An electric field accelerates ions and electrons in {HEAD ~ directions} parallel to {TAIL ~ the electric field} 
parallel to
An electric field accelerates ions and electrons in { HEAD ~ directions } parallel to { TAIL ~ the electric field }
OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL