1. SEWG Meeting G. Mazzitelli Ljubljana 01/10/09 Experiments with the FTU liquid lithium limiter G. Mazzitelli a Many thanks to: M.L. Apicella a, V. Pericoli Ridolfini a, G.Maddaluno a, G. Apruzzese a, R. Cesario a, C. Castaldo a,A.Botrugno a,M.Marinucci a, C. Mazzotta a, O. Tudisco a, A. Alekseyev b, I. Lyublinski c,A.Vertkov c a Associazione EURATOM-ENEA sulla Fusione, C. R. Frascati,00044 Frascati, Roma, Italy b TRINITI, Troitsk, Moscow reg., Russia c FSUE,RED STAR, Moscow, Russia

2. SEWG Meeting G. Mazzitelli Ljubljana 01/10/09 2 Introduction Why Lithium ? –Very low Z (Z=3) –High impurity getter (C,O) –High H retention Recycling –Low melting point (180.6 ° C)

3. SEWG Meeting G. Mazzitelli Ljubljana 01/10/09 3 OUTLINE 1.Experimental Setup 2.Experimental Results 3.Future plans 4.Conclusions 5.Ga Experiments on ISTTOK

4. SEWG Meeting G. Mazzitelli Ljubljana 01/10/09 4 1. Experimental Setup

5. SEWG Meeting G. Mazzitelli Ljubljana 01/10/09 5 Liquid Lithium Limiter Langmuir probes Thermocouples Heater electrical cables

6. SEWG Meeting G. Mazzitelli Ljubljana 01/10/09 6 The LLL system is composed by three similar units Scheme of fully-equipped lithium limiter unit Liquid lithium surface Heater Li source S.S. box with a cylindrical support Mo heater accumulator Ceramic break Thermocouples 100 mm34 mm 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. and TUNGSTEN Capillary Porous System (CPS) Meshes filled with Li

7. SEWG Meeting G. Mazzitelli Ljubljana 01/10/09 7 Liquid Lithium Limiter Melting point 180.6 °C Boiling point 1342 °C Total lithium area ~ 170 cm 2 Plasma interacting area ~ 50- 85 cm 2 Inventory of lithium 80 g LLL initial temperature > 200 o C Toroidal Limiter

8. SEWG Meeting G. Mazzitelli Ljubljana 01/10/09 8 2. Experimental Results

9. SEWG Meeting G. Mazzitelli Ljubljana 01/10/09 9 Main features of lithium operations: 1.Better plasma performances with Lithium than with Boron 2.Zeff in ohmic discharges is well below 2( 0.15 10 20 <n e <3.10 20 m -3 ) O, Mo are strongly reduced 3.Radiation losses are very low less than 30% 4.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 5.Operations near or beyond the Greenwald limit are easily performed

10. SEWG Meeting G. Mazzitelli Ljubljana 01/10/09 10 Main features of lithium operations: 6.In lithium discharges, T e in the SOL is 50% higher than before while the increase in n e is negligible 7.Plasma operations, with LLL inserted in the shadow of the main toroidal limiter, are more reliable with good plasma reproducibility and easier recovery from plasma disruptions 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

11. SEWG Meeting G. Mazzitelli Ljubljana 01/10/09 11 Peaked electron density discharges Ip=0.5MA B t =6TIp=0.7MA B t =6 T At electron density greater than 1.0 10 20 m -3 spontaneously the density profile peaks

12. SEWG Meeting G. Mazzitelli Ljubljana 01/10/09 Shots at Ip= 0.5MA #30583 # 32243 #32240 The new density limit

13. SEWG Meeting G. Mazzitelli Ljubljana 01/10/09 13 20 40 60 80 100 120 01234 0.5 MA 0.8 MA 1.1 MA 1.4 MA 0.50 MA Li 0.75 MA Li E (ms) line averaged n e (x10 20 m -3 ) k = 7.1±0.6 E-linear = k n e,lin (10 20 m -3 ) q 1.41±0.07 pellet: open symbols Energy Confinement Time If the confinement time of lithiumazed discharges is compared with the general behaviour of the 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

14. SEWG Meeting G. Mazzitelli Ljubljana 01/10/09 Pellet discharges 32252 with LLL 25040 without LLL First attempts to inject pellets into LLL discharges at Ip=.5 MA Time(s ) n e (10 20 m -3 )

15. SEWG Meeting G. Mazzitelli Ljubljana 01/10/09 Pellet discharges Electron density relaxation time First pellet (ms) Second pellet (ms) 32552 Lithium 11743 250406028 The density relaxation time is longer in lithiumizated discharges

