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RFX Meeting G. Mazzitelli Padova 21/01/09
Lithization on FTU:tools and results
G. Mazzitellia
Many thanks to:M.L. Apicellaa, V. Pericoli Ridolfinia, A. Alekseyevb, G. Apruzzesea, W. Binc, P. Burattia, R. Cesarioa,, G. Calabròa, R. De Angelisa, B.
Espositoa, L. Gabellieria, F. Gandinic, E. Giovannozzia, R. Gomesd, G. Granuccic , H. Kroeglera, I. Lyublinskie , M.Marinuccia, C. Mazzottaa, A. Romanoa, O. Tudiscoa, A.
Vertkove, the FTU Teama and ECRH Teamc
a Associazione EURATOM-ENEA sulla Fusione, C. R. Frascati,00044 Frascati, Roma, Italy b TRINITI, Troitsk, Moscow reg., Russia
c Associazione EURATOM-ENEA, IFP-CNR,Via R. Cozzi,53-20125 Milano Italyd Centro de Fusao Nuclear, IST Av. Rovisc Pais,n.1 1049-Lisboa Portugal
e FSUE,“RED STAR”, Moscow, Russia
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RFX Meeting G. Mazzitelli Padova 21/01/09
Introduction
• Why Lithium ?– Very low Z (Z=3)– High impurity getter (C,O)– High H retention Recycling– Low melting point (180.6 ° C)– Strong reduction of total graphite sputtering
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RFX Meeting G. Mazzitelli Padova 21/01/09
Introduction• Where Lithium (How) ?
DIII-D (DIMES) Negative Alcator C-MOD (Pellet) Negative TFTR (Pellet) Good JIPP T_IIU (Evaporation) Good T-11 (Capillary Porous System) Good NSTX (Evaporation+Powder) Good CDX-U (Evaporation+liquid Tray)Good TJ-II (Evaporation) Good T-10 (Evaporation) Good LTX (Liquid wall) Starting FTU (Capillary Porous System) Good
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RFX Meeting G. Mazzitelli Padova 21/01/09
OUTLINE1. Experimental Setup2. Experimental Results
High density peaked discharges Quasi-quiescent MHD discharges ECRH + LH Discharges
3. Future plans4. Conclusions
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RFX Meeting G. Mazzitelli Padova 21/01/09
1. Experimental Setup
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RFX Meeting G. Mazzitelli Padova 21/01/09
Liquid Lithium Limiter
Langmuir probes
Thermocouples
Heater electrical cables
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RFX Meeting G. Mazzitelli Padova 21/01/09
The LLL system is composed by three similar units
Scheme of fully-equipped lithium limiter unit
Liquid lithium surface
Heater
Li source
S.S. box with a cylindrical support
Mo heater accumulator
Ceramic break
Thermocouples
100 mm 34 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.
Capillary Porous System (CPS)
Meshes filled with Li
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RFX Meeting G. Mazzitelli Padova 21/01/09
Liquid Lithium Limiter
Melting point 180.6 °CBoiling point 1342 °C
Total lithium area ~ 170 cm2 Plasma interacting area ~ 50- 85 cm2
Inventory of lithium 80 g LLL initial temperature > 200oC
Toroidal Limiter
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RFX Meeting G. Mazzitelli Padova 21/01/09
2. Experimental Results
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RFX Meeting G. Mazzitelli Padova 21/01/09
Main features of lithium operations:
1. Better plasma performances with Lithium than with Boron 2. Zeff in ohmic discharges is well below 2(0.15 1020<ne<3.1020m-3)
The VUV spectrum is dominated by the Li lines
O, Mo are strongly reduced
3. Radiation losses are very low less than 30%
4. With lithium limiter much more gas has to be injected to get the same electron density with respect to boronized and fully metallic discharges > 10 times
5. Operations near or beyond the Greenwald limit are easily performed
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RFX Meeting G. Mazzitelli Padova 21/01/09
Main features of lithium operations:6. In lithium discharges, Te in the SOL is 50% higher than
before while the increase in ne is negligible
7. Plasma operations are more reliable with good plasma reproducibility and easier recovery from plasma disruptions
8. The LLL is able to withstand heat load up to 5 MW/m2
More details:• Apicella et al. J. Nuclear Materials 363-365 (2007) 1346-1351
• V. Pericoli Ridolfini et al. Plas. Phys. Contr. Fusion 49 (2007) S123-S135
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RFX Meeting G. Mazzitelli Padova 21/01/09
