Measurements of dust movement by fast TV camera in JT-60U Nobuyuki Asakura, H.Kawashima, N.Ohno 1), T.Nakano, S.Takamura 2), Y.Uesugi 3) 1) Japan Atomic.

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Measurements of dust movement by fast TV camera in JT-60U Nobuyuki Asakura, H.Kawashima, N.Ohno 1), T.Nakano, S.Takamura 2), Y.Uesugi 3) 1) Japan Atomic Energy Agency, Naka, 2) EcoTopia Science Institute, Nagoya Univ., Nagoya, 3) Graduate School of Engineering, Nagoya Univ., Nagoya, 4) Faculty of Engineering, Kanazawa Univ., Kanazawa 10th meeting of ITPA "SOL and divertor physics" Topical Group Jan.7-10, 2008, Avila

CONTENTS 1.Introduction: Dust collection results Dust transport in plasma Fast visible TV camera measurement 2. Dust movement in main chamber (Case-1, -2) 3. Dust movement at divertor in ELMy H-mode (Case-3, -4, -5) 4. Influence of dusts from outer divertor on main plasma (2007 Dec.) 5. Summary

Under baffle tiles 10.5ms (26mg/m2) 1. Introduction Dusts were collected in one poloidal section (1/32 toroidal area), and they have been deposited in W-shaped divertor operation (1997/1999 to 2003). Ref. Masaki, et al.J. Nucl. Mater (2005) 609 Dusts were cumulated on lower PFCs: not only tile surface but also under tiles of the outer baffle.(  fig.) larger number of dusts were cumulated under the divertor plates. (  next page) Dust collection from PFC(#10-section): Dusts in fusion devices potentially cause: Damage to Plasma Facing Components(PFCs) and viewing windows, Impurity source, Tritium reservoir in the shadowing area.

・ Collected dust was 170 mg (for 1/36 toroidal area): 95% was on the lower VV, and 90% was under the divertor plates: Number of dusts were found under divertor (shadow area) most dense area was under outer (Low-Field-Side) divertor and dome, i.e. on the exhaust route of gas flow by divertor pumping in experiments.

Dust production was smaller than C erosion at LFS divertor Erosion rate at LFS divertor surface Dust production rate is ~7% of averaged- erosion rate at outer divertor surface (3 mg/s). However, T-retention is potentially a problem in reactor: high (D+H)/C~ of co- deposition layers was found under dome. Extrapolation to total dust weight in the whole VV is 7 g ⇒ averaged Dust production rate is estimated to be ~0.2mg/s (7g is divided by NBI period of 3x10 4 s in shots) Carbon from the outer divertor may be transported and deposited to inner target. an order larger than co-deposition ratio at target and dome tiles. (Proc. 21th IAEA, Masaki et al.2006, EX-P4-14) ⇒ retention measurement in dusts should be required.

Dust transport in fusion plasma SOL flow F g (gravity) B // SOL plasma -q ErEr F E (Electro-static) F roc (ablation) F fric (friction) F fric FgFg B // Sheath plasma -q EpEp FEFE Drift flow SOL flow Dust in fusion plasma is generally charged negatively : Z ~ Dust movement ( M d dV d /dt = F ) is determined mainly by ・ F fric (friction force by SOL flow and diamagnetic & ExB drift flows), and F C (Coulomb scattering), ・ F E (electro-static force by potential) and F L (Lorentz force: small), ・ F g (gravitational force: small for normal size dust r d < 0.1mm), ・ F roc (rocket force by ablation: small for lower T d < K), Dust movement is influenced by PFC geometry (first wall, divertor), background plasma (core, SOL, sheath), plasma turbulence (blob, ELM). Dust mass ( M d ) is reducing by sputtering, RES, sublimation  Life time

Dust measurement with fast TV camera Visible light image was measured with fast TV camera from tangential port:  Typical frame rate of 2 kHz (1024x1024 pix, 3s) - 6 kHz (512x512 pix, 6s).  Narrow (9º) and wide (35º) viewing angles for divertor and main plasma, respectively, can be selected. Timing control (CAMAC) Camera & Image-Intensifier Lens shutter Memory& Controller Neutron shield (Photoron FastCAM II with full 6.5Gbyte memory)

