RFX Meeting G. Mazzitelli Padova 21/01/09 Lithization on FTU: tools and results G. Mazzitelli a Many...

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

2


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

3


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

4


OUTLINE1. Experimental Setup2. Experimental Results

High density peaked discharges Quasi-quiescent MHD discharges ECRH + LH Discharges

3. Future plans4. Conclusions

5


1. Experimental Setup

6


Liquid Lithium Limiter

Langmuir probes

Thermocouples

Heater electrical cables

7


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

8


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

9


2. Experimental Results

10


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

11


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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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

13


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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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

15


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

16


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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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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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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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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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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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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3. Future Plans

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No Surface Damage of CPS Structure

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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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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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Dilution Problem

It is strictly correlated with the plasma start-up phase and the absolute value of density

29



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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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)

31


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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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)

33


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

34


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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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

36


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


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.

RFX Meeting G. Mazzitelli Padova 21/01/09 Lithization on FTU: tools and results G. Mazzitelli a Many...

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