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Insulation between high voltage electrodes is often in the form of micro-gaps which leverage the high breakdown voltage that occurs on the near-side of Paschen’s curve. Structures on the electrodes are a concern due to electric field enhancement that can occur. The breakdown voltage in atmospheric pressure micro-gaps having multiple cathode field emitters was computationally investigated using a hybrid plasma hydrodynamics model in which electron transport following cathode emission is addressed using a Monte Carlo simulation [1]. Three mechanisms for electron emission from the cathode were included - ion-impact secondary emission, photo-electron emission, and thermionically enhanced electric field emission. The cathode had three post electron emitters with a work function of 4.0 eV, diameter of 5 μm and with a cathode-tip to anode distance of 30 μm. A linearly ramping voltage was applied to the anode and the cathode was grounded. The electric field at the top of the cathode posts was enhanced by a factor of 100 to account for surface roughness. The rate of applying voltage was varied from 1 to 100 V/ns. It was found that in the thermionic emission regime the electron emission induced by ions and photons have a minor impact on the breakdown, which is much different from the processes in Townsend mode regimes [2, 3]. The consequences of cathode work function, field enhancement factor, surface temperature and surface morphology on breakdown voltage will also be discussed.
[1] M. J. Kushner, J. Phys. D: Appl. Phys. 38, 1633, 2005.
[2] Y. Fu, P. Zhang, and J. P. Verboncoeur, Appl. Phys. Lett. 112, 254102, 2018.
[3] Y. Fu, J. Krek, P. Zhang, and J. P. Verboncoeur, Plasma Sources Sci. Technol. 27, 095014, 2018.
*This work was supported by the Air Force Office of Scientific Research (FA9550-18-1-0062, FA9550-18-1-0061) and the Department of Energy Office (DE-SC0001939).
