measurements of dust movement by fast tv camera in jt-60u nobuyuki asakura, h.kawashima, n.ohno 1),...

Measurements of dust movement by fast TV camera in JT-60U

Nobuyuki Asakura, H.Kawashima, N.Ohno1), T.Nakano, S.Takamura2), Y.Uesugi3)

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. 337-339 (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~0.7-0.8 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 3x104s in 13000 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

Fg (gravity)

B//

SOL plasma

-q

ErFE (Electro-static)

Froc (ablation)

Ffric (friction)Ffric

Fg

B//

Sheath plasma

-q

Ep

FE

Drift flow

SOL flow

Dust in fusion plasma is generally charged negatively : Z ~ 103-104

Dust movement ( MddVd /dt = F ) is determined mainly by ・ Ffric (friction force by SOL flow and diamagnetic & ExB drift flows), and FC (Coulomb scattering),・ FE (electro-static force by potential) and FL (Lorentz force: small),・ Fg (gravitational force: small for normal size dust rd < 0.1mm),・ Froc (rocket force by ablation: small for lower Td < 2000-3000K),Dust movement is influenced by PFC geometry (first wall, divertor), background plasma (core, SOL, sheath), plasma turbulence (blob, ELM).Dust mass (Md) is reducing by sputtering, RES, sublimation Life time

neutron shield

Fast TV camera& Optical system

Mechanical shutter Interference-filter

Camera Memory & Controller

Timing control system

Ip start

Ethernet+Optical link

JT-60U machine room

15m

scope

JT-60U

Viewing divertor area with Δ~3mm

-Image guide

Control room:PC

,Camera control ,Data acquisition Timing pulse control

Dust measurement with fast TV cameraVisible 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 shieldViewing main plasma with Δ~1cm

(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

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outer baffleIn

ner

baffle

P12P13 P14

NBI port

P11

ICRF antenna

Ip, Bt

Dust trajectory/plume

Dust movement or plume was observed only in one-two frames (30frame/s)

Dust movement in ELMy H-mode plasma

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NBI port (P12)

Main TMP (P14)

NBI port (P13)

Divertor

Good examples: many dusts were seen in high power ELMy H-mode plasmas (Ip=1.8MA, Bt=4T,PNBI=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 Ip plasma disruptions and overnight-GDC.


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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

1

2

3

4

Dust-1 moves in nearly toroidal (ion drift) direction: Vt ~4.5m(toroidal distance) / 14ms(28 frames) = 0.32km/s similar to SOL flow direction, but Vt 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): Vr ~0.5m(radial distance)/9ms = 0.06km/s, then changing toroidally.Dust 3: moving in toroidal (ion drift) direction: Vt ~2m/6.5ms =0.3km/s

13 frames (6.5ms)

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Divertor

NBI port (P12)

12

3

4

Bt, Ip

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,

Vt/p ~2m (toroidal&poloidal distance)/4ms =0.5km/s

4

5

Dust 5: moving downward, Vr ~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-modeBetter 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

domeLFS divertor

512x5121024x512

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 (0.2-0.3km/s):

Case 3: Vt = 0.8m/2.7ms ~0.3km/s, and Vt = 1m/5.5ms~0.2km/s

Case 4: Vt = 0.5m/2ms ~0.25km/s, and Vt = 0.5m/1.7ms~0.3km/s

ELM

dust1dust2



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,Vp/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:Vt ~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, Vr~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 (PNBI=12-16MW): strike-point is located on toroidal W-band C5+ line at edge was enhanced by 3-5 times (but W was not enhanced).

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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.

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Outer target tileswith VPD W-band (1cm width,5m thick)

119

mm

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: Vr/p ~1m/17ms = 0.06km/s.Dust 2: moving to main plasmasublimation?: Vp ~1m/8ms =0.13km/s


Divertor

NBI port (P12)

Bt, Ip

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 ΔWdia) 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 (0.2-0.5km/s) was faster than that of nearly radial movement (0.03-0.06km/s).

・ The toroidal movement was mostly ion drift (Ip) 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 nC & Zeff. 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.

measurements of dust movement by fast tv camera in jt-60u nobuyuki asakura, h.kawashima, n.ohno 1),...

Documents

divertor plates

divertor pumping

divertor shadow

outer divertor surface

measurements of dust

gaveraged dust production

dust mass md

total dust weight