Particles after time expressions like "三週間"


I am a beginner in Japanese so I was trying to write some simple sentences to
practice my vocabulary and grammar.

I wanted to write the sentence:

> My friend is in Japan for three weeks.

as:

> 私の友達が 三週間 日本に います。

I am unsure if I should put any particle after 三週間 and whether this sentence
is grammatically correct at all.




[[間]{かん}](http://jisho.org/search/%E9%96%93) itself is functioning as a suffix
indicating 'interval' or 'period of time'. In other words, '三週間' literally
translates to '三週 (three weeks) + 間 (during or for)'. Therefore, you don't
need any other particle or suffix after '三週間'.

One more important thing you should note is [Japanese normally doesn’t put
spaces between words](http://www.japanesereview.com/things-that-make-japanese-
hard/).

