Publications de Holger Reimerdes

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Power exhaust is a crucial issue for future fusion reactors. Divertor detachment and the required power dissipation fractions of about 95% are foreseen to be achieved by impurity seeding. In a tokamak, at high seeding levels the radiation often concentrate ...

A simple analytic model for the repartition of the Scrape-Off Layer (SOL) exhaust power between the inner and outer divertors in a diverted low-density tokamak plasma is introduced. Electron heat conduction is assumed to dominate the heat transport, from t ...

This paper presents a quantitative validation of Scrape-Off Layer Plasma Simulation-ITER (SOLPS-ITER) simulations against the TCV-X21 reference case and provides insights into the neutral dynamics and ionization source distribution in this scenario. TCV-X2 ...

A high-resolution spectroscopic system was installed on the Tokamak à Configuration Variable (TCV), whose toroidal lines-of-sight (LOS) cross the divertor region. This system simultaneously measures the Doppler broadening and Doppler shift of several spectral transitions to infer their associated ion temperatures (Ti) and the toroidal component of their flow velocities (Vi). Herein, TCV’s Tangential Divertor Spectroscopy System (TDSS) is described, along with its data analysis procedure and the first simult

The comparison of simulations of plasma turbulence carried out with the GBS code, employing its latest multi-component plasma–neutral model, against a dedicated set of TCV discharges (TCV-X23) designed to investigate high-density divertor conditions characterised by strongly reduced target heat flux with respect to attached conditions, is presented. The TCV-X23 scenario, based on L-mode plasmas with a long outer divertor leg at low toroidal field, provides a well-diagnosed reference for boundary turbule

Different types of central relaxation oscillations are observed in the presence of ECH depending on the location of the deposited power. In the TCV tokamak, normal sawteeth, i.e. triangular sawteeth similar to ohmic sawteeth, and saturated sawteeth are observed with central ECH power deposition, while giant sawteeth and 'humpback' oscillations occur when heating close to the sawtooth inversion surface of the local soft X ray emissivity. New measurements with high temporal resolution show that the crash phas

Recent TCV experiments confirm the predicted formation of an electric potential well, below the magnetic X-point, in configurations with unfavorable

B_t

field direction (ion

\nabla B

drift away from the divertor), that substantially reshapes the typica ...

This work advances the quantitative validation of SOLPS-ITER against TCV ohmic L-mode discharges. It demonstrates that the treatment of the ion parallel heat-flux limiter and the assumptions adopted for chemical sputtering provide a consistent explanation for the divertor over-cooling and excessive divertor density predicted by earlier simulations. A systematic heat-flux-limiter scan highlights that a strong restriction of ion heat conduction significantly reduces both electron target temperatures T e,t and

The high confinement regime (H-mode) is considered fundamental for high-performance operation in next-step tokamaks. It is generally characterized by the occurrence of edge localized modes (ELMs), even though several no-ELM and small-ELM regimes have extended their operational space in the past years (Viezzer et al 2023 Nucl. Mater. Energy 34 101308). The control and suppression of these modes is a priority for the development of scenarios with a confinements good enough for the ITER baseline (Sips et al 20

In this chapter, we review the progress in MHD stability, disruptions and control in magnetic fusion research that has occurred over the past (more than) one and a half decades since the publication by Hender et al in 2007 on the same topic as part of the update of ITER Physics Basis. During this period, remarkable progress has been achieved in the understanding of the basic physics and overall control of MHD instabilities through a wide spectrum of dedicated experiments, theory and modeling. The sawtooth a

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

The European roadmap to the realisation of fusion energy has identified a number of technological and scientific challenges towards the development of a DEMO reactor. Mission 2 'Heat-exhaust systems' includes the investigation of alternative divertor confi ...

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

In this work, we compare physics-based dynamic exhaust models with frequency response measurements (FRMs) of the global particle dynamics in the Tokamak à Configuration Variable (TCV). The aim is to understand and model the experimental in-vessel dynamic response of plasma and neutrals to deuterium gas puff modulations with three models of varying fidelity: a 0D three chamber model (TCM); DIV1D, which models the edge plasma in 1D, and SOLEDGE3X for 2D-axisymmetric modeling. We find that the dynamic behavior

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 situ, two-dimensional (2D) Langmuir probe measurements across a large part of the TCV outer divertor are reported in L-mode discharges with and without divertor baffles. This provides detailed insights into time averaged profiles, particle fluxes, and f ...

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

Particle and energy losses due to type-I edge-localized modes (ELMs) and the effect of H-mode pedestal parameters on global confinement are studied for H-Mode discharges in ASDEX Upgrade. ELM frequency as well as particle and heat losses during ELMs are strongly affected by gas puffing, impurity injection, variation of plasma current and heating power. However the average power loss due to ELMs P-ELM = f(ELM)Delta W shows much less variation, and cannot account for the variations of stored energy encountere

A first set of divertor gas baffles has recently been installed in the TCV tokamak. In order to explore the physics determining the benefits and limitations of divertor baffling and to guide the design of a possible second generation of baffles, the effect ...

Holger Reimerdes

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X-point radiation: From discovery to potential application in a future reactor

Conduction-based model of the Scrape-Off Layer power sharing between inner and outer divertor in diverted low-density tokamak plasmas

Validation of SOLPS-ITER simulations against the TCV-X21 reference case

High-resolution visible spectroscopy for ion temperature and flow velocity measurements of the TCV divertor plasma

Power exhaust and detachment with varying outer leg length using turbulence simulations and experiments designed for validation

Understanding sawtooth activity during intense electron cyclotron heating experiments on TCV

Experimental verification of X-point potential well formation in unfavorable magnetic field direction

Advancing SOLPS-ITER validation with TCV L-mode discharges

Experimental characterization of inter-ELM modes in type-I ELMy scenarios at TCV using the thermal helium beam diagnostic

MHD, disruptions and control physics: Chapter 4 of the special issue: on the path to tokamak burning plasma operation

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

Evaluation of feasibility and costs of alternative magnetic divertor configurations for DEMO

Overview of TCV results

A multi-model system-identification comparison with the global particle dynamics in TCV

Stability and energy confinement of highly elongated plasmas in TCV

Effect of plasma shape on confinement and MHD behaviour in TCV

New insights on divertor parallel flows,E x B drifts, and fluctuations from in situ, two-dimensional probe measurement in the Tokamak a Configuration Variable

Effect of triangular and elongated plasma shape on the sawtooth stability

Effects of type-I edge-localized modes on transport in ASDEX upgrade

Numerical investigation of optimal divertor gas baffle closure on TCV