[Gmsh] refining the mesh of a circle with Attractor Fields

[Matthias Sitte]

Hi all,

I'm trying to set up the following problem:

1) Create a circular geometry with radius R_outer using 4 Circles and a 
Line Loop which defines the outer boundary of the mesh.

2) Create another closed circle (again made out of 4 Circles) with 
radius R_inner inside the circular mesh.

3) Goal is to reduce lchar and create a finer mesh close the inner 
circle, but keep the coarser mesh everywhere else.

So far I've started from the example t10.geo and mostly got what I 
wanted. But I observed that if I close the inner circle, all of the mesh 
within the circle is meshed with reduced lchar, not the lchar I would've 
expected. When I open the circle by leaving out segment(s), the result 
looks better w.r.t. mesh size, but it's of course not what I want. Am I 
missing something here?

Best,

Matthias