1. A. Alfier – RFX-mod PROGRAMME WORKSHOP 2009 – 20/22 Jan 2009 Density issues & Lithization in RFX-mod A. Alfier, A. Canton, R. Cavazzana, S. Dal Bello, P. Innocente, P. Scarin

2. A. Alfier – RFX-mod PROGRAMME WORKSHOP 2009 – 20/22 Jan 2009 Summary Density issues in RFX-mod Proposed lithization techniques on RFX-mod –Lithium pellet injector –Capillary Porous System Status, schedule, application, advantages, disadvantages Expectations & open issues on Lithium in RFX-mod

3. A. Alfier – RFX-mod PROGRAMME WORKSHOP 2009 – 20/22 Jan 2009 Density issues on RFX-mod RFX-mod first wall (graphite tiles) is an extended reservoir of particles -> density at flat top (FT) it does not depend on the fuelled particles -> it is entirely sustained by particles fluxes from the wall Wall condition affects density: the capability of the wall to absorb particles influences the value of I/N more than the absolute number of particles stored in the wall Absorbing wall: wide range of density regimes Not absorbing wall: I/N forced to the value 2x10 -14 Am Des% (desorption)= outpumped-part. / filled-part (%)

4. A. Alfier – RFX-mod PROGRAMME WORKSHOP 2009 – 20/22 Jan 2009 Plasma itself extracts particles from the wall (PWI): Density depends on Ohmic Power, that regulates particle influxes from the wall.  Particles stored in the wall are not enterely accessible by plasma (implantation depth, toroidal and poloidal asymmetries).  In RFX-mod we outgas a minimum part of the particles that we inject  we should always fuel the discharge with the minimum gas to allow breakdown.  Wall pre-loading by means of H2 GDC is under test as a reproducible method to obtain a discharge with desired flat top density. Density issues on RFX-mod

5. A. Alfier – RFX-mod PROGRAMME WORKSHOP 2009 – 20/22 Jan 2009 Why Lithium? - More pronounced pumping effect than Boron (strong H and H + retention, LiH) - High impurity getter (O 2, N 2, CO, H 2 O, CO 2 …) - Reduction of C chemical and physical sputtering (H. Sugai, JNM 1998) - Ionization potential (1s 2 2s 1 ): 5.6 eV (I), 75 eV (II), 122 eV (III) - Highest specific heat capacity of any solid element Total wall inventory > 3 times, no sign of saturation Sanchez and the TJ-II Team, PSI 2008

6. A. Alfier – RFX-mod PROGRAMME WORKSHOP 2009 – 20/22 Jan 2009 1.Non-cryogenic pellet injector 262.30° equatorial port 2. Capillary Porous System 262.30° central bottom oblong port Available lithization techniques on RFX-mod Top view of RFX-mod

7. A. Alfier – RFX-mod PROGRAMME WORKSHOP 2009 – 20/22 Jan 2009 Injector characteristics Pellet speed: 50÷200 m/s Pellet size: Ø 0.5÷2 mm x 1÷4 mm 30 pellets in the charger Materials: Li, C, B Aims Measurement of the pitch of the magnetic field lines Transport studies First wall conditioning On RFX-mod: Non-cryogenic pellet injector

8. A. Alfier – RFX-mod PROGRAMME WORKSHOP 2009 – 20/22 Jan 2009 Pellet size: Ø 1.5 mm x 4 mm = 28 mm 3  N Li ≈ 10 21 & S RFX =36.3 m 2  ≈ 2.6 monolayers if uniformely distributed Schedule: Installation at middle/end of february ’09; Delivery of interface system with vessel (the injector is already here) at end of february ’09; Tests on RFX-mod available since middle/end of march (related to the RFX-mod 2009 experiments schedule). On RFX-mod: Non-cryogenic pellet injector

9. A. Alfier – RFX-mod PROGRAMME WORKSHOP 2009 – 20/22 Jan 2009 Strategy: 1. first wall conditioning with He glow discharge; 2. injection in standard and then performing RFP discharges at the end of the current flat-top; hint: the injection on tokamak discharge could be usefull to obtain a more uniform distribution of Lithium, but probably a tokamak discharge will not ablate entirely the pellet and sustain the incraese of density. Advantages: - control the amount of the injected Lithium; - easy to use (well-established technique) and to compare with similar discharge w/o pellet; - injected lithium of good pureness; - lithium effective during the discharge; - non uniform deposition (only where plasma touches the wall); Disadvantages: - thin Lithium layer deposited (few monolayers)  short length beneficial effects (few shots); - maybe non uniform deposition also where plasma touches the wall; - Li-pellet injection perturbs plasma before its beneficial effects appear  being at the end of the flat-top, it prepares the first wall for next discharge On RFX-mod: Non-cryogenic pellet injector

