Be wall sources and migration in L-mode discharges after Be evaporation in the JET tokamak

Krieger, K.; Brezinsek, S.; Jachmich, S.; Lisgo, S.; Stamp, M.; Esser, H. G.; Kreter, A.; Menmuir, S.; Mertens, Ph.; Philipps, V.; Sundelin, Per; Contributors, Jet

doi:10.1016/j.jnucmat.2009.01.131

Cited by 15 publications

(8 citation statements)

References 12 publications

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“…Due to the transient behaviour only these first four discharges were applied later for analysis of the wall inventory. However, the decay of the Be flux in the divertor phase in time is faster than in previous experiments with extended Be evaporation in L-mode plasmas without limiter phase and larger wall clearance [7]. The higher Be erosion flux in the divertor phase may be attributed to a stronger wall interaction during ELM burst in the applied H-mode plasmas in comparison with L-mode plasmas studied before.…”

Section: Be Evaporationmentioning

confidence: 50%

“…Figure 2 shows the impact of the extended Be evaporation on the erosion of the first wall measured by optical spectroscopy at one of the inner poloidal limiter. Details about the spectroscopic system and the line of sight at the vessel midplane are described in [7]. All photon fluxes have the same scale for a relative comparison of the source strength and coverage of Be and C, measured by the localized impurity flux of Be + and C + ions which results from sputtering by mainly impinging deuterium ions and CXRS neutrals.…”

Section: Be Evaporationmentioning

confidence: 99%

“…The Be evaporation executed in this experiment is referred to below as extended evaporation due to the fact that 50 times more Be is evaporated with respect to regular performed standard evaporations for conditioning of the JET vessel. Although such an extended Be evaporation [7] provides only a transient and inhomogeneous coverage of the first wall, it can still be seen as a first small step on the way from a CFC to a Be first wall, providing an outlook on what can be expected from the ILW. Moreover, this integrated and ILWcompatible experiment can be re-executed as plasma operation in H-mode resumes and will thereby assess the ILW concerning changes in fuel retention and divertor radiation.…”

Section: Introductionmentioning

confidence: 99%

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Fuel retention in impurity seeded discharges in JET after Be evaporation

Brezinsek¹,

Krieger

Jachmich³

et al. 2011

Nucl. Fusion

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Preparatory experiments for the ITER-Like Wall in JET were carried out to simulate the massive Be first wall by a thin Be layer, induced by evaporation of about 2.0g Be, and to study its impact on fuel retention and divertor radiation with reduced C content and N seeding. Residual gas analysis reveals a reduction of hydrocarbons by one order of magnitude and of O by a factor 5 in the partial pressure owing to the evaporation. The evolution of wall conditions, impurity fluxes, and divertor radiation have been studied in ELMy H-mode plasmas (B t = 2.7T, I p = 2.5MA, P aux = 16MW) whereas a non-seeded reference discharge was executed prior to the evaporation.The in-situ measured Be flux at the midplane increased by about a factor 40 whereas the C flux decreased by ~50% in the limiter phase of the first discharge with respect to the reference, but erosion of the Be layer and partial coverage with C takes place quickly. To make best use of the protective Be layer, only the first four discharges were employed for a gas balance analysis providing a D retention rate of 1.94×10 21 Ds -1 which is comparable to rates with C walls. But the Be evaporation provides a non-saturated surface with respect to D and short term retention is not negligible in the balance; the measured retention is overestimated with respect to steady-state conditions like for the ILW. Moreover, C was only moderately reduced and co-deposition of fuel with eroded Be and C occurs.The lower C content leads to a minor reduction in divertor radiation as the reference phase prior to seeding indicates. N adds to the radiation of D and remaining C, and the N content rises due to the legacy effect which has been quantified by gas balance to be 30% of the injected N. C radiation increases with exposures time, and both contributors causing an increase of the radiated fraction in the divertor from 50% to 70%. The radiation pattern suggests that N dominates the increase in the first discharges though C is still the dominating radiator. Therefore, the validity of a proxy of the Be first wall by a thin Be layer is limited and restricted to plasma operation directly after the Be evaporation.

