Experimental Study of Reconnection Heating and Acceleration by use of Glass-Tube-Pair Type Doppler Probe Array

We had developed a glass-tube-pair type Doppler probe array for 1D profile measurement of two component ion flow vector and ion temperature. It needs just two parallel glass-tube insertion, realizing low plasma perturbation and 1D ion flow vector measurement on a single discharge. Using four mirrors and optical fibers, this system can measure ion light emissions of each measurement volume from four different directions, enabling us to measure its local ion flow vector and temperature. All set of mirrors and optical fibers are aligned in the two parallel glass tubes for 1D profile measurement on a single discharge. Using Doppler shift measurement along bi-directional viewing lines, we can significantly decrease calibration error of the Doppler shifts. By use of this system, we measured successfully ion outflow speed of two merging tokamak plasmas, about 80% of poloidal Alfvén speed in agreement with recent reconnection experiments and theories. For more precise survey of reconnection heating and acceleration mechanisms, we have been improving spatial resolution and measurement accuracy of parallel component of ion velocity to glass-tube. By making the mirror holders of the array thinner, we reduced the mirror interval to 2.5 cm which is 1/2 of the previous one. By increasing the incident angle of light to 30 degrees twice as large as the previous one, we improved the measurement accuracy of ion velocity parallel to glass-tube.