10. A. Alfier – RFX-mod PROGRAMME WORKSHOP 2009 – 20/22 Jan 2009 On RFX-mod: Capillary Porous System (CPS) 500mm Hint: The gate valve should be installed below coils  additionl 500÷800mm CPS unit operating position CPS unit storage position Schematic layout of CPS on RFX-mod

11. A. Alfier – RFX-mod PROGRAMME WORKSHOP 2009 – 20/22 Jan 2009 On RFX-mod: Capillary Porous System 120mm clearness Ø150mm valve ~120mm General view of the CPS RFX-mod oblong window port with CPS

12. A. Alfier – RFX-mod PROGRAMME WORKSHOP 2009 – 20/22 Jan 2009 Modification of the FTU support On RFX-mod: Capillary Porous System

13. A. Alfier – RFX-mod PROGRAMME WORKSHOP 2009 – 20/22 Jan 2009 Capillary Porous System on FTU

14. A. Alfier – RFX-mod PROGRAMME WORKSHOP 2009 – 20/22 Jan 2009 Strategy: 1. First wall conditioning in H 2 GDC + Baking  decrease impurity content; hint: Li reacts with O, C, N (LiOH, Li 3 N, Li 2 CO 3 ) 2. He discharge  decrease H content (Li reacts with H); 3 Baking  decrease He content. hint: He can be captured in Li voids, and it could then released during several discharges 4. Define a “suitable” Tokamak dicharge (60-80 kA, n=1-2  10 18 m -3, t=400ms, q=2-4); 5. Condition the first wall with CPS in tokamak discharges. 6. Extract the CPS. 6. RFP plasma @ Ip ~ 0.5-1.5MA, F=-0.03 ÷ -0.08. 7. …. We’ll keep you informed! On RFX-mod: Capillary Porous System Schedule: Procurements of materials on loan from FTU: end of summer 2009. Installation and test : autumn 2009. Tests on RFX-mod available beginning of winter 2009.

15. A. Alfier – RFX-mod PROGRAMME WORKSHOP 2009 – 20/22 Jan 2009 Advantages: - on loan from FTU for first attempt on RFX-mod. - easy to handle; - injected lithium of good pureness; - high heat load threshold ( 10 MW/m2 )  compatible with reactorial previsions Disadvantages: - not usefull during RFP discharges (Li would be deposited in +-20 tor. deg. from CPS) - the amount of Li deposited on the first wall not straighforward to control. - requires first wall conditioning with tokmak discharges. - never used before on other RFP experiments. On RFX-mod: Capillary Porous System

16. A. Alfier – RFX-mod PROGRAMME WORKSHOP 2009 – 20/22 Jan 2009 Expectations & open issues on Lithium in RFX-mod Expected effects (from experience on other machines): -lower & controlled recycling with absorbing wall -lower Zeff and radiation losses -Te increase  E improved Open issues: Lithium deposition on optics  if Li + born in field lines, it does not result in window coating Effects on internal probes :  Li does not react with Mb, Fe, Ti, Stainless steel  Li reacts with Cu, but no effect reported in literature & no relevant effect on NSTX and TFTR if not with evaporator (priv. com.) Effect of Li penetration (“intercalation”) in graphite tiles  experience from other experiments Too low recycling  fuelling issues 3-8 hours He GDC used to recover wall condition w/o lithium (Vershkov, IAEA ’08 & in Sugai, J. Nucl. Material ’95).

17. A. Alfier – RFX-mod PROGRAMME WORKSHOP 2009 – 20/22 Jan 2009 Further tasks: Real time or inter-shot measurement of the deposited Lithium (e.g.: quartz crystal oscillator). Expose samples (of graphite, mirror and windows) to plasma.  three experimental proposal for 2009.

