تعالی بسمهFast 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

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

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Motivations

• A non perturbative approach is fast visible imaging of plasma turbulence. An ultimate goal of plasma imaging is extracting plasma characteristics as much as possible from images.

• We need to reconstruct the plasma emissivity profiles in order to analyze plasma structures.

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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 fpsAnd 4.2 seconds at 250,000 fps.

Capability of synchronization with the Other diagnostics such as probes(error < 100nsec)

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Fast visible plasma imaging

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NSTX, S.Zweben CSDX, G.AntarTORPEX D.Iraji

•ELMs•Blobs/Filaments•Modes

Camera + GP Camera +Image Intensifier

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

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Langmuir probe

Hot filament source

2.45 GHz source

Modular device in which the magnetic field configuration can be easily modified.

# of Coils 10Max current 1000 AMax magnetic field 0.13 TCooling water rate 22 l/min Power supply (d.c.) 1000A/50V

Vacuum chamber (m):Length 2.11Diameter 0.25

GyM

Electron Temperature profileElectron density profile

B average ~ 80 mT

Line integrated images (raw data)H2, RF power: 1500 W

875000 fps, 4 us exposure time

I(t): Camera image frame at time (t)

Reconstruction of the emissivity profile

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B

I =T g

r

Z

Solving least square using SVD approachMN NM

1cm×1cm

and g >=0

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ReconstructionCalculation of the Transformer Matrix T :

•Triangulation of reference images to find the camera pixels positions related to the machine coordinates (P)

• Length of the intersection of LOS corresponding to each camera pixel (i) with plasma pixel (j) is Tij

I ref Triangulation

Reconstruction NR < 5%

P LOS T

g

I exp

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75000 fps, 4 us exposure time

Reconstructed emissivity profilesH2, RF power: 1500 W

g(t): Reconstructed emissivity profile at time (t)

Each frame Cnsums ~ 2 s of Four 2.4 GHz CPUs, NR < 5%

Fluctuations

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Maximum fluctuations level (MFL) PSD of the MFL signal

Fluctuations level

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Fluctuations

r-Scan of PSDZ-Scan of PSD

Zr

B

Conditional Average Sampling (CAS)

E×B rotation and Te

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V E×B ~ 1km/s, B~80 mT: E~80 V/m

L ~5.5cm, Te~ E L ~ 4.4 eV-1-1

Probe measurement

2 L = FWHM-1

E×B rotation and B

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

E E

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.

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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.

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Thank you

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Extra slides

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Tomographic reconstruction of the plasma emissivity profile in TORPEX

Tomographic reconstruction of the plasma emissivity profile in TORPEX

Before reconstruction

After reconstruction