EU Plasma-Wall Interaction Task Force meeting 13-15 November 2006 Lubljana, Slovenia "Interaction of a liquid Gallium jet with ISTTOK's edge plasmas: first.

EU Plasma-Wall Interaction Task Force meeting 13-15 November 2006 Lubljana, Slovenia

"Interaction of a liquid Gallium jetwith ISTTOK's edge plasmas: first

experimental results"

R. B. Gomes, H. Fernandes, C. Silva, ISTTOK team and the Latvian association

Associação EURATOM/IST, Centro de Fusão Nuclear, Av. Rovisco Pais, 1049-001 Lisboa, Portugal.


Introduction

Advantage of liquid metal as plasma facing components.

• protection capability.

• power exhaustion capability.

Metal candidates (Li, Ga, Sn…).

• Li : very good compatibility with plasmas (Z=3)

• Ga: wider temperature range: 30 to ~ 700 ºC (at 10-7 mBar)

Aim of the project:

• to verify the feasibility of ISTTOK operation with a LM limiter

• to study the influence of a Gallium jet on the main plasma parameters,

incl. impurity content, the plasma stability and confinement;

• to measure the heat deposited on the LM jet

• to study dynamic behaviour of liquid metal jets in a magnetic field


Experimental setup

LML design constraints:

• UHV ambient (10-6 mBar)

• Gallium Corrosion

• Gallium expansion

• Gallium oxidation

• Electrical isolation requirements


Testing of the Liquid Metal Loop outside ISTTOK chamber

Aim of this experimental campaign:

• Assess the operating conditions of the Liquid Metal Loop.

• Assess the reliability of every components of the system.

• Detailed characterization of the produced liquid metal jets.

• Study of the influence of magnetic field gradients on the jet in conditions as close as

possible to ISTTOK field.

Test conditions:

• Testing chamber: 33 mm diameter, 276 mm heigth pyrex tube.

• All the tests are performed with ~1,3 mGa pressure on the nozzle.

• Nozzle sizes tested: (1.45, 1.80, 2.09 and 2.30 mm).

• Measured parameters: jet flow rate, BUL and time to reach stability.

• Magnetic field: 0.25T, 60 ms pulse generated by two coils in the Helmoltz

configuration.


Results of the testing of the LML in the experimental rig

Achieved operating conditions compatible with ISTTOK operation.

Only non crictical failures in the LML components after one year operation

High speed jet movies used to check stability and BUL measurements

Stable jet sucessfully produced.

2,3 mm nozzle most suitable for ISTTOK operation: 13 cm BUL, 2.5 m/s flow velocity.

Tested magnetic field gradients do not affect the jet.


Installation of the LML in ISTTOK tokamak

ISTTOK’s experiment: (R=0.46 m, a=0.085 m, BT=0.45T, IP~4-8 kA, Vloop~4V).

Instalation of the LML from the test facility to the tokamak by modules: colector, injector, pumping + storage circuit. Ga in solid state and under Argon atmosphere to minimize oxidation.

Recovery of ISTTOK operating conditions and testing of magnetic field-jet interaction.

ISTTOK plasma discharges with Gallium jet interacting with plasma sucessfully performed.


Plasma-Gallium jet interaction in ISTTOK: first experimental results

Comparison of ISTTOK’s main parameters and radiated power with and without Gallium jet shows no evidence of strong plasma interaction

0 5 10 15 20 25 30

0

3

6

9

Vis

rad

(a.

u.)

Time (ms)

0,6

0,9

1,2

1,5

UV

rad

(a.

u.)

0

2

4

6

den

sity

(10

18 m

-2)

0

2

4

6

discharge with Gallium jet at r-a=2 cm discharge without Gallium jet

Ip (

kA)

0

2

4

Vlo

op

(V

)


Plasma-Gallium jet interaction in ISTTOK: Power measurement

Jet is not as efficient limiter : small area (2.3 mm thick, < ¼ perimeter).

Deposit power estimations:

• q[W/m2]=eT, e= jsat =0.5encs

• Copper wire with jet dimensions

Power density <2 MW/m2 , relevant as qjetq// (B ~ jet surface)

600 W (~5% Pin) for 30 ms <~20 J deposited in the jet 60 ºC increase in Gallium jet.

Significant damage in the copper wire


Plasma-liquid Gallium jet in ISTTOK: Spectroscopy measurements

Based on a ½ m imaging spectrograph+CCD camera and multifiber optics for collections: 5 points in the plasma (1,2 cm span)

Allows the measurement of Gallium and ions distributions in the plasma.

No lines of Gallium appears whithout jet

Distribution profiles shows high intensity for Ga in the vicinity of the jet and penetration of ions (Ga+ and Ga2+) into the center of the plasma


Plasma-liquid Gallium jet in ISTTOK: photodiode signals

Photosensor

at Ø=Øjet

Viewing port

Photosensor

at

Ø=Øjet+180º

Viewing port

0 5 10 15 20 25 30

0

400

800

1200

1600

2000

2400 without Gallium jet with Gallium jet in the chamber

H-a

lfa li

ne

inte

nsi

ty (

a. u

.)

Time (ms)

0 5 10 15 20 250

300

600

900

1200

1500

1800

without Gallium jet with Gallium jet in the chamber

Ga

lin

e in

ten

sity

(a

.u)

Time (ms)0 5 10 15 20 25 30

0

400

800

1200

1600

2000

H-a

lfa li

ne

inte

nsi

ty (

a. u

.)


Time (ms)

Interaction of Gallium with plasma appears to be only local

0 5 10 15 20 25

0

3000

6000

9000

12000

G

a li

ne

inte

nsi

ty (

a.u

)

Time (ms)



Conclusions

Plasma discharges with Gallium jet interaction doesn’t seem to significantly affect plasma performance.

Only Local effect. What would happen if Gallium would be the main limiter? (Unable to test in ISTTOK with the current setup).

After ~200 discharge of ISTTOK with Gallium there is not yet any clear signal of chamber conditions deterioration.

Future work:

• Absolute measurement of Gallium density profiles measurement by LIF

• Zeff diagnostic has to be implemented.

• Measurement of total power exaustion from plasma by jet.

• More detailed study of the jet-plasma interaction

EU Plasma-Wall Interaction Task Force meeting 13-15 November 2006 Lubljana, Slovenia "Interaction of a liquid Gallium jet with ISTTOK's edge plasmas: first.

Documents

plasma slide

plasma stability

isttok plasma discharges

gallium jet interaction

slovenia interaction

plasma performance

lm jet

main plasma parameters