Diagnostic mirrors for ITER: research in the frame of International Tokamak Physics Activity

Mirrors will be used as first plasma-viewing elements in optical and laser-based diagnostics in ITER. Deterioration of the mirror performance due to e.g. sputtering of the mirror surface by plasma particles or deposition of impurities will hamper the entire performance of the affected diagnostic and thus affect ITER operation. The Specialists Working Group on First Mirrors (FM SWG) in the Topical Group on Diagnostics of the International Tokamak Physics Activity (ITPA) plays an important role in finding solutions for diagnostic first mirrors. Sound progress in research and development of diagnostic mirrors in ITER was achieved since the last overview in 2009. Single crystal (SC) rhodium (Rh) mirrors became available. SC rhodium and molybdenum (Mo) mirrors survived in conditions corresponding to ~200 cleaning cycles with a negligible degradation of reflectivity. These results are important for a mirror cleaning system which is presently under development. The cleaning system is based on sputtering of contaminants by plasma. Repetitive cleaning was tested on several mirror materials. Experiments comprised contamination/cleaning cycles. The reflectivity SC Mo and Rh mirrors has changed insignificantly after 80 cycles. First in situ cleaning using radiofrequency (RF) plasma was conducted in EAST tokamak with a mock-up plate of ITER edge Thomson Scattering (ETS) with five inserted mirrors. Contaminants from the mirrors were removed. Physics of cleaning discharge was studied both experimentally and by modeling. Mirror contamination can also be mitigated by protecting diagnostic ducts. A deposition mitigation (DeMi) duct system was exposed in KSTAR. The real-time measurement of deposition in the diagnostic duct was pioneered during this experiment. Results evidenced the dominating effect of the wall conditioning and baking on contamination inside the duct. A baffled cassette with mirrors was exposed at the main wall of JET for 23,6 plasma hours. No significant degradation of reflectivity was measured on mirrors located in the ducts. Predictive modeling was further advanced. A model for the particle transport, deposition and erosion at the port-plug was used in selecting an optical layout of several ITER diagnostics. These achievements contributed to the focusing of the first mirror research thus accelerating the diagnostic development. Modeling requires more efforts. Remaining crucial issues will be in a focus of the future work of the FM SWG.

[1]  A. Alekseev,et al.  Estimation of neutral fluxes on the first mirror of H-alpha diagnostics in ITER , 2019, Fusion Engineering and Design.

[2]  W. Treutterer,et al.  Diagnostics for plasma control – From ITER to DEMO , 2019, Fusion Engineering and Design.

[3]  Romain Boman,et al.  On the use of rhodium mirrors for optical diagnostics in ITER , 2019, Fusion Engineering and Design.

[4]  J. Contributors,et al.  First mirror test in JET for ITER: Complete overview after three ILW campaigns , 2019, Nuclear Materials and Energy.

[5]  Hyun-Yong Lee,et al.  A passive mitigation strategy of impurity deposition on the first mirrors using duct with baffles: A case study at a port of KSTAR with in-situ deposition monitoring , 2018 .

[6]  Junling Chen,et al.  Sputtering tests of single crystal molybdenum and rhodium mirrors at high ion fluence for in situ plasma cleaning of first mirrors in ITER , 2018 .

[7]  C. Linsmeier,et al.  First direct comparative test of single crystal rhodium and molybdenum mirrors for ITER diagnostics , 2017 .

[8]  Ivo Furno,et al.  Plasma cleaning of ITER first mirrors , 2017 .

[9]  P. Petersson,et al.  Plasma impact on diagnostic mirrors in JET , 2017 .

[10]  V. Kotov.  Can gas puff be used for cleaning of the diagnostic first mirrors in ITER , 2017 .

[11]  L. Marot,et al.  In situ cleaning of diagnostic first mirrors: an experimental comparison between plasma and laser cleaning in ITER-relevant conditions , 2017 .

[12]  Vladislav Kotov,et al.  Engineering estimates of impurity fluxes on the ITER port plugs , 2016 .

[13]  A. F. Bardamid,et al.  Experimental Simulation of the Behaviour of Diagnostic First Mirrors Fabricated of Different Metals for ITER Conditions , 2016 .

[14]  J. Contributors,et al.  Optical Coatings as Mirrors for Optical Diagnostics , 2016 .

[15]  Boseong Kim,et al.  Suppression of Ag deposition by Ar gas in mtorr range and its implication to mitigation of impurity deposition on first mirrors , 2015 .

[16]  Olaf Neubauer,et al.  Studies of protection and recovery techniques of diagnostic mirrors for ITER , 2015 .

[17]  V. Russo,et al.  Laser cleaning of diagnostic mirrors from tokamak-like carbon contaminants , 2015 .

[18]  S. Möller,et al.  Linear Plasma Device PSI-2 for Plasma-Material Interaction Studies , 2015 .

[19]  P. Chu,et al.  Metal oxide coating on first mirror in fusion reactor with carbon wall , 2014 .

[20]  E. Meyer,et al.  Can aluminium or magnesium be a surrogate for beryllium: A critical investigation of their chemistry , 2013 .

[21]  C. Skinner,et al.  Laser Cleaning of Candidate Diagnostic Mirrors for ITER , 2013 .

[22]  V. S. Voitsenya,et al.  First studies of ITER-diagnostic mirrors in a tokamak with an all-metal interior: results of the first mirror test in ASDEX Upgrade , 2013 .

[23]  O. Schmitz,et al.  Active control over carbon deposition on diagnostic components and in remote areas of ITER , 2011 .

[24]  Marek J. Rubel,et al.  Removal of beryllium-containing films deposited in JET from mirror surfaces by laser cleaning , 2011 .

[25]  A. Khare,et al.  Mirrorlike pulsed laser deposited tungsten thin film. , 2011, The Review of scientific instruments.

[26]  M. C. Ubaldi,et al.  Nanostructured rhodium films produced by pulsed laser deposition for nuclear fusion applications , 2010 .

[27]  V. Veiko,et al.  Progress in the development of deposition prevention and cleaning techniques of in-vessel optics in ITER , 2009 .

[28]  V. S. Voitsenya,et al.  Progress in research and development of mirrors for ITER diagnostics , 2009 .

[29]  P. Oelhafen,et al.  Characterization of magnetron sputtered rhodium films for reflective coatings , 2008 .

[30]  P. Oelhafen,et al.  Rhodium coated mirrors deposited by magnetron sputtering for fusion applications. , 2007, The Review of scientific instruments.

[31]  A. Donné,et al.  Diagnostic mirrors for ITER: A material choice and the impact of erosion and deposition on their performance , 2007 .

[32]  Andrey Litnovsky,et al.  Investigations of single crystal and polycrystalline metal mirrors under erosion conditions in TEXTOR , 2007 .

[33]  V. S. Voitsenya,et al.  Some problems arising due to plasma–surface interaction for operation of the in-vessel mirrors in a fusion reactor , 2001 .

[34]  V. S. Voitsenya,et al.  Diagnostic first mirrors for burning plasma experiments (invited) , 2001 .

[35]  N. Lecis,et al.  Nanostructured rhodium films for advanced mirrors produced by Pulsed Laser Deposition , 2013 .

[36]  V. N. Gorshkov,et al.  First mirrors in ITER: material choice and deposition prevention/cleaning techniques , 2011 .

[37]  Gerald Pintsuk,et al.  First tests of diagnostic mirrors in a tokamak divertor : An overview of experiments in DIII-D , 2008 .