r ). ▁ ▁Saf ety ▁factor ▁In ▁the ▁case ▁of ▁an ▁axis ym metric ▁system , ▁which ▁was ▁common ▁in ▁earlier ▁fusion ▁devices , ▁it ▁is ▁more ▁common ▁to ▁use ▁the ▁safety ▁factor , ▁which ▁is ▁simply ▁the ▁inverse ▁of ▁the ▁rot ational ▁transform : ▁ ▁The ▁safety ▁factor ▁is ▁essentially ▁a ▁measure ▁of ▁the ▁" wind iness " ▁of ▁the ▁magnetic ▁fields ▁in ▁a ▁re actor . ▁If ▁the ▁lines ▁are ▁not ▁closed , ▁the ▁safety ▁factor ▁can ▁be ▁expressed ▁as ▁the ▁pitch ▁of ▁the ▁field : ▁ ▁As ▁the ▁fields ▁vary ▁across ▁the ▁minor ▁axis , ▁q ▁also ▁var ies ▁and ▁is ▁often ▁expressed ▁as ▁q ( r ). ▁On ▁the ▁inside ▁of ▁the ▁cyl inder ▁on ▁a ▁typical ▁to k am ak ▁it ▁converges ▁on ▁ 1 , ▁while ▁at ▁the ▁outside ▁it ▁is ▁near er ▁ 6 ▁to ▁ 8 . ▁ ▁Kr us kal - Sh af ran ov ▁limit ▁Tor oid al ▁arrang ements ▁are ▁a ▁major ▁class ▁of ▁magnetic ▁fusion ▁energy ▁re actor ▁designs . ▁These ▁are ▁subject ▁to ▁a ▁number ▁of ▁inher ent ▁inst abilities ▁that ▁cause ▁the ▁pl asma ▁to ▁exit ▁the ▁conf in ement ▁area ▁and ▁hit ▁the ▁walls ▁of ▁the ▁re actor ▁on ▁the ▁order ▁of ▁mill iseconds , ▁far ▁too ▁rapidly ▁to ▁be ▁used ▁for ▁energy ▁generation . ▁Among ▁these ▁is ▁the ▁k ink ▁inst ability , ▁which ▁is ▁caused ▁by ▁small ▁variations ▁in ▁the ▁pl asma ▁shape . ▁Are as ▁where ▁the ▁pl asma ▁is ▁slightly ▁further ▁from ▁the ▁center