Plasma heating power dissipation in low temperature hydrogen plasmas

Abstract

Theoretical framework for power dissipation in low temperature plasmas in corona equilibrium is developed. The framework is based on fundamental conservation laws and reaction cross sections and is only weakly sensitive to plasma parameters, e.g. electron temperature and density. The theory is applied to low temperature atomic and molecular hydrogen laboratory plasmas for which the plasma heating power dissipation to photon emission, ionization and chemical potential is calculated. The calculated photon emission is compared to recent experimental results.

Experimental evidence on photo-assisted O− ion production from Al2O3 cathode in cesium sputter negative ion source

“…It is expected that in cesiated plasma ion sources, the benefits of exposing the negative ion production surface to a photon flux from an external source are limited as plasmas naturally radiate up to several tens of percent of the discharge power in UV/VUV-range, 30 resulting in significant photoelectron emission from cesiated surfaces. 31 However, if the follow-up experiments on cesium sputter ion sources with an adjustable wavelength laser were to reveal a significant contribution by the resonant pair production effect, experiments on laser-assisted negative ion production in the discharge volume of cesiated plasma ion sources would be justified.…”

Experimental evidence on photo-assisted O$^-$ ion production from Al$_2$O$_3$ cathode in cesium sputter negative ion source

“…It is expected that in cesiated plasma ion sources the benefits of exposing the negative ion production surface to a photon flux from an external source are limited as plasmas naturally radiate up to several tens of percent of the discharge power in UV/VUV-range 26 resulting in significant photoelectron emission from cesiated surfaces 27 . However, if the follow-up experiments on cesium sputter ion sources with an adjustable wavelength laser were to reveal a significant contribution by the resonant pair production effect, experiments on laserassisted negative ion production in the discharge volume of cesiated plasma ion sources would be justified.…”

Hydrogen plasma induced photoelectron emission from low work function cesium covered metal surfaces

“…Theoretical calculations based on fundamental conservation laws and reaction cross sections show that at least 10% of plasma heating power is dissipated via photon emission in low temperature hydrogen plasmas. 9 The theoretical result is supported by experimental evidence showing that low temperature hydrogen plasmas are strong sources of vacuum ultraviolet (VUV) radiation with up to 15%-30% of the discharge power radiated at wavelengths of 120-250 nm in filamentdriven arc discharge, 10 up to 8% of the injected microwave power at 80-250 nm in ECR discharge, 11 and up to 21% of RF power at 117-280 nm in RF discharge. 12 Electrons in the conduction band of a metal follow the Fermi-Dirac distribution which can be used to derive the following relation for the quantum efficiency Y of the PE emission: 13 Y / ðh À /Þ 2 ðU 0 À hÞ 1=2 ; when h !…”

“…Nevertheless, the effect of PEs on the plasma sheath structure may be significant for example in Penning type ion sources, 54 where a few kW discharge power is deposited into a small plasma volume (<1 cm 3 ), which can lead to high PE emission density from the walls as a significant part of the injected power is dissipated via photon emission. [9][10][11][12] On the contrary, in neutral beam injection sources the current density can be expected to be smaller, but this does not exclude the PEs effect on the reaction rates.…”