短語詞組短語helical flow field 螺旋流場helical magnetic field 螺旋磁場spatially periodic helical magnetic field 周期性磁場poloidal helical field 垂環(huán)螺旋場resonant helical field 共振螺旋場transverse helical wiggle magnetic field 橫向螺旋搖擺磁場helical coil steam generator field 螺旋場 返回 helical field