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Lithium technologies for edge plasma control

Lithium technologies for edge plasma control. Vladimir Yu. Sergeev 1) , Boris V. Kuteev 2) , Aleksey S. Bykov 1) , Sergey V. Krylov 2) , Viacheslav G. Skokov 1) , Vladimir M. Timokhin 1)

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Lithium technologies for edge plasma control

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  1. Lithium technologies for edge plasma control Vladimir Yu. Sergeev1), Boris V. Kuteev2), Aleksey S. Bykov1), Sergey V. Krylov2), Viacheslav G. Skokov1), Vladimir M. Timokhin1) 1)State Polytechnic University, Polytekhnicheskaya 29, Saint Petersburg, 195251, Russia 2)NRC “Kurchatov Institute”, Kurchatov Square 1, Moscow, 123182, Russia ISLA 2011

  2. Outline • Background • Experimental setup • Results and discussion • Summary • Lithium in reactor ISLA 2011

  3. Outline • Background • Experimental setup • Results and discussion • Summary ISLA2011

  4. Background • Lithium technologies are extensively considered and used for discharge control in magnetic confinement devices (T&S) • The major goal of lithium supply to plasma is control of plasma-wall interaction • Approaches to deliver lithium into the plasma: Li pellet injection [1], liquid [2] and/or capillary-pore limiters [3] and divertor plates [4], prior evaporation [5], dust injection [6] • Li pellets had been injected at T-10 tokamak earlier [7] • J.A. Snipes et al., J. Nucl. Mat.196-198 (1992) 686 • R. Majeski et al., Nucl. Fusion 45 (2005) 519–523 • Mirnov S.V. et al., Plasma Phys. Control. Fusion 48 (2006) 821 • M.L. Apicella et al., J. of Nucl. Mater.363-365 (2007) 1346 • M.G. Bell et al. Plasma Phys. Control. Fusion 51 (2009) 124054 • D. Mansfield et al., NIFS-CRC SymposiumToki, Japan, 2010 • Timokhin V.M. et al., 33nd EPS Conf. on Plasma Phys. Roma, 19 - 23 June 2006, P-4.092 (2006) ISLA 2011

  5. Background (continued) • Models which couple core and SOL regions of multi-species plasma(like with Li dust injection) are necessary for the technology development. • An improved version of simple semi-analytical model [1] for simulation of steady state tokamak regimes with a broad range of plasma actuators was developed and applied to study the influence of Li dust injection in ITER&DEMO conditions [2]. • Recently improved version of the model explore the “2 point onion skin” approach of [3]. This model has been applied for simulations of divertor operation in the compact fusion neutron source based on spherical tokamak [4]. • New injector for Li dust had been designed and tested at T-10 tokamak. First results are presentedhere. 1. V. Sergeev, B. Kuteev, Contrib. Plasma Phys. 2010, 50, No. 3-5, 285 – 291. 2. B.V. Kuteev et al., Nucl. Fusion, 2010, 50 075001. 3. P.C. Stangeby 2004, The Plasma Boundary of MF Devices, Inst. of Phys. Publ., Bristol, Philadelphia. 4. B.V. Kuteev et al. in Fusion Energy 2010 (Proc. 23rd Int. Conf. Daejon, 2010) (Vienna: IAEA) CD-ROM file FTP/P6-10. ISLA 2011

  6. Edge plasma control for reactor SSO is a challenge • Steady state and long term operation of tokamak reactor requires a sufficient reduction and distribution over the first wall the heat loads coming from the core plasma due to heat and particle transport • Impurity injection into the radiative scrape-off layer (SOL) seems like a reasonable way to solve the problem • Recently, the interest to lithium injection has started to grow up. This material has the lowest Z and highest acceptable concentration in the plasma core. However, its radiation is rather low, so it was not clear whether the reactor regimes in tokamak be controlled by lithium injection ISLA 2011

  7. Layout of heat, particle and radiation flows in a tokamak • The droplets are ablated in SOL and the lithium ionized migrates to divertor plates that etermines its density level in SOL • Lithium is injected in small droplet form with the characteristic size of 20-30 microns and the velocity 30-500 m/s • Collectors in divertor region provide closed cycle Lithium collectors Contrib. Plasma Phys.3 (2010) 285 Nucl. Fusion 50 (2010) 075001 ISLA 2011

  8. Outline • Background • Experimental setup • Results and discussion • Summary Major problems for Lithium technology, experiment and modeling Closed cycle - T Acceptable injection rate + E Radiation level recycling controlled! E Core transport +/- E/M Divertor loads + E/M AH compatibility + E ISLA 2011

  9. Experimental setup: dust feederschematic B.V. Kuteev et al. JNM, 2011 DOI information 10.1016/j.nucmat. 2011.02.23 ISLA 2011

  10. Photos: dust feeder and dust particles • The industrially produced SLMPTM powder [1] is used as the injection material. • SLMPTM - metal Li particles of ~40 m diameter covered by the micron layer of lithium carbonate (passivated surface). 1. FMC Lithium – Headquarters, Seven LakePointe Plaza 2801, Yorkmont Road, Suite 300 Charlotte, NC 28208, USA, http://www.fmclithium.com ISLA 2011 ISLA2011

