▁basis . ▁As ▁such , ▁T EM s ▁are ▁equ ipped ▁with ▁multiple ▁p ump ing ▁systems ▁and ▁air lock s ▁and ▁are ▁not ▁perman ently ▁vac u um ▁se aled . ▁ ▁The ▁vac u um ▁system ▁for ▁ev acu ating ▁a ▁T EM ▁to ▁an ▁operating ▁pressure ▁level ▁consists ▁of ▁several ▁stages . ▁Initial ly , ▁a ▁low ▁or ▁rough ing ▁vac u um ▁is ▁achieved ▁with ▁either ▁a ▁rot ary ▁van e ▁p ump ▁or ▁dia ph rag m ▁p umps ▁setting ▁a ▁sufficiently ▁low ▁pressure ▁to ▁allow ▁the ▁operation ▁of ▁a ▁tur bo - m ole cular ▁or ▁diffusion ▁p ump ▁establish ing ▁high ▁vac u um ▁level ▁necessary ▁for ▁operations . ▁To ▁allow ▁for ▁the ▁low ▁vac u um ▁p ump ▁to ▁not ▁require ▁continuous ▁operation , ▁while ▁contin ually ▁operating ▁the ▁tur bo - m ole cular ▁p umps , ▁the ▁vac u um ▁side ▁of ▁a ▁low - press ure ▁p ump ▁may ▁be ▁connected ▁to ▁ch amb ers ▁which ▁accommod ate ▁the ▁exhaust ▁g ases ▁from ▁the ▁tur bo - m ole cular ▁p ump . ▁Se ctions ▁of ▁the ▁T EM ▁may ▁be ▁isolated ▁by ▁the ▁use ▁of ▁pressure - lim iting ▁a pert ures ▁to ▁allow ▁for ▁different ▁vac u um ▁levels ▁in ▁specific ▁areas ▁such ▁as ▁a ▁higher ▁vac u um ▁of ▁ 1 0 − 4 ▁to ▁ 1 0 − 7 ▁Pa ▁or ▁higher ▁in ▁the ▁electron ▁gun ▁in ▁high - resol ution ▁or ▁field - em ission ▁T EM