16. SEWG Meeting G. Mazzitelli Ljubljana 01/10/09 Only traces of the same mode are observed after the insertion of LLL A reduction of the MHD activity is observed with LLL. Shots before insertion of LLL Shots after insertion of LLL First shot with LLL A m=2 mode is present in discharges before LLL

17. : Lithiumizated vessel utilised for mitigating the LH physics of the edge Hard X-ray produced by 0.35 MW of coupled LH power vs. operating plasma density LH effect at ITER_relevant operating plasma densiities are produced in FTU provided that the physcis of the edge should be mitigated by utilising Lithiumizated vessel : boronised Lithiumizated

18. SEWG Meeting G. Mazzitelli Ljubljana 01/10/09 18 Impurities When the LLL is inserted in all electron density range the VUV spectrum is dominated by lithium lines VUV Spectrum Electron density Li lines Time (s) (10 20 m -3 ) (counts)

19. SEWG Meeting G. Mazzitelli Ljubljana 01/10/09 19 3. Future Plans

20. SEWG Meeting G. Mazzitelli Ljubljana 01/10/09 20 No Surface Damage of CPS Structure

21. SEWG Meeting G. Mazzitelli Ljubljana 01/10/09 21 Heat load exceeding 5 MW/m 2 N e (x10 20 m -3 ) T1,2,3T1,2,3 0.91.1 1.3.6 1.0 1.4 450 º C - 0.2 0. 2. 1. Z (cm) midplane Time(s) High capability to sustain high thermal loads Strong density peaking Vertical Plasma Position Next experimental campaign during the week 16-19 October

22. SEWG Meeting G. Mazzitelli Ljubljana 01/10/09 22 The new project

23. SEWG Meeting G. Mazzitelli Ljubljana 01/10/09 23 The new project

24. SEWG Meeting G. Mazzitelli Ljubljana 01/10/09 24CONCLUSIONS Lithiumization is a very good and effective tool for plasma operations and performancesLithiumization is a very good and effective tool for plasma operations and performances Exposition of a liquid surface on tokamak has been done on FTU with very promising resultsExposition of a liquid surface on tokamak has been done on FTU with very promising results

25. Gallium-plasma interaction study: ongoing tasks (1) jet power exhaustion capability Measurement of total power exhaustion from plasma by jet: surface temperature by IR sensor has to be performed. 3 channel detector is now available. Suitable for low (<200 ºC) temperature measurements. Absolute calibration requires some hardware replacement. A radial displacements of the droplets have been detected during temperature measurements using the IR sensor (0.5 m away from the tokamak chamber). IR sensor preliminary testing

26. Gallium-plasma interaction study: ongoing tasks (2) jet dynamic behavior / retention measurements The reason for the shift is not fully understood : MHD or plasma effect? shift believed to be due to 3-D magnetic field structure & gradients: detailed modelization is required. ½ oxide-free gallium sample will be exposed to ISTTOK plasmas for hydrogen retention measurements. In depth (1 m) sample analysis will be performed in a ion beam laboratory. Sample preparation chamber is currently being commissioned & positioning system (with variable sample temperature control) is ready. Oxide-free gallium sample preparation chamber schematic

27. SEWG Meeting G. Mazzitelli Ljubljana 01/10/09 27 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. Quasi-quiescent MHD activity R. Cesario et. EPS Conference 2007 T e at the edge is geneally higher than in boronized discharges

28. SEWG Meeting G. Mazzitelli Ljubljana 01/10/09 28 Peaked electron density discharges The SOL densities do not follow the FTU scaling law Central density increases while edge and SOL densities do not change

29. SEWG Meeting G. Mazzitelli Ljubljana 01/10/09 29 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 R (m) n e [x10 20 m -3] The strong particle depletion in the outermost plasma region is due to the strong pumping capability of lithium #30583 #26793

30. SEWG Meeting G. Mazzitelli Ljubljana 01/10/09 30 Dilution Problem It is strictly correlated with the plasma start-up phase and the absolute value of density

31. SEWG Meeting G. Mazzitelli Ljubljana 01/10/09 31 ECRH + LH Discharges Very interesting features are obtained with combined ECR+LH Power t(s) 0.54 s 0.59 s 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 #30620 With LLL P ECH =0.80 MW P LH =0.75 MW #27923 Without LLL P ECH =1.20 MW P LH =1.50 MW

