나마 : 어떤 상황이 마음에는 차지 아니하나 아쉬운 대로 접어주는 조건의 뜻을 나타내는 연결 어미. 나마 is a suffix of meaning "though; however; but anyway; if only" 잠시 means "for a moment" 잠시나마 means "for a moment, though" 잠시 행복했어 I was happy for a moment. 잠시나마 행복했어 Though it was a short time, I was happy.

It's very tricky! We use '잠시나마' When we emphasis specific period of time. For example, If you enjoyed something for a short time and you wanted to say it was nice time, albeit short, you could say "잠시나마 즐거웠어요." On the other hand, '잠시' is used for 'for a short time or for a moment'. There is no emphasis when we use it. e.g) one second = 잠시만요