Secondary electron emission yield from carbon samples
Secondary electron emission yield from carbon samples
Measurements of Secondary Electron Emission (SEE) yield are reported for samples of clean 5890PT graphite and for the same material exposed for some months in the JET Tokamak. The samples exposed in the Tokamak give substantially higher values than the clean samples. Controlled experiments show that deposition of thin metal films increases the yield. These experimental data have been integrated over a 3D Maxwellian distribution to obtain the values of effective SEE yields, theoretical values of sheath potential and sheath energy transmission factor have been calculated. The implications for ion sputtering and power loss are discussed. Controlled experiments are also carried out on clean pocographite samples. Initially maximum SEE yield was 0.86 which was reduced to 0.53 after heating to 500°C. After the sample was exposed to hydrogen gas and argon gas, yield increased to 0.63 in both cases. The implantation with hydrogen ions increased the yield to 1.02 whereas by argon ions bombardment left the SEE yield unchanged at 0.63.
The yield value of 1.02 is lower than that of 5890 PT graphite after hydrogen implantation but similar to graphite exposed to plasma. The desorption curve shows a weak peak near 150°C and a strong peak near 450°C, corresponding to activation energies of 1 and 2.1 eV respectively. For graphite bombarded by argon, the desorption curve shows a weak peak at 500°C. The yield was reduced from 1.02 to 0.53 at 550°C, but for argon implanted graphite, the yield rises to 0.82 at 200°C and then returns to 0.53 at 550°C. Back scattering coefficients and SEE yields at low energies are also reported. The results show that the SEE yield falls to a value less than 0.1 at 15 eV and then rises with energy. For the first time, backscattering coefficients and SEE yields of graphite have been simulated for carbon in the range from zero to 1000 eV. These results agree well with published results to within 2%. (DX192447)
University of Southampton
Farhang, Mohammad Hossein
1992
Farhang, Mohammad Hossein
Farhang, Mohammad Hossein
(1992)
Secondary electron emission yield from carbon samples.
University of Southampton, Doctoral Thesis.
Record type:
Thesis
(Doctoral)
Abstract
Measurements of Secondary Electron Emission (SEE) yield are reported for samples of clean 5890PT graphite and for the same material exposed for some months in the JET Tokamak. The samples exposed in the Tokamak give substantially higher values than the clean samples. Controlled experiments show that deposition of thin metal films increases the yield. These experimental data have been integrated over a 3D Maxwellian distribution to obtain the values of effective SEE yields, theoretical values of sheath potential and sheath energy transmission factor have been calculated. The implications for ion sputtering and power loss are discussed. Controlled experiments are also carried out on clean pocographite samples. Initially maximum SEE yield was 0.86 which was reduced to 0.53 after heating to 500°C. After the sample was exposed to hydrogen gas and argon gas, yield increased to 0.63 in both cases. The implantation with hydrogen ions increased the yield to 1.02 whereas by argon ions bombardment left the SEE yield unchanged at 0.63.
The yield value of 1.02 is lower than that of 5890 PT graphite after hydrogen implantation but similar to graphite exposed to plasma. The desorption curve shows a weak peak near 150°C and a strong peak near 450°C, corresponding to activation energies of 1 and 2.1 eV respectively. For graphite bombarded by argon, the desorption curve shows a weak peak at 500°C. The yield was reduced from 1.02 to 0.53 at 550°C, but for argon implanted graphite, the yield rises to 0.82 at 200°C and then returns to 0.53 at 550°C. Back scattering coefficients and SEE yields at low energies are also reported. The results show that the SEE yield falls to a value less than 0.1 at 15 eV and then rises with energy. For the first time, backscattering coefficients and SEE yields of graphite have been simulated for carbon in the range from zero to 1000 eV. These results agree well with published results to within 2%. (DX192447)
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Published date: 1992
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Local EPrints ID: 459523
URI: http://eprints.soton.ac.uk/id/eprint/459523
PURE UUID: c52b3e71-cde4-46a3-ae1f-25b85fb7fff7
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Date deposited: 04 Jul 2022 17:13
Last modified: 04 Jul 2022 17:13
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Author:
Mohammad Hossein Farhang
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