18. A. Alfier – RFX-mod PROGRAMME WORKSHOP 2009 – 20/22 Jan 2009 Thank you

19. A. Alfier – RFX-mod PROGRAMME WORKSHOP 2009 – 20/22 Jan 2009 Available lithization techniques 1. Lithium pellet injection (TFTR) J.A. Snipes et al. J. of Nucl. Mater. (1992) 686 - 2 mm Ø x 2 mm 1-2 Monolayers coated on TFTR graphite limiter Pellet injected in conditioning He discharges and standard discharges 2. Lithium aerosol - DOLLOP (TFTR) D.K. Mansfield et al. Nucl. Fusion 41 (2001) 1823 Li contained in a small (17.5 cm 3 ) boron nitride cauldron positioned 15 cm below the shadow of the TFTR RF limiter edge The highest total energy confinement time was obtained in TFTR with this technique (about 80% improvement, Z eff = 1.2-1.3)

20. A. Alfier – RFX-mod PROGRAMME WORKSHOP 2009 – 20/22 Jan 2009 Available lithization techniques 3. LIThium EvaporatoR - LITER (NSTX) R. Kaita & H. Kugel, APS 2008 Li heated inside an “oven”  E improved, Te profile broadened Lowered recycling 4. Lithium aerosol with powder (NSTX) Mansfield, APS 2008 98.5% Li +1.5% Li 2 CO 3 particles (Ø =50  m) Similar effect of LITER, with even more reduced impurity accumulation 100  m

21. A. Alfier – RFX-mod PROGRAMME WORKSHOP 2009 – 20/22 Jan 2009 5. Li Capillary Pore System (CPS) Tested in T-11M and FTU Tokamaks (S.V. Mirnov et al. Fusion Eng. Des. 65 (2003) 455, M.L. Apicella at al. J. of Nucl. Mater. (2007) 1346. See previous talk. Available lithization techniques 6. CDX-U low aspect ratio tokamak (PPPL) Lithium tray limiter filled with a total of 300 g (0.6 l) of lithium + evaporator  E improved, lower Zeff, lowered recycling

22. A. Alfier – RFX-mod PROGRAMME WORKSHOP 2009 – 20/22 Jan 2009 Lithium chemistry Low thermal expansion: 46 µm·m −1 ·K −1 Highest specific heat capacity of any solid element: 24.860 J·mol −1 ·K −1 Thermal conductivity: (300 K) 84.8 W·m −1 ·K −1  heat transfer applications Melting point: 180.54 °C Boiling point: 1342 °C High electrochemical potential, light weight, and high current density  lithium-ion batteries 6 Li + n → 4 He + 3 H (blanket of ITER) high surface tension  effect on physical sputtering

23. A. Alfier – RFX-mod PROGRAMME WORKSHOP 2009 – 20/22 Jan 2009 Ion Li +, which have a smaller diameter, can easily displace K + and Na + and even Ca 2+, in spite of its greater charge, occupying their sites in several critical neuronal enzymes and neurotransmitter receptors. Although Li + cannot displace Mg 2+ and Zn 2+, because of these ions' small size and greater charge (higher charge density, hence stronger bonding), when Mg 2+ or Zn 2+ are present in low concentrations, and Li + is present in high concentrations, the latter can occupy sites normally occupied by Mg 2+ or Zn 2+ in various enzymes. Lithium hydroxide (LiOH) is an important compound of lithium obtained from lithium carbonate (Li 2 CO 3 ). It is a strong base, and when heated with a fat, it produces a lithium soap. Lithium soap has the ability to thicken oils and so is used commercially to manufacture lubricating greases lithium peroxide (Li 2 O 2 ) 2 Li 2 O 2 + 2 CO 2 → 2 Li 2 CO 3 + O 2. lithium hydroxide (LiOH and LiOH·H 2 O), lithium nitride (Li 3 N) and lithium carbonate (Li 2 CO 3, the result of a secondary reaction between LiOH and CO 2 ). Lithium carbide, Li 2 C 2 : molten lithium + graphite are reacted at high temperature Lithium chemistry

24. A. Alfier – RFX-mod PROGRAMME WORKSHOP 2009 – 20/22 Jan 2009 Before Li with Li CarbonHigh Z imp. Vershkov, IAEA ‘08 Effect on impurity on T-10

25. A. Alfier – RFX-mod PROGRAMME WORKSHOP 2009 – 20/22 Jan 2009 Wall control on T-10 Vershkov, IAEA ‘08 He GDC used to recover wall condition w/o lithium (also in Sugai, J. Nucl. Material ’95).

26. A. Alfier – RFX-mod PROGRAMME WORKSHOP 2009 – 20/22 Jan 2009 Scanning quartz deposition monitor (QDM).

27. A. Alfier – RFX-mod PROGRAMME WORKSHOP 2009 – 20/22 Jan 2009 Expose samples (of graphite, mirror and windows) to plasma.

28. A. Alfier – RFX-mod PROGRAMME WORKSHOP 2009 – 20/22 Jan 2009 Kaita et al. IAEA 2008

29. A. Alfier – RFX-mod PROGRAMME WORKSHOP 2009 – 20/22 Jan 2009 Kaita et al. IAEA 2008