Li use for mitigation of divertor power loading and disruption mitigation in ITER S.Mirnov, E.Azizov, Yu.Kareev, V.Lazarev TRINITI, Troitsk, Moscow reg. Russia I.Lublinsky, A.Vertkov, V.Evtikhin “Krasnaya Zvezda”, 1A, Elektrolitny pr., Moscow, Russia V.Vershkov, P.Hvostenko Insitute of Nuclear Fusion, RRC “Kurchatov Institute”, Moscow, Russia. M.L.Apicella, G.Mazzitelli Associazione ENEA-EURATOM sulla Fusione CR Frascati, Italy contact of author:

Two problems of DEMO and ITER we hope to decide by Li use: 1.decrease of divertor power load during steady state and ELMs 2. fast mitigation of major disruption consequents

Two ideas of softening plasma–wall interaction in ITER are suggested. The first one is the additional lithium limiter insertion in divertor SOL (Li emitter-collector model). The second suggestion is the fast (2km/s) massive Li (10gr) killer pellets injection for mitigation of major disruption consequents.

Li properties Electric conductivity (ohm cm) , Specific weight (g/cm 3 ) - 0,5 Heat conductivity (W/cm grade) - 0,53 (627 0 С) Heat capacity (kal/cm 3 grade) - 0,5 Melting temperature - 180,5 0 С Evaporation temperature С (P=1atm) Evaporation heat 1,5 (eV/at) First ionization potential 5.6 eV Second ionization potential 75 eV (!) Third ionization potential 122 eV Total “ionization cost” – eV ”Radiation cost” of Li +++ ionized by electrons with Т е =20-100eV equal 1 keV/at

Lithium radiation in regime of coronal equilibrium and non coronal ( with account the real Li confinement n in plasma periphery) by D.Yu.Prokhorov

Lithium radiation in non-coronal regime per 1 Li atom and 1 electron in cm 3

“Energy cost” of Li ion before its transition to coronal equilibrium, as Te function

We chose the Li capillary pore structure (CPS) as a practically method of prevention of Li splashing and as a method of liquid Li transportation cross toroidal magnetic field from lithium collector to emitter by capillary forces (“lithium weak”)

Li capillary pore structure (CPS) The idea to use LM in tokamaks as PFC was advanced basing on the surface tension forces in capillary channels for compensation of ponder- motive forces. These capillary channels ( microns) may be realized in the form of so called capillary-pore systems (CPS) (V.A.Evtikhin et al.1995). Self-regeneration of liquid metal surface, contacted with plasma is an intrinsic property of such structures. Mo-mesh with lithium filling and without it - CPS as PFC element

Li limiter based on the Capillary-Pore System concept has been tested in T-11M and in FTU tokamaks An ability of capillary forces to confine the liquid Li in the CPS limiter during plasma discharge has been demonstrated. All tokamak lithium experiments demonstrated effect of lithium screening – poor penetration lithium to plasma center (Zeff(0) equal 1). In T-11M, for example, almost 80% of total plasma heat flux can be passed to the first wall by lithium radiation. And its radial distribution showed that up to 90 % of the total light emitted from a relative thin (5cm) boundary layer and only 10% - from a plasma centre.

For transformation of plasma heat flux to Li radiation we use idea of Li limiter as lithium emitter-collector. S.V. Mirnov, E.A. Azizov, V.A. Evtikhin, V.B. Lazarev, I.E. Lyublinski, A.V. Vertkov, D.Yu. Prokhorov. Experiments with Lithium Limiter on T-11M Tokamak and Applications of the Lithium Capillary-Pore System in Future Fusion Reactor Devices. Plasma Physics and Controlled Fusion, 48 (March 2006)

Idea of Li CPS limiter insertion in ITER SOL The k ey question of emitter-collector model is the relation between heat and lithium penetration in SOL

T-11M, FTU Li experiments

T-11M rail limiter Mo road, coated by thin 1-2mm Li CPS. SXR

T-11M limiter “Cold exposition” initial Tlim 200C

Lithium penetration in T-11M limiter shadow

behavior in T-11M SOL Li

FTU experiment. Li CPS limiter after plasma exposition No Surface Damage

lim. Scheme of experiment

Li in FTU chamber

AB A B w/o Li w Li J lim.

Zeff behaviour during all the experimental campaign After lithium limiter insertion Shots Zeff

The next step: Proposal of steady state Li CPS limiter experiment with power load equal 10 MW/ m (T-15) 2

T-15 a=70 cm, R=243 cm, Bt =3.6T, Nb3Sn J=1MA T=5-30sec, Paux =10MW

T-15 CFC limiters

T-15 Li CPS limiter, W, water cooling (proposal)

For mitigation of divertor power load in ITER can be suggested two Li CPS limiters placed in two symmetrical ITER port-limiters.

The preliminary estimation shows, that two Li limiters in ITER port-limiters can spread in steady state regime equal MW of total power flux to the first wall by radiation

Our second suggestion is the use of the fast massive Li pellets for mitigation of major disruption consequents. For this aim the fast (1ms) acceleration of lithium killer pellet (10g 2.7x2.7x2.7 cm3) up to 2km/sec by the simple rail-gun with 1m length. If we take to account “energy cost” of lithium ion, three or four such pellets will be enough to cool the ITER plasma with 0.5GJ total energy by radiation to the wall and by ionization losses.

Li (2.7x2.7x2.7cm ) fast railgun injector B =5T T 3 Railgun scheme: rail 1 L=1m, accelerated body 2 (Li 2.7x2.7x2.7cm3), distance between rails y=2.7cm, rail width d=2.7cm, body velocity vector V.

Rail-gun cross-section

W=0.1MJ

Evolution of the main features of acceleration

Conclusion1 The preliminary estimation shows, that two Li limiters in ITER port-limiters can spread in steady state regime equal MW of total power flux to the first wall by radiation. The effect of Li radiation shielding has been observed in T-11M and FTU tokamaks with pulse durations 0.3 (T-11M), 2 (FTU) sec. This experiments can be extended. Li radiation shielding can be investigated in future experiments (FTU, T-15) with steady state limiter and pulse durations 3-30 sec.

Conclusion 2 1.For the fast (1ms) acceleration of lithium killer pellet (10g 3x3x3 cm3) up to 2km/sec can be used the simple rail-gun with 1m length and capacitor bank energy 0.1MJ. 2. Three or fourth such pellets will be enough to cool the ITER plasma with 0.5GJ total energy. 3. The preliminary investigation of ITER lithium limiter and lithium rail-gun can be carried out in framework of voluntary program of Russia and Italy, but it needs support this activity from ITER and ITPA

The lithium amount (N) used for 0.5GJ plasma cooling by fast Li- injection If the Li atom cost = 1000eV (Te=15-100eV), 5x10 = Nx1.6x10 N≈3x10 Li atoms ~ 35g of lithium The total permitted amount of Li in ITER is 24kg. That is equivalent of 650 permitted shots with use of Li killer pellets

Deuterium removal from liquid lithium

Liquid lithium shielding of solid metals: J.Bohdansky and J.Roth Temperature dependence of sputtering behavior of Cu-Li alloys Nucl. Instr.and Methods in Physics Research B23 (1987) 518

Several potential technological problems prevented the active Li application in tokamak operations. The most serious were: 1) the liquid metal splashing under the JxB forces during MHD instabilities and disruptions, 2) the possible anomalous lithium erosion as a result of plasma-liquid lithium interaction, 3) the problem of heat removal as prevention of strong lithium evaporation, 4) the problem of the tritium removal from lithium.