  Significant effects of impurities on residual zonal flow (ZF) in deuterium
(D)-tritium (T) plasmas are found. When the gyroradius of impurities is larger
(smaller) than that of main ions, the intermediate scale (radial wavelength
between trapped ion radial width $\rho_{bi}$ and trapped electron radial width
$\rho_{be}$) residual ZF level is increased (decreased) due to the presence of
various impurities with the tolerance concentration in JET and ITER, even for
trace tungsten (W). For short scale (radial wavelength comparable to
$\rho_{be}$) region, the residual ZF level is increased by most of the
impurities. Moreover, the trend of stronger intermediate residual ZF in D-T
plasmas with heavier effective isotope mass is weakened by non-trace
impurities, but is not influenced by trace W. These results reveal that the
presence of impurities can modify residual ZF, and possibly further affect the
ZF regulation of turbulence as well as the associated anomalous transport and
confinement in magnetic fusion plasmas. The potential relevance of our findings
to experimental observations and simulation results is discussed.
