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  1. Lithization on FTU:tools and resultsG. MazzitelliaMany thanks to:M.L. Apicellaa, V. Pericoli Ridolfinia, A. Alekseyevb, G. Apruzzesea, W. Binc, P. Burattia, R. Cesarioa,, G. Calabròa, R. De Angelisa, B. Espositoa, L. Gabellieria, F. Gandinic, E. Giovannozzia, R. Gomesd, G. Granuccic , H. Kroeglera, I. Lyublinskie , M.Marinuccia, C. Mazzottaa, A. Romanoa, O. Tudiscoa, A. Vertkove, the FTU Teama and ECRH Teamca Associazione EURATOM-ENEA sulla Fusione, C. R. Frascati,00044 Frascati, Roma, Italyb TRINITI, Troitsk, Moscow reg., Russiac Associazione EURATOM-ENEA, IFP-CNR,Via R. Cozzi,53-20125 Milano Italyd Centro de Fusao Nuclear, IST Av. Rovisc Pais,n.1 1049-Lisboa Portugale FSUE,“RED STAR”, Moscow, Russia

  2. Introduction • Why Lithium? • Very low Z (Z=3) • High impurity getter (C,O) • High H retention Recycling • Lowmelting point (180.6 °C) • Strong reduction of total graphite sputtering

  3. Introduction • Where Lithium(How) ? • DIII-D (DIMES) Negative • Alcator C-MOD (Pellet) Negative • TFTR (Pellet) Good • JIPP T_IIU (Evaporation) Good • T-11 (Capillary Porous System) Good • NSTX (Evaporation+Powder) Good • CDX-U (Evaporation+liquid Tray) Good • TJ-II (Evaporation) Good • T-10 (Evaporation) Good • LTX (Liquid wall) Starting • FTU (Capillary Porous System) Good

  4. OUTLINE • Experimental Setup • Experimental Results • High density peaked discharges • Quasi-quiescent MHD discharges • ECRH + LH Discharges • Future plans • Conclusions

  5. 1. Experimental Setup

  6. Liquid Lithium Limiter Langmuir probes Thermocouples Heater electrical cables

  7. Capillary Porous System (CPS) Mo heater accumulator Liquid lithium surface Thermocouples Heater Li source S.S. box with a cylindrical support 100 mm 34 mm Ceramic break • The LLL system is composed by three similar units CPS is made as a matt from wire meshes with porous radius 15 m and wire diameter 30 m Structural material of wires is S.S. Scheme of fully-equipped lithium limiter unit Meshes filled with Li

  8. Toroidal Limiter Total lithium area ~ 170 cm2 Plasma interacting area ~ 50- 85 cm2 Inventory of lithium  80 g LLL initial temperature > 200oC Liquid Lithium Limiter Melting point 180.6 °C Boiling point1342 °C

  9. 2. Experimental Results

  10. Main features of lithium operations: • Better plasma performances with Lithium than with Boron • Zeff in ohmic discharges is well below 2(0.15 1020<ne<3.1020m-3) • The VUV spectrum is dominated by the Li lines • O, Mo are strongly reduced • Radiation losses are very low less than 30% • With lithium limiter much more gas has to be injected to get the same electron density with respect to boronized and fully metallic discharges> 10 times • Operations near or beyond the Greenwald limit are easily performed

  11. Main features of lithium operations: • In lithium discharges, Te in the SOL is 50% higher than before while the increase in ne is negligible • Plasma operations are more reliable with good plasma reproducibility and easier recovery from plasma disruptions • The LLL is able to withstand heat load up to 5 MW/m2 • More details: • Apicella et al. J. Nuclear Materials 363-365 (2007) 1346-1351 • V. Pericoli Ridolfini et al. Plas. Phys. Contr. Fusion 49 (2007) S123-S135

  12. Peaked electron density discharges Ip=0.5MA Bt=6T Ip=0.7MA Bt =6 T At electron density greater than 1.0 1020 m-3spontaneouslythe density profile peaks

  13. Peaked electron density discharges Central density increases while edge and SOL densities do not change The SOL densities do not follow the FTU scaling law

  14. Peaked electron density discharges The profile is peaked as with pellet injection The profiles are taken at different times but at the same line-averaged density #30583 #26793 ne [x1020 m-3] R (m) The strong particle depletion in the outermost plasma region is due to the strong pumping capability of lithium

  15. 20 -3 1.41±0.07 t 120 = k n (10 m ) q e,lin E-linear 100 k = 7.1±0.6 80 (ms) 60 0.5 MA E t 0.8 MA 40 1.1 MA 1.4 MA pellet: open symbols 20 0.50 MA Li 0.75 MA Li 0 1 2 3 4 20 -3 line averaged n (x10 m ) e Energy Confinement Time If the confinement time of lithized discharges is compared with the general behaviour ofthe confinement time of the ohmic and pellet fuelled FTU discharges database, it clearly results that the threshold of the SOC regime is raised from ~45÷50 ms to ~65÷70 ms, suggesting a behaviour which is akin to that shown by multiple-pellet PEP regimes

