Theoretical analysis of the current and energy flow to the anode in the diffuse vacuum arc

The current energy flow to the anode in a diffuse vacuum arc is investigated using a simple multicathode-spot fluid description of the interelectrodic plasma. Decisive for the current constriction and the energy flow to the anode center is the space-charge sheath in front of the anode. This sheath not only determines the current-density distribution at the anode, but also may lead to a strong energy gain of the electrons before they reach the anode surface (in case the anode drop appears to be positive in the anode center). Numerical results are given and two possible scenarios for the transition from the diffuse to the anode-spot mode are discussed.>