Analysis method for Thomson scattering diagnostics in GAMMA 10/PDX

Abstract

We have developed an analysis method to improve the accuracies of electron temperature measurement by employing a fitting technique for the raw Thomson scattering (TS) signals. Least square fitting of the raw TS signals enabled reduction of the error in the electron temperature measurement. We applied the analysis method to a multi-pass (MP) TS system. Because the interval between the MPTS signals is very short, it is difficult to separately analyze each Thomson scattering signal intensity by using the raw signals. We used the fitting method to obtain the original TS scattering signals from the measured raw MPTS signals to obtain the electron temperatures in each pass.

High time resolved electron temperature measurements by using the multi-pass Thomson scattering system in GAMMA 10/PDX

“…Figure 3 shows the clear multi-pass TS signals of summed with all TS signals from all output channels of the polychromator after subtracting the noises and polychromator pre-amplifier characteristic decay signals using the newly constructed analyzing method which is shown in Ref. 21, with the pass numbers. The 8 and 10 passing TS signal intensities are larger than those of 7 and 9, respectively.…”

Development of a laser amplification system for the multi-pass Thomson scattering system for GAMMA 10/PDX

“…16 By adding a polarization control device, a polarizer, and a high-reflection mirror to the double-pass TS system, we previously successfully constructed over three passing MPTS systems. [17][18][19] We achieved approximately 3.6 times increased TS signals by the first to the sixth passing probing lasers through the plasma in a single laser shot. 17 Moreover, the time-dependent electron temperature measurement every 65 ns was successfully obtained.…”

“…The electron temperatures are calculated by the chi-squared method. 8,19 To increase the degraded MP laser beam power, we newly added the laser amplification system onto the normal MP configuration. We switched on the second Pockels cell to change the laser beam trajectory to the laser amplification system after passing through the polarizer, half-wave plate, Faraday rotator, and mirrors.…”

“…[9][10][11][12][13] In GAMMA 10/PDX (Potential-control and Divertor-simulator eXperiments), the MPTS system of the polarization-based system with imagerelaying optics has been developed. [14][15][16][17][18][19] GAMMA 10/PDX is an effectively axisymmetric minimum-B anchored tandem mirror with a thermal barrier at both end mirrors. 20 The plasma is created by plasma guns, and it is then heated and sustained using ion cyclotron heating (ICH) systems.…”

“…17 Moreover, the time-dependent electron temperature measurement every 65 ns was successfully obtained. 18,19 However, in the normal MPTS system, the MPTS signal intensities decrease with the pass number because of the laser power damping due to the optical components. Subsequently, we have developed a new MPTS system by adding the laser amplification system.…”