Transcript SOFT 2010 - Consorzio RFX

Last experiments in FTU with
a Li conditioned wall
G.Mazzitelli
RFX-mod 2011 Programme Workshop
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OUTLINE
1. Experimental Setup
2. Experimental Results


Peaked density discharges
Heat load
3. Conclusions
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1. Experimental Setup
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Liquid Lithium Limiter
Langmuir probes
Thermocouples
Heater electrical
cables
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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
CPS is made as a
matt from
wire
meshes with porous
radius 15 m and
wire diameter 30 m
Structural material
of wires is S.S. and
TUNGSTEN
34 mm
Ceramic break
Scheme of fully-equipped lithium limiter unit
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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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Peaked electron density discharges
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
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neSO L  n1.e46
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Peaked electron density discharges
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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Peaked electron density discharges
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
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Peaked electron density discharges
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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Peaked electron density discharges
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 kqri
-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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Peaked electron density discharges
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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Peaked electron density discharges
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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Heat load
The heat loads on the three units are evaluated
starting from the measure of the surface temperature.
The temperature rise in a planar surface under a
power flux density q (t) can be written :
1
T (t ) 
rC p k
q (t  t ' )
0 t ' dt'
t
where CP is specific heat of the material, r its density
and k the thermal conductivity.
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Heat Loads
T is the difference
between the maximum
temperature and the
initial value for each
shot.
The difference among
the three LLL units is a
cloud
without
any
systematic behavior
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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 rise 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 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
wall
Prad
TZM e-side
LLL
TZM iside
CCD camera view: the bottom
brigth annular ring develops
just in between LLL and TZM
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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 n
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HEAT LOADS
q(MW/m2)
q(MW/m2)
q(MW/m2)
For the central unit heat load 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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Future Works
• Plasma performance with LLL in
presence of additional heating
•Injection of pellets/high plasma
current discharges with LLL
•Gyrokinetics simulations
•Edge2D-EIRENE Simulations
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Backup Slides
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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
0
Surface temperature T ( C)
HEAT LOADS- Thermal analysis
450
400
350
300
T1
T2
T3
T2
250
Calculation
with
TECXY code support
this hypothesis
(exp. )
(exp. )
(exp. )
(ANSY S)
200
0
0.5
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time (s)
1.5
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