Speaker
Description
Residual zonal flow level $R_{ZF}$ [1] is one of the key relevant quantities which determine turbulence and transport of tokamak plasmas [2]. While there have been various theoretical extensions of the original work in Ref. [1] including the isotopic dependence [3], most previous works have assumed Maxwellian equilibrium distribution function $F_{0}$ with rare exceptions, for instance Refs [4,5]. Neoclassical polarization shielding determines the long term behavior of zonal flows and it can be derived in the context of modern gyrokinetic [6] and bounce-kinetic theories [7]. This approach not only elucidates the underlying physics of residual zonal flows, is but also applicable to an arbitrary $F_{0}$. Using this method, we show that the long wavelength, high aspect ratio result, $R_{ZF}=\frac{1}{1+1.63q^{2}/\sqrt{\epsilon}}$ derived for a Maxwellian $F_{0}$ in Ref. [1] remains valid for any $F_{0}$ which is isotropic in velocity space. In addition, it is found that presence of high energy ions such as fusion product $\alpha$-particles described by slowing-down $F_{0}$ can enhance $R_{ZF}$ considerably in the intermediate wavelength regime $k_{r}\rho_{Ti}\sim 0.1$ [4]. This presentation will cover the physics behind the neoclassical polarization shielding and long term asymptotic behavior of zonal flows and the effects of the fusion product $\alpha$-particles on these.
References :
[1] M.N. Rosenbluth and F.L. Hinton, Phys. Rev. Lett. 80 724 (1998)
[2] P.H. Diamond et al., Plasma Phys. Control. Fusion 47 R35 (2005)
[3] T.S. Hahm et al., Nucl. Fusion 53 072002 (2013)
[4] Y.W. Cho and T.S. Hahm, Nucl. Fusion 59 066026 (2019)
[5] Z.X. Lu et al., Plasma Phys. Control. Fusion 61 044005 (2019)
[6] T.S. Hahm, Phys. Fluids 31 2670 (1988)
[7] B.H. Fong and T.S. Hahm, Phys. Plasmas 6 188 (1999)
| Country or International Organization | Korea, Republic of |
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