  16. Quasi-quiescent MHD activity Te at the edge is geneally higher than in boronized discharges A possible theoretical explanation is proposed in which electrostatic waves excited by thermal background in the plasma core enhance the turbulence at the edge via non-linear mode coupling. R. Cesario et. EPS Conference 2007

  17. ECRH + LH Discharges 0.59 s 0.54 s #30620 With LLL PECH=0.80 MW PLH =0.75 MW #27923 Without LLL PECH=1.20 MW PLH =1.50 MW Strong and wide ITB develops after LH injection, with very high central Te up to 8 KeV in spite of the lower value of additional power t(s) Very interesting features are obtained with combined ECR+LH Power

  18. Te[keV] Te[keV] Padd=1.6MW Padd=1.2MW Padd=1.6MW Padd=2.2MW r (m) ECRH + LH Discharges rITB/a Radial extension of ITB 0.6 0.4 0.2 ρ*T Strength of ITB 0.02 0.01 0.6 0.5 0.3 0.4 t (s) ρ*T,max=Max of the normalized Te gradient A wide ITB is formed with a strong Te gradient

  19. Mo Fe O ECRH + LH Discharges The strong difference between the two discharges is in the impurity content. Zeff is reduced by at least a factor 2 in lithium discharges that increases the LH current drive efficiency

  20. ECRH + LH Discharges But Zeff ~ 2 means about 50% of dilution as indicated by the strong reduction in neutron signal. The dilution is strictly correlated with the plasma start-up phase and the low value of electron density

  21. 1.0 Dilution At higher electron densities dilution is negligible 0.5 Ip [MA] 30584 LLL Inside 29919 lithized 28847 metallic 28833 boronized 3.0 ne [x1020 m-3] 2.0 1.0 2.0 Te [KeV] 1.0 4.0 Neutrons/s [x1011] 2.0 0. 0.2 0.4 0.6 0.8 1.0

  22. 3. Future Plans

  23. No Surface Damage of CPS Structure

  24. A new limiter panel type actively cooled and equipped with a system for lithium refilling Preliminary design Top view Toroidal lmiter LLL LLL This limiter should be able to act as main limiter for withstanding heat loads up to 10 MW/m2 for 3 s

  25. CONCLUSIONS • Lithization is a very good and effective tool for plasma operations • Exposition of a liquid surface on tokamak has been done on FTU with very promising results Thank you for your attention

  26. Dilution Problem It is strictly correlated with the plasma start-up phase and the absolute value of density

  27. r (m) Te[keV] Te[keV] Padd=1.6MW Padd=1.2MW Padd=1.6MW Padd=2.2MW r (m) r (m) ECRH + LH Discharges Te[keV] Te[keV] Padd=0.8MW No Padd Padd=0.0MW #30620 #27923 r (m) Comparison of electron temperature profiles showing ITB formation

  28. Comparison betweenLithizationand Boronization ne(x1019m-3) Ohmic shots Ip=0.5MA Bt=6T Te(keV) TheLieffects are similar or even better than those ofB Prad(%) Vloop(V) Zeff Time(s)

  29. After liquid Lithium limiter insertion 0.15x1020 m-3<ne<2.7x1020 m-3 0.5MA<Ip<0.7MA Bt=6 T Zeff Shots Zeff was well below 2 during all the experimental campaign Zeff is always well below 2 with lithizated wall

  30. Np(×1020 plasma particles) Ng(×1021 injected particles) Strong D2 pumping capability After Lithization much more gas has to be injected to get the same electron density with respect to boronized and fully metallic discharges

  31. Thermal analysis Surface temperature deviation from ANSYS calculation at about 1s is probably due to Li radiation in front of the limiter surface. Calculation with TECXY code support this hypothesis

  32. 1.4 Ne (x1020m-3) 1.0 .6 2. T1,2,3 450 º C 1. midplane 0. - 0.2 Z (cm) 1.3 0.9 1.1 High capability to sustain high thermal loads Strong density peaking Heat load exceeding 5 MW/m2 Vertical Plasma Position Time(s)

  33. Electron thermal diffusivity e Electron thermal diffusivity is significantly lower for the lithizated discharge with respect to the metallic one

  34. Lithium • Isotopic Abundances 6Li 7.59% 7Li 92.41% • Melting point 180.54 °C • Boiling point 1342 °C • Nuclear Reactions 6Li + n T + a + 4.8 MeV 7Li + n T + a + n’ - 2.87 MeV