CST PARTICLE STUDIO里Particle Tracking和PIC solve有什么区别？

我在用CST仿真真空管，看帮助文件，2011带了两个例子。Electron Gun（电子枪）是用Particle Tracking计算的。而Output Cavity (workflow)的说明是This workflow example demonstrates how to build up the output cavity of a klystron for a PIC simulation。是用PIC计算的。我看了简介。
Gun Solver & Particle Tracking
The particle tracking solver can be used to compute trajectories of charged particles within electrostatic, magnetostatic or eigenmode fields. The implemented gun-iteration enables the computation of a self-consistent electrostatic field which considers the reaction of the particle movement to the electrostatic potential distribution. As particle sources arbitrary shaped surfaces of solids can be defined. These surfaces  emit particles considering a predefined  emission model. The main task for  the solver is to calculate the particle trajectories, the self-consistent electrostatic field, the space charge distribution and the particles' current. These results appear automatically in the navigation tree after the solver run.
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PIC Solver
The PIC solver can simulate charged particles in self-consistent electromagnetic fields. Moreover static or analytic field distributions can be added to the PIC simulation. Charged particles can be emitted from arbitray surfaces or single points. Moreover electromagnetic fields can be stimulated by previously defined ports.
看两者的说明都是计算在电场和磁场内粒子运动的，那这两者有什么区别?在实际使用的时候我怎么知道应该用哪个?
还有一个问题是：self-consistent是什么意思啊?
刚刚学习CST一个月不到的菜鸟求教。

PIC是自洽的吧
按照我的理解，Particle Tracking就是仿真粒子在场中的轨迹
而PIC仿真是粒子和场相互影响，粒子运动产生场，场和场相互作用，又对粒子产生影响。

哦，谢谢回复，大概懂了，就是说PIC是加上电场或者磁场，tracking是什么都不加的

什么都不加轨迹不就是直线了么，理解“自洽”