  11. Experimental setup: installation at T-10 • Mechanical decoupling • Dust jet mechanical cutting off • Dust flow rate diagnostics • Independent pumping • Dust jet redirection to T-10 port axis • (Forced) dust jet cross-section profile forming and dust jet velocity decrease due to a system containing three funnels Pumping Rail limiter ISLA 2011

  12. Experimental setup: connector • The motion axis of dust jet particles falling due to gravitation was tilted to the axis of tokamak port at 6 degree angle. • A system composed of three sequential funnels inside the connector was used. • The system shrunk the dust jet cross-section profile and changed essentially the temporal behavior of the flow rate of dust particles leaving the rotary feeder. Pumping Li Fast valve Funnel system Light barrier ISLA 2011

  13. Experimental setup: injection modes • Two modes of the injection operation (I&II) were realized: • 3 rps, rotation axis angle 0, rotation duration time 500 ms • 3 rps, rotation axis angle -1, rotation duration time 200 ms • At the exit of the funnel system the time evolution of dust flow rate depends on the rotation axis angle and differs for modes I&II • The injection duration time grows and the measured transient time of the dust flow rate are significantly longer than those of the rotary feeder • This time behavior is reproducible in more than 10 sequential T-10 shots for each mode of operation • Following slides illustrate the mode operation in T-10 experiments ISLA 2011

  14. Outline • Background • Experimental setup • Results and discussion • Summary ISLA 2011

  15. Results and discussion: mode I (SS) Mode I of Li dust injection, OH Black - #59471 without Li, blue - #59481 with Li • A steady state behavior of LiII radiation in plasma was observed. • Plasma density is slightly increasedfor a small (up to 81020 at/s) lithium flow rate. Most diagnostics signals are practically undisturbed at these conditions. • A slight decrease of the radiation level from plasma (bolometer) at higher plasma density can be considered as footprints of discharge conditioning. ISLA 2011

  16. Results and discussion: mode II Mode II of Li dust injection, OH. Black - #59609 without Li, red - #59707 with Li. • A moderate flow rate injection (up to 1.5  1021 at/s) • The disturbance of plasma parameters is more significant. • A decrease of the D signal when the electron density increases may be explained by a decrease of the recycling coefficient of plasma main component. ISLA 2011

  17. Results and discussion: mode II with disruption Mode II of Li dust injection with disruption, OH. Black - #59609 without Li, magenta - #59702 with Li. • Enhanced flow rate (up to 51021 at/s). • A decrease of the D along with the density growth during first 50 ms after the injection reveals the significant drop of the deuterium recycling coefficient. • After a series of minor plasma disruptions the major disruption occurs at 900 ms. ISLA 2011

  18. 2 Density 1013 cm-3 ECRH 0 2 LiII a.u. 0 1 a.u. Bolometer 0 a.u. D 2 0 V U 4 0 a.u. CIII 10 0 1021at/s Li flow 2 0 0 500 1000 time, ms Results and discussion: mode II with ECRH Mode II of Li dust injection, OH+ECRH (140 GHz, 1.5 MW) Black - #59660 without Li, red - #59711 with Li • Moderate flow rate injection (up to 1.01021 at/s) • A rise of density and a decay of both bolometer and D signals due to Li injection during the ECRH pulse can be seen in comparison with the reference shot • The discharge conditioning effects are evident ISLA 2011

  19. Outline • Background • Experimental setup • Results and discussion • Summary ISLA 2011

  20. Summary • Two operation modes with a novel rotary feeder of lithium dust have been realized on the T-10 tokamak • A quasi steady-state and pulse regimes with the Li flow rate up to 21021 atoms/s are compatible with both OH and OH+ECRH plasmas • A higher flow rate of ~51021 atoms/s initiated a series of minor disruptions, which were completed by the discharge termination (major disruption) • Effects of wall conditioning during lithium dust injection have been detected. The injection reduced hydrogen recycling which was observed as the decrease of D signal accompanied by growing electron density. (Might be unfavorable for divertor loads) ISLA 2011

  21. Lithium in Reactor • Inherent safety mission for major disruption mitigation • A liter of lithium placed on the first wall surface might be evaporated without any external control by the radiation emitted during thermal quench • The energy needed for ablation 10kJ/cm-3*1000cm-3 = 10 MJ • Plasma energy in DEMO 500MW*2 s = 1 GJ • This amount is sufficient to overcome the Rosenbluth density and might provide a safe current quench • The technology will be tested on T-10. The disruption will be initiate after massive Li-dust injection and such disruption characteristics will be compared with disruption without lithium ISLA 2011

  22. Lithium in Reactor • Corrosion problem is extremely sensitive to impurities. Purification system is critical issue • Divertor plates nearby strike points will be definitely at higher temperatures than those acceptable for lithium (200-400 C). Functions of divertor targets and lithium collectors should be separated • ELM loads at a level of 3% of plasma energy (about 50 MJ) are capable to evaporate 5 liters of lithium from capillary targets. This is inacceptable without lithium recycling • Recycling with characteristic time of 100 microseconds may reduce the ablated amount like the ratio tELM/tRec ~5 Reduction seems too small. Recycling is critical issue. Transverse flows are needed. ISLA 2011

  23. Lithium in Reactor • What do we need for Lithium in Reactor? We need new machines like NHTX and FNS-ST -steady state -high power density ( 10 MW/m3) -flexible first wall thermo-hydraulic and shaping -special design of divertor • What should we do? “We must work harder!” J. Hogan. EPS-discussions, 1980, Moscow ISLA 2011

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