N. Nishino, T. Mizuuchia, S.Kobayashia, S.Yamamotoa, H.Okadaa, K.Nagasakia, T.Minamia, F.Sanoa

ISHW20092009/10/13

PPPL

Peripheral plasma measurement in Heliotron J using fast cameras

Graduate School of Engineering, Hiroshima Universitya Institute of Advanced Energy, Kyoto University

Introduction Background

Various methods of peripheral plasma study (movable Langmuir probe, Mach probe, magnetic probe, and Supersonic molecular beam injection=SMBI, and fast cameras) are available in Heliotron J

Using fast cameras filamentary structure in peripheral plasma were observed successfully and the apparent motion of these filaments was identified in L-mode, L-H transition and H-mode.

Aim To understand the relationship between energy/particle

confinement properties and peripheral plasma behavior clearly using combination of fast cameras and peripheral plasma measurement.

Recently in the SMBI experiment the best performance of stored energy plasma was obtained in Heliotron J.

Using fast cameras we examine SMBI effect on peripheral plasma behavior.

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3

Filament motion during L- and H-mode

Apparent rotation direction was measured with tangential view

up

Field of view from tangential port(Initial discharge phase)

Thomson scattering window

ICRF

R

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Behavior during L- and H-mode, transition

From left, the picture of L-mode, transition, H-mode (40000FPS)

Anti-clockwise motion of filament was observed in L-mode In H-mode

filament rotated inversely

Structure was not easily seen during transition with raw image

Two-dimensional phase diagram for L to H transition

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To look the motion of filaments easily, using time-dependent FFT the phase of each pixel with the strong Fourier component are shown.

250ms-265ms (40,000FPS)

0.1

0.15

0.2

250 255 260 2650

0.1

0.2

time (ms)

Diamag

H

Apparent rotation of H-mode was inverse that of L-mode.Rotation speed in H-mode was almost double comparison with that of L-mode.During transition the rotation stopped.

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Two-dimensional phase diagram （ L-mode)

Time

Time

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Two-dimensional phase diagram （ transition)

Time

Time

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Two-dimensional phase diagram （ H-mode)

Time

Time

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Apparent motion = Plasma rotation ? If these apparent motion would indicate plasma rotation, the

rotation speed in polodal direction is roughly estimated ~ 3000m/s in H-mode, and ~-1500m/s in L-mode.

If the rotation mechanism would be EXB, then Er=~-2kV/m in H-mode Er=~+ １ kV/m in L-mode

During the transition it looks like the motion of filament stopped.

Also, the motion of filament dithered sometimes. From Langmuir probe signal during dithering period low frequency

perturbation was suppressed, and it was the same as Phase I in Heliotron J

In Heliotron J experiment, Phase I does not have high confinement characteristics such as H-mode. However, the electron density was controlled during Phase I.

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ECH+NBI+SMBI

Movable probe

SMBIITC16

Magnetic probe

SMBI

Reverse B

Phase I in Heliotron J was maintained due to SMBI Success to avoid the ‘radiation collapse’ using SMBI

Normal B

190 200 210 220 2300

0.25Diamag

0

0.1

0.2#3.5

0

0.1 #7.5

0

0.25#11.5

0

0.25#15.5

Density

Waveform of successful SMBI plasma

Target Plasma ECH+NBI

Time of SMBI is shown as red line

H near SMBI

H

H

H far SMBI

time (ms)

#32816

Raw data of SMBI at the fastest speed

(red & blue)

#30131

180,000FPS

ICRF antenna

Motion of filamentary structure is shown.

Near the ICRF antenna was very bright.It should be due to plasma-surface interaction.

As a streaming camera

To look the fast movement easily, the streaming method is also useful.

This line is almost perpendicular to filamentary structure

Apparent motion of filaments was almost L-mode,However, sometimes the motion direction changed. Phase I in Heliotron J

Power spectra of point data

Time dependent FFT is applied to the specific point data to get the power spectra.

Point is shown in the left figure.

SMBI SMBIThis point is on the previous line.

Question for the Power spectra

SMBI affected the power spectra in frequency domain.

Although, Typical H signal showed that light intensity lasted ~10ms. However, the effect of SMBI in frequency domain at the

specific point did not last so long time. Typical period of strong turbulent signal in frequency

domain was a few ms.

Amplitude of apparent k-spectra on the line

Using FFT, we can transform the streaming data to apparent wave-number k domain.

Apparent k-spectra shows that SMBI affects long period.

