Collective Thomson scattering diagnostic system

Though fusion generated alpha particles play an important role in plasma heating and alpha-driven instabilities, an effective measurement method has not been established yet. A collective Thomson scattering diagnostic system using a carbon dioxide (CO2) laser has been developed for the purpose of establishing measurement technique of fast alpha particles and ion temperature in a fusion reaction plasma in collaboration with Oak Ridge National Laboratory.

[Diagnostic Method]
Ions do not interact strongly with CO2 laser but collective motion of the electron which is drawn by ions can scatter the laser. Ion velocity distribution is evaluated by measuring Doppler shift of the scattered light of CO2 laser in the plasma. It is necessary to choose a small scattering angle to that a scattering wave length may be larger than Debye length.

Fig.1 Schematic view of the scattering geometry

CO2 laser Wave length : 10.6mm
Energy : 15J
Pulse width : 1ms
Repetition late : 2s
Divergence : 0.5mRad
Diameter : 4cm
Stray light notch filter
(Hot CO2 gas cell)
Attenuation : 10-4 - 10-7 (10.6mm)
Width : ~ 500MHz
Temperature : ~ 400C
Heterodyne receiver Noise equivalent power : 910-19 W/Hz
Band width : ~8 GHz

Fig. 2 Schematic view of the Collective Thomson scattering system

[1] T. Kondoh, S. Lee, D.P.Hutchinson, R.K.Richards, Rev. Sci. Instrum. 72, 1143 (2001)
[2] T.Kondoh, S.Lee. Y.Miura, J. Plasma Fus. Res.76, 883 (2000) (in Japanese)
[3] S. Lee, T. Kondoh, Rev. Sci. Instrum, 71,3718(2000)
[4] S. Lee, T. Kondoh, Y. Yonemoto, Y. Miura, Rev. Sci. Instrum, 71, 4445 (2000)