However, it has been found that the currently preferred approach is to use {HEAD ~ a multipole} focusing {TAIL ~ magnetic or electrostatic field} 
focusing
However , it has been found that the currently preferred approach is to use { HEAD ~ a multipole } focusing { TAIL ~ magnetic or electrostatic field }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL