Electrolytic Radial Capacitor 18x31x7mm. As a low ESR capacitor it allows for very rapid charging and discharging. This is what we want because the faster the rate of change the better results we get.
This is for the mini DualPole motor capacitor pulser circuit that transduces the negative energy to positive for the charging battery. See the following video:
Also for use in resonant high frequency circuits.