I have made a simple plasma chamber that can emulate the cold plasma. The following picture shows the plasma that it generates.
When I put a dielectric disk (Acrylic disk) on the bottom electrode, which is the ground and put a single copper disk on it that is connected to the bottom electrode through the dielectric with a wire, the plasma seems to converge only to the area covered by the copper plate and doesn't hit other areas on the dielectric disk. Following image shows what I'm saying.
The following picture shows how the copper plate has been placed on the dielectric plate. The copper plate is connected to the ground electrode through the dielectric with a wire.
The following pictures shows the plasma generated due to copper plate on the dielectric plate.
You can clearly see that the plasma is generated only in the area covered by the small copper plate. Here I'm using a 23kHz sinusoidal power signal with a voltage of about 10-20 kV to generate the plasma.
My question is if I put a dielectric in between the electrodes why does the plasma is not generated ? the images show the plasma is generated where it can see the ground potential, small copper plate.
Is it because ions cannot pass through the dielectric?
When I put the dielectric in between the electrodes, what happens is, it creates a capacitor, but AC current can pass through a capacitor. Then why does it still unable to generate the plasma ?