Should I mention my target audience / the aim of the paper in the
abstract? Should it be in the introduction? Should it be in the paper
In my experience you should mention the target audience / the aim of the paper in the both the abstract and the introduction, if possible. If you have to go with one of the two then mention it in the introduction, probably in the penultimate paragraph, where you move from explaining what has been done before to explaining what the paper will do.
I think that mentioning the the target audience / the aim of the paper is important as papers are often rejected due to misunderstandings, for instance where they are directed at practitioners, but evaluated by reviewers based on other "quality" criteria. Accordingly, you should be very careful to set up the criteria that you want to be evaluated on. As one academic in my field once told me "you need to be very clear about the stick you want them to beat you with".
There are different ways you can do this sort of subtle scoping and expectation setting. It really depends on the field and venue you are targeting. Sometimes you can just start with "The paper aims to...". If that is too clunky, or you need to state things more subtly, you could use something like:
- To address the research gaps previously outlined (e.g., x,y,z), this paper therefore aims to...
- "As the aim of the paper is to provide a foundation overview of..., it mimics prior exemplars in this area (e.g., x) to (do) x, y and z".
The benefit of doing something like the second one is that the linking to templates will let reviewers (not all of whom may understand your type of intended contribution) see that it i) has been done before (which reviewers often value), and ii) give them something to compare your paper against to determine its quality.