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. Wauters & 4 others A. Garcia-Carrasco, P. Petersson, I. Bogdanovic Radovic, Z. Siketic

Research output: Contribution to journalArticleScientificpeer-review

6 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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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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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

VL - 57

JO - Nuclear Fusion

JF - Nuclear Fusion

SN - 0029-5515

IS - 6

M1 - 066015

ER -