逐次近似 meaning in English

progression approximation
progressive approximation

From the exact expression of the field , we obtain a multipole polynomial expansion , and under the paraxial condition we furthermore obtain the approximate expression . the loffe trap , consisting of two coils with parallel currents and four straight conductors with currents in alternating directions , is one of the most important traps . we specially study the field structure of it by using both the exact expression and a multipole polynomial expansion that facilitates studies of classical or quantum orbits . if the region near the origin is of interest , we may obtain a simple expression of the field and this configuration may be called idealized loffe trap
若只讨论阱中的近原点区域时，阱中的磁场可以呈现出一种简洁的形式，人们把它称为理想ioffe阱。磁矩反平行于磁场的中性粒子在阱中与磁场发生相互作用，借助相互作用势，可以获得粒子在阱中的经典运动方程。在一定的近似条件下，我们可以采用逐次近似的方法，使方程简化，其中三个分量式中关于z的方程比较容易求解，而关于x 、 y的方程则演化为我们熟悉的马丢方程的形式。