Publications de Holger Reimerdes

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In a previous paper, a Self-Organizing Map had proven to be able to identify the regions of the plasma operative space characterizing the pre-disruptive phase at JET without relying on any a priori information. One of the strengths of this disruption predictor lies in its inherent self-organization capability. The Self-Organizing Map discovers non-trivial relationships and captures the complicated interplay of device diagnostics on the internal plasma states directly from the experimental data. Moreover, th

The TCV tokamak contributes to the development of nuclear fusion energy with proof-of-principle experiments and by validating models that are used to predict reactor performance. In the next upgrade of the TCV divertor it is planned to test a tightly baffled, long-legged divertor (TBLLD), a novel concept designed to enhance power exhaust handling with minimal modification to the magnetic configuration. The project is guided by simulations using the SOLPS-ITER code that indicate that a TBLLD can improve TCV’

Negative triangularity tokamak plasmas are subject of an increased interest both in existing experiments and in studies of core physics as well as power handling relevant to the fusion demonstration power reactor. The ideal MHD stability calculations for the negative triangularity plasma extend the investigation of the TCV tokamak beta limits and edge stability to double null shapes, lower aspect ratio and negative shear. In case of the negative triangularity, the 2nd stability access is closed for ballooni

TCV’s operating regime with an X-point radiator (XPR) has been broadened by changing the magnetic geometry. XPRs have properties that could make them an attractive power exhaust solution for fusion reactors. These include the conversion of a high fraction ...

Nuclear fusion could offer clean, abundant energy. However, managing the power exhausted from the core fusion plasma towards the reactor wall remains a major challenge. This is compounded in emerging compact reactor designs promising more cost-effective pathways towards commercial fusion energy. Alternative Divertor Configurations (ADCs) are a potential solution. In this work, we demonstrate exhaust control in ADCs, employing a novel method to diagnose the neutral gas buffer, which shields the target. Our w

Plasma-molecular interactions generate molecular ions which react with the plasma and contribute to detachment through molecular activated recombination (MAR), reducing the ion target flux, and molecular activated dissociation (MAD), both of which create e ...

Within the 9th European Framework programme, since 2021 EUROfusion is operating five tokamaks under the auspices of a single Task Force called ‘Tokamak Exploitation’. The goal is to benefit from the complementary capabilities of each machine in a coordinat ...

Obtaining acceptable conditions at the divertor targets of a next-step fusion experiment based on the tokamak concept is expected to be particularly challenging because of the small predicted value of the plasma power exhaust channel width. An increased co ...

The understanding of the time-scales and associated transient behavior of fusion exhaust plasmas plays a crucial role in its dynamic modeling and its control. This work presents an overview of experimental investigations of the exhaust dynamics in TCV, MAST-U, ASDEX-Upgrade, WEST, DIII-D, and JET. From the presented experiments, a clear picture arises on properties of the exhaust dynamics across machines. Particularly, we observe that the scrape-off layer equilibrates on fast time-scales ( >70 Hz) and that

SOLPS-ITER simulations of the European DEMO reactor with a Super-X divertor, which has larger major radius at the outer target and increased connection length, show an increased operational space for divertor power exhaust compared to the conventional sing ...

Nitrogen seeded detachment has been achieved in the tokamak a configuration variable (TCV) in alternative divertor configurations (ADCs), namely X-divertor and X-point target, with and without baffles in H-mode plasmas with high core confinement. Both ADCs ...

The effect of divertor closure and nitrogen seeding on the detachment process has been studied by performing 2D numerical simulations of tokamak a configuration variable (TCV) H-mode divertor scenarios with the SOLEDGE3X-EIRENE edge plasma transport code. ...

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

Evidence that density shoulder broadening is dependent on high main-chamber neutral density is presented. Shoulder broadening does notoccur when the sources for main-chamber neutrals are minimized using divertor baffles and wide gaps to the first wall (sim ...

Stability limits of highly elongated, D-shaped plasmas have been measured in the TCV (tokamak a configuration variable) tokamak. It is found that the plasma current is limited by kink-type disruptions, preceded by magnetohydrodynamic (MHD) mode activity. The mode structure has been analyzed using magnetic fluctuation and soft x-ray diagnostics. Mode numbers, growth rates, and experimental stability limits are consistent with ideal and resistive MHD models, based on measured plasma shapes and profiles. These

Self-consistent full-size turbulent-transport simulations of the divertor and scrape-off-layer (SOL) of existing tokamaks have recently become feasible. This enables the direct comparison of turbulence simulations against experimental measurements. In this ...

Research on the Tokamak à Configuration Variable (TCV) addresses a wide range of key questions relevant to ITER and future fusion power plants. Over the past two years, highly productive experimental campaigns have led to major advances across several areas: the ITER baseline scenario; pedestal properties in low-collisionality, peeling-limited conditions; and the development of high-

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, non-inductive regimes. Alternative high-confinement scenarios have likewise received significant attention, with re

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

Holger Reimerdes

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A procedure for rule extraction from a Self-Organising plasma disruption predictor for JET

Implementation of a Tightly-Baffled, Long-Legged Divertor (TBLLD) in TCV

Stability limits for tokamak plasma with negative triangularity

Access to an ELM-suppressed X-point radiator regime in TCV snowflake minus configurations

Demonstration of Super-X divertor exhaust control for transient heat load management in compact fusion reactors

Investigating the impact of the molecular charge-exchange rate on detached SOLPS-ITER simulations

Overview of the EUROfusion Tokamak Exploitation programme in support of ITER and DEMO

H-mode scrape-off layer power width in the TCV tokamak

Systematic Multi-machine Analysis of the Exhaust Time-dependent Behavior in Tokamaks

The operational space for divertor power exhaust in DEMO with a super-X divertor

Improved heat and particle flux mitigation in high core confinement, baffled, alternative divertor configurations in the TCV tokamak

Numerical study of divertor detachment in TCV H-mode scenarios

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

Evidence on the effects of main-chamber neutrals on density shoulder broadening

Experimental and theoretical stability limits of highly elongated tokamak plasmas

Validation of edge turbulence codes against the TCV-X21 diverted L-mode reference case

Progress and innovations in the TCV tokamak research programme

An overview of results from the TCV tokamak