A cast steel magnetic sector mass analyzer is developed for studies of hydrogen and helium ion beams generated by a gas discharge compact ion source. The optimum induced magnetic flux density of 3500 G made it possible to scan the whole spectrum of hydrogen and helium ion species. Analysis of beam characteristics shows that the mass spectrometer sensitivity, and resolving power are approximately inversely proportional. The resolution is enhanced at higher pressures and lower current discharges. In contrast, the instrument sensitivity increased at higher current discharges and decreased at higher pressures. Calculations of the ultimate resolving power with reference to analyzer dimensions yield a numerical value of 30. System anomaly in the form of spherical aberrations was also analyzed using the paraxial beam envelope equation. Beam divergence is most significant at high discharge conditions where angular spread reaches an upper limit of 8.6°.
Helium beams in a compact gas discharge source lose their transverse symmetry when the extracting electrode is biased at high potentials. Further, this condition gives rise to excessive formation of electrons within the vicinity of the beam line of propagation. A plausible explanation for these abnormalities is explained via the effects of the source extractor's lens property on the beams' physical configuration. The optical relation of the extractor shows that when the extraction voltage ( V e ) exceeds half the discharge voltage ( V d ), its focal length extends backward pass the discharge region's emitting orifice. As a consequence, beam divergence is increased akin to light beams expanding when the source is positioned between a negative lens and its principal focus. Numerical simulations of the beams' envelopes at different discharge and biasing conditions provide further proof of the theory's validity. When V e > V d /2, the construct shows exiting beams to have waists greater than the diameter of the drift tube suggesting increased interaction between beam edge and the tube's interior walls resulting in secondary electron emissions. The presence of electrons inexorably leads to charge neutralization thus creating asymmetric beams downstream. Mass spectroscopic detection of O - ions most likely from surface oxides, and increased electron densities obtained by way of Langmuir measurements are phenomenological evidences to this effect. This work intends to establish the explicit causality relation between secondary electron emission and the formation of asymmetric beams in miniaturized ion sources.
A gas discharge ion source (GDIS) was used as test facility to produce and study the characteristics of diffused, low-energy hydrogen ion showers. Narra wood samples were then exposed to the showers to investigate topographical effects of ion irradiation. Analysis of beam constituents by mass spectroscopy shows H + ions to be the dominant species suggesting an essential participatory role for this particular monatomic ion in the surface modification process. Low energy irradiation (600–700 eV) produced hydrophobic surfaces with scanning electron micrographs showing partial closure of surface pores. Whereas, a reversion to hydrophilicity was observed for higher energy irradiation (>900 eV), with surface images showing exterior degradation believed to be the etching effects of the chemically active H + species. The irradiated samples absorbency was quantified via the wetting model wherein the contact angle's time rate equation was numerically solved and fitted onto experimental data. The change rate proportionality constant K with value 0.0015 corresponding to 600 eV beam energy, exhibited the longest moisture absorptive inhibition time of more than 10 min. An increasing value of K indicates increased wetting behavior.
The porosity and wettability properties of hydrogen ion treated polytetrafluoroethylene (PTFE) materials are related using contact angle, scanning electron microscopy (SEM), and ellipsometry tests.PTFE are irradiated using a low energy hydrogen ion shower (LEHIS) produced by a Gas Discharge Ion Source (GDIS).The plasma discharge current (I d ) is varied at intervals of 1 mA.Results show that treatment using lower I d enhances the hydrophobic property of the PTFE material with contact angle value of as high as 118.6.It also becomes less porous as indicated by the increase in the index of refraction, decrease in optical transmittance, and increased scissions and striations in the SEM images.Opposite effects are observed for higher I d .
It is observed in the operation of the Sheet Plasma Negative Ion Source (SPNIS), that the sheet configuration of the plasma cannot be maintained at pressures above a certain limit. For instance hydrogen plasma disperses and shows spatial inhomogeneity at pressures above 0.05 Torr, while at pressures higher than 0.01 Torr the same occurs for argon plasma. The cause of the dispersion is not understood, as yet. This paper is the first of a series of attempts to find the root of the dispersing phenomenon. Focus was done on Streaming Instability as a probable cause.
Hydrogen ion showers (Hn +) of current densities 50 to 400 mA/m2 were irradiated on AlyllDiglycol Carbonate (CR-39) ophthalmic lenses. The substrate lenses measured 6×6×2 mm3 and were fabricated through hot deformation polymerization process. Irradiation time was fixed at 15 minutes per sample. The study aimed to correlate Hn + ion beam characteristics to the physicochemical and optical changes of the treated lenses. Beam current densities were measured using a cast steel mass spectrometer and emittance contours at 90 % beam fraction were measured using a single-slit multi-detector emittance meter. Unnormalized emittances ranged from 180 to 310 mm-mrad for 1 to 5 mA discharges. Low energy beams ( 8 produced a ubiquitous feature of tapered nanostructures on the surfaces. AFM histograms showed that average substrate surface roughness decreased from 30.91 nm (pristine sample) to 12.94 nm (treated samples) when low energy beams were used, but increased to 20.33 for high energy beams. Lens hydrophobicity improved with contact angles increasing from 61.23o (pristine) to 122.64o (treated). Spectral transmittance improved by about 1.5 times from 60% (pristine) to 90% (treated). An interplay between the roughening action of ion etching and the smoothing action of surface diffusion serves as the physical basis for the formation of sharp-tipped, tapered nanostructures on the lens surfaces. The introduction of nanostructures on the surface effectively created a hydrophobic, antireflective interface. Pre- and post-treatment FTIR-ATR transmittance peaks remained unaltered. Hence surface changes are attributed to physical factors and not to any chemical reactions.
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