eu plasma-wall interaction task force meeting 13-15 november 2006 lubljana, slovenia...
TRANSCRIPT
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.
EU Plasma-Wall Interaction Task Force meeting 13-15 November 2006 Lubljana, Slovenia
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
EU Plasma-Wall Interaction Task Force meeting 13-15 November 2006 Lubljana, Slovenia
Experimental setup
LML design constraints:
• UHV ambient (10-6 mBar)
• Gallium Corrosion
• Gallium expansion
• Gallium oxidation
• Electrical isolation requirements
EU Plasma-Wall Interaction Task Force meeting 13-15 November 2006 Lubljana, Slovenia
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.
EU Plasma-Wall Interaction Task Force meeting 13-15 November 2006 Lubljana, Slovenia
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.
EU Plasma-Wall Interaction Task Force meeting 13-15 November 2006 Lubljana, Slovenia
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.
EU Plasma-Wall Interaction Task Force meeting 13-15 November 2006 Lubljana, Slovenia
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
)
EU Plasma-Wall Interaction Task Force meeting 13-15 November 2006 Lubljana, Slovenia
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
EU Plasma-Wall Interaction Task Force meeting 13-15 November 2006 Lubljana, Slovenia
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
EU Plasma-Wall Interaction Task Force meeting 13-15 November 2006 Lubljana, Slovenia
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
.)
without Gallium jet with Gallium jet in the chamber
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)
without Gallium jet with Gallium jet in the chamber
EU Plasma-Wall Interaction Task Force meeting 13-15 November 2006 Lubljana, Slovenia
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