docs: def plot(self, **kwds):
          r"""The plotting function for MOT fields."""
          plo = self.lx.plot(dist_to_center=3, **kwds)
          plo += self.ly.plot(dist_to_center=3, **kwds)
          plo += self.lz.plot(dist_to_center=3, **kwds)
          plo += self.lx_r.plot(dist_to_center=3, **kwds)
          plo += self.ly_r.plot(dist_to_center=3, **kwds)
          plo += self.lz_r.plot(dist_to_center=3, **kwds)
          return plo