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Density issues & Lithization in RFX-mod A. Alfier , A. Canton, R. Cavazzana,

Density issues & Lithization in RFX-mod A. Alfier , A. Canton, R. Cavazzana, S. Dal Bello, P. Innocente, P. Scarin. Summary. Density issues in RFX-mod Proposed lithization techniques on RFX-mod Lithium pellet injector Capillary Porous System

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Density issues & Lithization in RFX-mod A. Alfier , A. Canton, R. Cavazzana,

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

  2. 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 A. Alfier – RFX-mod PROGRAMME WORKSHOP 2009 – 20/22 Jan 2009

  3. Absorbing wall: wide range of density regimes Not absorbing wall: I/N forced to the value 2x10-14 Am 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 Des% (desorption)= outpumped-part. / filled-part (%) A. Alfier – RFX-mod PROGRAMME WORKSHOP 2009 – 20/22 Jan 2009

  4. Density issues on RFX-mod • 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. A. Alfier – RFX-mod PROGRAMME WORKSHOP 2009 – 20/22 Jan 2009

  5. Why Lithium? • More pronounced pumping effect than Boron (strong H and H+ retention, LiH) • - High impurity getter (O2, N2, CO, H2O, CO2…) • - Reduction of C chemical and physical sputtering (H. Sugai, JNM 1998) • Ionization potential (1s2 2s1): 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 A. Alfier – RFX-mod PROGRAMME WORKSHOP 2009 – 20/22 Jan 2009

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

  7. On RFX-mod:Non-cryogenic pellet injector • 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 A. Alfier – RFX-mod PROGRAMME WORKSHOP 2009 – 20/22 Jan 2009

  8. On RFX-mod:Non-cryogenic pellet injector • Pellet size: Ø 1.5 mm x 4 mm = 28 mm3 •  NLi≈ 1021 &SRFX=36.3 m2 •  ≈ 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). A. Alfier – RFX-mod PROGRAMME WORKSHOP 2009 – 20/22 Jan 2009

  9. On RFX-mod:Non-cryogenic pellet injector • 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 A. Alfier – RFX-mod PROGRAMME WORKSHOP 2009 – 20/22 Jan 2009

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

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

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

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

  14. On RFX-mod:Capillary Porous System • Strategy: 1. First wall conditioning in H2 GDC + Baking  decrease impurity content; hint: Li reacts with O, C, N (LiOH, Li3N, Li2CO3) 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1018 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! • 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. A. Alfier – RFX-mod PROGRAMME WORKSHOP 2009 – 20/22 Jan 2009

  15. On RFX-mod:Capillary Porous System • 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. A. Alfier – RFX-mod PROGRAMME WORKSHOP 2009 – 20/22 Jan 2009

  16. 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 • tE 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). A. Alfier – RFX-mod PROGRAMME WORKSHOP 2009 – 20/22 Jan 2009

  17. 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. A. Alfier – RFX-mod PROGRAMME WORKSHOP 2009 – 20/22 Jan 2009

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

  19. 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 cm3) 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, Zeff = 1.2-1.3) A. Alfier – RFX-mod PROGRAMME WORKSHOP 2009 – 20/22 Jan 2009

  20. Available lithization techniques 3. LIThium EvaporatoR - LITER (NSTX) • R. Kaita & H. Kugel, APS 2008 • Li heated inside an “oven” • tE improved, Te profile broadened Lowered recycling 4. Lithium aerosol with powder (NSTX) • Mansfield, APS 2008 • 98.5% Li +1.5% Li2CO3 particles (Ø =50mm) • Similar effect of LITER, with even more reduced impurity accumulation 100 mm A. Alfier – RFX-mod PROGRAMME WORKSHOP 2009 – 20/22 Jan 2009

  21. Available lithization techniques 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. 6. CDX-U low aspect ratio tokamak (PPPL) • Lithium tray limiter filled with a total of 300 g (0.6 l) of lithium + evaporator • tE improved, lower Zeff, lowered recycling A. Alfier – RFX-mod PROGRAMME WORKSHOP 2009 – 20/22 Jan 2009

  22. 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 • 6Li + n → 4He + 3H (blanket of ITER) • high surface tension  effect on physical sputtering A. Alfier – RFX-mod PROGRAMME WORKSHOP 2009 – 20/22 Jan 2009

  23. Lithium chemistry • Ion Li+, which have a smaller diameter, can easily displace K+ and Na+ and even Ca2+, in spite of its greater charge, occupying their sites in several critical neuronal enzymes and neurotransmitter receptors. • Although Li+ cannot displace Mg2+ and Zn2+, because of these ions' small size and greater charge (higher charge density, hence stronger bonding), when Mg2+ or Zn2+ are present in low concentrations, and Li+ is present in high concentrations, the latter can occupy sites normally occupied by Mg2+ or Zn2+ in various enzymes. • Lithium hydroxide (LiOH) is an important compound of lithium obtained from lithium carbonate (Li2CO3). 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 (Li2O2) • 2 Li2O2 + 2 CO2 → 2 Li2CO3 + O2. • lithium hydroxide (LiOH and LiOH·H2O), lithium nitride (Li3N) and lithium carbonate (Li2CO3, the result of a secondary reaction between LiOH and CO2). • Lithium carbide, Li2C2: molten lithium + graphite are reacted at high temperature A. Alfier – RFX-mod PROGRAMME WORKSHOP 2009 – 20/22 Jan 2009

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

  25. 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). A. Alfier – RFX-mod PROGRAMME WORKSHOP 2009 – 20/22 Jan 2009

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

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

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

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

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