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Nucl. Fusion 57 (2017) 076018
T. Asai et al
Figure 11. The trajectories of the FRC axis before (blue dashed line) and after (red solid line) single-sided (a) and counter
(b) injection. The CT injection times are (a) 2.0 ms and (b) 1.0 ms, respectively.
absolute extreme ultraviolet photodiode array with pinholes. A total of 176 channels cover almost the entire FRC volume and a 3D reconstruction of the emission pro le is performed. The emission pro le is modeled as the ensemble of the three parts, which are the rigid-rotor emission pro le for the FRC core, the exponential decay pro le in the SOL and constant background emission [17, 18]; thus, the reconstructed signals can indicate the FRC’s global motion/instabilities, such as wobble (n = 1) motion.
Figure 11 shows the effect of CT injection on the trajec- tories of the FRC axis. Figure 11(a) is the trajectory on the single-sided injection case and (b) traces the counter injec- tion case. In the case of single-sided injection, wobble motion is triggered, and the FRC plasma rotates in the diamagnetic direction of the ion due to CT injection. To reduce the effect of asymmetrical momentum injection, counter injection was conducted. In the counter injection case, the wobble motion is not observed because the horizontal momenta injected by the two CTs cancel each other out.
4. Summary
In this project, a CT injector, which fuels 0.5–1.0 × 1019 of the particles with 1kHz of repetition frequency was devel- oped. The injection velocity evaluated on the test stand remained in the range of ~100 km s−1 while in a transverse magnetic eld, even after passing through the 1 m long drift tube. This is high enough to penetrate the external magnetic eld of the C-2U FRC. The CTs injected perpendicularly into the geometrical axis of the C-2U demonstrated suc- cessful fueling with a signi cant build-up in density of 20–30% of the total particle inventory per single CT injec- tion without any serious deleterious effects on the C-2/C-2U FRC. Dα emission indicates possible pollution by trailing gas. However, this can be reduced drastically using the PI technique on the MCPG. The wobble motion driven by the CT injection can be suppressed by counter CT injection. An effective technique for particle fueling is a common devel- opment issue in any magnetically con ned fusion reactor. This work would provide an effective fueling technique for magnetically con ned plasmas.
Acknowledgments
The authors wish to thank the entire TAE team for their technical assistance on the experiments as well as for fruit- ful discussions in the collaborative research. The authors also gratefully acknowledge the support of Quartz Lead Co., Ltd and nac Image Technology Inc. This work was partially sup- ported by JSPS KAKENHI grant number 16K06939.
References
[1] Matsumoto T. et al 2016 Development of a magnetized coaxial plasma gun for compact toroid injection into the C-2 eld- reversed con guration device Rev. Sci. Instrum. 87 053512
[2] Binderbauer M. et al 2015 A high performance eld-reversed con guration Phys. Plasmas 22 056110
[3] Steinhauer L.C. 2011 Review of eld-reversed con gurations
Phys. Plasmas 18 070501
[4] Binderbauer M. et al 2016 Recent breakthroughs on C-2U:
Norman’s legacy AIP Conf. Proc. 1721 030003
[5] Perkins L.J. et al 1988 Deep penetration fuelling of reactor- grade tokamak plasmas with accelerated compact toroids
Nucl. Fusion 28 1365
[6] Raman R. et al 1997 Experimental demonstration of
tokamak fuelling by compact toroid injection Nucl. Fusion
37 967
[7] Nagata M. et al 2005 Experimental studies of the dynamics of
compact toroid injected into the JFT-2M tokamak
Nucl. Fusion 45 1056
[8] Xiao C. et al 2004 Improved con nement induced by
tangential injection of compact torus into the Saskatchewan Torus-Modi ed (STOR-M) tokamak Phys. Plasmas
11 4041
[9] Asai T. et al 2005 First results of magnetized plasma ow injection on the TPE-RX reversed- eld pinch J. Plasma Fusion Res. 81 335
[10] Allfrey I. et al 2015 Development of multi-pulse compact toroid injector system for C-2U (http://meetings.aps.org/ link/BAPS.2015.DPP.BP12.24)
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