What is the unique design of the Zeeman slower in PRA 71 023409 2005?

[nanguaa]

There are two kinds of Zeeman slower as everyone konws :6+ and 6-.But yestoday ,I saw a strange one in a paper(PRA 71 023409 2005).It has a different magnetic field coils.Is there anyone knows some detail about it?

 

[Yuri1]

It is a spin-flip Zeeman slower, in which the magnetic field changes its sign in the middle of the slower.