2. Dust movement in main chamber (L-mode Hydrogen plasma during NBI in all graphite first wall) Fast TV scope was installed at the same port of CCD monitor camera Tangential viewing from P17 viewing port: CCD monitor camera outer baffle Inner baffle P12 P13 P14 NBI port P11 ICRF antenna I p, B t Dust trajectory /plume Dust movement or plume was observed only in one-two frames (30frame/s)

Dust movement in ELMy H-mode plasma NBI port (P12) Main TMP (P14) NBI port (P13) Divertor Good examples: many dusts were seen in high power ELMy H-mode plasmas (I p =1.8MA, B t =4T,P NBI =17MW) First wall photo from P17 Dust trajectory in main chamber has been measured in L-& H-mode plasmas. outer (LFS) midplane Divertor NBI port (P12) Main TMP (P14) NBI port (P13) Fast TV camera image at ELM Port edge (P17)

Dust movements in ELMy H-mode plasma (case 1) A number of dusts were observed, in particular, at start of the first NB shot after high I p plasma disruptions and overnight-GDC. t= 0ms (#1) t= 2ms (#4) t= 4.5ms(#9) t= 9ms(#18) t= 11ms(#22) t= 13ms(#26) t= 15ms(#30)t= 17ms(#34) Shot#46034 ： Start of an ELM even (at 5.26s) is defined as t = 0ms Dust-1 moves in nearly toroidal (ion drift) direction: V t ~4.5m(toroidal distance) / 14ms(28 frames) = 0.32km/s  similar to SOL flow direction, but V t was small (plasmaV // SOL ~10km/s)

28 frames (14ms) 18 frames (9ms) ELM Dust movements in ELMy H-mode plasma (case 1) Dust 2: moving in nearly radial direction (exhausted from NBI port): V r ~0.5m(radial distance)/9ms = 0.06km/s, then changing toroidally. Dust 3: moving in toroidal (ion drift) direction: V t ~2m/6.5ms =0.3km/s 13 frames (6.5ms) outer (LFS) midplane Divertor NBI port (P12) B t, I p Shot#46034

Fast movement across field lines in SOL (case 2) LFS midplane P14 Divertor After a few shots of the first NB shot, number of dusts decreased. ELM 8 frame (4ms) 25 frame (12.5ms) Dust 4: fast dust was observed towards toroidal&poloidal direction, V t/p ~2m (toroidal&poloidal distance)/4ms =0.5km/s 4 5 Dust 5: moving downward, V r ~0.5m (radial distance)/12.5ms =0.04km/s then accelerating toroidally or sublimated in edge ?. Shot#46034 ?

3. Dust movement at divertor in ELMy H-mode Better spatial and time resolutions are required for dust measurement in divertor: narrow viewing scope was used (  r ~3 mm, 4-6 k-frame/s) 512x512 (6k frame/s) A few dusts were observed in most ELMy H- mode plasmas for normal strike-point location. LFS baffle HFS baffle dome LFS divertor 512x x512 Viewing port edge

Dusts were ejected into inner (HFS) divertor (Case 3) Dusts were ejected into HFS divertor after ELMs: when the inner strike-point was at upper target (on carbon-deposition layers), ⇒ Part of deposition layers was removed by ELM heat and particle fluxes. Plume of C- and D-ionization from dust along the field line. 512x512 (6k frame/s) Dusts move outward and toroidally (ion drift direction). t= 0ms(#1) t= 0.67ms(#5) t= 3ms(#19) t= 3.5ms(#22) t= 4.3ms(#22) t= 4.8ms(#30) t= 5.2ms(#32) t= 6.3ms(#39) t= 7.8ms(#48) dust1 dust2 Shot#46950 dust1

