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The role of negative hydroxyl ions in liquid-phase plasma discharge formation is investigated using an inhouse modeling framework. Two tunneling sources for electrons are considered—tunneling ionization of water molecules and tunneling detachment of negative hydroxyl ions together with additional reaction steps. The simulations are conducted for a needle-like powered electrode with two different nanosecond rise time voltage profiles—a linear and an exponential rise. Both the profiles have a maximum voltage of 15 kV. The predictions show that the electron detachment, which has a much lower threshold energy requirement, provides a stream of electrons at low applied voltage during the initial rise time. The electrical forces from the electron detachment process generate stronger compression but a weaker expansion regime in the liquid resulting in ∼40% increase in the density and only ∼1% decrease. The electron detachment tunneling process is found to be not limited by the electric field, but rather by the availability of negative hydroxyl ions in the system and ceases when these ions are depleted. The tunnel ionization of water molecules forms the electron wave at a higher applied voltage, but the resulting peak electron number density is typically six orders of magnitude larger than the detachment tunneling. The higher electron number density allows the recycling of depleted negative hydroxyl ions in the system and can reestablish tunneling detachment. In addition, the system experiences a larger variation in density; specifically, a decrease in density due to tunnel ionization. The prediction also shows that irrespective of the initial electron sources (i.e. tunnel ionization or tunnel detachment) the reduced electric field is not sufficient enough to allow electron impact ionization to be active and make a significant contribution. Path flux analysis is conducted to determine the kinetics responsible for the recycling of the negative hydroxyl ions.
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Controlling the breakdown delay time in pulsed gas discharge
Abstract In experiment and 2D3V PIC MCC simulations, the breakdown development in a pulsed discharge in helium is studied forU= 3.2 kV and 10 kV andP= 100 Torr. The breakdown process is found to have a stochastic nature, and the electron avalanche develops in different experimental and simulation runs with time delays ranging from 0.3 to 8μs. Nevertheless our experiments demonstrate that the breakdown delay time distribution can be controlled with a change of the pulse discharge frequency. The simulation results show that the breakdown process can be distinguished in three stages with (a) the ionization by seed electrons, (b) the ions drift to the cathode and (c) the enhanced ionization within the cathode sheath by the electrons emitted from the cathode. The effects of variation of seed electron concentrations, voltage rise times, voltage amplitudes and ion–electron emission coefficients on the breakdown development in the pulsed gas discharge are reported.
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- Award ID(s):
- 1747760
- PAR ID:
- 10364516
- Publisher / Repository:
- IOP Publishing
- Date Published:
- Journal Name:
- Plasma Sources Science and Technology
- Volume:
- 31
- Issue:
- 3
- ISSN:
- 0963-0252
- Page Range / eLocation ID:
- Article No. 03LT01
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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