▁consider ations ▁apply ▁in ▁stell ar ators , ▁by ▁convention ▁the ▁inverse ▁value ▁is ▁used , ▁the ▁rot ational ▁transform , ▁or ▁i . ▁ ▁The ▁concept ▁was ▁first ▁developed ▁by ▁Martin ▁David ▁Kr us kal ▁and ▁V ital y ▁Sh af ran ov , ▁who ▁noticed ▁that ▁the ▁pl asma ▁in ▁pin ch ▁effect ▁react ors ▁would ▁be ▁stable ▁if ▁q ▁was ▁larger ▁than ▁ 1 . ▁Mac ro scop ically , ▁this ▁implies ▁that ▁the ▁w avel ength ▁of ▁the ▁potential ▁inst ability ▁is ▁longer ▁than ▁the ▁re actor . ▁This ▁condition ▁is ▁known ▁as ▁the ▁Kr us kal - Sh af ran ov ▁limit . ▁ ▁Background ▁The ▁key ▁concept ▁in ▁magnetic ▁conf in ement ▁fusion ▁is ▁that ▁ ions ▁and ▁electrons ▁in ▁a ▁pl asma ▁will ▁rotate ▁around ▁magnetic ▁lines ▁of ▁force . ▁A ▁simple ▁way ▁to ▁conf ine ▁a ▁pl asma ▁would ▁be ▁to ▁use ▁a ▁sol en oid , ▁a ▁series ▁of ▁circular ▁magnet s ▁mounted ▁along ▁a ▁cyl inder ▁that ▁generates ▁uniform ▁lines ▁of ▁force ▁running ▁down ▁the ▁long ▁axis ▁of ▁the ▁cyl inder . ▁A ▁pl asma ▁generated ▁in ▁the ▁center ▁of ▁the ▁cyl inder ▁would ▁be ▁conf ined ▁to ▁run ▁along ▁the ▁lines ▁down ▁the ▁inside ▁of ▁the ▁t ube , ▁keeping ▁it ▁away ▁from ▁the ▁walls . ▁However , ▁it ▁would ▁be ▁free ▁to ▁move ▁along ▁the ▁axis ▁and ▁out ▁the ▁ends ▁of ▁the ▁cyl inder . ▁ ▁One ▁can ▁close ▁the ▁ends ▁by ▁b ending ▁the ▁sol en oid ▁around ▁into ▁a