indicates that if the emission frequency becomes higher, the value of $E_{||}$ would approach $E_{||} \sim 0$. However, it is difficult to remove such an artificial effect in the global particle simulation due to a limited computational power. It is not clear at the moment whether the $|E_{||}|$ above the poles includes the essential electric field or not.

The pairs generated in the OG are accelerated in opposite directions by the $E_{||}$. The positive particles are accelerated outward, and flowed out as a pulsar wind. On the other hand, the negative particles are accelerated toward the star by the outward-directed $E_{||}$. If the star solely absorbs the negative particles continuously, it would be charged up negatively. To prevent such charging up, the negative particles are re-emitted from the stellar surface around the magnetic poles and spread into the magnetosphere. In this way, a current passing through the PC originates the negative particles generated in the OG.

In our simulation, particles are traced up to the distance of $10 R_{\mathrm L}$. Most of them flow out beyond the outer boundary as a pulsar wind, but some negative particles emitted from the PC region return to the star. This circulating flow can 