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Initial operation of ASDEX Upgrade with 100 % tungsten PFCs

Rudolf Neu With contributions from: V. Bobkov, R. Dux, A. Kallenbach, T. Pütterich, H. Greuner, Ch. Hopf, C.F. Maggi, H. Maier, M. Mayer, V. Rohde, ASDEX Upgrade Team. Initial operation of ASDEX Upgrade with 100 % tungsten PFCs. Transition to W PFCs in ASDEX Upgrade

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Initial operation of ASDEX Upgrade with 100 % tungsten PFCs

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  1. Rudolf Neu With contributions from: V. Bobkov, R. Dux, A. Kallenbach, T. Pütterich, H. Greuner, Ch. Hopf, C.F. Maggi, H. Maier, M. Mayer, V. Rohde, ASDEX Upgrade Team Initial operation of ASDEX Upgrade with 100 % tungsten PFCs

  2. Transition to W PFCs in ASDEX Upgrade Boundary Conditions for Experimental Campaign Arguments on boronisation First Results of initial operation Operation with 100 % W PFCs R.Neu

  3. Steps in ASDEX Upgrade towards a full W device Steady increase of area of main chamber W PFCs since 1999 Rationales: • risk minimisation • physics investigations • partitioning of installation time • production capacity 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 R.Neu

  4. Optimisation of VPS coatings / HHF tests in GLADIS • Thermal Screening: • surface temperatures • > 2000°C •  no macroscopic defects 200 µm W VPS (Plansee) on SGL R6710 R.Neu

  5. Optimisation of VPS coatings / HHF tests in GLADIS • Cyclic • Loading: • 200 pulses @ • - 10.5 MW/m² • 3.5 s • Tsurf > 1600°C • coatings qualified for use in the lower divertor R.Neu

  6. Steps in ASDEX Upgrade towards a full W device R.Neu

  7. Steps in ASDEX Upgrade towards a full W device R.Neu

  8. Transition to W PFCs in ASDEX Upgrade Boundary Conditions for Experimental Campaign Arguments on boronisation First Results of initial operation Operation with 100 % W PFCs R.Neu

  9. AUG is operated with the help of three flywheel generators: EZ2 (1.45 GJ / 167 MVA): toroidal field EZ3 (500 MJ /144 MVA) + EZ4 (650MJ/220MVA): OH, pol.field, aux. heating Reconfiguration of power supplies necessary: less power, less energy available Ip  1.0 MA, pulse length 3-4 s, Paux 7.5 MW, intermediate densities / triangularities (@ 1 MA) EZ3 > 11 kA EZ3 ≤ 11 kA 20 15 Limit: 11 kA New-EZ3 (kA) 10 5 0 0.4 0.6 0.8 1.0 1.2 Ip(MA) Constraints imposed by damage of EZ4 R.Neu

  10. Setup of program for 2007 campaign priority envisaged rel. weight (whole campaign) I. Exploration of W compatibility (discharges in agreement with general boundary conditions) II. Extension of working space - rad. cooled plasmas - impr. H-Mode (high  low density) III. Other ITER related physics investi- gations, compatible with above results and requirements 30% 20% 50% R.Neu

  11. Boundary conditions set by W-PFCs (during phase I., to be refined): density:  7e19/m³ (gas puff rate > 6e21/s) q-edge: > 3.2 f(ELM): > 60 Hz dominant central heating (no pure off axis heating) Pheat < H-mode threshold or Pheat > 2xH-Mode threshold power/energy limits for upper divertor (5 MW 4s, 10MW 1s) monitoring of limiter (and divertor) glow (restrictions on shape, power, energy: to be adjusted) power/energy limits for lower divertor from operation / results of radiatively cooled plasmas Guidelines during initial operation R.Neu

