Daaz1, BRAVO for your fine efforts and progress.
We used wideband CTs for HID and arc lamp ignitors and SMPS designs, decades ago 1980s ..1990s
We had contact to Mr. Pearson, a pioneer in the field.
A few moments for a trip down memory lane...
1/ Cores are high perm, besides 10k..15k ferrite, I believe thin tapewound cores and amorphous tapewound cores were used.
2/ Application with high DC bias need a gapped core or powdered iron.
3/ Commonly the problem is sidestepped with a DC bucking technique on a second primary.
Thus the core sees only the AC component, the DC component is cancelled by the buck winding.
A TEK high current clamp on extender CT-4 comes with an accessory DC buck coil.
https://w140.com/tekwiki/wiki/CT-44/ Winding is sectionalized and a distributed termination is used. Each section has a term resistor.
5/ Coil term is optimized for best BW or HF transient response, independent of required system Zo eg 50 Ohm.
6/ The coil term is then adapted to the BNC or connector Zo with a matching network.
7/ Calibration constant is adjusted in the term and matching network eg 100 mV = 1 A
8/ Number of turns increase with required LF corner.
9/ You can test at higher excitation with a multiturn primary eg 10 T multiplies the primary A*T by 10.
10/ The finished toroid is shielded against EMI and capacitive noise by a metal shield which has breaks to avoid shorted turns.
11/ occasionally can find a used Pearson 410, 411 at Ham fleas, surplus, or epay. Patience and persistence.
We have several, paid $25.....$75 over the decades.
12/ I think the design details are in old fine papers, app notes and patents from Pearson and others.
Just the ramblings of an old retired EE.
Jon