Collective Thomson scattering using a pulsed CO2 laser in JT-60U

A collective Thomson scattering (CTS) diagnostic system using a carbon dioxide (CO2) laser has been developed for the purpose of establishing measurement technique of ion temperature and fast alpha particle in a fusion reaction plasma. A pulsed CO2 laser (15 J, 1 μs at 10.6 μm) and a heterodyne receiver with a stray light notch filter has been successfully installed. The noise equivalent power of the heterodyne receiver is below 9×10−19 W/Hz up to a frequency of 8 GHz. A six-channel filter bank analyzes the spectrum of the scattered light in the frequency range from 0.4 to 4.5 GHz to measure ion temperature and to detect fast ions generated by negative-ion source neutral beam injection of the JT-60U (Japan Atomic Energy Research Institute Tokamak 60-Upgrade) plasmas [S. Ishida, JT-60U Team, Nucl. Fusion 39, 1211 (1999)]. Test of the CTS system by injecting the CO2 laser into the vacuum vessel of JT-60U has started. Stray light signal around the JT-60U vacuum vessel was detected and optimization of the opt...