Study of a CW, two-dimensional Thomson scattering diagnostic system

We describe an approach to Thomson scattering diagnostic that relies upon a high power CW laser cavity and a rf signal detection technique, instead of the more usual pulsed high energy laser. The system has three major elements: an ultra long (similar to150 m) laser resonance cavity that includes the plasma region; an array of CW diode lasers of high power and high modulation frequency that pumps and maintains the average cavity energy (similar to10 mJ); and a lock-in detection system of narrow frequency bandwidth (similar to2 kHz). The resonance cavity consists of a pumping chamber for power input from diode lasers, and many relay chambers (similar to30) distributed across the plasma cross section for Thomson measurement. The cavity has a low energy loss (similar to2% round trip) and zero output power. It is estimated that signal-to-noise of the system is similar to100 times better than the present pulsed system on DIII-D Tokamak due to the increase in usable laser energy and the improved background signal rejection. (C) 2004 American Institute of Physics.