Publications by Roland Behn | EPFL Graph Search

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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

Electron heat transport experiments are performed in L-mode discharges at various plasma triangularities, using radially localized electron cyclotron heating to vary independently both the electron temperature T-e and the normalized electron temperature gr ...

A large variety of plasma conditions has been created in TCV (Tokamak a Configuration Variable, B-T < 1.5 T, R-0 = 0.88 m, a < 0.25 m). They include limited and diverted discharges with elongations in the range 1-2.58, triangularities between -0.7 and 1 as well as 'square' shapes with plasma currents in the range 0.1-1 MA. Over the entire range of quasi-stationary ohmic conditions investigated we observe a correlation between electron pressure profiles and conductivity profiles, suggesting that [p]/p(0) app

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 impact of plasma shaping on electron heat transport is investigated in TCV L-mode plasmas. The study is motivated by the observation of an increase in the energy confinement time with decreasing plasma triangularity which may not be explained by a chan ...

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:

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

The aim of this paper is to present a signal processing algorithm that, applied to the raw Locked Mode signal, allows us to obtain a disruption indicator in principle exploitable on different tokamaks. A common definition of such an indicator for different ...

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

Density limit disruptions have been studied during the current flat-top of TCA. Disruption occurs at two different densities, depending on discharge programming. The highest densities are achieved by a strong influx of neutral gas called 'hard gas puffing'. This allows the plasma density to cross a range which is otherwise unstable and to reach a second region of stability with high internal inductance. When disruption occurs after hard gas puffing, the internal inductance decreases in time, in contrast to

Electron internal transport barriers (elTBs) are generated in the TCV tokamak with strong electron cyclotron resonance heating in a variety of conditions, ranging from steady-state fully noninductive scenarios to stationary discharges with a finite inducti ...

In noninductively driven discharges, 0.9 MW second harmonic (X2) off-axis co-electron cyclotron current drive deposition is combined with 0.45 MW X2 central heating to create an electron internal transport barrier (eITB) in steady plasma conditions resulting in a 1.6-fold increase of the confinement time (tau(Ee)) over ITER-98L-mode scaling. The eITB is associated with a reversed shear current profile enhanced by a large bootstrap current fraction (up to 80%) and is sustained for up to 10 current redistribu

In ASDEX Upgrade, the propagation of cold pulses induced by type-I edge localized modes (ELMs) is studied using electron cyclotron emission measurements, in a dataset of plasmas with moderate triangularity. It is found that the edge safety factor or the pl ...

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

During initial studies of ECRH in the TCV tokamak, non-standard central MHD activities, such as humpbacks and saturated and inverted sawteeth, have been observed while changing the heating location, the ECRH power, the plasma shape and the safety factor. For edge safety factors q(alpha) > 4.5, safety factors on-axis q(0) < 1 and small plasmas, complete sawtooth stabilization was achieved with the present 1 MW gyrotron power, and it is likely that sawtooth stabilization can be achieved for all conditions at.

Current profile tailoring by electron cyclotron heating (ECH) and current drive (ECCD) is used to improve central electron energy confinement in the TCV tokamak. Counter-ECCD on axis alone achieves this goal in a transient manner only. A stable scenario is obtained by a two-step sequence of err-axis ECH, which stabilizes magnetohydrodynamics modes, and on-axis counter-ECCD, which generates a flat or inverted current profile. This high-confinement regime, with central temperatures up to 9 keV (at a. normaliz

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

Roland Behn

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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

Electron heat transport in shaped TCV L-mode plasmas

'Profile consistency' features in shaped sawtoothing ohmic TCV plasmas

Recent Results from the Tcv Tokamak

Impact of plasma triangularity and collisionality on electron heat transport in TCV L-mode plasmas

Control of electron internal transport barriers in TCV

Preliminary Confinement Studies during ECRH in TCV

A locked mode indicator for disruption prediction on JET and ASDEX upgrade

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

Density Limits and Disruptions in the Tca Tokamak

The physics of electron internal transport barriers in the TCV tokamak

Recent results from the electron cyclotron heated plasmas in Tokamak à Configuration Variable (TCV)

ELM-induced cold pulse propagation in ASDEX Upgrade

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

Behaviour of central plasma relaxation oscillations during localized electron cyclotron heating on the TCV tokamak

Long-pulse improved central electron confinement in the TCV tokamak with electron cyclotron heating and current drive

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