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The foam you are talking about is normally called "kraüsen" (mostly) or "barm" (sometimes, UK). The sediment at the bottom is excess yeast and trub that has dropped out of your beer. Even if a fermentation is going on for a longer time, this layer will form, so do not worry about that.
Looking at the picture, I see that you had a very vigorous fermentation. ...
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It is bitter due to the ginger and the yeast eating all the sugar. You really should backsweeten. Here is a really good article explaining all the different parts of this.
https://homebrewsupply.com/learn/make-alcoholic-ginger-ale.html
good luck
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