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OUTLINE Experimental Setup Experimental Results Main features of lithium operations

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OUTLINE Experimental Setup Experimental Results Main features of lithium operations

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  1. Plasma behaviour in presence of a liquid lithium limiterG. Mazzitelli1on behalf of FTU Team1P.Innocente2, S.Munaretto21Ass. Euratom-ENEA sulla Fusione, CR Frascati, C.P.65, 00044 Frascati, Roma, Italy2Consorzio RFX, -EURATOM/ENEA Ass. C.so Stati Uniti 4, Padova,Italy 351272nd International Symposium on Lithium Applications for Fusion DevicesApril 27 - 29, 2011Princeton, New Jersey, USA

  2. OUTLINE • Experimental Setup • Experimental Results • Main features of lithium operations • Peaked electron density discharges • Effect of Lithium onMHD Activity at FTU • Heat load • CPS Damages 3. Work in progress 4. Conclusions 2nd Int. Symp on Lithium Appl for Fusion Devices G. Mazzitelli

  3. 1. Experimental Setup 2nd Int. Symp on Lithium Appl for Fusion Devices G. Mazzitelli

  4. Liquid Lithium Limiter Langmuir probes Thermocouples Heater electrical cables 2nd Int. Symp on Lithium Appl for Fusion Devices G. Mazzitelli

  5. 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. and TUNGSTEN Scheme of fully-equipped lithium limiter unit Meshes filled with Li 2nd Int. Symp on Lithium Appl for Fusion Devices G. Mazzitelli

  6. Total lithium area ~ 170 cm2 Plasma interacting area ~ 50- 85 cm2 Total amount of lithium  80 g LLL initial temperature > 200oC Liquid Lithium Limiter Melting point 180.6 °C Boiling point1342 °C 2nd Int. Symp on Lithium Appl for Fusion Devices G. Mazzitelli

  7. 2. Experimental Results 2nd Int. Symp on Lithium Appl for Fusion Devices G. Mazzitelli

  8. Main features of lithiums operations • Better plasma performance with Lithium than boronization • 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 • For q>5 the Greenwald limit has been exceed by more than a factor 1.5 at Ip=.5 MA Bt=6T (ne=3.2 1020 m-3) and nG>1.3 at Ip=.7MA Bt=7.2T Bt=6T (ne=4 1020 m-3) 2nd Int. Symp on Lithium Appl for Fusion Devices G. Mazzitelli

  9. Main features of lithiums operations • Te in the SOL is 50% higher while increase in ne is much smaller in lithium discharges • Operations are generally more easy to perform and the behavior of the machine is more reliable. • Discharge recovery after a disruption is prompt 2nd Int. Symp on Lithium Appl for Fusion Devices G. Mazzitelli

  10. Peaked electron density discharges Spontaneouslythe density profile peaks for ne > 1.0 1020 m-3 Central density increases while edge and SOL densities do not change The SOL densities do not follow the FTU scaling law 2nd Int. Symp on Lithium Appl for Fusion Devices G. Mazzitelli

  11. Peaked electron density discharges • Very similar peaked density profiles with Li and B at least up to <ne>vol ≈ 1.5*1020m-3 but: • with Li it is possible to operate at higher <ne>vol • ne(0)/<ne>vol => 2.5 only with Li, in a regime not accessible with B 2nd Int. Symp on Lithium Appl for Fusion Devices G. Mazzitelli

  12. Peaked electron density discharges From JETTO code: χe≈0.2 m2/s a factor 2 lower than in the unpeaked phase χi≈0.2-0.3 m2/s close to its neoclassical value. • For lithizated discharges the linear ohmic confinement (LOC) extends at higher values, from 54 ms up to 76 ms, that corresponds to the new saturated ohmic confinement (SOC). • The ion transport is negligible with respect to the electron one. 2nd Int. Symp on Lithium Appl for Fusion Devices G. Mazzitelli

  13. Gyrokinetic code GKW has been used for microinstability analisys Peaked electron density discharges • At 0.3 s Li is the onlyimpurity (Zeff=1.9). Li ions change the turbulence spectrum of ITG modes moving the peak of ITG modes toward higher kqri -At 0.3 s, with Li, the amplitude of the turbolence of ETG modes is lower than without Li At 0.8 s, with or without Li no difference (Zeff=1) 2nd Int. Symp on Lithium Appl for Fusion Devices G. Mazzitelli

  14. Effect of Lithium onMHD Activity at FTU • Without lithium: • Instability starts after rump-up • Disruption at 0.580 s. • With lithium: • Instability starts after rump-up • No disruption.

  15. Effect of Lithium onMHD Activity at FTU • Without lithium: • Instability starts after rump-up • Disruption at 1.2 s. • With lithium: • Low intensity instability during discharge.

