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Hydrogen recycling and transport in the helical divertor of TEXTOR

Abstract

The aim of this thesis was to investigate the hydrogen recycling at the target plates of the helical divertor in TEXTOR and by this the capability of this divertor configuration to access such favourable operational regimes. In order to study the different divertor density regimes in TEXTOR, discharges were performed in which the total plasma density was increased continuously up to the density limit. The recycling was investigated in a fixed helical divertor structure where four helical strike points with a poloidal width of about 8-10 cm are created at the divertor target plates. The experimental investigation of the hydrogen recycling was carried out using mainly spectroscopic methods supplemented by Langmuir probe, interferometric and atomic beam measurements. In the framework of this thesis a spectroscopic multi camera system has been built that facilitates the simultaneous observation of four different spectral lines, recording images of the divertor target plates and the plasma volume close to the target. The system facilitates the simultaneous measurement of the poloidal and toroidal pattern of the recycling flux at the divertor target without the need for sweeping the plasma structure. The simultaneous observation of different spectral lines reduces the uncertainty in the analysis based on several  More>>
Authors:
Publication Date:
Jul 01, 2010
Product Type:
Thesis/Dissertation
Report Number:
INIS-DE-1149
Resource Relation:
Other Information: TH: Diss.; Related Information: Schriften des Forschungszentrums Juelich. Reihe Energie und Umwelt/Energy and Environment v. 87
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; CARBON; CROSSED FIELDS; DIVERTORS; ELECTRIC DISCHARGES; ELECTRIC FIELDS; HELICAL CONFIGURATION; HYDROGEN; MAGNETIC FIELD CONFIGURATIONS; MAGNETIC FIELDS; PLASMA; PLASMA IMPURITIES; PLASMA SIMULATION; RECYCLING; TEXTOR TOKAMAK
OSTI ID:
21461302
Research Organizations:
Forschungszentrum Juelich (Germany). Inst. fuer Energieforschung (IEF), Plasmaphysik (IEF-4); Duesseldorf Univ. (Germany)
Country of Origin:
Germany
Language:
English
Other Identifying Numbers:
Other: ISBN 978-3-89336-673-6; ISSN 1866-1793; TRN: DE11F7817
Availability:
Commercial reproduction prohibited; INIS; OSTI as DE21461302
Submitting Site:
DEN
Size:
197 pages
Announcement Date:
Jul 29, 2011

Citation Formats

Clever, Meike. Hydrogen recycling and transport in the helical divertor of TEXTOR. Germany: N. p., 2010. Web.
Clever, Meike. Hydrogen recycling and transport in the helical divertor of TEXTOR. Germany.
Clever, Meike. 2010. "Hydrogen recycling and transport in the helical divertor of TEXTOR." Germany.
@misc{etde_21461302,
title = {Hydrogen recycling and transport in the helical divertor of TEXTOR}
author = {Clever, Meike}
abstractNote = {The aim of this thesis was to investigate the hydrogen recycling at the target plates of the helical divertor in TEXTOR and by this the capability of this divertor configuration to access such favourable operational regimes. In order to study the different divertor density regimes in TEXTOR, discharges were performed in which the total plasma density was increased continuously up to the density limit. The recycling was investigated in a fixed helical divertor structure where four helical strike points with a poloidal width of about 8-10 cm are created at the divertor target plates. The experimental investigation of the hydrogen recycling was carried out using mainly spectroscopic methods supplemented by Langmuir probe, interferometric and atomic beam measurements. In the framework of this thesis a spectroscopic multi camera system has been built that facilitates the simultaneous observation of four different spectral lines, recording images of the divertor target plates and the plasma volume close to the target. The system facilitates the simultaneous measurement of the poloidal and toroidal pattern of the recycling flux at the divertor target without the need for sweeping the plasma structure. The simultaneous observation of different spectral lines reduces the uncertainty in the analysis based on several lines, as the contribution from uncertainties in the reproducibility of plasma parameters in different discharges are eliminated and only the uncertainty of the measurement method limits the accuracy. The spatial resolution of the system in poloidal and toroidal direction (0.8 mm{+-}0.01 mm) is small compared to the separation of the helical strike points, the capability of the measurement method to resolve these structures is therefore limited by the line-of-sight integration and the penetration depth of the light emitting species. The measurements showed that the recycling flux increases linearly with increasing plasma density, a high recycling regime is not observed. Its absence can be explained using an extended two point model including heat convection applied to the region dominated by parallel transport (laminar region). The radial penetration depth of the neutral hydrogen particles ({lambda}{sub n} {approx} 3-4 cm) estimated from spectroscopic measurements was found to be often larger than the varying radial extent of this laminar region (few mm up to 6 cm) which finally leads to convective heat transport reducing parallel temperature gradients. Increasing the radial extent of the laminar region especially in front of the divertor strike points could lead to an improvement in this respect and provide access to a high recycling regime. The radiation instability developing at high plasma densities in the helical divertor in TEXTOR is preceded by a transient partial detachment of the plasma from the divertor target plates and leads to the formation of a poloidally structured and helically inclined radiating belt, a helical divertor MARFE. While typically leading to a density limit disruption, this MARFE has been stabilised using a feedback system and could provide some divertor functionality such as low target temperature, increased neutral density and increased radiation within the stochastic boundary. Simulations using two different cross-field transport coefficients showed, that an agreement is only found at a certain level of cross-field transport (D {sub perpendicular} {sub to} =1 m{sup 2}s{sup -1}). The inclusion of carbon impurities in the simulations results in the experimentally observed reduction of the recycling flux. (orig.)}
place = {Germany}
year = {2010}
month = {Jul}
}