The neutral gas in a ff device is at low pressure. When the electrical discharge occurs in the chamber the neutral gas is changed to a plasma that is a good conductor. A powerful electrical current creates a very strong magnetic field in the plasma and squeezes the plasma to a very dense state. The effort now is to increase the current enough so that the plasma is squeezed to a solid state. At that point the temperature, density and time should be sufficient to create good fusion yields.
Look at this description: https://lppfusion.com/fusion-power/dpf-device/
