas, against calculations with the TOPICA code. We compare the output of both codes for the ASDEX Upgrade 2-strap ante ...

Roland Behn

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"Profile consistency" features in strongly shaped Ohmic tokamak plasmas

EFFECT OF LOCALISED ELECTRON CYCLOTRON HEATING ON ENERGY CONFINEMENT AND MHD IN TCV

Central electron temperature enhancements due to sawtooth stabilization during counter electron cyclotron current drive in Tokamak a Configuration Variable

SOLPS5 modelling of the type III ELMing H-mode on TCV

Model for humpback relaxation oscillations

Physics Insight and Performance Benefit from Plasma Shaping Experiments in MHD and Energy Transport in the TCV Tokamak

Analysis of phase measurements in combined interferometer and polarimeter systems

Shear modulation experiments with ECCD on TCV

Divertor target profiles and recycling studies in TCV single null lower standard discharges

Studies of Electron Transport and Current Diffusion in Switched ECCD experiments on TCV

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

Influence of plasma shape on transport in the TCV Tokamak

Energy Confinement in Shaped TCV Plasmas with Electron Cyclotron Heating

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

Effect of plasma shape on confinement and MHD behaviour in the TCV tokamak

Impact of Plasma Shaping on Electron Heat Transport in TCV L-mode Plasmas at Various Collisionalities

Electron heat transport dependence on plasma shape and collisionality in EC heated L-mode TCV plasmas

The influence of molecular dynamics on divertor detachment in TCV

Time-dependent modelling of ELMing H-mode at TCV with SOLPS5

Validation of the ICRF antenna coupling code RAPLICASOL against TOPICA and experiments