▁to ▁an ▁atomic ▁nucle us , ▁as ▁condu ction ▁electrons ▁in ▁the ▁atomic ▁lattice ▁of ▁met als , ▁or ▁as ▁free ▁electrons ▁in ▁vac u um . ▁ ▁Free ▁electrons ▁in ▁vac u um ▁can ▁be ▁acceler ated , ▁with ▁their ▁paths ▁controlled ▁by ▁electric ▁and ▁magnetic ▁fields . ▁In ▁this ▁way ▁narrow ▁be ams ▁of ▁electrons ▁carrying ▁high ▁kin etic ▁energy ▁can ▁be ▁formed , ▁which ▁upon ▁collision ▁with ▁atoms ▁in ▁sol ids ▁transform ▁their ▁kin etic ▁energy ▁into ▁heat . ▁Electron - be am ▁w eld ing ▁provides ▁excellent ▁w eld ing ▁conditions ▁because ▁it ▁involves : ▁ ▁Str ong ▁electric ▁fields , ▁which ▁can ▁acceler ate ▁electrons ▁to ▁a ▁very ▁high ▁speed . ▁Thus , ▁the ▁electron ▁beam ▁can ▁carry ▁high ▁power , ▁equal ▁to ▁the ▁product ▁of ▁beam ▁current ▁and ▁acceler ating ▁voltage . ▁By ▁increasing ▁the ▁beam ▁current ▁and ▁the ▁acceler ating ▁voltage , ▁the ▁beam ▁power ▁can ▁be ▁increased ▁to ▁pract ically ▁any ▁desired ▁value . ▁Using ▁magnetic ▁l enses , ▁by ▁which ▁the ▁beam ▁can ▁be ▁sh aped ▁into ▁a ▁narrow ▁cone ▁and ▁focused ▁to ▁a ▁very ▁small ▁diameter . ▁This ▁allows ▁for ▁a ▁very ▁high ▁surface ▁power ▁density ▁on ▁the ▁surface ▁to ▁be ▁w eld ed . ▁Val ues ▁of ▁power ▁density ▁in ▁the ▁c ros so ver ▁( focus ) ▁of ▁the ▁beam ▁can ▁be ▁as ▁high ▁as ▁ 1 0 4 ▁– ▁ 1 0 6 ▁W / mm 2 . ▁Sh allow ▁pen etr ation ▁depth s ▁in ▁the ▁order ▁of ▁hundred