Numerical simulation of the initial stage of unipolar arcing in fusion-relevant conditions

Abstract

A model for the initial phase of unipolar arcing has been developed with account of an externalenergy source which triggers the arcing, the vaporization of the atoms from the heated surface, the ions and electrons produced by ionization of the vapor, the electron emission from the metal surface, and melt motion and surface deformation. Current transfer outside the arc attachment is taken into account and the potential difference between the plasma and the metal surface (the plate) is evaluated from the condition that the net current transferred to the plate is zero at each moment. The model is used for simulation of the interaction of an external energy load (laser beam) with a tungsten plate immersed in a helium background plasma. The results revealed the formation of a crater, but no jet formation or droplet detachment. If the plate is large ( = R 100 mm), the peak temperature attained is 5200 K, and the plate potential remains below the plasma potential. If the plate is small ( = R 10 mm), a peak temperature of 7500 K is reached, the potential of the plate surpasses the plasma potential, circulation of the melt at the pool periphery occurs, and the erosion (which is mainly due to the vaporization of the metal atoms in the spot) reaches the value of 37 μg.

Wall cratering upon high velocity normal dust impact

“…Some characteristic examples are provided in figure 6. Note that the excavated material from a single impact crater is much larger than the excavated material from a single unipolar arc crater [51,52], but much smaller than the material excavated during an edge-localized mode or major disruption driven melt event [53].…”

Analysis of processes leading to explosive phenomena on the surface of a liquid cathode at the time of the dc electric arc ignition

“…That is, during the development of instability followed by an explosion, dissipative processes do not play a significant role, especially viscosity. The numerical simulation at times of ∼ 10μs with the formation of a crater and detachment of drops can be found in [12].…”

Analytical expressions for thermophysical properties of solid and liquid beryllium relevant for fusion applications

“…The thermophysical properties of interest are the latent heats of phase transitions (fusion, hcp-to-bcc polymorphic transition, vaporization), the specific isobaric heat capacity, the electrical resistivity, the thermal conductivity, the mass density, the vapor pressure, the work function, the total hemispherical emissivity and the absolute thermoelectric power (for the solid and the liquid phases) as well as the surface tension and the dynamic viscosity (only for the liquid phase). The primary objective is to identify and to critically evaluate reliable experimental datasets in order to propose accurate empirical expressions for the temperature dependence of these thermophysical quantities that will standardize their description in the multiple thermal analysis [11,12], vapor shielding [13,14,15], macroscopic melt motion [16,17,18], arcing [19,20,21], dust generation [22,23] and dust transport codes [24,25,26,27,28,29] that are being developed by the fusion community. In the case when no reliable experimental datasets are available, the objective is to propose analytical extrapolations that do not violate general statistical mechanics principles and are consistent with well-established semi-empirical rules.…”