free flow[@arons83] is then inevitable in the open field line regions, so that the atmosphere materials above the polar caps, which are composed of normal hadrons, will be pulled out. In neutron stars, such a flow could persist throughout the pulsars’ whole lifetimes since the thick crusts of the neutron stars can supply copious ions and electrons to be pulled out. In the case discussed here (a strange star with an atmosphere), the particles available for this extracting is limited, which is only the part of atmosphere right above the polar caps. The time scale for pulling out this atmosphere is short. With a Goldreich-Julian flow, the extracting column number density flux is $F=(\Omega B/2\pi e)\sim 2.1\times 10^{21}B_{12}P^{-1}{\rm cm}
^{-2}{\rm s}^{-1}$. Given the atomic mass unit $u=1.66\times 
10^{-24}$ g, the extracting column mass density flux is then $F_{\rm m}\sim 2 u F$, therefore the extracting time scale is typically $$\tau=\sigma_{\rm a}/F_{\rm m} \sim
3.6 \times 10^{-2} B_{12}P^{-1}v_9^{-2}R_6^4 M_1^{-1}~{\rm yr},
\label{tau}$$ which is much shorter than a pulsar’s lifetime. Furthermore, if the timescale for the ejecta to fall back is longer than the timescale of forming a Gorldreich-Julian magnetosphere, the space-charge-limited flow from the polar cap region will effectively block the 