▁the ▁lines ▁of ▁magnetic ▁flux . ▁ ▁A ▁solid ▁conf in ement ▁vessel ▁is ▁also ▁needed , ▁both ▁to ▁shield ▁the ▁magnet s ▁and ▁other ▁equipment ▁from ▁high ▁temper atures ▁and ▁ener get ic ▁phot ons ▁and ▁particles , ▁and ▁to ▁maintain ▁a ▁near - v acu um ▁for ▁the ▁pl asma ▁to ▁populate . ▁The ▁contain ment ▁vessel ▁is ▁subject ed ▁to ▁a ▁bar rage ▁of ▁very ▁ener get ic ▁particles , ▁where ▁electrons , ▁ ions , ▁phot ons , ▁alpha ▁particles , ▁and ▁neut rons ▁constantly ▁bomb ard ▁it ▁and ▁deg rade ▁the ▁structure . ▁The ▁material ▁must ▁be ▁designed ▁to ▁end ure ▁this ▁environment ▁so ▁that ▁a ▁power ▁station ▁would ▁be ▁econom ical . ▁Test s ▁of ▁such ▁materials ▁will ▁be ▁carried ▁out ▁both ▁at ▁I TER ▁and ▁at ▁IF M IF ▁( Intern ational ▁F usion ▁Material s ▁Ir rad iation ▁Fac ility ). ▁ ▁Once ▁fusion ▁has ▁begun , ▁high ▁energy ▁neut rons ▁will ▁radi ate ▁from ▁the ▁re active ▁regions ▁of ▁the ▁pl asma , ▁crossing ▁magnetic ▁field ▁lines ▁easily ▁due ▁to ▁charge ▁neutral ity ▁( see ▁neut ron ▁flux ). ▁Since ▁it ▁is ▁the ▁neut rons ▁that ▁receive ▁the ▁majority ▁of ▁the ▁energy , ▁they ▁will ▁be ▁I TER ' s ▁primary ▁source ▁of ▁energy ▁output . ▁Ide ally , ▁alpha ▁particles ▁will ▁exp end ▁their ▁energy ▁in ▁the ▁pl asma , ▁further ▁he ating ▁it . ▁ ▁Bey ond ▁the ▁inner ▁wall ▁of ▁the ▁contain ment ▁vessel ▁one ▁of ▁several ▁test ▁blank et ▁modules