N. Nishino, T. Mizuuchi a, S.Kobayashi a, S.Yamamoto a, H.Okada a, K.Nagasaki a, T.Minami a, F.Sano a ISHW /10/13 PPPL Peripheral plasma measurement in Heliotron J using fast cameras Graduate School of Engineering, Hiroshima University a 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. 2

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

4 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 5 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) time (ms) Diamag H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.

6 Two-dimensional phase diagram （ L-mode) Time 

7 Two-dimensional phase diagram （ transition) Time 

8 Two-dimensional phase diagram （ H- mode) Time 

9 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.

10 ECH+NBI+SMBI Movable probe SMBI ITC16 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

Waveform of successful SMBI plasma Target Plasma ECH+NBI Time of SMBI is shown as red line H  near SMBI HH HH H  far SMBI time (ms) #32816

Raw data of SMBI at the fastest speed (red & blue) # ,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 This 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

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

18 Comparison plasma features with and without SMBI SMBI NBI & ECH H  signal (near SMBI) electron density Diamagnetic signal #32783 #32816 Diamag signal goes up due to SMBI !!

19 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

20 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 k perp -domain, but it affected strongly k perp -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.

21 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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23 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

24 Measurement of ECH plasma Langmuir probe and fast camera measurement simultaneously Normal direction with Horizontal port Langmuir probe Object Lens FPS 64x64pixels time Filamentary structure Probe head n e ≧ 2.6x10 19 m -3 Fig. 1 Life time profile of bursts estimated by eye Filament-like structure was measured

25 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) ＃ ： 80,000FPS Strong fluctuation L-mode H-mode SMBI IIIIIIIV 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? 26 SMBI

Apparent k domain 27 SMBI

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29 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 30 For example: time slice at 202.5ms

FFT at peak value of k-profile 31 Low k peak has low frequency peak region, and High k peak has high frequency peak Low k & low freq.