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Section: Be Evaporationmentioning

confidence: 50%

Section: Be Evaporationmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Fuel retention in impurity seeded discharges in JET after Be evaporation

Brezinsek¹,

Krieger

Jachmich³

et al. 2011

Nucl. Fusion

Self Cite

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“…On the other hand, if the background W density resulting from the W divertor source turns out to be low enough, the W influx from the high field side could be used for transport experiments using beam modulation, similar to the experiments performed with ICRH modulation in AUG [92]. The migration of Be from the main chamber into the divertor was investigated in a series of L-Mode discharges preceded by massive Be evaporation, where 50 times more Be was evaporated compared to regularly performed standard evaporations for conditioning [133].…”

Section: Preparatory Work For An Efficient Exploitation Of the Jet Ilwmentioning

confidence: 99%

Preparing the scientific basis for an all metal ITER

Neu

Taskforce²,

Contributors³

2011

Plasma Phys. Control. Fusion

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Abstract. The use of beryllium, carbon and tungsten as plasma-facing materials (PFMs) in ITER calls for dedicated investigations on their behaviour under the expected particle and power loads and neutron irradiation. Their simultaneous use implies the formation of mixed materials during plasma operation, which can have significantly different properties compared to the initial materials concerning thermo-mechanical behaviour and T retention. This contribution presents the latest results on these issues mainly achieved under the umbrella of the European taskforce on Plasma Wall Interaction. While laboratory results provide the basis for the understanding of the basic properties and the behaviour of PFMs, experiments in fusion devices are indispensable in order to test their integral performance, incorporating also the internal feedback on the plasma properties. For this reason ASDEX Upgrade has been converted to a full W device, while JET is beginning operation with its ITER-like wall consisting of a Be main chamber plasma-facing components and a W divertor. In parallel, dedicated W experiments are performed in several devices in order to investigate specific uncertainties such as the characteristics of melt layer movement in the presence of a strong magnetic field. Based on the results on ASDEX Upgrade, which reveal a narrower operational space as compared to the operation with graphite plasma facing components but also provide tools for a successful operation with tungsten, the experiments at JET will provide a unique opportunity to address specific issues related to the parallel use of Be and W as PFMs with plasma parameters closest to those of ITER. Amongst these are the anticipated but still to be demonstrated reduction in hydrogen retention compared to a carbon device, the test of conditioning procedures, mixed materials effects, erosion and transport, the effect of ELMs and ELM mitigation methods as well as the behaviour of melt layers and their influence on plasma operation under steady state and transient heat loads.

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“…In order to reduce this fuel retention and the production of dust, the ITER technology concept is based on using beryllium [3] and tungsten as main plasma-facing materials. To evaluate the consequences of such a major change it has been decided to test this configuration at the Joint European Torus (JET).…”

Section: Introductionmentioning

confidence: 99%

Tritium retention measurements by accelerator mass spectrometry and full combustion of W-coated and uncoated CFC tiles from the JET divertor

et al. 2016

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Accelerator mass spectrometry (AMS) and the full combustion method (FCM) followed by liquid scintillation counting were applied to quantitatively determine the tritium retention in the tungsten-coated carbon fibre composites (CFC), in comparison to uncoated CFC tiles from the JET divertor. The tiles were adjacent and exposed to plasma operations between 2007 and 2009. The tritium depth profiles are showing that the tritium retention on the W-coated tile was reduced by a factor of 13.5 in comparison to the uncoated tile whereas the bulk tritium concentration is approximately the same for both tiles.

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Be wall sources and migration in L-mode discharges after Be evaporation in the JET tokamak

Cited by 15 publications

References 12 publications

Fuel retention in impurity seeded discharges in JET after Be evaporation

Fuel retention in impurity seeded discharges in JET after Be evaporation

Preparing the scientific basis for an all metal ITER

Tritium retention measurements by accelerator mass spectrometry and full combustion of W-coated and uncoated CFC tiles from the JET divertor

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