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

Outlines Motivations Fast imaging of GyM plasmas Reconstruction of the emissivity profiles Fluctuations profiles CAS for detection and visualization of plasma structures ( a comparison with probe measurements ) Summary 2

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. 3

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) 4

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

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

Langmui r probe Hot filament source 2.45 GHz source 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 GyM Electron Temperature profile Electron density profile B average ~ 80 mT

Line integrated images (raw data) H 2, RF power: 1500 W fps, 4 us exposure time I(t): Camera image frame at time t

Reconstruction of the emissivity profile 9 Z r B

fps, 4 us exposure time NR~ 0.05 Reconstructed emissivity profiles H 2, RF power: 1500 W Z r B 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 TT

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

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

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

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

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

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. 16

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. 17

Thank you 18