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Journal ArticleDOI

Global erosion and deposition patterns in JET with the ITER-like Wall

TL;DR: A set of Be and W tiles removed after the first ITER-like wall campaigns (JET-ILW) from 2011 to 2012 has been analyzed in this article, and the results indicate that the primary erosion site is in the main chamber (Be) as in previous carbon campaigns.
About: This article is published in Journal of Nuclear Materials.The article was published on 2015-08-01 and is currently open access. It has received 50 citations till now. The article focuses on the topics: Divertor.

Summary (3 min read)

1. Introduction

  • Plasma wall interactions create some of the greatest challenges for the realisation of a fusion reactor.
  • This is also true for ITER where tritium trapping due to implantation and codeposition and plasma pollution due to impurities migrating from PFCs to the plasma are major concerns.
  • After over two decades of JET operation with a carbon wall, the ITER-like wall project at JET (JET-ILW) was initiated to explore plasma performance and plasma-wall interaction processes with a full metal wall: bulk beryllium (Be), Be-coated Inconel in the main chamber and bulk tungsten (W) or W-coated carbon fibre composites (CFC) in the divertor [1, 2] .
  • An extensive post-mortem surface analysis program on PFC has been carried out after the ILW campaign and initial results were published elsewhere [5, 6, 7] .

2. Experimental

  • The marker tiles were analysed prior to installation and after removal from the vessel by a set of ion beam analytical methods (IBA) to determine the extent of erosion/deposition.
  • Ion beam analyses were carried out using a Van de Graaff accelerator at the IST/ITN in Lisbon.
  • Three complementary techniques were used: nuclear reaction analysis (NRA), Rutherford Backscattering Spectrometry (RBS) and Particle Induced X-ray Emission (PIXE).
  • He 3 beam at normal incidence, with the detector positioned at 135to the direction of the incident beam.
  • IBA analysis is supported by extensive analysis of surface profile changes of the selected marker tiles using a tile profiler.

3. Results

  • In this section the material migration pattern is summarised for key areas of the main chamber and divertor.
  • The implications are discussed in the next section.

3.1.1. Outer poloidal limiters (OPL)

  • The erosion/deposition at the outer poloidal limiters (OPL) tiles is illustrated by the analyses of tiles 4D3, 4D14 and 4D23 located as indicated (Fig. 1 ).
  • At the centre of a tile near the midplane (4D14) the marker coating has been eroded and only bulk Be remains (Fig 2 , region a ).
  • IBA shows re-deposition of Be and Ni onto both left and right sides (Fig. 2 , region b).
  • Finally, surface profilometry results confirm that any profile changes were below the detection limit (±5µm), so these tiles do not contribute anything to the net erosion/deposition in the vessel during the ILW.
  • Tiles B and C placed between outer divertor tiles and the main chamber (Fig 1 ) were also analysed by means of IBA.

3.1.2. Inner wall guard limiters (IWGL)

  • Surface profilometry and IBA analysis of marker tiles 2XR3, 2XR10 and 2XR19 has been completed recently.
  • Towards the ends of the tile there is deposition of some Be and plasma impurities such as W and Ni, Mo, Cr, Fe (identified by PIXE) typical for Inconel composition.
  • At the very ends of the tile the composition reverts to the original marker composition.
  • The marker layers at the centre part of the top limiter 2XR19 are conserved so no measurable erosion has occurred, there are traces of W and Ni deposition on the tile.

3.2.Deposition pattern in the divertor

  • The composition of the deposit consist mainly Be with traces of W, Ni, Mo, Cr and Fe.
  • By fitting the spectra using a series of Be -W layers with varying Be/W ratio a relatively good agreement with the measured spectra is obtained and from this the integrated Be and W amounts inferred.
  • It should be kept in mind that the data analysis assumes a flat surface.
  • Nevertheless, it has been already shown that in case of ambiguities between depth profiles and surface roughness the total amounts of elements are still correct even if the depth profiles may not reflect the sample structure correctly [12] .
  • Recent scanning electron microscopy (SEM) of sample cross-sections has brought some clarification for interpreting RBS spectra and confirmed a multi-layered structure of the deposited material, which is clearly observed on Tile 1, as shown in Fig. 4a .

Furthermore, SEM mass analysis indicates that W is the main element present in what IBA

  • The SEM analysis can not resolve individual layers.
  • Nevertheless, combining the information of the BSE microscopy, the SEM analysis and IBA, it can be concluded that the deposited material has a multi-layered structure consisting of an outer layer of pure.
  • The oxygen concentration was not possible to evaluate directly in this work by IBA but it might be likely that the inner layer contains also a significant amount of oxygen (up to 10 %, based on NDF data fitting).
  • For Tiles 3, 4 and 6 the small amount of deposition observed probably offsets any erosion (despite some indications of erosion at the top of Tile 3), but one can only set an upper limit on their contribution to overall deposition in the divertor.

