Page 4 - Plasma and Fusion Research,ISSN 1880-6821

Plasma and Fusion Research: Regular Articles
Volume 13, 3405062 (2018)
Fig. 6
Typical ion temperature estimated by Doppler broaden- ing of C III line at 0.276 MPa and 0.172 MPa with the PI system. The darkened areas are full width at half maxi- mum (FWHM) at each case in the signal of the collimated fiber at the same cross-section of the spectrometer.
Fig. 5
CT parameters at lower bias current and gas pressure with the PI system.
therefore, the MCPG can operate at lower gas pressure, reduced by approximately 40 %. CT performance is im- proved due to the lowered gas pressure operation; the CT has a higher ejection velocity and ion temperature without being cooled down by excess neutral gas.
Acknowledgements
This work was supported in part by the MOU as a part of research cooperation between the University of Califor- nia at Irvine (School of Physical Science, Department of Physics and Astronomy) and Nihon University (College of Science and Technology, Department of Physics). The authors would like to thank the TAE team for their sup- ports in the collaborative research. The work of past and present members of our laboratory is also gratefully ac- knowledged.
[1] T. Matsumoto et al., Rev. Sci. Instrum. 87, 053512 (2016).
[2] H.Gotaetal.,Nucl.Fusion57,116021(2017).
[3] T. Asai et al., Nucl. Fusion 57, 076018 (2017).
[4] T. Asai et al., Rev. Sci. Instrum. 81, 10E119 (2010).
[5] The Comsol Group, Comsol Multiphysics User’s Guide, http://www.comsol.com
Figure 6 shows the typical ion temperature Ti at 0.276 and 0.172 MPa gas pressure operations with the PI system. Here, t = 0 is the start time of the MCPG’s current. It clearly shows that the ion temperature is increased from 40 - 50 eV level to ∼ 70 eV by reducing the amount of ini- tial gas. As a result, the ejected CT is not cooled by the neutral gas, and the CT performance is improved at low gas pressure operation.
4. Summary
We have examined two newly adopted techniques for a MCPG: iron-core bias coil, and miniature gun as a new PI system. The iron-core bias coil can generate an equiv- alent stationary bias magnetic field with a much smaller current. By changing iron-core length and coil position, the amount of poloidal flux and velocity of the generated CT can be easily controlled. Also, the PI system can ef- ficiently and certainly produce breakdown of the MCPG;
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