1 / 48

Overview over plasma operation with full tungsten wall in ASDEX Upgrade

Overview over plasma operation with full tungsten wall in ASDEX Upgrade. R. Neu A . Kallenbach, M. Balden , V. Bobkov , J.W. Coenen a , R . Dux, H . Greuner , A. Herrmann, H. Höhnle b , J . Hobirk , K . Krieger, M . Kočan , P. Lang, T. Lunt,

axel
Download Presentation

Overview over plasma operation with full tungsten wall in ASDEX Upgrade

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Overview over plasma operation with full tungsten wall in ASDEX Upgrade R. Neu A. Kallenbach, M. Balden, V. Bobkov, J.W. Coenena, R. Dux, H. Greuner, A. Herrmann, H. Höhnleb, J. Hobirk, K. Krieger, M. Kočan, P. Lang, T. Lunt, H. Maier, M. Mayer, H.W. Müller, S. Potzel, T. Pütterich, J. Rappc, V. Rohde, F. Ryter, Ph. Schneider, J. Schweinzer, M. Sertoli, J. Stober, W. Suttrop, K. Sugiyama, G. van Rooijd, M. Wischmeier, ASDEX Upgrade Team MPI für Plasmaphysik, Garching, Germany aIEK-4, Forschungszentrum Jülich, Germany bInstitut für Plasmaforschung, Universität Stuttgart, Germany cOakRidge National Laboratory, OakRidge, Tennessee, USA dFOM-Institute for Plasma PhysicsRijnhuizen, Nieuwegein, The Netherlands 20th Int. Conf. on Plasma Surface Interaction, May 21 – 25, 2012, Aachen, Germany

  2. Operation with full tungsten wall in AUG 2012 R. Neu

  3. Operation with full tungsten wall in AUG • Conditioning and Plasma Behaviour • Retention of Gases • W influx and W penetration • Influence of Auxiliary Plasma Heating / W control • Scenario Integration • Outlook • Conclusions R. Neu

  4. Conditioning and Plasma Behaviour • quick recoveryafter vents even without boronisation • suppression of high W influx by optimized current-ramp • strong increase of peak power load in the divertor after first boronisations • lower H-mode threshold under typical discharge conditions • pedestal pressure similar as in C, but pedestal temperatures typically lower R. Neu

  5. 3 Start-up of un-boronisedmachineQuick restart with assisted break down and ramp-up Several restarts without boronisation: optimized scheme of additional heating (shortly) after break down and during current ramp up  after 5# 800 kA plasma, after 8# H-mode 2008 campaign transition to divertor R. Neu

  6. Effect of BoronisationStrong increase of maximum target load Before boronisation After boronisation 7.5 15 outer divertor outer divertor inner divertor inner divertor 30 15 outer divertor outer divertor inner divertor inner divertor R. Neu

  7. Evolution of H-Mode Threshold AUG: Bt≈ -2.5 T , ne ≈ 51019m-3 2011 2008 ITER H-mode power threshold scaling: Y. Martin et al. J. Phys. Conf. 123 (2008) 012033 2012 2009 C dominated AUG: Pth/Pscal08= 1, large (± 25 %) scatter depending on conditioning full W PFCs: Pth (AUG) ≈ 0.75 Pscal08 with reduced scatter (net heating power: Pnet = Pabs + POH - dW/dt) R. Neu

  8. Pedestal Parameters in the C / W Dominated Device Unfuelled discharges 2005(C-W) 2008 (full W),Ip=1 MA, Bt=2.4-2-5T neped Teped peped H98y2 • For all investigated additional heating powers: • pedestal density higher / pedestal temperature lower • pedestal pressures similar, increasing with heating power • similar H~1 (except for discharges with improved confinement) R. Neu

  9. Retention of Gases K. Sugiyama, Phys. Scr. T145 (2011) 014033 • reduction of H-retention (some co-deposition with C) • H-retention in W bulk close to values from laboratory experiments • retention in blisters low in technical W surfaces • dynamic inventory important in gas balance investigations • large potential for He storage and release • N legacy manageable, but asks for FB control in rad. cooling • surface reactions producing ammonia seem to play important role for short term N storage coatings Formation of W blisters: M. Balden, O16 R. Neu

  10. Dynamical behaviour of D-Retention • injection of 4-51022 D to saturate • dynamic inventory, almost • independent fuelling rate • after saturation, retention is • typically in %-level • (accuracy of the method) pressure [Pa] • gas balance by investigation of pressure rise • at least 3 time-constants (~ 1, 14, 200s) • largest release on longest timescale! Time [s] R. Neu

