Jumps in dispersion relation at high kperp

[danielver02]

At high kperp, the dispersion relation sometimes exhibits jumps in the frequency and growth rate solutions. A change to positions_principal and n_resonance_interval does not mitigate this significantly.

If these jumps occur, they usually occur at the same kperp, independently of kpar. This suggests that they are related to the Bessel function routine at high kperp.

This problem primarily occurs when the code calculates high-frequency electron waves. It especially occurs also when working in electron mode for these solutions.