Improved performance of ELMy H-modes at high density by plasma shaping in JET

Saibene, G.; Sartori, R.; Loarte, A.; Campbell, D.J.; Lomas, P. J.; Parail, V.; Zastrow, K.‐D.; Andrew, Y.; Sharapov, S. E.; Korotkov, A.; Bécoulet, M.; Huysmans, G.; Koslowski, H. R.; Budny, R.; Conway, G. D.; Stober, J.; Suttrop, W.; Kallenbach, A.; Hellermann, M. von; Beurskens, M.

doi:10.1088/0741-3335/44/9/301

Cited by 144 publications

(223 citation statements)

References 36 publications

(62 reference statements)

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“…As the fuelling level is increased from low, ( D ~ 0.2x10 22 el/s, n e,ped /n gw =0.7), to high dosing ( D ~ 2.6x10 22 el/s, n e,ped /n gw =1.0) the variation in ELM behaviour is consistent with a transition from 'pure Type I' to 'mixed Type I/II' ELMs [1]. However, the pulses in Scattering (HRTS) system.…”

supporting

confidence: 56%

Pedestal study across a deuterium fuelling scan for highδELMy H-mode plasmas on JET with the carbon wall

Leyland¹,

Beurskens²,

Frassinetti³

et al. 2013

Nucl. Fusion

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We present the results from a new fuelling scan database consisting of 14 high triangularity ( ~ 0.41), Type I ELMy H-mode JET plasmas. As the fuelling level is increased from low, ( D ~ 0.2x10 22 el/s, n e,ped /n gw =0.7), to high dosing ( D ~ 2.6x10 22 el/s, n e,ped /n gw =1.0) the variation in ELM behaviour is consistent with a transition from 'pure Type I' to 'mixed Type I/II' ELMs [1]. However, the pulses in Scattering (HRTS) system. We continue by presenting, for the first time, the role of pedestal structure, as quantified by a least squares mtanh fit to the HRTS profiles, on the performance across the fuelling scan. A key result is that the pedestal width narrows and peak pressure gradient increases during the ELM cycle for low fuelling plasmas, whereas at high fuelling the pedestal width and peak pressure gradient saturates towards the latter half of the ELM cycle. An ideal MHD stability analysis shows that both low and high fuelling plasmas move from stable to unstable approaching the ideal ballooning limit of the finite peeling ballooning stability boundary. Comparison to EPED predictions show on average good agreement with experimental measurements for both pedestal height and width however when presented as a function of pedestal density, experiment and model show opposing trends. The measured pre-ELM pressure pedestal height increases by ~ 20% whereas EPED predicts a decrease of 25% from low to high fuelling. Similarly the measured pressure pedestal width widens by ~ 55%, in poloidal flux space, whereas EPED predicts a decrease of 20% from low to high fuelling. We give two possible explanations for the disagreement. First, it may be that EPED under-predicts the critical density, which marks the transition from kink-peeling to ballooning limited plasmas. Second, the stronger broadening of the experimental pedestal width than predicted by EPED is an indication that other transport related processes contribute to defining the pedestal width such as enhanced inter-ELM transport as observed at high fuelling, for mixed Type I/II ELMy pulses.M. Leyland

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supporting

confidence: 56%

Pedestal study across a deuterium fuelling scan for highδELMy H-mode plasmas on JET with the carbon wall

Leyland¹,

Beurskens²,

Frassinetti³

et al. 2013

Nucl. Fusion

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“…Furthermore H 98 and W th decrease with increasing deuterium fuelling for JET-ILW plasmas unlike the JET-C plasmas. As reported in [Leyland 2013] the JET-C plasmas maintain and even improve overall performance (H 98 and W th ) with increasing deuterium fuelling due to a transition from pure Type I ELMs to the so called mixed Type I/II ELMs [Saibene 2002, Saibene 2005]. …”

Section: Plasma Performancementioning

confidence: 84%

“…The plasma performance was not only maintained but even improved with increased fuelling up to a density pedestal normalised to the Greenwald density (n e,ped /n GW )  1. This improvement in performance was attributed to an increase in pedestal stored energy which coincided with a transition from pure Type I ELMs to mixed Type I/II ELMs [Saibene 2002, Saibene 2005, Giroud 2012. A key result was that the pre-ELM electron temperature and density pedestal width increased from low to high deuterium fuelling.…”

Section: Introductionmentioning

confidence: 97%

The H-mode pedestal structure and its role on confinement in JET with a carbon and metal wall

Leyland

Beurskens

Frassinetti³

et al. 2014

Nucl. Fusion

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We present the pedestal structure, as determined from the high resolution Thomson scattering (HRTS) measurements, for a database of low and high triangularity (  0.22-0.39) 2.5MA, Type I ELMy H-mode JET plasmas after the installation of the new ITER-like Wall (JET-ILW). The database explores the effect of increasing deuterium fuelling and nitrogen seeding with a view to explain the observed changes in performance (edge and global). The low triangularity JET-ILW plasmas show no significant change in performance and pedestal structure with increasing gas dosing. These results are in good agreement with EPED1 predictions. At high triangularity, for pure deuterium fuelled JET-ILW plasmas, there is a 20-30% reduction in global performance and pressure pedestal height in comparison to JET-C plasmas. This reduction in performance is primarily due to a degradation of the temperature pedestal height. The global performance and pressure pedestal height of JET-ILW plasmas can be partially recovered to that of JET-C plasmas with additional nitrogen seeding [Giroud 2013]. This observed improvement in performance is predominately due to a significant increase in density pedestal height as well as a small increase in the temperature pedestal height. A key result with increasing deuterium fuelling for JET-ILW plasmas is there is no improvement in pressure pedestal height however the pedestal still widens which is inconsistent with the  = 0.076√ pol,ped scaling. Furthermore, a key result with increasing nitrogen seeding is the pressure pedestal widening is due to an increase in the temperature pedestal width whilst the density pedestal shows no clear trend. The comparison of EPED1 predictions with the measurements at high triangularity is complex as, for example, for pure deuterium fuelled plasmas there is very good agreement for the pedestal height but not the width. In addition, current EPED1 runs under-predict the pedestal height and width at high nitrogen seeding for JET-ILW plasmas however further work is required to determine the significance of these deviations. Understanding these deviations is essential as provides an insight to the physical mechanisms governing the pedestal structure and edge performance.

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“…This has been exceeded in JET with highly shaped discharges, in which pedestal densities up to n ped /n Green =1 have been reached [470]. Because of the coupling of separatrix and pedestal densities with standard gas fuelling, a sufficiently high pedestal density may not be accessible in ITER.…”

Section: Fig 427-2 Modelled Diii-d Density Profiles Normalised Tmentioning

confidence: 99%

Chapter 4: Power and particle control

Loarte¹,

et al. 2007

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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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Improved performance of ELMy H-modes at high density by plasma shaping in JET

Cited by 144 publications

References 36 publications

Pedestal study across a deuterium fuelling scan for highδELMy H-mode plasmas on JET with the carbon wall

Pedestal study across a deuterium fuelling scan for highδELMy H-mode plasmas on JET with the carbon wall

The H-mode pedestal structure and its role on confinement in JET with a carbon and metal wall

Chapter 4: Power and particle control

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