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FIG. 6. Comparison of blue and monochrome images at (a) 70 and (b) 150 pixels on the x-axis. The blue line shows a line of blue color image, and the black line shows a line of monochrome image. The maximum range of the output intensity of a color image is 255, so these traces are not saturated.
where rl is the probe radius, p and v are the magnetic flux
inside the loop with plasma and in vacuum conditions, and
Bp and Bv are the magnetic field with plasma and in vacuum
conditions at the probe location, respectively. The excluded-
flux radius is a close approximation to the separatrix radius of
7
Figure 7 shows the results of magnetic probe and triple Langmuir probe measurements. Two CTs start to collide around t = 30–40 μs, as seen in Fig. 7, and the camera image also shows that the collision and merging happen around that
moid, the magnetic axis R is described as R = rs/p2, which 7
the FRC-like plasmoid.
IV. CONCLUSION
New CT collision/merging experiments using two MCPGs have been conducted and successfully produced/ formed a single FRC-like plasmoid. To investigate and under- stand the global shape/behavior and process of CT collisional merging, the fast-framing camera was adopted in the confine- ment region, in which the camera captured the merging process as well as some color changes in the plasma. During the CT collision and merging, the plasma emitted strongly. By sepa- rating color images of the camera to RGB images, we were able to identify the hot and cold regions of the plasma. The camera images clearly showed the FRC-like CT’s shape as well as open field lines in the red color images. This was not apparent in the full-color image; however, by splitting it, the behavior of the core plasma was able to be observed.
ACKNOWLEDGMENTS
We thank our shareholders for their support and trust and all fellow TAE staff for their dedication, excellent work, and extra efforts.
1C. A. Romero-Talamas, C. Holcomb, P. M. Bellan, and D. N. Hill, Phys. Plasmas 13, 022502 (2006).
2H. Gota et al., Nucl. Fusioin 57, 116021 (2017).
3E. M. Granstedt, P. Petrov, K. Knapp, M. Cordero, and V. Patel, Rev. Sci.
Instrum. 87, 11D416 (2016).
4T. Asai et al., Nucl. Fusion 57, 076018 (2017).
5T. Matsumoto et al., Rev. Sci. Instrum. 87, 11D406 (2016).
6T. Matsumoto et al., Rev. Sci. Instrum. 87, 053512 (2016).
7 W. T. Armstrong, R. K. Linford, J. Lipson, D. A. Platts, and E. G. Sherwood,
Phys. Fluids 24, 2068 (1981).
8M. Tuszewski, Nucl. Fusion 28, 2033 (1988).
9
FIG. 7. (a) Contour map of the internal magnetic field using the magnetic probe array and (b) contour plot of ne scanned over the radius at the mid-plane using the triple Langmuir probe, compared with the typical excluded-flux radius r.
M. Tuszewski, Phys. Fluids 24, 2126 (1981).
time. From the comparison between the camera image and magnetic probe array, the probe signal around that time can infer that magnetic fluctuations on the probe array are due to the magnetic reconnection event of the collided/merging CTs. After t = 40 μs, the CTs have fully formed into a single closed- field line. During this time, the poloidal surface clearly shows a closed-field line. Figure 7(a) also shows the magnetic axis which separates the region between the axial field direction and opposite direction, which means that the collided CTs are formed as an FRC-like plasmoid.
Figure 7(b) shows a comparison of the excluded-flux
radius r and electron density ne profile measurement by
scanning over the radius. The electron density dramatically
increased after merging CTs and is distributed inside the
excluded-flux radius. In the radial distribution of the elec-
tron density, the peak density is located around r = 8 cm.
Assuming the collided CTs turn into single FRC-like plas-
is the field-null point, where rs is a separatrix radius. From this relationship, the separatrix radius rs can be estimated as 11.3 cm with R = 8 cm using the magnetic probe/loop measure- ments. The excluded-flux radius from the magnetic probe and flux loop was approximately 11 cm around the peak, as shown in Fig. 7(b). From these results, this profile can be assumed to be the rigid-rotor (RR) profile which is a theoretical model of the FRC plasma.