  11. Surface storage of He K. Schmid et al. NF 2007 • gradual build-up of He content by inter-discharge He-glow •  reduced density control in current ramp-up phase • apparently negative influence on confinement •  reduction / finally abandoning of He glow (no negative impact on breakdown! R. Neu

  12. Latencyof Nitrogen • latency of N after seeding noticeable, but controllable (RT - feedback!) • storage on surface as • W nitride and • partly as ammonia seeded nitrogen pumped nitrogen pumped ammonia N atoms (1021) D. Neuwirt et al., toappear in PPCF (2012) R. Neu

  13. W sources and W penetration • divertor W source depends strongly on plasma temperature • ELM erosion accounts for significant fraction • W penetration from main chamber sources significant larger (x 20) than from the divertor • W divertor strongly depends on ‚force balance‘ for parallel transport • dedicated melt experiment to characterize melt layer behaviour and to quantify effect of transient W influxes • arcs seem to be important for dust production Melt Experiments: J.W. Coenen, I1 Trajectoryofdroplets: Z. Yiang, P2-064 Arcerosion: V. Rohde, P2-050 R. Neu

  14. W erosion in the AUG divertor strongly depends on plasma temperature ELMs contribute significantly to total erosion W sputter yields • W erosion • vanishes for Te < 5 eV (Type III ELMs) • much larger as in pure D plasmas • agrees with simulations using typical • low-Z impurity concentrations 1018 m-2s-1 R. Neu

  15. Controlling the W content via gas puff D-puff and outer radius scan Ip =1 MA, Paux=8.8 MW (max.) discharges (#22895,898,900,901) • W density and ELM frequency strongly correlated • effect on C density less pronounced • strong influence of main chamber source • note: • confinement strongly affected by puff rate R. Neu

  16. ELM flushing and Impurity Transport in the H-mode Edge Barrier • ELM flattens steep gradients • ELM causes W erosion / redeposition • after ELM, gradients steepen again • influx due to ELM ‘refills’ gradients very fast • SOL cleans up (parallel transport!) and pedestal keeps building up slowly • ELM flushing dominates ELM source • excellent agreement for resulting W content of the plasma R. Neu

  17. Investigations on W edge transport EMC-3 Modelling of #25513 W-LBO & W-melting W-LBO (seen from the top) flux density W-density (LBO) W-density (melt) film sequence: 1ms • Comparison of observed divertor retention to transport simulation using a • localized W source (EMC3/DIVIMP) • reasonable agreement achieved (R~25) • however: retention strongly dependent on detailed divertor source location! R. Neu

  18. Influence of Auxiliary Heating / W control • central deposition of heating power suppresses W peaking • NBI only heated discharges usually show peaked W profile • ICRH & ECRH mitigate central accumulation (critical power density needed) • additional W-influx during ICRH may outweigh beneficial effect on central transport • pellet ELM pace-making helps to keep edge cWlow Very centre of plasma Suppression of neo- classical accumulation Tungsten density Confinement region - turbulent transport - weak gradients H-mode Edge- Transport Barrier Control W-influx control of ELM frequency Plasma radius central power deposition R. Neu

  19. Influence of Heating Methods on W Source and Content centralcW • tailoring of ECRH results in strong reduction of peaking of cWand moderateconfinement degradation • threshold for mitigation of peaking seems to depend on central radiation (transport reacts on local power balance?) R. Neu

  20. Influence of Heating Methods on W Source and Content NBI • W limiter source (rather) low • W concentration profile usually peaked ICRH • strongly increased W limiter source • typically lower divertor source (lower power deposition) • reduced central cW / increased edge cW (flat profile!) • much higher W radiation losses R. Neu

  21. Optimisation of ICRF Operation broad limiter a4 a3 a1 a2 ‚broad‘ limiter B-coated side limiters B-coated Antenna a4 (2011): ‚broad‘ limiter to reduce electrical field at W surfaces: - slightly reduced increase of W content - better balance central heating / W source Antennae a1 & a2 (2012): Boron coating of side limiters (as short term workaround) B VPS coating (~50 µm), tested in GLADIS (6 MW/m², 4 s, 75 pulses) 20th Conf. on PSI, May 21-25, 2012, Aachen, Germany R. Neu

  22. 2012: B-coated limiters for 2 antennas ASDEX Upgrade # 27745 • B coated antennae: • strongly reduced increase of W contentfor all frequencies tested • consistent with hypothesis of dominant local limiter W sources B lim W lim approx. increaseofcW: 0.7e-5/MW 1.8e-5/MW 20th Conf. on PSI, May 21-25, 2012, Aachen, Germany R. Neu

