بسمه تعالی

1. بسمه تعالی Fast Imaging of turbulent plasmas in the GyM device D.Iraji, D.Ricci, G.Granucci, S.Garavaglia, A.Cremona IFP-CNR-Milan 7th Workshop on Fusion Data Processing Validation and Analysis Frascati-March 2012

2. Outlines Motivations Fastimaging of GyM plasmas Reconstruction of the emissivity profiles Fluctuations profiles CAS for detection and visualization of plasma structures (a comparisonwith probe measurements) Summary

3. Motivations Basic understanding of fluctuations and turbulence in magnetized plasmas is an important issue for magnetic fusion, as they cause a high degree of particle and energy losses. A full spatio-temporal imaging system with reasonable resolution in time and space is needed to study plasma turbulence . A non perturbative approach is fast visible imaging of plasma turbulence. An ultimate goal of plasma imaging is extracting plasma turbulence characteristics from images. Fast imaging is often used in fusion devices however detailed comparisons with other diagnostics are needed for justification.

4. Fast Visible Imaging system Camera Characteristics: Photron ultima APX-RS Full, 1024 by 1024 pixel resolution, up to 3,000 fps, 10-bit monochrome CMOS sensor with pixels in dimension of 17×17µm Top recording speed is 250,000 fps Image memory can be expanded to facilitate 6 second recordings at 1,000 fps And 4.2 seconds at 250,000 fps. Capability of synchronization with the Other diagnostics such as probes (error < 100nsec)

5. Fast visible plasma imaging CSDX, G.Antar TORPEX D.Iraji NSTX, S.Zweben • ELMs • Blobs/Filaments • Modes

6. High Speed gated Image Intensifier Hamamatsu C10880-03 Max. gain 10000 Spectral response 185-900 nm Gating 10ns-10ms Repetition rate 200kHz Resolution 38 lp/mm

7. GyM Electron density profile Electron Temperature profile Modular device in which the magnetic field configuration can be easily modified. # of Coils 10 Max current 1000 A Max magnetic field 0.13 T Cooling water rate 22 l/min Power supply (d.c.) 1000A/50V Vacuum chamber (m): Length 2.11 Diameter 0.25 B average ~ 80 mT Langmuir probe 2.45 GHz source Hot filament source

8. Line integrated images (raw data)H2, RF power: 1500 W I(t): Camera image frame at time t 75000 fps, 4 us exposure time

9. Reconstruction of the emissivity profile Z r B

10. Reconstructed emissivity profilesH2, RF power: 1500 W g(t): Reconstructed emissivity profile at time t I=T*g T=U*S*V , U*U =V*V = unitary V*S *U *I=g T T T -1 T 75000 fps, 4 us exposure time NR~ 0.05 Z r B

11. Plasma structures in reconstructed profiles (fluctuations) ~ g(t)=g(t)-<g(t)> Fluctuation profile of reconstructed emissivity at time t • Individual structures can be distinguished • Structures appear rotate, merge and split after a while Z r B

12. Fluctuations Fluctuations level PSD of the MFL signal Maximum fluctuations level (MFL)

13. Fluctuations Z-Scan of PSD r-Scan of PSD Z r B

14. Conditional Average Sampling (CAS) E×B rotation and Te Probe measurement -1 2 L = FWHM V E×B ~ 1km/s, B~80 mT: E~80 V/m L ~5.5cm, Te~ E L ~ 4.4 eV -1 -1

15. E×B rotation and B . × E E B B E×B is responsible for the rotation of the plasma column

16. Summary The intensified fast camera is able to image plasma with spatial resolution of 2cm and temporal resolution of 4µs. .Plasma emissivity profiles are reconstructed using pixel methode and singular value decomposition approach. Fourier analysis of the reconstructed images show presence of a distinct mode at ~4 kHz which is radially extended between -3cm<r<2 cm and vertically located at the bottom. CASed images show rotation of the structures associated with the mode due to E×B drift.

17. Outlooks Structural analysis of the reconstructed emissivity profiles to estimate plasma transport. The establishment of comparisons between the experimental plasma transport related to the plasma structures with theoretical predictions and confirmation using probe data.

18. Thank you