Bob, I am sure the are aero guys that can explain it far better, but here is the way I remember it from my aero classes. They are Mach diamonds in the after burner's exhaust. They form along the shock wave lines, internal to the burner's exhaust, as the shock waves reflect back and forth, in the aft direction. Without a functioning after burner on your P-200, I don't think there is any way that you will be able to generate visible Mach diamonds, if that's what you are after.