  23. Scenario Integration • radiatively cooled plasmas provide - good confinement - acceptable divertor power loads and reduced W influx - flat W profiles at acceptable level • use of MP coils • - compatible with • W PFCs • - strong ELM • mitigation while • retaining good • confinement AUG record: 23 MW total heating power R. Neu

  24. Development of an integrated scenario:Mitigation of power load by radiative cooling in AUG R. Neu

  25. control of plasma temperature and power in the divertor good confinement retained Development of an integratedscenario:Mitigationof power loadbyradiativecooling in AUG small, frequent ELMs no increased cW / no W accumulation strong suppression of W influx in ELM type III H-Modes with H98~1 R. Neu

  26. Evolution of the Confinement in Improved H-Modes R. Neu

  27. Confinement Improvement with N2-Seeding • H98(y,2) improves with N2 seeding • (moderate Zeffincrease) by • up to 25% • improvement is largely an effect of • the pedestal extending to the core • via profile stiffness • supported by gyro-kin. simulations • collisionality * gets higher at Rsep • and lower at pedestal top • empirical ‚scaling‘ of confinement shows less power degradation than H98(y,2) R. Neu

  28. Development of an integrated scenario:ELM Mitigation and W control with MP Coils • successful ELM mitigation • no negative impact on confinement • peak W divertor erosion reduced • no increase of W concentration / no W accumulation 2011 2012 MP experiments: H.W.Müller I6 R. Neu

  29. Outlook • Dedicated W melting / injection experiments for penetration studies (revitalised W(CO)6 probe) • Strongly upgraded divertor manipulator for investigation with actively cooled / heated W PFCs • Hardening of divertor: bulk-W at the outer strikepoint increase of pumping conductance • Reduction of W-Influx during ICRH by 3-strap antenna • Enhancementof ECRH upto 8 MW / 10s  allow operation at low * bulk W tiles R. Neu

  30. Conclusions • W PFCs constitute (meanwhile) a natural environment in AUG • many operational procedures have been adapted and are now part of routine operation • implementation of tools, as high power ECRH, pellet centrifuge, magnetic perturbation coils, real time protection of W PFCs, efficient feedback control for radiation cooling allow investigations to increase operational space • the increased W influx during ICRF operation is still an issue, but use of B coatings as a workaround is very successful • modification of ICRF antennae to reduce of electrical field (and thereby W sputtering) under way • installation of bulk-W divertor (2013) will allow higher divertor power loads and therefore high power low density experiments (low *) • remaining W specific experiments concentrate on diagnostic issues, melt behaviour and W edge transport R. Neu

  31. aux aux . . limiter limiter W W - - coating coating starting starting with with campaign campaign 2003/2004 2003/2004 guard guard / / ICRH ICRH 2004/2005 2004/2005 limiter limiter 2005/2006 2005/2006 2007 2007 lower lower PSL PSL hor. hor. plate plate roof roof baffle baffle Full W ASDEX Upgrade 2012 2011 W coatings on finegraingraphitetoinvestigate- plasmacompatibiliy - erosion, retention - diagnostic R. Neu

  32. Start-up of un-boronized machine Early transition to divertor (full bore plasma) 0.06 s 0.50 s 0.70 s 0.20 s 1.0 0.5 z(m) 0.0 -0.5 -1.0 Shot: 23677 1.0 1.5 2.0 2.5 1.0 1.5 2.0 2.5 1.0 1.5 2.0 2.5 1.0 1.5 2.0 2.5 R(m) R(m) R(m) R(m) • breakdown on outer limiter (conditions faster compared to inner wall) • early X-point formation • - inner wall conditioned in flat top and ramp down phases Ramp-down: inverse sequence avoid early HL transition with inboard limiter contact by additional heating R. Neu

  33. Suppression of central W accumulation • Reduction of peaking by increased anomalous transport • Moderate reduction of total confinement • ECRH more efficient than ICRH (ICRH: additional W source by sheath accelerated ions) • Similar effect observed in many devices • Code simmulation predict favourable scaling to ITER R. Neu

  34. Investigations on W edgetransport plasmaparameters (@ target) ... ne(1019 m-3) Te, Ti (eV) EMC-3 predicts strong dependency of divertor retention from source position relative to separatrix  check with ‘plasma-independent’ source! R. Neu

  35. Meltingunder divertor conditions Investigation of melt layer redistribution molten material structure impact on plasma operation #27379 Nocleardamageamelioration, while strong material changes disruptiveevent trajectoryofdroplets: Z. Yiang, P Quiescentmeltingwithdropletexpulsion 2012 7 exposures incl. 2 disruptions Melt Experiments: J.W. Coenen, I1

