Dust Studies in Fusion Devices D.L. Rudakov Presented at the PFC Meeting Boston MA July 7-10, 2009 10 µm Including contributions from A. Litnovsky, N. Asakura, N. Ashikawa, G. DeTemmerman, S. Ratynskaia J.Yu B t
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 DSOL 1. 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 volume TEXTOR, 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 priority TRINITI, 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 priority TRINITI, 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, AUG 5. 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 urgent tasks
Stereoscopic imaging of dust motion in MAST Camera configuration/location easily changed on MAST (no need for periscope) 2 synchronized IR cameras installed on the same port (slightly shifted toroidally) Stereoscopic dust imaging LWIR camera: 5mm resolution MWIR camera: 7mm resolution Y pixel 240 220 200 180 160 140 120 100 80 60 40 20 LWIR camera view 4 Particle 1 Particle 2 Particle 3 Particle 4 0 0 20 40 60 80 100 120 140 160 180 200 220 240 Pixel X LWIR Pixel Y MWIR camera view 4 240 220 200 180 MWIR 160 140 120 100 80 60 40 20 0 0 50 100 150 200 250 300 Pixel X Particle 1 Particle 2 Particle 3 Particle 4 Contribution from G. DeTemmerman
Stereoscopic imaging of dust motion in MAST Reconstructed tracks for MAST shot 19374 (2008 restart) Z (m) X (m) -1.55-1.60-1.65-1.70-1.75-1.80 0.8 1.0 1.2 1.4-0.4-0.2 0.0 0.2 0.4 Y (m) 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 Contribution from G. DeTemmerman
3D reconstruction of particle trajectory in LHD Dust Reflection D1 LHD center 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 I p and W dia > 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. 60 50 40 30 20 10 SOL edge core after disruption after normal shot 49530 49533 49536 49537 0 0 5 YAG ch# 10 15 shots after disruption (49530,3,6) 10 ch1 SOL Contribution from N. Asakura 1 core (ch11-13) edge (ch5-6) 0 0.5 1 1.5 2 2.5 Intensity (au)
TEXTOR: Multi topical research program In-situ detection of natural dust Dust density and energies of dust particles Ex-situ analyses of natural dust Dust inventory, fuel retention in dust and particle size distribution Fast probe equipped with aerogel catchers for detection of dust particles in the SOL plasmas of TEXTOR Studies of artificially introduced dust Dust mobilization, motion and impact on core and edge plasmas B t Shot 106265 B t t=1580 msec. t=1660 msec. Shot 106265 Dust launch, vertical view of the limiter (no filter) DSOL 21 2009 Dust launch, horizontal view of the limiter (CIII filter) 2 1 3 4 4 Dust sampling places: deposition (1) and erosion (2) zones on ALT tiles, bottom of the liner (3), main poloidal limiters (4), DED bottom shield (5) and DED tiles (6) 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. 5 6 Contribution from A. Litnovsky
TEXTOR: summary of results In-situ detection of natural dust Most of dust was collected during a flattop 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.cm 2.. 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. Ex-situ analyses of natural dust 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 350 o C releases only 8-10% of deuterium; Efficient fuel removal requires baking to 800 o C 1000 o C. Contribution from A. Litnovsky
New Dust Collection Technique: Aerogel Highly 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
New ITPA Joint Experiment DSOL-21 Title: Goals: Introduction of pre-characterized dust for dust transport studies in the divertor and SOL 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
Motivation for Dust Injection and Technique Used The aims of the dust injection: Calibrate dust diagnostics Benchmark modeling of dust dynamics 10 µm Different types of dust are used: Graphite flakes Graphite spheres Diamond 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 10 µm 5 µm
Newest Results from DIII-D Injection of Spherical Dust Spherical graphite dust manufactured by Tokai Carbon Co (Japan), provided by Naoko Ashikawa (NIFS) Spherical shape, narrow size distribution good to benchmark modeling! 10 µm 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 Diameter (µm) Dried dust crust Loose dust
Dust from DiMES kills the discharge Shot number 136002 DiMES Full light, 2000 f/s, total duration ~ 90 ms
Observations From Spherical Dust Injection Dust becomes visible 13 ms into the discharge From the fast camera data, dust velocities are low, 10 m/s Dust could not travel a from DiMES into camera view in 13 ms Thomson 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 discharge The 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
Dust injection experiment on MAST Injection of known shape/size particles in the divertor plasma to study transport Tungsten dust 50 µm D. Rudakov (UCSD) Provided by Buffalo tungsten (USA) Design of the dust injection head Minimize the amount of particles introduced at once to maximize the chances of observation Observation with 2 IR cameras + 1 filtered fast camera (CII, WI) Contribution from G. DeTemmerman 16
Dust injection campaign on TEXTOR I. Carbon flake-like dust II. Carbon spherical killer dust Photo and analysis by Phil Sharpe 10 µm Fraction (a.u.) 0.1 1 10 100 Diameter (µm) Manufactured by Toyo Tanso Co (Japan), supplied by Dmitry Rudakov III. Diamond dust 10 µm Diameter µm) Manufactured by Tokai Carbon Co (Japan), supplied by Naoko Ashikawa (NIFS) IV. Tungsten dust TEXTOR experiment was with 4-8 micron dust, photo on the left is of 2-4 micron 5 µm dust Diamond dust by DiamondTech: http://www.diamondtech.com Supplied by Dmitry Rudakov +V. Mixed (W+C) dust a combination of I and IV Contribution from A.Litnovsky Tungsten dust manufactured by Buffalo tungsten (USA) Supplied by Gregory De Temmerman
Slow and fast motion of dust The following are preliminary results It seems, that two independent types of motion co-exist: 1. Relatively fast (v 1 >100 m/s) motion of individual dust particles along B field; 2. Really slow (v 2 ~1-5 m/s) motion of the entire mass of dust across B field Spherical carbon killer dust # 110258 Valid for both conductive and dielectric dust Diamond dust # 110271 B t B t B t B t # 110274 Launch of W+C dust Recorded from fast camera Contribution from A.Litnovsky