7th Asia-Pacific Conference on Plasma Physics, 12-17 Nov, 2023 at Port Messe Nagoya

Investigation of inward particle flux formation on the PKU Plasma Test (PPT)
deviceT. C. Xu1, Z. B. Guo1, C. J. Xiao1, Z. Y. Zhang1, R. X. Yuan1, R. C. He1, X. Y. Yang2, X. G. Wang2
1
State Key Laboratory of Nuclear Physics and Technology, School of Physics, Peking University,
Beijing 100871, China
2
School of Physics, Harbin Institute of Technology, Harbin 150001, Chinae-mail (speaker): xutianchao90@126.com
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The up-gradient particle transport (inward particletransport) is conducive to transport barrier formation andconfinement improvement. It is associated with theformation of a peaked density profile, which contributes
to improve the fusion rate and the realization ofsteady-state discharge [1]. Experimental results
demonstrate that shear flow influences the production of
inward particle flux, but the formation mechanism of
inward particle transport is still not studied thoroughly inthe experiment. During the fusion process, plasma
burning is concentrated in the plasma core region. The
existing feeding technologies include pellet injection,
molecular beam injection, cluster jet injection andfueling by CT injection [2-5]. The fuel injection locationis generally at the plasma edge and the fuel particles,
limited by the depth of injection, cannot enter the core to
replenish the consumption of fusion reaction. Therefore,
the investigation of inward particle transport mechanism
is also helpful to solve the challenge of plasma fueling.
More deep studies are needed for a thoroughunderstanding of inward particle transport.
Recently, inward particle flux and outward particle flux
are observed simultaneously in the PKU Plasma Test(PPT) device, a linear plasma device. And the inward
particle flux is induced by streamer structure shown inFigure1. Based on the theoretical and experimental
analysis, the nonlinear interaction of streamers is thecritical factor of inward particle flux formation in theregion without the boundary effect. As shown in Figure 2,
in the r = 23-30 mm, i.e., the blue box region, thenonlinear interaction term induces an inward particleflux. The particle flux induced by the nonlinear term in
the blue box region is almost equal to the experimentallymeasured particle flux induced by this mode. Therefore,
the nonlinear interaction of streamer modes is the kinetic
mechanism of inward particle flux formation when thedensity perturbation reaches saturation without the
influence of boundary effects.
When the nonlinear interaction of streamers isdominating, the particle orbit is quasi-periodic and theinward particle flux forms for the decrease of entropy.
The particle orbit is chaotic when the nonlinear
interaction between streamers and DWs is predominant
and then the particle flux is down-gradient for theincrease of entropy. These results provide a newperspective for the investigation of inward particle
transport mechanism.

Figure 1. (a) Frequency averaged velocity fields obtained
streamer structure by 2D TDE analysis. (b) The
fluctuation of radial velocity calculated by camera data.
(c) The particle flux driven by streamers calculated bycamera and probe data. (d) The particle flux calculatedby and probe data.

Figure 2: (a) The cosine of floating potential. (b)Thecross-phase between potential and density. (c) Reynold
stress. (d) Particle flux measured. (e) Particle flux
induced by the nonlinear interaction with the other twomodes.

References[1] C Bourdelle.: Plasma Phys. Control. Fusion, Vol.47,A317 (2005)[2] S. K. Combs.: Rev. Sci. Instrum. Vol.64, 1679 (1993)[3] L. H. Yao et al. Nucl. Fusion. Vol.38, 631. (1998)[4] L. H. Yao et al. Nucl. Fusion, Vol.47, 1399. (2007)[5] R. Raman et al.: Nucl. Fusion, Vol. 37 967. (1997)