  36. Controlling the W content ELM frequency depends on distance to H/L threshold, machine conditions,… • higher gas puff rate • larger heating power • ELM pacemaking keep impurity content low modellingshows: neoclassicaleffectssmaller in ITER  ELM flushinglessimportant, but consistentwithneedfor ELM mitigation R. Neu

  37. Peaking of W concentration and edge W concentration in N-seeded discharges moderate peaking moderate cWedge R. Neu

  38. W influx in Nitrogen seededplasmas Type I ELMy H-mode Type III ELMy H-mode scale x 100! 1018 1020 strongly reduced power load and complete suppression of W influx combined with H98  1 Te / W influx with low and high N seeding rate (coherent ELMaveraging) R. Neu

  39. Low densities feasible with sufficient ECRH H98 WMHD Ip D2 puff ncore nedge H PNBI PECRH Te ECE, TS even/odd n CTR increased ECRH capabilities allow strong decrease of puff-rate / target densities provide powerful tool toinvestigate strong decoupling of electrons and ions currentdriveat high Te R. Neu

  40. First Investigation at Low Density / High Power good confinement / high beta achieved at low density without density peaking R. Neu

  41. Successfulcombinationof MP and Pellets R. Neu

  42. Broad limiter ICRF antenna shows better W accumulation behaviour (code benchmark step) Modified antenna 4: z 20 total gas injection [×1021 s-1] #26746 #26745 10 0 a3 a4 (new) PICRF [MW] a1 a2 0.8 0.4 0 bolometer central channel [a.u.] 4 2 W accumulation appears with new antenna at smaller gas injection rate new antenna has better balance central heating / W source  proceed to 3-strap antenna 0 bolometer edge channel [a.u.] 4 2 0 time [s] 2 4 3 R. Neu

  43. Experience with ICRF and W 7.1 m2 14.6 m2 24.8 m2 28 m2 36 m2 2011 / 1 new antenna full-W 2009 10-4 - boronizations - PICRF > 0.5 MW 10-5 - PICRF > 0.5 MW and W accumulation filtered out DCW /PICRF 10-6 - median values over campaigns 10-7 24000 shot Nr. 16000 18000 20000 22000 26000

  44. HHF Gladis Tests of Boron Coatings 50 µm B VPS coating on finegraingraphite Cycling:6 MW/m² (4 s) in cyclic testing (75 pulses) Screening:up to 23 MW/m² (1 s) • very good performance • of coatings: • no defects up to melting (~ 2000°C) • very benign failure mechanism • - no cracking • - no delamination • qualified for use at ICRF limiters

  45. Test of Bulk W Divertor Tiles 2 max. surfacetemperature Test of 2 tiles at outer strike-point position • NO problems during operation • max. surface temperature always < 2000 K • ~ 150 shots with Tmax > 1000K • NO melting at the rim of the castellation (180/300 µm width) • cracks in the region of the fixation bore holes (higher temperatures!)  avoid bore holes in the high heat flux region  alternative clamping design foreseen in DIV III temperature (1000 K) 1 0 400 800 1200 frequency R. Neu

  46. Bulk W divertor for ASDEX Upgrade - DIV-III Solid W divertor will expand the operational range by avoiding delamination and lifetime issues of W coatings will allows physics investigation on • Hretention of solid tungsten • effects of castellation and • melt damage Successful tests with ‘tungsten bricks’ in GLADIS 300 cycl. 10.5 MW/m², 3.5 s (Tsurf~1700 K) 30 cycles 30 MW/m², 2.8 s (Tsurf~3500 K) AUG (1 campaign) 150 discharges Tsurf>1000 K (always <2000 K) R. Neu

  47. 3-strap ICRF antennaforreduced W influx 1 2 3 3 straps: experiment-based optimisation feeder  0 0 IRF c b a a b c P2/P13 … depending on plasma, for fixed phasing (2D problem) shunts to measure IRF intercepting plates • optimised for compensation of -phased contributions to image currents • flexible by design, power and phase balance optimization in experiments •  progressing from calculations-based to experiment-based optimisation • (using calculations as guidelines)

  48. Outlook revitalised W(CO)6 probe • Dedicated W injection experiments for penetration studies • Strongly upgraded / divertor manipulator for investigation with actively cooled / heated W PFCs • Hardening of divertor: bulk-W at the outer strikepoint/ increase of pumping conductance • Reduction of W-Influx during ICRH by 3-strap antenna • Enhancementof ECRH to 8 MW / 10s allow operation at low * R. Neu

More Related