THE EFFECT OF DEUTERIUM ION BOMBARDMENT ON THE OPTICAL PROPERTIES OF BERYLLIUM MIRRORS Page: 3 of 9
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2. Optical Properties of Beryllium and BeO
The majority of experimental data on the published optical properties of Be were
reviewed by Arakawa et. al. [1]. Their data demonstrate that the reflectance, R, of Be is
practically independent of wavelength in the range k=300-700 nm and significantly
increases for shorter wavelengths, reaching a maximum at -200 nm. The reflectance
strongly depends on the technology of mirror preparation and was highest for a Be film
deposited in a high vacuum: up to R 55% in the visible range. As for the different bulk
processed beryllium mirrors the reflectance was at the level R-45% [1] in the same
range of wavelength. The approximate constancy of R in the indicated wavelength
range is an attractive peculiarity of a Be mirror, compared to mirrors of some other
materials, such as Cu for example [4].
It has been shown by other work [5,6] that a beryllium oxide film is very transparent,
having an extinction index equal to zero in the wavelength range of interest. The index
of refraction of BeO is near 1.7 and is also practically independent of wavelength.
3. Features of Behavior of BeO Under Bombardment by D Ions
As has been shown by Sharapov and co-workers (e.g. [7,8]), under D ion bombardment
the BeO film on the Be surface is transformed into a Be(OD)2 film by the process:
2BeO + 2D -> Be(OD)2 + Be + 0.7 eV/D. (1
It is seen from this reaction that one free Be atom is liberated per every molecule of
hydroxide production. This atom, in the case of an imperfect high vacuum, can again
react with a residual oxygen atom. Thus, in spite of continuing bombardment of the Be
specimen by deuterium ions, the oxygen-containing film can grow with time on its
surface. In practice, the increase in thickness of an oxygen-containing film on a Be
surface bombarded by D ions has been observed in other experiments [9,10].
The hydroxide film is not absolutely stable and disintegrates to oxide and water.
Sharapov, et. al. [8] estimated that at room temperature the characteristic time for
hydroxide film disintegration is (1-3)-104 min. With an increase of exposure
temperature this time should decrease [11].
4. Experimental
A CW electron cyclotron resonance discharge at frequency of 2.37 GHz sustained in a
conventional mirror type magnetic field was used as a plasma source. The stainless steel
vacuum vessel was evacuated by a turbomolecular pump down to a pressure of -2x10-4
Pa. During sample exposure the deuterium was continuously fed into the vessel at a
pressure of (3-5)-10-2 Pa. Typical plasma parameters at injected UHF power of 200-400
W were as follows: ne<1010 cm-3 and Te - 5 eV. The polished mirror sample (a round
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JACOBSON, L. A. THE EFFECT OF DEUTERIUM ION BOMBARDMENT ON THE OPTICAL PROPERTIES OF BERYLLIUM MIRRORS, article, June 1, 2001; New Mexico. (https://digital.library.unt.edu/ark:/67531/metadc721001/m1/3/: accessed March 28, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.