Page 4 - Fast-framing camera based observations ...ing two magnetized coaxial plasma guns

10E108-4
Matsumoto et al.
Rev. Sci. Instrum. 89, 10E108 (2018)
FIG.4. MeasurementresultofthedominantwavelengthbyusingtheOcean Optics. The Balmer lines, D↵ and D , are the predominant wavelength in the confinement vessel.
plasma region compared with the red color image, Fig. 5(a). In addition, the blue color image captured a rotational mode
7,8
In order to compare the blue and original color images, the original color image is converted to monochrome. Thereby, the monochrome image can be used to compare the behavior of the CT with the blue color image using its intensity pro- file. See Fig. 6 for a comparison of those images at 70 and
150 pixels on the x-axis. The lineouts in Fig. 6 remain below the saturation threshold of 255. As mentioned above, the blue color image contains information about the CT’s behavior. The edge and around the middle of CT are chosen for comparison. Figure 6(a) shows that the CT has started a rotational insta- bility and then the intensity of the image decreases around the center of Fig. 6(a). On the other hand, the edge profile of Fig. 6(b) changed widely. Figure 6(b) shows that the blue color profile is clearly wider than the monochrome profile; i.e., the CT was rotating after merging. From these results, it can be determined that using the RGB images makes it possible to determine more information, not only the pro- file of the light emission but also the size and motion of the CT.
C. Probe measurements
To evaluate the plasmoid parameters, pairs of magnetic probe and flux loop, magnetic probe array, and triple Langmuir probe at the mid-plane were used. The pairs of the magnetic probe and flux loop along the z-axis are used to estimate the velocity from time-of-flight and the excluded-flux radius at each probe location. If the axial field coil works as a flux conserver, the magnetic probe and flux loop can be used to estimate the averaged excluded-flux radius r as the radius
that is well-known instabilities of FRCs.
were able to define the hot plasma region and cold region by splitting the color image to RGB images. Moreover, global motion of the plasmoid can also be captured from the blue image.
As a result, we
of the CT,
9s
r = rl 1 , (1)
p Bv v Bp
FIG.5. RGBimagesbysplittingthecolorimage:(a)red color image, (b) green color image, (c) blue color image, and (d) original color image. The open magnetic field lines are clearly visible in red and green color images, and the blue color image clearly captured the closed magnetic field (poloidal surface).