Low k was omitted due to the ICRF antenna structure.

SMBI SMBI

If line angle was parallel to filament,

SMBI did not affect so much on the space parallel to filament (probably parallel to the magnetic field line)

Neutral particle does not affect the magnetic field, and vice versa.

SMBI SMBI

SMBI perturbs kperp on space strongly. Also, it looks that SMBI perturbs kperp domain rather than the frequency domain.

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Comparison plasma features with and without SMBI

180 200 220 240 2600

0.10.20.3

time (ms)

DIA

MA

G (

A.U

.) 0

0.2

0.4

Ha

(A.U

.)

0

0.5

1

1.5

00.10.20.30.40.5

NB

I

EC

H

-1.5

-1

-0.5

0Ne

(1013

cm-2

)

SMBI

NBI & ECH

H signal(near SMBI)

electron density

Diamagnetic signal

180 200 220 240 2600

0.1

0.2

0.3

time (ms)

DIA

MA

G (

A.U

.) 0

0.2

0.4

Ha

(A.U

.)

0

0.5

1

1.5

00.10.20.30.40.5

NB

I

EC

H

-1.5

-1

-0.5

0Ne

(1013

cm-2

)

#32783#32816

Diamag signal goes up due to SMBI !!

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Comparison magnetic probe

signal with and without

SMBI

Fluctuation in the low frequency region was suppressed due to SMBI.

Is this the reason that the energy confinement of SMBI plasma is better than that of L-mode w/o SMBI ?

GAE were observed in the middle frequency region, but they are not the matter for this presentation.

SMBI

Suppression with fluctuation in the low frequency range

The end of plasma due to lose the input power

Fluctuation in the low frequency range continued to the end of plasma

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Summary of Phenomenology on SMBI

Magnetic probe signal Low frequency fluctuation was suppressed due to SMBI

Fast camera image Dithering of the apparent motion of filaments SMBI affected both Fourier components for frequency

and apparent kperp-domain, but it affected strongly kperp-domain

Plasma performance Electron density rose over the L-H threshold, however,

radiation collapse did not always occur. Confinement properties may not so much such as H-

mode Phase I state continued due to SMBI. Therefore, it was inferred that particle confinement of

Phase I was worse than that of H-mode.

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Conclusion

Using fast cameras peripheral plasma behavior was measured successfully in Heliotron J plasma

Apparent motion of filamentary structure in the camera image was looked like rotation, and its direction in L-mode was inverse that in H-mode.

That motion was coincidence with ExB poloidal rotation predicted by many theory.

Probably SMBI affects the wave number domain rather than the frequency domain.

However, SMBI physics is still unknown. To understand the interaction between SMBI and peripheral plasma is the urgent problem to be solved.

Peripheral plasma behavior such as filamentary structure should be understood in the near future.

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Experimental condition

Discharge & Additional heating ECH ECH+NBI

Fueling Gas puff (normal) Supersonic Molecular Beam Injection (SMBI)

Plasma condition L-mode Phase I H-mode

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Measurement of ECH plasma

Langmuir probe and fast camera measurement simultaneously

Normal direction with Horizontal port

Langmuir probe

Object Lens

105000FPS64x64pixels

timeFilamentary structure

Probe head

0

5

10

15

20

25

30

0 0.5 1 1.5 2 2.5 3

time (ms)

Num

ber

ne 2.6≧ x1019m-3

Fig. 1 Life time profile of bursts estimated by eye

Filament-like structure was measured

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Change of filamentary structure before and after L-H transition

L-H transition

L-mode Just after transition

H-mode

before H-L transition

SMBI (L-mode)

＃ 21448 ：　 80,000FPS

Strong fluctuation L-mode H-mode SMBI

I II III IV

Two-dimensional phase diagram

Time dependent FFT on other point

FFT results depend on the point position? Fast camera views SMBI, therefore we need to

compare the other images that does not include SMBI directly?

May be yes?

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SMBI

Apparent k domain

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SMBI

SMBI

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Future plan

Combination of various peripheral plasma measurement More probes Density measurement Thomson scattering

Combination with Spectroscopy Fast two-dimensional spectroscopy using Liquid

Fabry-Perot Interferometer

Fast Plasma-Surface measurement

Development of the image analysis

Find peak apparent-k value

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For example: time slice at 202.5ms

FFT at peak value of k-profile

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Low k peak has low frequency peak region, and High k peak has high frequency peak

Low k & low freq.