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

e-mail contact of author: mirnov@triniti.ru

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)-1 - 2,2 104 

• Specific weight (g/cm3) - 0,5• Heat conductivity (W/cm grade) - 0,53 (6270С)• Heat capacity (kal/cm3grade) - 0,5• Melting temperature - 180,50С• Evaporation temperature - 13170С (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” – 204.6 eV

• ”Radiation cost” of Li+++ ionized by electrons with Те=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 regimeper 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 (10-200 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) 821-827.

Idea of Li CPS limiter

insertion in ITER SOL

The key question of emitter-collector

model isthe 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<100C(depth of heat penetration is

equal 1cm)

“Hot exposition”initial Tlim>200C

Lithium penetration in T-11M limiter shadow

behavior in T-11M SOLLi

FTU experiment. Li CPS limiter after plasma exposition

No Surface Damage

lim.

lim.

Scheme of experiment

Li in FTU chamber

A B

A

B

w/o Li

w Li

J

lim.

lim.

0

0,5

1

1,5

2

2,5

3

3,5

4

0 50 100 150 200 250

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 40-50

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 =5TT

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 40-50 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 21.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-

injectionIf the Li atom cost = 1000eV (Te=15-100eV),

5x10 = Nx1.6x10

N≈3x10 Li atoms ~ 35g of lithiumThe total permitted amount of Li in ITER is 24kg. That is equivalent of 650 permitted

shots with use of Li killer pellets

8 -16

24

Deuterium removal

from liquid lithium

Liquid lithium shielding of solid metals: J.Bohdansky and J.Roth

Temperature dependence of sputtering behavior of Cu-Li alloysNucl. 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.