Plasma-wall interaction studies in the full-W ASDEX upgrade during helium plasma discharges

A. Hakola, S. Brezinsek, D. Douai, M. Balden, V. Bobkov, D. Carralero, H. Greuner, S. Elgeti, A. Kallenbach, K. Krieger, G. Meisl, M. Oberkofler, V. Rohde, P. Schneider, T. Schwarz-Selinger, A. Lahtinen, G. De Temmerman, R. Caniello, F. Ghezzi, T. WautersA. Garcia-Carrasco, P. Petersson, I. Bogdanovic Radovic, Z. Siketic

    Research output: Contribution to journalArticleScientificpeer-review

    7 Citations (Scopus)

    Abstract

    Plasma-wall interactions have been studied in the full-W ASDEX Upgrade during its dedicated helium campaign. Relatively clean plasmas with a He content of >80% could be obtained by applying ion cyclotron wall conditioning (ICWC) discharges upon changeover from D to He. However, co-deposited layers with significant amounts of He and D were measured on W samples exposed to ICWC plasmas at the low-field side (outer) midplane. This is a sign of local migration and accumulation of materials and residual fuel in regions shadowed from direct plasma exposure albeit globally D was removed from the vessel. When exposing W samples to ELMy H-mode helium plasmas in the outer strike-point region, no net erosion was observed but the surfaces had been covered with co-deposited layers mainly consisting of W, B, C, and D and being the thickest on rough and modified surfaces. This is different from the typical erosion-deposition patterns in D plasmas, where usually sharp net-erosion peaks surrounded by prominent net-deposition maxima for W are observed close to the strike point. Moreover, no clear signs of W nanostructure growth or destruction could be seen. The growth of deposited layers may impact the operation of future fusion reactors and is attributed to strong sources in the main chamber that under suitable conditions may switch the balance from net erosion into net deposition, even close to the strike points. In addition, the absence of noticeable chemical erosion in helium plasmas may have affected the thickness of the deposited layers. Retention of He, for its part, remained small and uniform throughout the strike-point region although our results indicate that samples with smooth surfaces can contain an order of magnitude less He than their rough counterparts.
    Original languageEnglish
    Article number066015
    JournalNuclear Fusion
    Volume57
    Issue number6
    DOIs
    Publication statusPublished - 20 Apr 2017
    MoE publication typeA1 Journal article-refereed

    Fingerprint

    helium plasma
    plasma jets
    erosion
    conditioning
    interactions
    cyclotrons
    nanostructure growth
    fusion reactors
    destruction
    vessels
    ions
    chambers
    helium

    Keywords

    • erosion
    • helium
    • plasma-wall interaction
    • retention
    • tungsten fuzz

