Transcript Li use for mitigation of divertor power loading and

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: [email protected]
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
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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 regime
per 1 Li atom and 1 electron in cm3
“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 pondermotive forces. These
capillary channels (10-200
microns) may be realized
in the form of so called
capillary-pore systems
Mo-mesh with lithium filling and without it
(CPS) (V.A.Evtikhin et
al.1995). Self-regeneration
of liquid metal surface,
contacted with plasma is
an intrinsic property of
such structures.
- 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) 821827.
Idea of Li CPS
limiter
insertion in
ITER SOL
The key 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<100C
(depth of heat
penetration is
equal 1cm)
“Hot exposition”
initial Tlim>200C
Lithium penetration in T-11M
limiter shadow
Li
behavior in T-11M SOL
FTU experiment. Li CPS limiter
after plasma exposition
No Surface Damage
lim.
lim.
Scheme of experiment
Li in FTU chamber
A
J
w/o Li
w Li
lim.
lim.
A
B
B
Zeff behaviour during all the
experimental campaign
4
After lithium limiter insertion
3,5
3
2,5
Zeff
2
1,5
1
0,5
0
0
50
100
150
Shots
200
250
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.
3
Li (2.7x2.7x2.7cm ) fast railgun
injector
B T =5T
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 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 Liinjection
If the Li atom cost = 1000eV (Te=15-100eV),
5x10
24
8
= Nx1.6x10
-16
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
N≈3x10
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.