  12. Research Topics of W-programme at AUG for the upcoming campaign(s) Investigation will concentrate on: • transition to C-(low-Z) free machine: - radiatively cooled (integrated) scenarios by simultaneous use of noble gas puff, central heating and ELM pacemaking - optimization of gas species/injection • evolution of hydrogen retention: - influence on gas balance and D inventory in PFCs • disruption characteristics: - differences in current decay / run-aways • optimization of ICRF: - is the simultaneous use of with high-Z PFCs possible R.Neu

  13. Transition to W PFCs in ASDEX Upgrade Boundary Conditions for Experimental Campaign Arguments on boronisation First Results of initial operation Operation with 100 % W PFCs R.Neu

  14. main H ~ 1, Prad ~ 30 % Reminder: Unboronized start-up with W HS successful R.Neu

  15. Conditioning - large O getter (even in non plasma exposed areas):  easier break down  higher density limit  facilitates start up - use of BD6  pre-loading of wall,  strong pumping larger D puffing rates  easier transition to D: Why Boronisation • Coating of surfaces - suppression of W influx - suppression of other intrinsic metallic impurities R.Neu

  16. Estimates for B Erosion Thickness of boron layer Main chamber: 50 nm  3e21/m² Limiter: 50 nm  3e21/m² Divertor: 10 nm  5e20/m² Particle fluxes / Particle temperatures (energies) / B Yield Main Chamber: 1e21 / (E  100 eV) / 1e-2 Limiter: 1e22 / T= 20 eV / 1e-2 Divertor: 1e23 / T=5 eV / 5e-4 Live-time of boron layer Main chamber: 300 s (100 disch) Limiter: 30 s (10 disch) Divertor: 10 s (3 disch) R.Neu

  17. strong reduction of W influx and concentrations for ICRH only, H-Mode threshold increases stronger than for NBI for aged boronisation time constants shorter than typical distance between boronisations recovery of W influx depends on particle and energy load Effect of boronisation 800 kA 1.8MW ICRH R.Neu

  18. strong reduction of W influx and concentrations for ICRH only, H-Mode threshold increases stronger than for NBI for aged boronisation time constants shorter than typical distance between boronisations recovery of W influx depends on particle and energy load Effect of boronisation R.Neu

  19. Operation/investigation of W machine without (any) intrinsic low-Z radiator Comparison of boronised / un-boronised machine:  maybe able to proof of hypothesis on B influence D retention ‚without‘ low-Z (C,B) contamination Comparison of D pumping W wall / boronised W wall and H-D transition Benefits of start-up without boronization R.Neu

  20. Milestone: Steady state H-Mode at intermediate density and heating power with H~1 Specific Investigations: Exposure of deposition probes to measure: evolution B,C,W impurities, D retention Particle Balance (in co-op. TS) Influence of ICRH Documentation of edge plasma parameters / radiative cooling (if applicable/necessary) Aims for the unboronized phase R.Neu

  21. Transition to W PFCs in ASDEX Upgrade Boundary Conditions for Experimental Campaign Arguments on boronisation First Results of initial operation Operation with 100 % W PFCs R.Neu

  22. Conditioning by baking - He / He-D glow • 10 days baking @ 150°C • overnight glow in He • (He+10%D2,  500V, 4x1.8A) •  Strong pumping of C and O • (through CO and CO2) R.Neu

  23. Re-start since 24/4/07 (5 days of operation) Reconfiguration of power supplies for OH/V-coils main issue Reliability of break-down not yet satisfactory (low-Z impurities, gas release) Divertor configurationsucces- fully acchieved W contaminationnot important First Results of initial operation R.Neu

  24. Re-start since 24/4/07 (5 days of operation) Reconfiguration of power supplies for OH/V-coils main issue Reliability of break-down not yet satisfactory (low-Z impurities, gas release) Divertor configurationsucces- fully acchieved W contaminationnot important First Results of initial operation R.Neu

  25. Long term evolution of W concentrations • reduced cW at relevant auxiliary heating power and densities R.Neu

  26. P prerequiste first few weeks R related first half of campaign E extended end of first half of campaign C compatible first few months (lower priority) O orthogonal second half of campaign Priority within categories by TFs Classification of proposals R.Neu

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