A mathematical model for the biodegradation of magnesium is developed in this study to inspect the corrosion behaviour of biodegradable implants. The aim of this study was to provide a suitable framework for the assessment of the corrosion rate of magnesium which includes the process of formation/dissolution of the protective film. The model is intended to aid the design of implants with suitable geometries. The level-set method is used to follow the changing geometry of the implants during the corrosion process. A system of partial differential equations is formulated based on the physical and chemical processes that occur at the implant-medium boundary in order to simulate the effect of the formation of a protective film on the degradation rate. The experimental data from the literature on the corrosion of a high-purity magnesium sample immersed in simulated body fluid is used to calibrate the model. The model is then used to predict the degradation behaviour of a porous orthopaedic implant. The model successfully reproduces the precipitation of the corrosion products on the magnesium surface and the effect on the degradation rate. It can be used to simulate the implant degradation and the formation of the corrosion products on the surface of biodegradable magnesium implants with complex geometries.

X-ray spectra of n = 2 to 1 transitions in hydrogen-like Ca19 +, helium-like Ca18 + and nearby satellites have been obtained from Alcator C-Mod tokamak plasmas using a spatially imaging high resolution x-ray spectrometer system. For Ca19 +, the intensity ratio of Lyα2 (1s 1S1/2–2p 2P1/2) to Lyα1 (1s 1S1/2–2p 2P3/2) was found to be ∼0.531 ± 0.005 over a range of plasma parameters, which is somewhat greater than the ratio of the statistical weights of the upper n = 2 levels, 1/2. This difference is mainly due to interaction with the 2S1/2 fine structure sub-level. Experimental results are compared to calculations from COLRAD, a collisional-radiative modelling code, and good agreement is shown. For Ca18 +, the intensity ratio of the dielectronic satellite k (1s22p 2P1/2–1s2p2 2D3/2) to the resonance line w (1s2 1S0–1s2p 1P1) is sensitive only to the electron temperature. The observed brightness ratio scaling with Te is in good agreement with the calculated ratio of the respective dielectronic recombination to the collisional excitation rates.

X-ray spectra of H-and He-like ions (and satellites) from argon, calcium and chlorine have been obtained from Alcator C-Mod tokamak plasmas using a high resolution x-ray spectrometer system. For H-like charge states, the Ly α doublet intensity ratio is found to be slightly greater than 1/2 due to interaction with the 2 S 1/2 fine structure sub-level. Neighbouring satellites with spectator electrons occupying n = 2 through n = 7 have been modelled. The Ly α doublet ratio scalings with electron density and temperature are shown to be in good agreement with collisional-radiative modelling. For He-like ions, the n = 2 satellite intensities are in good agreement with calculations and can be used as an electron temperature diagnostic. The high n Rydberg series has been resolved up to 1s 2 -1s16p, and satellites with spectator electrons up to the n = 12 level have been identified.

High-quality spectra of hydrogen-like Ar17 + have been obtained from Alcator C-Mod tokamak plasmas using a spatially imaging high-resolution x-ray spectrometer system in an extensive study of the underlying high-n satellite lines. The ratio of Lyα2 (1S1/2–2P1/2) to Lyα1 (1S1/2–2P3/2) was found to be ∼0.52 regardless of plasma parameters, which is somewhat greater than the ratio of the statistical weights of the upper n = 2 levels, 0.5. This difference is mainly due to the effects of collisional excitation of fine-structure sub-levels. For the observations presented here, electron densities were in an extended range from 3×1019 to 4×1020 m−3 with electron and ion temperatures between 1 and 4 keV. Experimental results are compared to calculations from COLRAD, a collisional-radiative modelling code, and good agreement is shown.

Brightness profiles of x-ray emission from H-like Ar 17+ exhibit a distinct up/down asymmetry under certain operating conditions in C-Mod plasmas, indicating that impurity densities are not constant on flux surfaces with r/a between ∼0.8 and ∼0.95. In Land I-mode plasmas, there is an x-ray brightness excess, up to a factor of 8, on the side opposite to the ion B×∇B drift direction. This effect is not observed in H-mode plasmas, presumably due to edge impurity transport being dominated by a strong inward pinch, which is absent in L-and I-mode. The magnitude of the asymmetry in L-and I-mode decreases with increasing plasma current, similar to the observed decrease in radial impurity diffusivity. In I-mode, where the codependence between electron density and temperature can be broken with ICRF heating power, the asymmetry magnitude is found to decrease with increasing density and with increasing edge temperature at fixed density. These measurements exhibit some qualitative features of neo-classical expectations but the observed asymmetry magnitude is much larger than predicted and some scalings with plasma parameters are not seen. The up/down asymmetry appears to be largest when the cross field impurity diffusivity is the highest.