    Cite this

    Hakola, A., Brezinsek, S., Douai, D., Balden, M., Bobkov, V., Carralero, D., ... Siketic, Z. (2017). Plasma-wall interaction studies in the full-W ASDEX upgrade during helium plasma discharges. Nuclear Fusion, 57(6), [066015]. https://doi.org/10.1088/1741-4326/aa69c4
    Hakola, A. ; Brezinsek, S. ; Douai, D. ; Balden, M. ; Bobkov, V. ; Carralero, D. ; Greuner, H. ; Elgeti, S. ; Kallenbach, A. ; Krieger, K. ; Meisl, G. ; Oberkofler, M. ; Rohde, V. ; Schneider, P. ; Schwarz-Selinger, T. ; Lahtinen, A. ; De Temmerman, G. ; Caniello, R. ; Ghezzi, F. ; Wauters, T. ; Garcia-Carrasco, A. ; Petersson, P. ; Bogdanovic Radovic, I. ; Siketic, Z. / Plasma-wall interaction studies in the full-W ASDEX upgrade during helium plasma discharges. In: Nuclear Fusion. 2017 ; Vol. 57, No. 6.
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    title = "Plasma-wall interaction studies in the full-W ASDEX upgrade during helium plasma discharges",
    abstract = "Plasma-wall interactions have been studied in the full-W ASDEX Upgrade during its dedicated helium campaign. Relatively clean plasmas with a He content of >80{\%} could be obtained by applying ion cyclotron wall conditioning (ICWC) discharges upon changeover from D to He. However, co-deposited layers with significant amounts of He and D were measured on W samples exposed to ICWC plasmas at the low-field side (outer) midplane. This is a sign of local migration and accumulation of materials and residual fuel in regions shadowed from direct plasma exposure albeit globally D was removed from the vessel. When exposing W samples to ELMy H-mode helium plasmas in the outer strike-point region, no net erosion was observed but the surfaces had been covered with co-deposited layers mainly consisting of W, B, C, and D and being the thickest on rough and modified surfaces. This is different from the typical erosion-deposition patterns in D plasmas, where usually sharp net-erosion peaks surrounded by prominent net-deposition maxima for W are observed close to the strike point. Moreover, no clear signs of W nanostructure growth or destruction could be seen. The growth of deposited layers may impact the operation of future fusion reactors and is attributed to strong sources in the main chamber that under suitable conditions may switch the balance from net erosion into net deposition, even close to the strike points. In addition, the absence of noticeable chemical erosion in helium plasmas may have affected the thickness of the deposited layers. Retention of He, for its part, remained small and uniform throughout the strike-point region although our results indicate that samples with smooth surfaces can contain an order of magnitude less He than their rough counterparts.",
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    author = "A. Hakola and S. Brezinsek and D. Douai and M. Balden and V. Bobkov and D. Carralero and H. Greuner and S. Elgeti and A. Kallenbach and K. Krieger and G. Meisl and M. Oberkofler and V. Rohde and P. Schneider and T. Schwarz-Selinger and A. Lahtinen and {De Temmerman}, G. and R. Caniello and F. Ghezzi and T. Wauters and A. Garcia-Carrasco and P. Petersson and {Bogdanovic Radovic}, I. and Z. Siketic",
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    Hakola, A, Brezinsek, S, Douai, D, Balden, M, Bobkov, V, Carralero, D, Greuner, H, Elgeti, S, Kallenbach, A, Krieger, K, Meisl, G, Oberkofler, M, Rohde, V, Schneider, P, Schwarz-Selinger, T, Lahtinen, A, De Temmerman, G, Caniello, R, Ghezzi, F, Wauters, T, Garcia-Carrasco, A, Petersson, P, Bogdanovic Radovic, I & Siketic, Z 2017, 'Plasma-wall interaction studies in the full-W ASDEX upgrade during helium plasma discharges', Nuclear Fusion, vol. 57, no. 6, 066015. https://doi.org/10.1088/1741-4326/aa69c4

    Plasma-wall interaction studies in the full-W ASDEX upgrade during helium plasma discharges. / Hakola, A.; Brezinsek, S.; Douai, D.; Balden, M.; Bobkov, V.; Carralero, D.; Greuner, H.; Elgeti, S.; Kallenbach, A.; Krieger, K.; Meisl, G.; Oberkofler, M.; Rohde, V.; Schneider, P.; Schwarz-Selinger, T.; Lahtinen, A.; De Temmerman, G.; Caniello, R.; Ghezzi, F.; Wauters, T.; Garcia-Carrasco, A.; Petersson, P.; Bogdanovic Radovic, I.; Siketic, Z.

    In: Nuclear Fusion, Vol. 57, No. 6, 066015, 20.04.2017.

    Research output: Contribution to journalArticleScientificpeer-review

    TY - JOUR

    T1 - Plasma-wall interaction studies in the full-W ASDEX upgrade during helium plasma discharges

    AU - Hakola, A.

    AU - Brezinsek, S.

    AU - Douai, D.

    AU - Balden, M.

    AU - Bobkov, V.

    AU - Carralero, D.

