Plasma Globe

Plasma globes are filled with low-pressure noble gasses (krypton, xenon and neon). An electrode is located in the center of the container, with a high-voltage, high frequency transformer underneath. 

The transformer generates a large AC current (a few kV), with a frequency in the vicinity of 35 kHz. The voltage is strong enough to ionize the gas, turning the ordinary gas into a plasma. The plasma organizes itself into a filament structure (visibly seen as paths of ionized gas from the electrode to the surface of the glass).