The diameter of {TAIL ~ channel} 34 of {HEAD ~ magnet} 36 should increase with length, as shown in FIG 1, so as to have the radius of the poles always equal to the off axis displacement of the outermost molecules to be focused 
The diameter of { TAIL ~ channel } 34 of { HEAD ~ magnet } 36 should increase with length , as shown in FIG 1 , so as to have the radius of the poles always equal to the off axis displacement of the outermost molecules to be focused
OTH OTH OTH TAIL TAIL TAIL TAIL TAIL OTH OTH HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH