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Theory and simulation of anode spots in low pressure plasmas

Physics of Plasmas

Scheiner, Brett; Barnat, Edward; Baalrud, Scott D.; Hopkins, Matthew M.; Yee, Benjamin T.

When electrodes are biased above the plasma potential, electrons accelerated through the associated electron sheath can dramatically increase the ionization rate of neutrals near the electrode surface. It has previously been observed that if the ionization rate is great enough, a double layer separates a luminous high-potential plasma attached to the electrode surface (called an anode spot or fireball) from the bulk plasma. Here, results of the first 2D particle-in-cell simulations of anode spot formation are presented along with a theoretical model describing the formation process. It is found that ionization leads to the build-up of an ion-rich layer adjacent to the electrode, forming a narrow potential well near the electrode surface that traps electrons born from ionization. It is shown that anode spot onset occurs when a quasineutral region is established in the potential well and the density in this region becomes large enough to violate the steady-state Langmuir condition, which is a balance between electron and ion fluxes across the double layer. A model for steady-state properties of the anode spot is also presented, which predicts values for the anode spot size, double layer potential drop, and form of the sheath at the electrode by considering particle, power, and current balance. These predictions are found to be consistent with the presented simulation and previous experiments.

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TYPE Journal Article YEAR 2017
DOIOSTIScopus

Carrier dynamics model for laser-solid interactions

Chow, Weng W.; Moore, Christopher H.; Biedermann, Laura B.; Hopkins, Matthew M.; Dagel, Daryl; Cartwright, Keith

This report describes a model for the time development of carrier distributions within a metallic or semiconductor target after the onset of an incident laser pulse. The dynamics of electron and hole populations in momentum-resolved conduction- and valence-band states are treated at the level of carrier-carrier and carrier-phonon scattering. These scattering events result in plasma and lattice heating, which in turn lead to electron thermionic emission and tunneling, and target material ablation. A fairly phenomenological approach is taken to mitigate numerical computation demands, in order to facilitate parametric studies. Two examples of application are presented. One involve s the incident of an intense near-infrared laser pulse on a solid aluminum target, where the goal is to connect excited species emission to physics at a band-structure level. The second involves modeling the trigger mechanism in laser-triggered high-voltage switches, where the results are used as input to highly intensive particle-in-cell (PIC) plasma simulations of switch operation.

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TYPE SAND Report YEAR 2017
DOIOSTI
Results 101–125 of 225
Results 101–125 of 225