0
1
2
3
0 0,4 0,8 1,2 1,6
#30583
n elin
e [x10
20 m
-3]
t (s)
r=0.0 m
r=0.235 m
Peaked electron density dischargesIp=0.5MA Bt=6T Ip=0.7MA Bt =6 T
At electron density greater than 1.0 1020 m-3 spontaneously the density profile peaks
0
1
2
3
0 0,3 0,6 0,9 1,2n e,
line [x
1020
m-3
]t(s)
r=0.0 m
r=0.235 m
#30584
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RFX Meeting G. Mazzitelli Padova 21/01/09
Peaked electron density discharges
The SOL densities do not follow the FTU scaling law
461.eeSOL nn
Central density increases while edge and SOL densities do not change
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RFX Meeting G. Mazzitelli Padova 21/01/09
0
1
2
3
4
5
0,6 0,7 0,8 0,9 1 1,1 1,2 1,30
1
2
3
4
5
0 0,5 1 1,5
n e,lin
e [x 1
020 m
-3]
t(s)
r=0
r=0.2 m
Peaked electron density dischargesThe profile is peaked as with pellet injection
The profiles are taken at different times but at the same line-averaged density
R (m)
ne [x1020 m-3]
The strong particle depletion in the outermost plasma region is due to the strong pumping capability of lithium
#30583#26793
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RFX Meeting G. Mazzitelli Padova 21/01/09
20406080
100120
0 1 2 3 4
0.5 MA0.8 MA1.1 MA1.4 MA 0.50 MA Li0.75 MA Li
E (m
s)
line averaged ne (x1020 m-3)
k = 7.1±0.6
E-linear
= k ne,lin
(1020 m-3) q1.41±0.07
pellet: open symbols
Energy Confinement TimeIf the confinement time of lithized discharges is compared with the general behaviour of the confinement time of the ohmic and pellet fuelled FTU discharges database, it clearly results that the threshold of the SOC regime is raised from ~45÷50 ms to ~65÷70 ms, suggesting a behaviour which is akin to that shown by multiple-pellet PEP regimes
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RFX Meeting G. Mazzitelli Padova 21/01/09
A possible theoretical explanation is proposed in which electrostatic waves excited by thermal background in the plasma core enhance the turbulence at the edge via non-linear mode coupling.
Quasi-quiescent MHD activity
R. Cesario et. EPS Conference 2007
Te at the edge is geneally higher than in boronized discharges
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RFX Meeting G. Mazzitelli Padova 21/01/09
Te [KeV]264
Ip [MA]
.5
ne[1019 m-3]3
57
Te [KeV]
2
64
LHECH
#27923P [MW]1
2
P [MW]
#30620LH
ECH0.40.3 0.5 0.6
12
ECRH + LH Discharges
Very interesting features are obtained with combined ECR+LH Powert(s)
0.54 s 0.59 s
Strong and wide ITB develops after LH injection, with very high central Te up to 8 KeV in spite of the lower value of additional power
#30620 With LLL
PECH=0.80 MW
PLH =0.75 MW
#27923 Without LLL
PECH=1.20 MW
PLH =1.50 MW
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RFX Meeting G. Mazzitelli Padova 21/01/09
ECRH + LH Discharges
A wide ITB is formed with a strong Te gradient
ρ*T
t (s)0.3 0.4 0.5 0.6Padd=2.2MW
Padd=1.2MW
0
1
2
3
4
5
6
-0,2 -0,1 0 0,1
0.59 s
B
Te[keV]
r (m)
Padd=1.6MW
Padd=1.6MW
-0,2 -0,1 0 0,10
2
4
6
8
B
0.54 sTe[keV]
ρ*T,max=Max of the normalized Te gradient
Radial extension of ITBrITB/a
Strength of ITB
0.6
0.4
0.2
0.02
0.01
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RFX Meeting G. Mazzitelli Padova 21/01/09
ECRH + LH Discharges
The strong difference between the two discharges is in the impurity content. Zeff is reduced by at least a factor 2 in lithium discharges that
increases the LH current drive efficiency
0
5000
1 104
1,5 104
100 150 200 250 300
Counts #30620
Li lines
0
5000
1 104
1,5 104
Counts #27923
)A(
MoFe
O
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RFX Meeting G. Mazzitelli Padova 21/01/09
ECRH + LH Discharges
The dilution is strictly correlated with the plasma start-up phase and the low value of electron density
But Zeff ~ 2 means about 50% of dilution as indicated by the strong reduction in neutron signal.
0
1
2
3
4
5
0 0,2 0,4 0,6
neutrons/s [x1011]
t(s)
#27823
#30620
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RFX Meeting G. Mazzitelli Padova 21/01/09
Dilution
At higher electron densities dilution is negligible
30584 LLL Inside
29919 lithized
28847 metallic
28833 boronized
0.5
0.80.60.40.20.