  16. Heat load The heat loads on the three units are evaluated starting from the measure of the surface temperature. The temperature rise in a planar surface under a power flux density q (t) can be written : where CP is specific heat of the material,  its density and k the thermal conductivity. 2nd Int. Symp on Lithium Appl for Fusion Devices G. Mazzitelli

  17. Heat Loads DT is the difference between the maximum temperature and the initial value for each shot. The difference among the three LLL units is a cloud without any systematic behavior 2nd Int. Symp on Lithium Appl for Fusion Devices G. Mazzitelli

  18. Heat loads - 1° Case Standard dischargeusedforlithization Ip = 0.5 MA Bt = 6 T DLCMS=1.5 cm #33206 2nd Int. Symp on Lithium Appl for Fusion Devices G. Mazzitelli

  19. Heat loads – 1° Case q(MW/m2) #33206 #33206 The temperature rise up to 450 °C at the end of the pulse and 1.5 MW/m2 are withstood for about 1 sec 2nd Int. Symp on Lithium Appl for Fusion Devices G. Mazzitelli

  20. HEAT LOADS – 2° Case Ip [x105 A] z(m) LiI [a.u.] LiIII [a.u.] t (s) Heat load on LLL is increased by shifting plasma 2nd Int. Symp on Lithium Appl for Fusion Devices G. Mazzitelli

  21. HEAT LOADS #33209 Although the heat load on the LLL is increasing or it should be constant during the time in which the plasma is pushed on the LLL, the temperature doesn’t increase in time but saturates at a maximum value. 2nd Int. Symp on Lithium Appl for Fusion Devices G. Mazzitelli

  22. Heat Load Rate of lithium evaporation in vacuum versus temperature 2nd Int. Symp on Lithium Appl for Fusion Devices G. Mazzitelli

  23. wall Prad TZM e-side LLL TZM i-side core HEAT LOADS #28568 - Ip=0.5MA,ne=1.1020m-3, Bt=6T CCD camera view: the bottom brigth green annular ring develops just in between LLL and TZM 3D sketch (TECXY) of Prad Most (60%) Li radiation (not in coronal equilibrium) in between TZM and LLL Strong interaction plasma - LLL => also density peaks in front of LLL => shorter n 2nd Int. Symp on Lithium Appl for Fusion Devices G. Mazzitelli

  24. HEAT LOADS q(MW/m2) q(MW/m2) q(MW/m2) For the central unit heat load in excess of 5 MW/m2 are withstood with a strong peak up to 14 MW/m2 during the plasma disruption. Of course the lithium radiating cloud around the units strongly reduces the heat load and avoids damages to CPS structure. 2nd Int. Symp on Lithium Appl for Fusion Devices G. Mazzitelli

  25. No Surface Damage on CPS 2nd Int. Symp on Lithium Appl for Fusion Devices G. Mazzitelli

  26. Damage by fast electrons with LH LLL-3 2nd Int. Symp on Lithium Appl for Fusion Devices G. Mazzitelli

  27. No surface damages Very good behaviour of tungsten structure 2nd Int. Symp on Lithium Appl for Fusion Devices G. Mazzitelli

  28. 3. Work In progress 2nd Int. Symp on Lithium Appl for Fusion Devices G. Mazzitelli

  29. B2-Eirene Code - FTU edge simulation Collaboration with RFX - Padua B2 EIRENE Neutral gas transport code It is a multi-species code It solves simultaneously a system of time dependent or stationary linear kinetic transport equations It is coupled to external databases for atomic and molecular data and for surface reflection data • Transport code for the SOL • Multifluid • Toroidally symmetric configurations (toroidal limiter or poloidal divertor) • It solves a reduced set of fluid equations (Braginskii) on a 2D grid in the poloidal cross-section of a Tokamak

  30. B2-Eirene Code - FTU edge simulation Lithization studies in 2 steps: Toroidal limiter covered by Li Influx of Li particles from the LLL In a first phase Be is used instead of Lithium PROBLEM: No Li database available for ionization and recombination in B2 yet The code is going to be improved to read ADAS database

  31. Preliminary simulation B2-Eirene Compared with electron density and temperature from Langmuir probes @ -70°in the poloidal plane • Particle flux from the core: 1021 m-2 s-1 • Power input from the core 0.5 MW • Recycling at the limiter: 0.75 • D = 1 Agreement with the density profile A sink of energy is needed (Molybdenum?)

  32. 1 1 3 4 5 2 The Cooled Lithium Limiter (CLL)

  33. CONCLUSIONS • Lithiumization is a very good and effective tool for plasma operations and performances • Exposition of a liquid surface on tokamak is possible but the temperature of the liquid lithium must be kept below 500 °C 2nd Int. Symp on Lithium Appl for Fusion Devices G. Mazzitelli

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