Volume recombination in divertor I of ASDEX Upgrade

Wenzel, U.; Behringer, K.; Carlson, A.; Gafert, J.; Napiontek, B.; Thoma, A.

doi:10.1088/0029-5515/39/7/304

Cited by 49 publications

(42 citation statements)

References 24 publications

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“…Analysis of the ratio of D γ and D α emission at the outer target indicated a decrease as the core density was increased, followed by an increase as the plasma made the transition to detachment. This observation is contrary to observations on other devices such as JET [91], ASDEX-Upgrade [92] and Alcator-Cmod [93] and no explanation was given for this behaviour. Furthermore, as the divertor diagnostics available at the time were limited, the quantity of data collected was insufficient to make conclusions on the physical mechanisms that gave rise to detachment in this case.…”

Section: Introductioncontrasting

confidence: 99%

Characterisation of detached plasmas on the MAST tokamak

Harrison

2011

Journal of Nuclear Materials

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The mitigation of the steady-state heat loading to plasma-facing components in the divertor structures is an essential prerequisite for the operation of next-generation conventional and tight aspect-ratio Tokamaks. Currently, the most attractive means of reducing this heat loading is the so-called "detached" regime, which is the primary focus of this study.This thesis describes work that was carried out on the MAST tokamak to accurately characterise the plasma conditions within divertor plasmas, and to test the validity of those measurements. To assist in this study, an interpretive code, OSM [1], has been upgraded with additional numerical schemes to ascertain the dominant mechanisms governing parallel scrape-off layer transport including flux expansion, dynamic viscosity and cross-field drift motion in attached conditions. It has been found that the invocation of flux expansion, parallel viscosity and diamagnetic drift motion assist the OSM numerical scheme to converge in the presence of (static+dynamic) parallel pressure gradients often observed between the outboard midplane and lower outer divertor leg.It has also been found that the ion pressure, which is currently unknown, could resolve the observed pressure discrepancy.Line-of-sight spectroscopy of high-n Balmer emission lines has been used to ascertain line averaged T e and line integrated n e during the detached phase of MAST discharges with high spatial resolution (≈ 7mm) to determine electron static pressure profiles along flux contours. Furthermore, narrow-bandwidth imaging spectroscopy of D α , D γ , CII and CIII emission during the onset and sustainment of detachment has been carried out with high temporal (5kHz) and spatial (≈ 3mm) resolution. These data have been combined with ion flux measurements to the divertor target plates using embedded Langmuir probes (6-9mm radial resolution) and upstream Thomson scattering measurements of n e , T e . The data was input into the OSM code, coupled with the kinetic neutral transport code EIRENE [2], to check the experimental data set for internal consistency. The experimental data collected has been used to reconstruct the plasma conditions within the detached divertor leg, heavily constrained by experimental data. EIRENE calculations with re-constructed plasma conditions are able to reproduce experimentally observed D γ /D α line emission ratios to within a factor iii iv of 2 within the recombining region. AcknowledgmentsThe work presented in this thesis is the culmination of the work of many people, who I gratefully acknowledge here. Foremost, I thank Dr. Steven Lisgo for his guidance, enthusiasm and assistance over the last 4 years. It is only on reflection that I appreciate how he kept this work on track, whilst encouraging me to explore my own ideas and how doing so has enhanced the quality of the work presented here. Drs. Andrew Kirk and Geoff Fishpool also deserve special thanks for their guidance, and above all, their understanding in the final months of this work. I also owe great thanks to...

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Section: Introductioncontrasting

confidence: 99%

Characterisation of detached plasmas on the MAST tokamak

Harrison

2011

Journal of Nuclear Materials

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“…The first experimental measurements of significant volume recombination in a tokamak divertor were made on Alcator C-Mod 41 where quantitative evidence was found in the emission spectrum of D 0 . After this initial C-Mod measurement, the existence of recombination was confirmed at other tokamaks [42][43][44] . Unfortunately, because of the difficulty of interpreting the D 0 spectra, most of the initial measurements from other tokamaks were limited to the 'signature' of recombination, namely the ratio of brightnesses from different The first step taken in determining the recombination rate was to develop a formalism for quantitative analysis 41,46 .…”

