Slides

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Slides

FTU results with the liquid
lithium limiter
G.Mazzitelli1, M.L.Apicella1, D. Frigione1, G. Maddaluno1,
M.Marinucci1, C.Mazzotta1,
V.Pericoli Ridolfini1 , M. Romanelli2, G. Szepesi3, O.
Tudisco1 and FTU team
1) Associazione EURATOM-ENEA sulla Fusione, Centro Ricerche di Frascati, C.P. 65
00044 Frascati, Rome, Italy
2) CCFE/Euratom Association, Culham Science Center, OX143DB, UK
3) CFSA University of Warwick, CV47AL, UK
23th IAEA Daejeon Oct 14,2010
1
OUTLINE
1. Experimental Setup
2. Experimental Results
Peaked electron density discharges
Impurities
Heat load/Damages
3. Conclusions
23th IAEA Oct 14,2010
G. Mazzitelli
2
1. Experimental Setup
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3
Liquid Lithium Limiter
Langmuir probes
Thermocouples
Heater electrical
cables
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4
Capillary Porous System (CPS)
The LLL system is composed by three similar units
Liquid lithium surface
Mo heater accumulator
Thermocouples
Heater
Li source
S.S. box with a
cylindrical support
100 mm
34 mm
Ceramic break
Scheme of fully-equipped lithium limiter unit
5
G. Mazzitelli
CPS is made as a
matt from
wire
meshes with porous
radius 15 µm and
wire diameter 30 µm
Structural material
of wires is S.S. and
TUNGSTEN
Meshes filled
with Li
Total lithium area
Plasma interacting area
Total amount of lithium
LLL initial temperature
~ 170 cm2
~ 50- 85 cm2
≅ 80 g
> 200oC
Liquid Lithium Limiter
Melting point 180.6 °C
Boiling point 1342 °C
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2. Experimental Results
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Spontaneously the density profile peaks for ne > 1.0 1020 m-3
Central density increases while edge and SOL densities do not change
The SOL densities do not follow the FTU scaling law
G. Mazzitelli
n eSOL ∝ n1.e 46
8
Very
similar
peaked
density profiles with Li and
B at least up to <ne>vol ≈
1.5*1020m-3 but:
with Li it is possible to
operate at higher <ne>vol
ne(0)/<ne>vol => 2.5 only
with Li, in a regime not
accessible with B
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9
The Greenwald density limit
(dashed line) has been
exceeded only in discharges
with an edge safety factor
q(a) > 5 (1/qa < 0.2). In
particular:
At Ip= 0.7MA, BT=7.1T,
qa=5.0, by gas puffing only, a
record electron density for
FTU has been reached
ne=4.0*1020 m-3 (30% beyond
Greenwald limit)
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10
From JETTO code:
χe ≈0.2 m2/s a factor 2
lower than in the
unpeaked phase
χi ≈0.2-0.3 m2/s close
to
its
neoclassical
value.
For lithizated discharges the linear ohmic confinement (LOC) extends
at higher values, from 54 ms up to 76 ms, that corresponds to the new
saturated ohmic confinement (SOC).
The ion transport is negligible with respect to the electron one.
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11
Gyrokinetic code GKW has been used for microinstability analisys
At 0.3 s Li is the only impurity (Zeff=1.9).
Li
ions change the turbulence
spectrum of ITG modes moving the
peak of ITG modes toward higher kθρi
-At 0.3 s, with Li, the amplitude
of the
turbolence of ETG
modes is lower than without Li
At 0.8 s, with or without Li no difference (Zeff=1)
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The particle flux driven by the ITG modes is dominant in the
strong gradient region of the discharge (r/a=0.6). At 0.3s it is
inward (negative) for e- and D and outward (positive) for Li, at
t=0.8s it is found to be outward for all the species
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IMPURITIES
1,5 10
Counts
4
1 10
4
#27923
Mo
Fe
O
5000
1,5 100
Counts
4
1 10
#30620
Li lines
4
5000
0
100
150
200
250
λ(A )
ο
300
Although FTU is a fully metallic machine (TZM +
SS) the only impurity in the discharge is lithium
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14
Heat load
The heat loads on the three units are evaluated
starting from the measure of the surface temperature.
The temperature rises in a planar surface under a
power flux density q (t) can be written :
1
∆T (t ) =
πρC p k
q(t − t ' )
∫0 t ' dt '
t
where CP is specific heat of the material, ρ its density
and k the thermal conductivity.
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Heat loads - 1° Case
Standard discharge
used for lithization
Ip = 0.5 MA
Bt = 6 T
∆LCMS=1.5 cm
#33206
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Heat loads – 1° Case
q(MW/m2)
#33206
#33206
The temperature rises up to 450 °C at the end of the
pulse and 1.5 MW/m2 are withstood for about 1 sec
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HEAT LOADS – 2° Case
Ip [x105 A]
z(m)
LiI [a.u.]
LiIII [a.u.]
t (s)
Heat load on LLL is increased by shifting plasma
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HEAT LOADS
#33209
Although the heat load on the LLL is increasing or it should
be constant during the time in which the plasma is pushed on
the LLL, the temperature doesn’t increase in time but
saturates at a maximum value.
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HEAT LOADS
q(MW/m2)
q(MW/m2)
q(MW/m2)
For the central unit heat loads in excess
of 5 MW/m2 are withstood with a strong
peak up to 14 MW/m2 during the plasma
disruption. Of course the lithium
radiating cloud around the units
strongly reduces the heat load and
avoids damages to CPS structure.
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20
No Surface Damage on CPS
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No Surface Damage on CPS
Very good behaviour of tungsten structure
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CONCLUSIONS
•Lithization is a very good and
effective tool for plasma operations
and performances
•Exposition of a liquid surface on
tokamak is possible but the
temperature of the liquid lithium
must be kept below 500 °C
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Backup Slides
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Heat Load
Rate of lithium evaporation in vacuum versus temperature
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HEAT LOADS
#28568 - Ip=0.5MA,ne=1.1020m-3, Bt=6T
Prad
wall
TZM e-side
LLL
TZM iside
CCD camera view: the bottom
brigth annular ring develops
just in between LLL and TZM
core
3D sketch (TECXY) of Prad
Most (60%) Li radiation (not in coronal
equilibrium) in between TZM and LLL
Strong interaction plasma - LLL => also
density peaks in front of LLL => shorter λn
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26
0
Surface temperature T ( C)
HEAT LOADS- Thermal analysis
500
Surface temperature
deviation from ANSYS
calculation at about 1s
is probably due to Li
radiation in front of
the limiter surface.
2
2 MW/m
450
400
350
300
250
200
Calculation
with
TECXY code support
this hypothesis
T1 (exp.)
T2 (exp.)
T3 (exp.)
T2 (ANSYS)
0
0.5
1
time (s)
1.5
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2
27
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Sensitivity analisys
The deuterium flux
changes its direction
only as a function of
lithium density
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30

Slides

Transcription

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