    AU - Greuner, H.

    AU - Elgeti, S.

    AU - Kallenbach, A.

    AU - Krieger, K.

    AU - Meisl, G.

    AU - Oberkofler, M.

    AU - Rohde, V.

    AU - Schneider, P.

    AU - Schwarz-Selinger, T.

    AU - Lahtinen, A.

    AU - De Temmerman, G.

    AU - Caniello, R.

    AU - Ghezzi, F.

    AU - Wauters, T.

    AU - Garcia-Carrasco, A.

    AU - Petersson, P.

    AU - Bogdanovic Radovic, I.

    AU - Siketic, Z.

    PY - 2017/4/20

    Y1 - 2017/4/20

    N2 - Plasma-wall interactions have been studied in the full-W ASDEX Upgrade during its dedicated helium campaign. Relatively clean plasmas with a He content of >80% could be obtained by applying ion cyclotron wall conditioning (ICWC) discharges upon changeover from D to He. However, co-deposited layers with significant amounts of He and D were measured on W samples exposed to ICWC plasmas at the low-field side (outer) midplane. This is a sign of local migration and accumulation of materials and residual fuel in regions shadowed from direct plasma exposure albeit globally D was removed from the vessel. When exposing W samples to ELMy H-mode helium plasmas in the outer strike-point region, no net erosion was observed but the surfaces had been covered with co-deposited layers mainly consisting of W, B, C, and D and being the thickest on rough and modified surfaces. This is different from the typical erosion-deposition patterns in D plasmas, where usually sharp net-erosion peaks surrounded by prominent net-deposition maxima for W are observed close to the strike point. Moreover, no clear signs of W nanostructure growth or destruction could be seen. The growth of deposited layers may impact the operation of future fusion reactors and is attributed to strong sources in the main chamber that under suitable conditions may switch the balance from net erosion into net deposition, even close to the strike points. In addition, the absence of noticeable chemical erosion in helium plasmas may have affected the thickness of the deposited layers. Retention of He, for its part, remained small and uniform throughout the strike-point region although our results indicate that samples with smooth surfaces can contain an order of magnitude less He than their rough counterparts.

    AB - Plasma-wall interactions have been studied in the full-W ASDEX Upgrade during its dedicated helium campaign. Relatively clean plasmas with a He content of >80% could be obtained by applying ion cyclotron wall conditioning (ICWC) discharges upon changeover from D to He. However, co-deposited layers with significant amounts of He and D were measured on W samples exposed to ICWC plasmas at the low-field side (outer) midplane. This is a sign of local migration and accumulation of materials and residual fuel in regions shadowed from direct plasma exposure albeit globally D was removed from the vessel. When exposing W samples to ELMy H-mode helium plasmas in the outer strike-point region, no net erosion was observed but the surfaces had been covered with co-deposited layers mainly consisting of W, B, C, and D and being the thickest on rough and modified surfaces. This is different from the typical erosion-deposition patterns in D plasmas, where usually sharp net-erosion peaks surrounded by prominent net-deposition maxima for W are observed close to the strike point. Moreover, no clear signs of W nanostructure growth or destruction could be seen. The growth of deposited layers may impact the operation of future fusion reactors and is attributed to strong sources in the main chamber that under suitable conditions may switch the balance from net erosion into net deposition, even close to the strike points. In addition, the absence of noticeable chemical erosion in helium plasmas may have affected the thickness of the deposited layers. Retention of He, for its part, remained small and uniform throughout the strike-point region although our results indicate that samples with smooth surfaces can contain an order of magnitude less He than their rough counterparts.

    KW - erosion

    KW - helium

    KW - plasma-wall interaction

    KW - retention

    KW - tungsten fuzz

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    U2 - 10.1088/1741-4326/aa69c4

    DO - 10.1088/1741-4326/aa69c4

    M3 - Article

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    JO - Nuclear Fusion

    JF - Nuclear Fusion

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