Dust Studies in Fusion Devices
D.L. RudakovPresented at the PFC MeetingBoston MA July 7-10, 2009
Including contributions fromA. Litnovsky, N. Asakura, N. Ashikawa, G. DeTemmerman, S. RatynskaiaJ.Yu
10 µm
Bt
Dust in ITER – a Licensing Issue
Dust accumulation is a licensing issue in ITER:The total in-vessel dust inventory in ITER will be limited to 1 tonne; a lower administrative limit of 670 kg has been proposed to take account of measurement uncertainties
The enhanced chemical activity of Be and C dust at high temperatures is more restrictive and a limit of ~10 kg for Be and C dust on hot surfaces (T > 400 C) is being considered
From operational standpoint, small amounts of W dust (<< 1 g) reaching core plasma can increase W concentration to unacceptable levels
Proposed Dust R&D work plan under ITPA DSOL1. Characterize dust production rates, recover conversion factor from
erosion/damage to dust production High priority• Link the quantity of collected dust to erosion/damage • Local dust production rates at different surfaces and in volumeTEXTOR, ASDEX-U, Tore Supra, JT-60U, DIII-D, LHD, MAST, NSTX, FTU, EAST…
2. Characterisation of ejection velocities, sizes of molten droplets and the morphology and size distributions of collected dust High priorityTRINITI, QSPA, PISCES
3. Study the role of T removal techniques in dust creation: subject samples of re-deposited material to transient heat fluxes, photonic and plasma, as well as oxygen cleaning. Quantify the dust created Medium priorityTRINITI, QSPA, PISCES, U. Toronto, Pilot-PSI,….
4. Cross-machine studies of dust injection DSOL-21 High priority • Investigate of dust launch velocities and subsequent transport • Benchmarking against dust transport models
DIII-D, TEXTOR, LHD, MAST, NSTX, AUG5. Dust measurements High priority
• Dust collection (see task #1)• Time-resolved detection: visible and IR imaging, electrostatic detectors,
capacitive microbalance, spectroscopy, Aerogel
6. Dust removal Medium priority
ITER
IO u
rgen
t tas
ks
LWIR camera view 4
Stereoscopic dust imaging
MWIR camera view 4
0 50 100 150 200 250 3000
20406080
100120140160180200220240
Pixe
l Y
Pixel X
Particle 1 Particle 2 Particle 3 Particle 4
MWIR
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20406080
100120140160180200220240
Y pi
xel
Pixel X
Particle 1 Particle 2 Particle 3 Particle 4
LWIR
Camera configuration/location easily changed on MAST (no need for periscope)
2 synchronized IR cameras installed on the same port (slightly shifted toroidally)
LWIR camera: 5mm resolutionMWIR camera: 7mm resolution
Stereoscopic imaging of dust motion in MAST
Contribution from G. DeTemmerman
Stereoscopic imaging of dust motion in MAST
Contribution from G. DeTemmerman
0.81.0
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-0.4 -0.2 0.0 0.2 0.4
Z (m
)
Y (m)
X (m
)Reconstructed tracks for MAST shot 19374 (2008 restart)
Particles are accelerated in the direction of the plasma flow
Slower particles seem to follow the field lines
Faster particles move outwards
Range of observed particle velocities: 10-60 m.s-1
Faster particles observed but need more analyses
3D reconstruction of particle trajectory in LHD
LHD LHD centercenter
D1
Reflection
Dust
Using camera position, virtual plane of dust and reflected images, real dust position is determined.
- Reflected image must be located on the first wall.
-Incident angle from dust to the wall is determined.
Contribution from N. Ashikawa
Recent result of dust in JT-60U: Dust distribution in plasma discharge was measured with YAG laser scattering (Mie scattering)Significant numbers of event signals (scattering light from dust) were observed just after large disruption (high Ip and Wdia > 3MJ): also measured by TV camera.
They stayed, particularly, at the far SOL. Number density and its size are decreased near the separatrix, suggesting that ablation becomes dominant near the separatrix.
0
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6049530495334953649537
SOL edge core
after disruptionafter normal shot
0 5 10 15YAG ch#
(ch5-6)core
SOL
shots after disruption (49530,3,6)
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ch1
0 0.5 1 1.5 2 2.5Intensity (au)
edge(ch11-13)
Contribution from N. Asakura
TEXTOR: Multi topical research programIn-situ detection of natural dust Ex-situ analyses of natural dust
Studies of artificially introduced dust
Shot 106265 t=1580 msec.Bt
Shot 106265t=1660 msec.
Bt
Dust launch, horizontal view of the limiter (CIII filter)
Dust launch, vertical view of the limiter (no filter)
1
2
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4 56
4
Dust sampling places: deposition (1) and erosion (2) zones on
ALT tiles, bottom of the liner (3), mainpoloidal limiters (4), DED bottom
shield (5) and DED tiles (6)
Fast probe equipped with aerogel catchers for detection of dust particles in the SOL plasmas of TEXTOR
Work made within the programs of EU TF PWI: WP09-PWI-03-01
and WP09-PWI-03-02, IEA-ITPA joint Experiments, task DSOL
21 and bilateral collaborations.
