Page 1 - Fast-framing camera based observations ...ing two magnetized coaxial plasma guns

REVIEW OF SCIENTIFIC INSTRUMENTS 89, 10E108 (2018)
Fast-framing camera based observations of spheromak-like plasmoid collision and merging process using two magnetized coaxial plasma guns
1,2,a) 1 1 1 3 3 3 T. Matsumoto, T. Roche, I. Allfrey, H. Gota, T. Asai, T. Edo, A. Hosozawa,
3 b) F. Tanaka, and TAE Team
1TAE Technologies, Inc., 19631 Pauling, Foothill Ranch, California 92610, USA
2Department of Physics and Astronomy, University of California, Irvine, California 92697, USA 3College of Science and Technology, Nihon University, Chiyoda-ku, Tokyo 101-8308, Japan
(Presented 16 April 2018; received 23 April 2018; accepted 13 June 2018; published online 14 September 2018)
We have been conducting compact toroid (CT) collision and merging experiments by using two magnetized coaxial plasma guns. As is well known, an actual CT/plasmoid moves macroscopically in a confining magnetic field. Therefore, three-dimensional measurements are important in understanding the behavior of the CTs. To observe the macroscopic process, we adopted a fast-framing camera (ULTRA Cam HS-106E) developed by NAC Image Technology. The characteristics of this camera are as follows: a CCD color sensor, capable of capturing 120 images during one sequence with a frame rate of up to 1.25 MHz. Using this camera, we captured the global motion of a CT inside the magnetic field and the collision of two CTs at the mid-plane of the experimental device. Additionally, by using a color sensor, we captured the global change in the plasma emission of visible light during the CT collision/merging process. As a result of these measurements, we determined the CT’s global motion and the changes in the CT’s shape and visible emission. The detailed system setup and experimental results are presented and discussed. Published by AIP Publishing. https://doi.org/10.1063/1.5037325
I. INTRODUCTION
Imaging systems using fast-framing cameras have been
used in spheromak experiments1 and have recently been
used on large plasma confining devices [for example, C-2/C-
2U field-reversed configuration (FRC) device2,3]. The main
advantage of a camera system is that the image and picture
include not only intensity of line-of-sight but also a wide field
of view. In typical diagnostic suites, magnetic and electri-
cal probes are used for magnetic field and electron temper-
ature/density measurements at each probe location. Plasma
emission measurements have also been adopted to investigate
the plasma using a two-dimensional tomography system. Con-
sequently, experiments require many diagnostics to observe
macroscopic plasma behavior and need analysis methods to
convert the time evolution of data to cell data. On the other
hand, by using camera imaging, plasma motion can easily be
captured as a picture image; thereby, we can observe three-
dimensional information. In our recent study of the compact
toroid (CT) injection into C-2U FRC, the fast-framing camera
was adopted to capture the CT trajectory inside the confine-
4
To conduct a CT collision and merging experiment, using two CT injectors, we upgraded the CT injector (CTI) test
Note: Paper published as part of the Proceedings of the 22nd Topical Confer- ence on High-Temperature Plasma Diagnostics, San Diego, California, April 2018.
a)Electronic mail: TMatsumoto@tae.com
stand5 to include an axial magnetic field coil and CT injectors on both sides of the test stand.
The global motion of the plasmoid resulting from the colliding CTs is not easy to understand. Therefore, a global imaging system is an important diagnostic for observing this motion. For this reason, we have adopted a fast fram- ing camera. The camera has a red-green-blue (RGB) color image sensor. By splitting images, it is possible to capture the global motion/behavior of the target plasma. To evalu- ate the process of colliding and merging CTs, we installed not only a fast-framing camera but also a spectrometer, an internal magnetic probe array, and a Langmuir probe in the confinement chamber. By comparing the camera’s pictures and probe signals, the plasma’s response can be understood.
In this paper, we present an overview of a two-CT collision/merging experimental device on a CTI test stand with a fast camera diagnostic and a magnetic probe array in Sec. II. The typical experimental results are presented in Sec. III, including the result of imaging analysis, internal mag- netic field distribution, and electron temperature distribution using a Langmuir probe. We also discuss the change in the CT’s shape and visible emission. This paper is summarized in Sec. IV.
II. EXPERIMENTAL APPARATUS
A. CT collision and merging device
Figure 1 shows a schematic drawing of the CT collision and merging experimental device. A CT is a general mag- netized plasmoid [for example, spheromak and field-reversed configuration (FRC)], which has a poloidal and/or toroidal
ment vessel.
on the CT, and we determined the penetration depth as well as the CT’s motion around the FRC plasma. In addition, we captured the distribution of the neutral gas outside the FRC.
The camera was able to take an image focused
b)TAE Team members are listed in Nucl. Fusion 57, 116021 (2017). 0034-6748/2018/89(10)/10E108/5/$30.00
89, 10E108-1 Published by AIP Publishing.