Section: Recombination and Ion Lossmentioning

confidence: 86%

Divertor Physics Research on Alcator C-Mod

Lipschultz

LaBombard

Terry

et al. 2007

Fusion Science and Technology

101

108

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“…This leads to a decrease of the D α divertor emission at the ELMs (so-called "negative" ELMs) [202,206].…”

Section: Ability Of Radiating Plasmas To Buffer Elmsmentioning

confidence: 99%

“…This lowers power flux by removing the internal energy (13.6 eV + 2.2 eV dissociation potential) of each ion-electron pair, thus further reducing divertor power deposition, beyond the drop in T e associated with detachment, and reducing physical sputtering and b) volume recombination affects divertor performance by strongly changing the ionisation balance across the divertor region. Deuterium recombination has been observed on most diverted tokamaks [254,255,256,257,206].…”

Section: The Role Of Recombination In Divertor Processesmentioning

confidence: 99%

“…3-body recombination has been shown in some cases to account for large fractions (> 50%) of the ion sink in the divertor [260,206] and in the MARFE [261]. However, in some detached plasmas [206,260,262,263], in particular those with high SOL heat flux which detach after impurity puffing [260], recombination appears not to be a significant ion sink. This variation in recombination is due to the strong dependence of 3-body recombination on the local plasma density (n e 3 ).…”

Section: The Role Of Recombination In Divertor Processesmentioning

confidence: 99%

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Chapter 4: Power and particle control

Divertor¹,

Database²,

Editors³

1999

Nucl. Fusion

282

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Abstract.Progress, since the ITER Physics Basis publication, in understanding the processes that will determine the properties of the plasma edge and its interaction with material elements in ITER is described. Experimental areas where significant progress has taken place are : energy transport in the SOL in particular of the anomalous transport scaling, particle transport in the SOL that plays a major role in the interaction of diverted plasmas with the main chamber material elements, ELM energy deposition on material elements and the transport mechanism for the ELM energy from the main plasma to the plasma facing components, the physics of plasma detachment and neutral dynamics including the edge density profile structure and the control of plasma particle content and He removal, the erosion of low and high Z materials in fusion devices, their transport to the core plasma and their migration at the plasma edge including the formation of mixed materials, the processes determining the size and location of the retention of tritium in fusion devices and methods to remove it and the processes determining the efficiency of the various fuelling methods as well as their development towards the ITER requirements. This experimental progress has been accompanied by the development of modelling tools for the physical processes at the edge plasma and plasma-materials interaction and the further validation of these models by comparing their predictions with the new experimental results. Progress in the modelling development and validation has been mostly concentrated in the following areas : refinement of the predictions for ITER with plasma edge modelling codes by inclusion of detailed geometrical features of the divertor and the introduction of physical effects, which can play a 2 major role in determining the divertor parameters at the divertor for ITER conditions such as hydrogen radiation transport and neutral-neutral collisions, modelling of the ion orbits at the plasma edge, which can play a role in determining power deposition at the divertor target, models for plasma-materials and plasma dynamics interaction during ELMs and disruptions, models for the transport of impurities at the plasma edge to describe the core contamination by impurities and the migration of eroded materials at the edge plasma and its associated tritium retention and models for the turbulent processes that determine the anomalous transport of energy and particles across the SOL. The implications for the expected performance of the reference regimes in ITER, the operation of the ITER device and the lifetime of the plasma facing materials are discussed. Introduction.This chapter outlines the significant progress achieved since the ITER Physics Basis in understanding basic scrape-off layer (SOL) and divertor processes in a tokamak. The interaction of plasma with first-wall surfaces will have considerable impact on the performance of fusion plasmas, the lifetime of plasma facing components, and the retention of tritium in next step Burning Plasma E...

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Volume recombination in divertor I of ASDEX Upgrade

Cited by 49 publications

References 24 publications

Characterisation of detached plasmas on the MAST tokamak

Characterisation of detached plasmas on the MAST tokamak

Divertor Physics Research on Alcator C-Mod

Chapter 4: Power and particle control

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