▁both ▁the ▁def lect ing ▁co ils ▁as ▁well ▁as ▁to ▁the ▁necessary ▁electron ics . ▁Such ▁a ▁system ▁enables ▁not ▁only ▁“ static ” ▁def lection ▁of ▁the ▁beam ▁for ▁the ▁position ing ▁purposes ▁mentioned ▁above , ▁but ▁also ▁precise ▁and ▁fast ▁dynamic ▁control ▁of ▁the ▁beam ▁spot ▁position ▁by ▁a ▁computer . ▁This ▁makes ▁it ▁possible , ▁e . g .: ▁to ▁w eld ▁joint s ▁of ▁complicated ▁geometry , ▁and ▁to ▁create ▁image - en larg ed ▁pictures ▁of ▁objects ▁in ▁the ▁working ▁chamber ▁on ▁TV ▁or ▁PC ▁mon itors . ▁ ▁Both ▁possibilities ▁find ▁many ▁useful ▁applications ▁in ▁electron - be am ▁w eld ing ▁practice . ▁ ▁Pen etr ation ▁of ▁electron ▁beam ▁during ▁w eld ing ▁To ▁explain ▁the ▁cap ability ▁of ▁the ▁electron ▁beam ▁to ▁produce ▁deep ▁and ▁narrow ▁w eld s , ▁the ▁process ▁of ▁" pen etr ation " ▁must ▁be ▁explained . ▁First ▁of ▁all , ▁the ▁process ▁for ▁a ▁" single " ▁electron ▁can ▁be ▁considered . ▁ ▁Pen etr ation ▁of ▁electrons ▁ ▁When ▁electrons ▁from ▁the ▁beam ▁impact ▁the ▁surface ▁of ▁a ▁solid , ▁some ▁of ▁them ▁may ▁be ▁reflected ▁( as ▁" back sc atter ed " ▁electrons ), ▁while ▁others ▁pen et rate ▁the ▁surface , ▁where ▁they ▁col lide ▁with ▁the ▁particles ▁of ▁the ▁solid . ▁In ▁non - el astic ▁coll isions ▁they ▁lose ▁their ▁kin etic ▁energy . ▁It ▁has ▁been ▁proved , ▁both ▁theoret ically ▁and ▁experiment ally , ▁that ▁they ▁can ▁" tra