Energy to produce an electron-ion pair in SF6 and SF6 mixtures

Author

Youssef H. Hilal

Date of Award

3-1987

Degree Type

Thesis

Degree Name

Master of Science

Major

Electrical Engineering

Major Professor

Marshall O. Pace

Committee Members

L. G. Christophorou, D. Bouldin

Abstract

The resurgence of interest in the dielectric properties of SF₆ and mixtures containing SF₆ has resulted in increasing research activity related to the problems associated with the practical uses of SF₆. One problem relating to such use is the role of the initiatory electron (i.e., electron that initiates voltage breakdown in SF₆) which can be produced within the gas by cosmic and natural radiation, or by the collisional detachment processes from negative ions (i.e., SF₆^-). The proper assessment of the effect of cosmic radiation and gamma or x-radiography measurements for the detection of unwanted particles or broken insulators that might lead to a breakdown, required by a fast charged particle to create an electron-ion pair in a required by a charged particle to create an electron-ion pair in a given gas medium, i.e., W = E₀/N_i where E₀ is the initial energy of the charged particle, and N_i is the total number of electron-ion pairs produced by the complete absorption of E₀ in the gas. This last question is addressed hereby measuring the ionization produced in SF₆ and mixtures containing SF₆, when an alpha particle of energy E₀ produces N_i electron-ion pairs in becoming completely stopped in the gas or its gas mixtures.

The objectives of this work are:

1 . To measure the W values of SF₆ and SF₆ mixtures as a function of the applied voltage and pressure.

2. To determine the possibility of the existence of metastable states in SF₆ under electrically stressed conditions.

The W value of SF₆ was found to be 35.45 electron volt/ion pair (eV/ip); this rather high value is attributed to the large cross section for electron impact dissociation of SF₆ into neutral fragments. The W values of the gases N₂, C₂F₆, C₂H₂ and 2-C₄H₈, normally mixed with SF₆ for various insulating needs, have also been measured and are reported. Quantitative measurements of the W values for the binary gas mixtures SF₆/C₂H₂, SF₆/2-C₄H₈ and SF₆/C₆F₆ have also been studied.

No Penning ionization was observed for the binary gas mixtures; however, SF₆/2-C₄H₈ showed an increase of ionization due to the ionization of 2-C₄H₈ by metastable SF₆* molecules. This result, then, establishes the existence of SF₆* metastables and indicates that further studies are needed to explain the role of SF₆* metastables in ionization of the gas and electron ejection upon their collision with the electrode surface.

Recommended Citation

Hilal, Youssef H., "Energy to produce an electron-ion pair in SF6 and SF6 mixtures. " Master's Thesis, University of Tennessee, 1987.
https://trace.tennessee.edu/utk_gradthes/13483