TJ-II:Fast camera
TJ-II disposes of a fast camera for turbulence imaging in the plasma edge and scrape-off layer. [1] [2] [3] The camera is located in sector B8, port B8TANG, viewing the limiter in sector C3.
Camera
The camera employed at TJ-II is a Photron SA1 camera. Sampling speed (measured in frames per second, fps) and image size can be selected, but there is a trade-off:
- 3000 fps with 1024 x 1024 pixels (full frame)
- 5000 fps with 1024 x 1024 pixels
- 10000 fps with 512 x 512 pixels
- 200000 fps (maximum ever employed so far) with 182x80 pixels
- 650000 fps (maximum) with 64 x 16 pixels
The dynamic range of the sensor is 8 bits, and the memory size is 8 GB.
Image intensifier
Incoming photons are converted into electrons on a photocathode. The emitted electrons are multiplied in a Micro Channel Plates (MCP) element. These electrons impact on a phosphor screen, stimulating line emission. The phosphor material is specially selected for its short decay time (which is the main limitation for high speed operation).
A Hamamatsu C9548-03BL series image intensifier is used. This is a two stage intensifier, including a first GEN II stage with a fast phosphor (P-46) and gain adjustable via the voltage at the MCP, and a second GEN I one (booster) with a fixed gain of 50 and somewhat slower phosphor screen (P-24). Both stages are optically coupled by a Fiber Optic Plate (FOP) which transfers the output signal from the first to the second.
References
- ↑ J.A. Alonso et al, Impact of different confinement regimes on the two-dimensional structure of edge turbulence, Plasma Phys. Control. Fusion 48 (2006) B465-B473
- ↑ D. Carralero et al, Turbulence studies by fast camera imaging experiments in the TJII stellarator, Journal of Nuclear Materials 390-391 (2009) 457-460
- ↑ E. de la Cal et al, Visible intensified cameras for plasma imaging in the TJ-II stellarator, Rev. Sci. Instrum. (2009)