32. SEWG Meeting G. Mazzitelli Ljubljana 01/10/09 32 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 Mo Fe O

33. SEWG Meeting G. Mazzitelli Ljubljana 01/10/09 33 ECRH + LH Discharges A wide ITB is formed with a strong T e gradient ρ*Tρ*T t (s) 0.30.4 0.5 0.6 P add =2.2MW P add =1.2MW Te[keV] r (m) P add =1.6MW Te[keV] ρ* T,max =Max of the normalized T e gradient Radial extension of ITB r ITB /a Strength of ITB 0.6 0.4 0.2 0.02 0.01

34. SEWG Meeting G. Mazzitelli Ljubljana 01/10/09 34 ECRH + LH Discharges The dilution is strictly correlated with the plasma start-up phase and the low value of electron density But Zeff ~ 2 means about 50% of dilution as indicated by the strong reduction in neutron signal.

35. SEWG Meeting G. Mazzitelli Ljubljana 01/10/09 35 Dilution At higher electron densities dilution is negligible 30584 LLL Inside 29919 lithized 28847 metallic 28833 boronized 0.5 0.80.60.40.2 0. 1.0 4.0 2.0 1.0 2.0 1.0 2.0 3.0 Ip [MA] n e [x10 20 m -3 ] Te [KeV] Neutrons/s [x10 11 ]

36. SEWG Meeting G. Mazzitelli Ljubljana 01/10/09 36 ECRH + LH Discharges Comparison of electron temperature profiles showing ITB formation No P add P add =0.0MW P add =0.8MW Te[keV] P add =1.6MW Te[keV] r (m) P add =2.2MW P add =1.2MW Te[keV] r (m) #30620 #27923

37. SEWG Meeting G. Mazzitelli Ljubljana 01/10/09 37 Ohmic shots I p =0.5MA B t =6T The Li effects are similar or even better than those of B Comparison between Lithization and Boronization P rad (%) Z eff T e (keV) n e (x10 19 m -3 ) V loop (V) Time(s)

38. SEWG Meeting G. Mazzitelli Ljubljana 01/10/09 38 Z eff was well below 2 during all the experimental campaign After liquid Lithium limiter insertion Shots Z eff 0.15x10 20 m -3 <n e <2.7x10 20 m -3 0.5MA<Ip<0.7MA B t =6 T Zeff is always well below 2 with lithizated wall

39. SEWG Meeting G. Mazzitelli Ljubljana 01/10/09 39 Strong D 2 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 N g (×10 21 injected particles) N p (×10 20 plasma particles)

40. SEWG Meeting G. Mazzitelli Ljubljana 01/10/09 40 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

41. SEWG Meeting G. Mazzitelli Ljubljana 01/10/09 41 e Electron thermal diffusivity is significantly lower for the lithizated discharge with respect to the metallic one Electron thermal diffusivity

42. SEWG Meeting G. Mazzitelli Ljubljana 01/10/09 42 Lithium Isotopic Abundances 6 Li 7.59% 7 Li 92.41% Melting point 180.54 °C Boiling point 1342 °C Nuclear Reactions 6 Li + n T + + 4.8 MeV 7 Li + n T + + n - 2.87 MeV

43. SEWG Meeting G. Mazzitelli Ljubljana 01/10/09 LITHIUM DETECTION LITHIUM REACTS WITH WATER GIVING A BASIC SOLUTION: 2Li(s,l,g) + 2H2O(l,g) 2LiOH(aq,g)+ H2 (g) USING A A WHITE CLOTH IMBUED WITH A SOLUTION OF PHENOLPHTHALEIN (ACID-BASE INDICATOR ) WE CAN DETECT LITHIUM DROPS BECAUSE THE SOLUTION TURNS FROM COLORLESS(ACID-NEUTRAL SOLUTION) TO RED (BASIC SOLUTION) IN PRESENCE OF LITHIUM.

44. Impurezze metalliche su scariche con il pellet C.f.r P.Buratti, riunione TF A del 16/5/01 Le scariche disrompono per collasso radiativo quando: Profili di temperatura alla fine del re-heating dopo il 1°, 2° e 3° pellet. L'iniezione di un 4° pellet provoca una disruzione.

45. Pellet discharges 32252 Lithium 25040 Electron Temperature Time(s) (KeV)

46. SEWG Meeting G. Mazzitelli Ljubljana 01/10/09 46 A new limiter panel type actively cooled and equipped with a system for lithium refilling Preliminary design This limiter should be able to act as main limiter for withstanding heat loads up to 10 MW/m 2 for 3 s Toroidal lmiter LLL Top view LLL