SEWG Meeting G. Mazzitelli Ljubljana 01/10/09 Experiments with the FTU liquid lithium limiter G. Mazzitelli a Many thanks to: M.L. Apicella a, V. Pericoli

SEWG Meeting G. Mazzitelli Ljubljana 01/10/09

Experiments with the FTU liquid lithium limiter

G. Mazzitellia

Many thanks to: M.L. Apicellaa, V. Pericoli Ridolfinia, G.Maddalunoa, G. Apruzzesea, R. Cesarioa, C. Castaldoa,A.Botrugnoa,M.Marinuccia, C. Mazzottaa,

O. Tudiscoa, A. Alekseyevb, I. Lyublinskic,A.Vertkovc

a Associazione EURATOM-ENEA sulla Fusione, C. R. Frascati,00044 Frascati, Roma, Italy b TRINITI, Troitsk, Moscow reg., Russia c 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)


3

OUTLINE

1. Experimental Setup

2. Experimental Results

3. Future plans

4. Conclusions

5. Ga Experiments on ISTTOK


4

1. Experimental Setup


5

Liquid Lithium Limiter

Langmuir probes

Thermocouples

Heater electrical cables


6

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. and TUNGSTEN

Capillary Porous System (CPS)

Meshes filled with Li


7

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


8

2. Experimental Results


9

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)

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


10

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, with LLL inserted in the shadow of the main toroidal limiter, are more reliable with good plasma reproducibility and easier recovery from plasma disruptions

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


11

0

1

2

3

0 0,4 0,8 1,2 1,6

#30583

ne

lin

e [

x10

20 m

-3]

t (s)

r=0.0 m

r=0.235 m

Peaked electron density discharges

Ip=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,li

ne [

x10

20 m

-3]

t(s)

r=0.0 m

r=0.235 m

#30584


Shots at Ip= 0.5MA

#30583

#32243

#32240

The new density limit


13

20

40

60

80

100

120

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 lithiumazed 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


Pellet discharges

32252 with LLL

25040 without LLL

First attempts to inject pellets into LLL discharges at Ip=.5 MA

Time(s)


Pellet dischargesElectron density relaxation time

First pellet (ms)

Second pellet (ms)

32552 Lithium

117 43

25040 60 28

The density relaxation time is longer in lithiumizated discharges


Only traces of the same mode are observed after the insertion of LLL

A reduction of the MHD activity is observed with LLL.

Shots before insertion of LLL

Shots after insertion of LLL

First shot with LLL

A m=2 mode is present in discharges before LLL

: Lithiumizated vessel utilised for mitigating

the LH physics of the edgeHard X-ray produced by 0.35 MW of coupled LH power vs. operating plasma density

LH effect at ITER_relevant operating plasma densiities are produced in FTU provided that the physcis of the edge should be mitigated by utilising Lithiumizated vessel

: boronised

Lithiumizated


18

Impurities

When the LLL is inserted in all electron density range

the VUV spectrum is dominated by lithium lines

VUV SpectrumElectron density

Li lines

Time (s)Time (s)

(10 20 m-3)(counts)


19

3. Future Plans


20

No Surface Damage of CPS Structure


21

Heat load exceeding 5

MW/m2

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 loads

Strong density peaking

Vertical Plasma Position

Next experimental campaign during the week 16-19 October


22

3

2

5

1 4

3

2

5

3

2

5

1 4

The new project


23

FTU Port

FTU VacuumVessel

Lithium Limiter

FTU Port

FTU VacuumVessel

Lithium Limiter

The new project


24

CONCLUSIONSCONCLUSIONS

•Lithiumization is a very good and Lithiumization is a very good and effective tool for plasma operations effective tool for plasma operations and performancesand performances•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

Gallium-plasma interaction study: ongoing tasks (1) Gallium-plasma interaction study: ongoing tasks (1) jet power exhaustion capabilityjet power exhaustion capability

Measurement of total power exhaustion from plasma by jet: surface temperature by IR sensor has to be performed.

3 channel detector is now available. Suitable for low (<200 ºC) temperature measurements. Absolute calibration requires some hardware replacement.

A radial displacements of the droplets have been detected during temperature measurements using the IR sensor (0.5 m away from the tokamak chamber).

IR sensor preliminary testing

Gallium-plasma interaction study: ongoing tasks (2) Gallium-plasma interaction study: ongoing tasks (2) jet dynamic behavior / retention measurementsjet dynamic behavior / retention measurements

The reason for the shift is not fully

understood : MHD or plasma

effect?

shift believed to be due to 3-D

magnetic field structure &

gradients: detailed modelization is

required.

½” oxide-free gallium sample will be exposed to ISTTOK

plasmas for hydrogen retention measurements.

In depth (1m) sample analysis will be performed in a ion

beam laboratory.

Sample preparation chamber is currently being commissioned

& positioning system (with variable sample temperature

control) is ready.

Oxide-free gallium sample preparation

chamber schematic


27

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


28

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


29

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

ne

,lin

e [x

102

0 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


30

Dilution Problem

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


31

Te [KeV]264

Ip [MA]

.5

ne[1019 m-3]3

5

7

Te [KeV]

2

64

LH

ECH#27923P [MW]1

2

P [MW]

#30620LH

ECH0.40.3 0.5 0.6

1

2

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


32


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(

Mo

FeO


33


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


34


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


35

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

2.0

3.0

Ip [MA]

ne [x1020 m-3]

Te [KeV]

Neutrons/s [x1011]


36


Comparison of electron temperature profiles showing ITB formation

No PaddPadd=0.0MW

Padd=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


37

6

6.5

7

7.5after lith.after boron.

n e (x1019

m-3

)

1.6

1.8

2

Te (

KeV

)

1020304050

Pra

d/Poh

m (

%)

0.80.85

0.90.95

Vlo

op (

V)

time

1.2

1.41.61.8

0.6 0.8 1 1.2 1.4time (s)

Zef

f

Ohmic shots

Ip=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)


38

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


39

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(×

102

0 p

las

ma

pa

rtic

les

)


40

Thermal analysis

200

250

300

350

400

450

500

0 0.5 1 1.5 2

T1 (exp.)T2 (exp.)T3 (exp.)T2 (ANSYS)

Su

rfa

ce te

mp

era

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


41

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


42

Lithium

• Isotopic Abundances6Li 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.

Impurezze metalliche su scariche con il pellet

C.f.r P.Buratti, riunione TF A del 16/5/01

Le scariche disrompono per collasso radiativo quando:

Moecrite nBnn /105.3 235

Profili di temperatura alla fine del re-heating dopo il 1°, 2° e 3° pellet. L'iniezione di un 4° pellet provoca una disruzione.

Pellet discharges

32252 Lithium

25040

Electron Temperature

Time(s)

(KeV)


46

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

Documents

SEWG Meeting G. Mazzitelli Ljubljana 01/10/09 Experiments with the FTU liquid lithium limiter G. Mazzitelli a Many thanks to: M.L. Apicella a, V. Pericoli