4. Discussion and Conclusion

  • The latest quantitative assessment of the overall material migration balance based on a combination of surface profilometry and accelerator based ion beam techniques is summarized in the Table, which also compares these values with those for the last JET carbon campaign taken from the literature.
  • The rate of erosion at the IWGL during the limiter phases of ILW operations has been calculated to be similar to that during the previous carbon campaign [3] .
  • During the divertor phase of each discharge erosion is probably dominated by charge exchange neutral (CXN) bombardment of the main chamber wall, and is followed by migration along the SOL to the inner divertor.
  • This is evidenced by erosion measurements at the Inner Wall Cladding (IWC) tiles that line the vessel wall between the IWGL [14] which suggest that the IWC may account for a significant fraction of the Be deposition found in the divertor.
  • Furthermore, transient impurity events involving tungsten are relatively common [15] .

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Figures (1)
Citations
More filters
01 Jan 2013
Abstract: This paper reports the impact on confinement and power load of the high-shape 2.5 MA ELMy H-mode scenario at JET of a change from all carbon plasma-facing components to an all metal wall. In preparation to this change, systematic studies of power load reduction and impact on confinement as a result of fuelling in combination with nitrogen seeding were carried out in JET-C and are compared with their counterpart in JET with a metallic wall. An unexpected and significant change is reported on the decrease in the pedestal confinement but is partially recovered with the injection of nitrogen.

104 citations

Journal ArticleDOI
17 Oct 2016-Analyst
TL;DR: It is demonstrated that RBS can be used as a primary reference technique for the best traceable accuracy available for non-destructive model-free methods in thin films and it has become clear over the last decade that it can effectively combine synergistically the quite different information available from the atomic and nuclear methods.
Abstract: The analysis of thin films is of central importance for functional materials, including the very large and active field of nanomaterials. Quantitative elemental depth profiling is basic to analysis, and many techniques exist, but all have limitations and quantitation is always an issue. We here review recent significant advances in ion beam analysis (IBA) which now merit it a standard place in the analyst's toolbox. Rutherford backscattering spectrometry (RBS) has been in use for half a century to obtain elemental depth profiles non-destructively from the first fraction of a micron from the surface of materials: more generally, “IBA” refers to the cluster of methods including elastic scattering (RBS; elastic recoil detection, ERD; and non-Rutherford elastic backscattering, EBS), nuclear reaction analysis (NRA: including particle-induced gamma-ray emission, PIGE), and also particle-induced X-ray emission (PIXE). We have at last demonstrated what was long promised, that RBS can be used as a primary reference technique for the best traceable accuracy available for non-destructive model-free methods in thin films. Also, it has become clear over the last decade that we can effectively combine synergistically the quite different information available from the atomic (PIXE) and nuclear (RBS, EBS, ERD, NRA) methods. Although it is well known that RBS has severe limitations that curtail its usefulness for elemental depth profiling, these limitations are largely overcome when we make proper synergistic use of IBA methods. In this Tutorial Review we aim to briefly explain to analysts what IBA is and why it is now a general quantitative method of great power. Analysts have got used to the availability of the large synchrotron facilities for certain sorts of difficult problems, but there are many much more easily accessible mid-range IBA facilities also able to address (and often more quantitatively) a wide range of otherwise almost intractable thin film questions.

74 citations

Journal ArticleDOI
TL;DR: In this paper, the JET divertor during the first JET ITER-like wall campaign 2011 to 2012 using marker tiles was used to study erosion and deposition in a poloidal section consisting of tiles 0, 1, 3.
Abstract: Erosion and deposition were studied in the JET divertor during the first JET ITER-like wall campaign 2011 to 2012 using marker tiles. An almost complete poloidal section consisting of tiles 0, 1, 3 ...

68 citations

Journal ArticleDOI
TL;DR: The first dust survey in JET with the ITER-like wall (JET-ILW) is presented in this article, where the sampling was performed using adhesive stickers from the divertor tiles where the greatest material depos...
Abstract: Results of the first dust survey in JET with the ITER-Like Wall (JET-ILW) are presented. The sampling was performed using adhesive stickers from the divertor tiles where the greatest material depos ...

54 citations

Journal ArticleDOI
TL;DR: The necessity for determining new nuclear reaction cross-sections and improving the inter-laboratory comparability by defining international standards and testing these via a round-robin test is concluded.
Abstract: Following the IAEA Technical Meeting on “Advanced Methodologies for the Analysis of Materials in Energy Applications Using Ion Beam Accelerators”, this paper reviews the current status of ion beam analysis techniques and some aspects of ion-induced radiation damage in materials for the field of materials relevant to fusion. Available facilities, apparatus development and future research options and challenges are presented and discussed. The analysis of beryllium and radioactivity-containing samples from future experiments in JET or ITER represents not only an analytical but also a technical challenge. A comprehensive list of the facilities, their current status, and analytical capabilities comes alongside detailed descriptions of the labs. A discussion of future issues of sample handling and the current status of facilities at JET complete the technical section. To prepare the international ion beam analysis community for these challenges, the IAEA technical meeting concludes the necessity for determining new nuclear reaction cross-sections and improving the inter-laboratory comparability by defining international standards and testing these via a round-robin test.

