Fast Imaging of turbulent plasmas in the Gy

ﺗﻌﺎﻟی ﺑﺴﻤﻪ Fast Imaging of turbulent plasmas in the Gy. M 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 Gy. M 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 < 100 nsec) 4

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

High Speed gated Image Intensifier • • • Hamamatsu C 10880 -03 Max. gain 10000 Spectral response 185 -900 nm Gating 10 ns-10 ms Repetition rate 200 k. Hz Resolution 38 lp/mm 6

Gy. M Hot filament source Langmui r probe Modular device in which the magnetic field configuration can be easily modified. # of Coils Max current Max magnetic field Cooling water rate Power supply (d. c. ) 1000 A/50 V Vacuum chamber (m): Length Diameter 2. 45 GHz source Electron density profile Electron Temperature profile 10 1000 A 0. 13 T 22 l/min 2. 11 0. 25 B average ~ 80 m. T

Line integrated images (raw data) H 2, RF power: 1500 W I(t): Camera image frame at time t 75000 fps, 4 us exposure time 8

Reconstruction of the emissivity profile Z r B 9

Reconstructed emissivity profiles H 2, RF power: 1500 W g(t): Reconstructed emissivity profile at time t I=T*g T T=U*S*V , U*UT =V*VT = unitary -1 T V*S *U *I=g Z r B 75000 fps, 4 us exposure time NR~ 0. 05 10

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 Z r • Structures appear rotate, merge and split after a while B 11

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

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

Conditional Average Sampling (CAS) E×B rotation and Te Probe measurement -1 2 L = FWHM V E×B ~ 1 km/s, B~80 m. T: E~80 V/m -1 -1 L ~5. 5 cm, Te~ E L ~ 4. 4 e. V 14

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

Summary The intensified fast camera is able to image plasma with spatial resolution of 2 cm 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 k. Hz which is radially extended between -3 cm<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