Entropy Production in a DC Plasma Diode with a Fireball on the Anode

One of the consequences of driving a plasma discharge away from the thermodynamic equilibrium is the appearance of one or more fireballs in front of the anode. The formation of this self-organized space charge structure marks the transformation of part of the thermal energy of the electrical charges into the electric potential energy of the structure. The self-assembly of the fireball as well as its existence in a stable stationary state prove to be good candidates for testing the validity/selection of the proposed extremal (maximum or minimum) entropy production principles in the case of systems driven far from the thermodynamical equilibrium. The use of experimental results and of a basic mathematical model shows that the emergence of a fireball in a plasma diode maximizes the entropy production rate, while its subsequent existence minimizes the entropy production rate.