51 citations

References
More filters
Journal ArticleDOI
TL;DR: In this article, the successful installation of the JET ITER-like wall and the realization of its technical objectives is reported, and an overview of the planned experimental program which has been optimized to exploit the new wall and other JET enhancements in 2011/12.
Abstract: This paper reports the successful installation of the JET ITER-like wall and the realization of its technical objectives. It also presents an overview of the planned experimental programme which has been optimized to exploit the new wall and other JET enhancements in 2011/12.

281 citations

Journal ArticleDOI
TL;DR: The IBA DataFurnace (NDF) as mentioned in this paper is a general purpose program for analysis of IBA data, which includes Rutherford backscattering, elastic (non-Rutherford) backscatter, elastic recoil detection analysis (ERDA), non-resonant nuclear reaction analysis (NRA), and particle induced X-ray emission (PIXE).
Abstract: The IBA DataFurnace (NDF) is a general purpose program for analysis of IBA data. It currently includes Rutherford backscattering (RBS), elastic (non-Rutherford) backscattering (EBS), elastic recoil detection analysis (ERDA), non-resonant nuclear reaction analysis (NRA), and particle induced X-ray emission (PIXE). Here we discuss recent developments in the advanced physics capabilities implemented in NDF, supported by advanced algorithms. Examples of real life hard cases are given that illustrate the issues discussed.

149 citations

Journal ArticleDOI
TL;DR: In this paper, the ITER-like wall (ILW) was installed in the JET to enable a direct comparison of operation with all carbon plasma facing components (PFCs) to an all metal beryllium/tungsten first-wall under identical conditions.

146 citations

Journal ArticleDOI
TL;DR: In this article, the impact on confinement and power load of a high-shape 2.5-MA ELMy H-mode scenario at JET-C was investigated and an unexpected and significant change was reported on the decrease in pedestal confinement but is partially recovered with the injection of nitrogen.
Abstract: This paper reports the impact on confinement and power load of the high-shape 2.5 MA ELMy H-mode scenario at JET of a change from all carbon plasma-facing components to an all metal wall. In preparation to this change, systematic studies of power load reduction and impact on confinement as a result of fuelling in combination with nitrogen seeding were carried out in JET-C and are compared with their counterpart in JET with a metallic wall. An unexpected and significant change is reported on the decrease in the pedestal confinement but is partially recovered with the injection of nitrogen.

117 citations

Journal ArticleDOI
TL;DR: In this paper, the impact on confinement and power load of a high-shape 2.5MA ELMy H-mode scenario at JET with a change from an all carbon plasma facing components to an all metal wall was investigated.
Abstract: This paper reports the impact on confinement and power load of the high-shape 2.5MA ELMy H-mode scenario at JET of a change from an all carbon plasma facing components to an all metal wall. In preparation to this change, systematic studies of power load reduction and impact on confinement as a result of fuelling in combination with nitrogen seeding were carried out in JET-C and are compared to their counterpart in JET with a metallic wall. An unexpected and significant change is reported on the decrease of the pedestal confinement but is partially recovered with the injection of nitrogen.

113 citations

Related Papers (5)
Frequently Asked Questions (10)
Q1. What contributions have the authors mentioned in the paper "Global erosion and deposition patterns in jet with the iter-like wall" ?

In this paper, a set of Be and W tiles removed after the first ITER-like wall campaigns ( JET-ILW ) from 2011-2012 was analyzed. 

During the divertor phase of each discharge erosion is probably dominated by charge exchange neutral (CXN) bombardment of the main chamber wall, and is followed by migration along the SOL to the inner divertor. 

After over two decades of JET operation with a carbon wall, the ITER-like wall project at JET (JET-ILW) was initiated to explore plasma performance and plasma-wall interaction processes with a full metal wall: bulk beryllium (Be), Be-coated Inconel in the main chamber and bulk tungsten (W) or W-coated carbon fibre composites (CFC) in the divertor [1, 2]. 

Experimental data were processed using NDF [10] and/or SIMNRA [11] software to determine the chemical composition and thickness of deposits. 

The amount of material deposited on Tiles 4 and 6 was generally below ~2.5·1018 at/cm2, however areas of highier deposition (~6·1018 at/cm2 of Be over the 1 mm2 beam area) were found on the slopping of these tiles. 

The tiles are relatively clean, however there are traces of W, Ni, Mo, Cr, and Fe on the surface, and NRA shows some D retention. 

This is evidenced by erosion measurements at the Inner Wall Cladding (IWC) tiles that line the vessel wall between the IWGL [14] which suggest that the IWC may account for a significant fraction of the Be deposition found in the divertor. 

There are also many areas where widespread arcing has occurred that are visible on Be tiles: such arcing may also be widespread on W-coated CFC tiles but would not be easily visible, however could easily dislodge coating asperities from these rough surfaces. 

Some contribution may also be expected from re-erosion of the deposits on the IWGL, which may have a higher erosion yield than the bulk material. 

combining the information of the BSE microscopy, the SEM analysis and IBA, it can be concluded that the deposited  material has a multi-layered structure consisting of an outer layer of pure