YAG laser Thomson scattering system[1-2]


[Objectives]
Time evolutions of electron temperature and density profiles are measured throughout an entire plasma discharge by using a Nd-YAG laser.

[Detectors, Diagnostic Method]
When the YAG laser is injected into a plasma, Thomson scattered light is radiated from the electron. The local electron temperature and electron density in JT-60U plasmas are measured by the spectroscopic analysis of the Thomson scattering spectrum.

The polychromator is used as the spectroscopy of Thomson scattering spectrum with the YAG laser. A polychromator consists of 6 successive interference filters, and suitably designed for the wide temperature range (20eV-10keV). As the electron temperature becomes higher and higher, the Thomson scattering for YAG laser widens the spectrum region from infrared to long wavelength side of visible light . The APD (Avalanche photodiode) detector, which has a peak sensitivity near infrared region, is used to detect the spectrum.

The gain of APD detector is very sensitive against the operation temperature. In order to prevent the temperature effect on the gain change of APD, the temperature of APD element is controlled within the accuracy of 0.1 C due to the Peltier element, and the APD gain is kept the fixed value.

[Specification]
- Time resolution : 0.33ms (30Hz). 0.2ms(50Hz) will be available from April 2001.
- Spatial measuring points : 14 points are available
- Temperature range : 10eV - 20keV (typical)
- Density range : 11019-51020m-3
- Position : P-2 section, U2 port for laser beam
- Laser : Nd-YAG laser, Energy>2J, Pulse width~20ns, Wavelength=1064nm
- Detector : Si-APD (Avalanche Photodiode), 3mm in effective diameter
- Polychromator : Successive interference filter type, 6 wavelength channels

[Reference]
[1] T.Hatae et al., "First operation results of YAG laser Thomson scattering system on JT-60U", Fusion Engineering and Design 34-35 621-624 (1997).
[2] T.Hatae et al., "YAG laser Thomson scattering diagnostic on JT-60U", Rev. Sci. Instrum. 70 772-775 (1999).


Veiwing field and measuring points