1.0
1.0
4.0
2.0
1.0
2.0
1.0
2.03.0
Ip [MA]
ne [x1020 m-3]
Te [KeV]
Neutrons/s [x1011]
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RFX Meeting G. Mazzitelli Padova 21/01/09
3. Future Plans
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RFX Meeting G. Mazzitelli Padova 21/01/09
No Surface Damage of CPS Structure
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RFX Meeting G. Mazzitelli Padova 21/01/09
A new limiter panel type actively cooled and equipped with a system for lithium refilling
Preliminary design
This limiter should be able to act as main limiter for withstanding heat loads up to 10 MW/m2 for 3 s
Toroidal lmiter
LLL
Top view
LLL
25
3
25
1 4
3
25
3
25
1 4
26FTU Port
FTU VacuumVessel
Lithium Limiter
FTU Port
FTU VacuumVessel
Lithium Limiter
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RFX Meeting G. Mazzitelli Padova 21/01/09
CONCLUSIONSCONCLUSIONS
•Lithization is a very good and Lithization is a very good and effective tool for plasma operationseffective tool for plasma operations•Exposition of a liquid surface on Exposition of a liquid surface on tokamak has been done on FTU with tokamak has been done on FTU with very promising resultsvery promising results
Thank you for your attention
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RFX Meeting G. Mazzitelli Padova 21/01/09
Dilution Problem
It is strictly correlated with the plasma start-up phase and the absolute value of density
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RFX Meeting G. Mazzitelli Padova 21/01/09
ECRH + LH Discharges
Comparison of electron temperature profiles showing ITB formation
No PaddPadd=0.0MWPadd=0.8MW
0
1
2
3
4
5
-0,2 -0,1 0 0,1
0.48 s
B
Te[keV]Te[keV]
Padd=1.6MW
Padd=1.6MW
-0,2 -0,1 0 0,10
2
4
6
8
B
0.54 sTe[keV]
r (m)
0
1
2
3
-0,2 -0,1 0 0,1
0.40 s
Br (m)
Padd=2.2MW
Padd=1.2MW
0
1
2
3
4
5
6
-0,2 -0,1 0 0,1
0.59 s
B
Te[keV]
r (m)
r (m)
#30620#27923
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RFX Meeting G. Mazzitelli Padova 21/01/09
6
6.5
7
7.5after lith.after boron.
n e (x10
19m
-3)
1.6
1.8
2
T e (KeV
)
1020304050
P rad/P
ohm
(%)
0.80.85
0.90.95
V loop
(V)
ti me
1.21.41.61.8
0.6 0.8 1 1.2 1.4time (s)
Z eff
Ohmic shotsIp=0.5MA Bt=6T
The Li effects are similar or
even better than those of B
Comparison between Lithization and Boronization
Prad(%)
Zeff
Te(keV)
ne(x1019m-3)
Vloop(V)
Time(s)
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RFX Meeting G. Mazzitelli Padova 21/01/09
Zeff was well below 2 during all the experimental campaign
0
0,5
1
1,5
2
2,5
3
3,5
4
0 50 100 150 200 250
After liquid Lithium limiter insertion
Shots
Zeff
0.15x1020 m-3<ne<2.7x1020 m-3
0.5MA<Ip<0.7MA Bt=6 T
Zeff is always well below 2 with lithizated wall
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RFX Meeting G. Mazzitelli Padova 21/01/09
Strong D2 pumping capability
After Lithization much more gas has to be injected to get the same electron density with respect to boronized and fully metallic discharges
Ng(×1021 injected particles)
Np(×
1020
pla
sma
part
icle
s)
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RFX Meeting G. Mazzitelli Padova 21/01/09
Thermal analysis
200
250
300
350
400
450
500
0 0.5 1 1.5 2
T1 (exp.)T2 (exp.)T3 (exp.)T2 (ANSYS)
Sur
face
tem
pera
ture
T (
0 C)
time (s)
2 MW/m2
Surface temperature deviation from ANSYS calculation at about 1s is probably due to Li radiation in front of the limiter surface.
Calculation with TECXY code support this hypothesis
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RFX Meeting G. Mazzitelli Padova 21/01/09
Heat load exceeding 5
MW/m2
Vertical Plasma Position
Ne (x1020m-3)
T1,2,3
0.9 1.1 1.3
.6
1.0
1.4
450 º C
- 0.2
0.
2.
1.
Z (cm)
midplane
Time(s)
High capability to sustain high thermal loadsStrong density peaking
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RFX Meeting G. Mazzitelli Padova 21/01/09
0
0.4
0.8
1.2
1.6
0.05 0.1 0.15 0.2 0.25
metallic wall
lithized wall
(m2 /s
)
minor radius (m)
e Electron thermal diffusivity is significantly lower for the lithizated discharge with respect to the metallic one
Electron thermal diffusivity
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RFX Meeting G. Mazzitelli Padova 21/01/09
Lithium• Isotopic Abundances
6Li 7.59%7Li 92.41%
• Melting point180.54 °C
• Boiling point1342 °C
• Nuclear Reactions6Li + n T + + 4.8 MeV 7Li + n T + + n’ - 2.87 MeV
RFX Meeting G. Mazzitelli Padova 21/01/09
LITHIUM DETECTION LITHIUM REACTS WITH WATER GIVING A BASIC
SOLUTION:
2Li(s,l,g) + 2H2O(l,g) → 2LiOH(aq,g)+ H2 (g)
USING A A WHITE CLOTH IMBUED WITH A SOLUTION OF PHENOLPHTHALEIN (ACID-BASE INDICATOR ) WE CAN DETECT LITHIUM DROPS BECAUSE THE SOLUTION TURNS FROM COLORLESS(ACID-NEUTRAL SOLUTION) TO RED (BASIC SOLUTION) IN PRESENCE OF LITHIUM.