Since this may mean that some molecules which are not deflected may collide with the walls of the magnet, {TAIL ~ evacuation} of the openings between {HEAD ~ the poles} should be provided, as shown in FIG 2 
Since this may mean that some molecules which are not deflected may collide with the walls of the magnet , { TAIL ~ evacuation } of the openings between { HEAD ~ the poles } should be provided , as shown in FIG 2
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH