TJ-II:Fast camera: Difference between revisions

<ref name="delaCal2">[http://iopscience.iop.org/0741-3335/56/10/105003/ E. de la Cal et al, ''Double imaging with an intensified visible fast camera to visualize the fine structure of turbulent coherent plasma structures (blobs) in TJ-II'', 2014 Plasma Phys. Control. Fusion 56 105003)]</ref>, '''Dust'''

<ref name="delaCal3">[http://iopscience.iop.org/0741-3335/55/6/065001/ E. de la Cal et al, ''Dust observation with a visible fast camera in the TJ-II stellarator'', 2013 Plasma Phys. Control. Fusion 55 065001 )]</ref>, or '''Spectroscopic 2-Dimensional Te and ne imaging''',

The main system is located in [[TJ-II:Sectors|sector]] B8, [[TJ-II:Ports|port]] B8TANG, viewing the [[TJ-II:Limiter|poloidal limiter]] in sector C3 tangentially.

The TJ-II Visible Camera Team has installed in collaboration with NIFS (Japan) a Fast Camera in '''LHD Stellarator'''

== Cameras ==

The newest Fast Camera employed at TJ-II is a [http://www.photron.com/ Photron] SA1 camera.

5000 fps with 1024 x 1024 pixels(full frame) and up to 200000 fps (maximum ever employed so far) with 182 x 80 pixels

The dynamic range of the sensor is 8 bits, and the memory size is 8 GB.

== Image Intensifier for Fast Camera==

A [http://sales.hamamatsu.com/en/home.php 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.

[[File:TJ-II_Fast_camera_diagram.jpg|800px|thumb|center|Schematic diagram of the TJ-II fast camera installation]]

== Videos ==

Below are some examples of movies recorded with the fast camera system of TJ-II. Click on the images to see the corresponding movie.

=== Double imaging to visualize the fine structure of Blobs===

[[File:Double_Imaging.jpg|300px|link=http://www-fusion.ciemat.es/fileshare/doc_exchange/camaras/video_DOUBLE_IMAGING.mp4]]

A visible fast camera coupled with an image intensifier was employed to view turbulent coherent plasma structures (Blobs) at the gas plume being puffed through a poloidal limiter. The image intensifier amplifies the light intensity thereby allowing the imaging system to be operated at ultra-short exposure times down to 100 ns.

To distinguish real physical signal from noise we get two simultaneous images with the same view and compare them. We call this Double Imaging technique and it allowed us to validate the detected blob shape to scales down to a few millimetres, limited by our optical resolution.

=== Double Imaging of two He I lines    #25623===

[[File:25623wComm_Photo000001.jpg|300px|link=http://www-fusion.ciemat.es/camaras/25623wComm.avi|Limiter recycling movie]]

With He I filters (706 nm and 728 nm) and 75 mm lens. Speed: 16000 fps. Exposure time: 60&mu;s. V: 750 V.

ECH and NBI plasma with <n_e>.  Recycling at limiter inserted 25 mm inside the LCFS. Edge Mode Instabilities after density increase with strong crashes and collapse. From the ratio of the filtered lines the <n_e> and <T_e> can be obtained [4].

=== Limiter Recycling ===

[[File:24119.jpg|300px|link=media:24119.gif|Limiter recycling movie]]

Without filter and 75 mm lens. Speed: 54000 fps. Exposure time: 9&mu;s. V: 650 V.

ECH plasma with <n_e> = 5x10¹⁸ m^-3.  Recycling at limiter positioned on the LCFS. The bright spot is Blackbody radiation from a glowing Langmuir probe on the limiter corner.

=== Helium Puffing ===

[[File:24080.jpg|300px|link=media:24080.gif|Helium puffing movie]]

Without filter and 75 mm lens. Speed: 100000 fps. Exposure time: 1&mu;s. V: 700 V.

ECH plasma with <n_e> = 5x10¹⁸ m^-3.  Helium puffing through the limiter 35 mm outside LCFS.

=== Lithium emission (Li I filter) ===

[[File:18152.jpg|300px|link=media:18152.gif|Surface interaction movie]]

TJ-II plasma observed from a tangential port at 17.5 kHz sampling rate, with a lithium filter and image intensifier. In the field of view, the two most prominent areas of plasma-wall interaction can be seen:  the poloidal limiter (lower) and the hardcore (helical limiter). As the plasma transits form ECH to NBI plasmas, the interaction level diminishes and becomes predominantly centered in the limiter. <ref name="Carralero"></ref> From the lithium emission fluctuations  information on the electron density fluctuations can be gained. <ref name="delaCal"></ref>

=== Dust ===

[[File:Polvo1b.jpg|300px|link=media:Polvo1b.gif|Dust movie]]

First insertion of the poloidal limiter after a lithiation of the vacuum vessel. Tangential observation, 15 kHz sampling rate. The ejection of lithium flakes from the carbon surface can be seen clearly at the beginning of the discharge. At the end of the video, as the plasma becomes colder, the flakes penetrate deeper into it until they float freely in the post-discharge plasmoid.

== References ==

<references />