Power transformer toroid Design

I'm working on induction furnace project,, I'm facing a serious problem with my toroid transformer. As you may find in the attachment Pic, There's green toroid with 20 Turns, which transfer the current from 1500 Hz inverter to LC tank which in turn works in resonance. The problem is the core saturates before I reach the current level I need ( which 40 amps) as you may also find in the attachment file. It saturates at 3 amps. I'm seeking for help to design the core so that it doesn't saturate at the current level I need

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the yellow waveform is the output voltage of the inverter,, the blue waveform is the output current , as u can see the spike happens like that at certain voltage level ,, but at lower voltage level ,, the output current is pretty much sinusoidal wave until I increase the voltage and current spikes up like that