DSOL 21
2009
Dust density and energies of dust
particles
Dust mobilization, motion and impact on core and edge plasmas
Dust inventory, fuel retention in dust and particle size distribution
Contribution from A. Litnovsky
TEXTOR: summary of resultsIn-situ detection of natural dust Ex-situ analyses of natural dust
Studies of artificially introduced dust
No effect on the core performance;Carbon concentration in the edge rose from ~3% to ~6%, implying that around 0.01% of launched dust carbon entered the edge plasmas;Dust primarily deposited locally on the nearby located plasma facing components.
The total amount of collected loose „dust” is below 2 grams;Co-deposits peel-off when exposed to air;Long-term (3 days) baking of co-deposits at 350oC releases only 8-10% of deuterium;Efficient fuel removal requires baking to 800oC –1000oC.
.
Most of dust was collected during a flat-top phase of a discharge;Size of collected particles: from submicron up to hundreds of micrometers;Dust density assessment up to ~ 140 dust particles per sq.cm2.
Contribution from A. Litnovsky
New Dust Collection Technique: AerogelHighly porous, very low density material
Used in space programs to collect dust
Allows capture of dust particles without destroying them
From the penetration depth particle velocity can be derived
First tests of aerogel performed in HT-7 and TEXTOR
Example of EDX of the aerogel with C particle in it
Contribution from A. Litnovsky and S. Ratynskaia
Title: Introduction of pre-characterized dust for dust transport studies in the divertor and SOL
Goals:Characterization of core penetration efficiency and impact of dust of varying size and chemical composition on the core plasma performance in different conditions and geometries
Benchmarking of DustT and DTOKS modeling of dust transport and dynamics
Machines: DIII-D, TEXTOR, MAST, NSTX, LHD, AUG
Recent experiments: DIII-D, MAST, TEXTOR
New ITPA Joint Experiment DSOL-21
Motivation for Dust Injection and Technique Used
The aims of the dust injection:Calibrate dust diagnosticsBenchmark modeling of dust dynamics
Different types of dust are used: Graphite flakesGraphite spheresDiamond
Suspension of ~30-40 mg of dust in ethanol loaded in a graphite holder and allowed to dry
Holder with dust inserted in the lower divertor of DIII-D using Divertor Material Evaluation System (DiMES) manipulator
5 µm
10 µm
10 µm
Spherical graphite dust manufactured by Tokai Carbon Co (Japan), provided by Naoko Ashikawa (NIFS)
Spherical shape, narrow size distribution –good to benchmark modeling!
Suspension of ~30 mg of dust in ethanol loaded in a graphite holder and allowed to dry
~10 mg of loose dust sprinkled on top
Newest Results from DIII-D – Injection of Spherical Dust
10 µm
Diameter (µm)
Dried dust “crust”
Loose dust
Dust from DiMES kills the discharge
Full light, 2000 f/s, total duration ~ 90 ms
Shot number 136002
DiMES
Dust becomes visible 13 ms into the dischargeFrom the fast camera data, dust velocities are low, ≤10 m/sDust could not travel a from DiMES into camera view in 13 msThomson scattering diagnostic observed high level of scattered signal starting 300 ms before the discharge (when it was turned on)
Dust must have become mobile and spred around the vacuum vessel prior to the dischargeThe physical mechanism that mobilized and spred the dust is presently unclear. Best guess: dust charged up and got mobilized when the E-coil was turned on ~400 ms before the discharge
Can this happen in ITER?• Tritiated dust can charge up and levitate in electric field
[C. Skinner et al., Fus. Sci. Technol. 45 (2004) 11]• If 10 mg of dust can prevent DIII-D discharge from running,
~1 g may do that in ITER
Observations From Spherical Dust Injection
Dust injection experiment on MAST
16
Injection of known shape/size particles in the divertor plasma to study transport
Design of the dust injection head Minimize the amount of particles introduced at once to maximize the chances of observation
Tungsten dust
50 µm
D. Rudakov (UCSD)Provided by Buffalo tungsten (USA)
Observation with 2 IR cameras + 1 filtered fast camera (CII, WI)
Contribution from G. DeTemmerman
+V. Mixed (W+C) dust – a combination of I and IV
Manufactured by Toyo Tanso Co (Japan), supplied by Dmitry Rudakov
10 µm0.1 1 10 100
Frac
tion
(a.u
.)Diameter (µm)
Photo and analysis by Phil Sharpe
10 µm Diameter µm)
Manufactured by Tokai Carbon Co (Japan), supplied by Naoko Ashikawa (NIFS)
5 µmDiamond dust by DiamondTech:
http://www.diamondtech.com
Supplied by Dmitry Rudakov
Tungsten dust manufactured by Buffalo tungsten (USA)
Supplied by Gregory De Temmerman
TEXTOR experiment was with 4-8 micron
dust, photo on the left is of 2-4 micron
dust
III. Diamond dust IV. Tungsten dust
I. Carbon flake-like dust II. Carbon spherical “killer” dust
Dust injection campaign on TEXTOR
Contribution from A.Litnovsky
Slow and fast motion of dust
Spherical carbon “killer” dust Diamond dust# 110271
Bt
# 110258
Bt
Valid for both conductive and dielectric dust
It seems, that two independent types of motion co-exist:
2. Really slow (v2~1-5 m/s) motion of the entire mass of dust across B field
1. Relatively fast (v1>100 m/s) motion of individual dust particles along B field;
# 110274Launch of W+C dust
Recorded from fast camera
Bt
Bt
Contribution from A.Litnovsky
The following are preliminary results
