larger ICP model causing problems - singularity error

Hey,

I am using your thermal_plasma model as a basis to my model. It is almost the same. The only difference is that in my model the tube is straight (not curved) and longer (0.8 m). These are the dimensions of an ICP system we use in our plasma laboratory.
If I leave dimensions intact (length of 0.8 m) I always get a solver error (singularity). If I shorten the tube to about 0.2 m the solution works fine. Is there any solution to this problem?

Thank you,
Regards