One of the electrodes includes openings for allowing {HEAD ~ the vapor} to enter {TAIL ~ the space} 
One of the electrodes includes openings for allowing { HEAD ~ the vapor } to enter { TAIL ~ the space }
OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL TAIL