Various size of dusts are ejected after ELMs (Case 3, 4) 17 frames (3ms) 32 frames (5.5ms) HFS divertor Case 3: Two large dusts from HFS divertor Most dusts move in outboard and toroidal (ion drift / fast SOL flow) direction with similar velocity ( km/s): Case 3: V t = 0.8m/2.7ms ~0.3km/s, and V t = 1m/5.5ms~0.2km/s Case 4: V t = 0.5m/2ms ~0.25km/s, and V t = 0.5m/1.7ms~0.3km/s ELM dust1 dust2 many dusts from inner divertor Case 4: Many small dusts from HFS divertor ELM t = 4.8ms(#30) dust1 dust2 t = 4.8ms(#30) 12 frames (2ms) 10 frames (1.7ms)

Dust movement from outer divertor changed at ELM (case 5) 1024x512 (4k frame/s) t= 0ms(#22)t= 0.25ms(#23)t=-0.5ms(#20) t=-1.5ms(#16)t=-2.75ms(#11)t=-5.25ms(#1) t= 1ms(#26)t= 1.75ms(#33)t= 2.75ms(#37) Shot#46953 ： Start of an ELM even is defined as t = 0ms Case 5: Dust from outer divertor is moving towards the main plasma.  After ELM, the direction is reversed towards the outer baffle. dust2

ELM affects dust movement away from separatrix (Case 5) Dust-1 from outer divertor was moving: towards separatrix in radial/poloidal direction,V p/r ~0.25m/5ms =0.05km/s 40 frames (10ms) HFS divertor HFS baffle 16 frames (4ms) Dust-2 from inner divertor moves in toroidal direction:V t ~1m/4ms=0.25km/s 1024x512 ELM This was not seen at main plasma edge: more examples will be necessary. dust2 dust1 then, away from separatrix in radial direction, V r ~0.2m/4ms =0.05km/s Shot#46953

4. Dust from outer divertor and influence on main plasma However, large numbers of dusts were recently seen in some std. ELMy H- mode plasmas (P NBI =12-16MW): strike-point is located on toroidal W-band  C 5+ line at edge was enhanced by 3-5 times (but W was not enhanced). NBI port (P12) Main TMP (P14) NBI port (P13) Divertor First wall photo from P17 Relatively (2007 Dec.) many dusts were seen in some NB shots every days: No influence on carbon/metal lines(VUV) & Brems. signals was seen. Outer target tiles with VPD W-band (1cm width,5  m thick) 119mm 77mm Shadow area Torodal direction Lower target tile Upper target tile Erosion area

Mostly C dusts were ejected from the outer target with small toroidal velocity (here, W ion was large in core region) 16 frames (8ms) Dust movements from outer divertor (one of worst example) Dust 1: moving to core, change the direction: V r/p ~1m/17ms = 0.06km/s. Dust 2: moving to main plasma  sublimation?: V p ~1m/8ms =0.13km/s outer (LFS) midplane Divertor NBI port (P12) B t, I p Port edge (P17) CFC tile with ribbon-W (P14) was not seen by port edge 34 frames (17ms) dust1 dust2 dust1 dust2 Dusts ejected from outer target move poloidally/radially (small friction?).

5. Summary Trajectory and velocity of dust (emission) in ELMy H-mode plasmas were measured with a fast TV camera from tangential port. In main chamber, number of dusts with various directions were observed, particularly after hard disruptions (large  W dia ) and overnight GDC. Many dusts were ejected from deposition layer near INNER strike-point after ELMs: large heat and particle loading enhance thermal expand/RES. ・ Velocity of nearly toroidal /poloidal movement ( km/s) was faster than that of nearly radial movement ( km/s). ・ The toroidal movement was mostly ion drift (I p ) direction: it is consistent with SOL flow measurement in HFS and LFS SOLs. ・ The radial movement (at LFS divertor) was affected by ELM events: inward movement from LFS divertor changed to outward (after ELM). ・ Dust ejection did not correlate to the main n C & Z eff. But influence of many dust ejections on main plasma were recently observed. Future work and proposals: UEDGE/DUSTT simulation for dynamics study started by Kanazawa Univ. Measurement from different angles is required for accurate trajectory.