In this thesis I study the magnetic activity of young stars via observations of stellar prominences on single stars and by applying the Zeeman Doppler imaging (ZDI) technique to map the magnetic fields and measure differential rotation of a young binary system. Stellar prominences can be observed as absorption transients in the rotationally broadened chromospheric lines of rapidly rotating stars. Observations of Speedy Mic(K3V) reveal a densely packed prominence system at heights far above the stellar co-rotation radius. Further observations were used to estimate prominence column densities and masses. From very high signal-to-noise observations, loops of emission are found that trace the path of prominences seen transiting the stellar disc. I also present what appears to be the first observation of an erupting stellar prominence on AB Doradus (K0V). I modify an existing ZDI code so that it can recover the magnetic maps of a binary system. The new code is applied to observations of the pre-main sequence binary system HD 155555 (G5IV+K0IV). The radial magnetic maps reveal a complex surface magnetic topology with mixed polarities at all latitudes and rings of azimuthal field present on both stars. The evolution of the relative field strengths between observations in 2004 and 2007 could be indicative of a magnetic activity cycle. I adapt the sheared image technique for measuring differential rotation parameters to the binary case. Both stellar components of HD 155555 are found to have rates of differential rotation similar to those of the same spectral type main sequence single stars. This is in apparent conflict with previous work on evolved binary systems where low rates of differential rotation were found, leading to the suggestion of suppression by binary tidal forces. I find that the depth of convection zone alone can likely explain the differential rotation results without invoking tidal forces.

This master's thesis describes the process of the design and instrument selection for a future optical table, part of a plasma flow monitor diagnostic system at the international thermonuclear experimental reactor, ITER. The diagnostic system is designed to detect the presence of edge localized mode, low to high confinement mode transition of plasma, and plasma flow velocity in the divertor region of the reactor. It accomplishes this by performing spectroscopic measurements of visible light radiating from specific elements inside the reactor. The selection of these elements are based on previous experiments performed at the joint european torus (JET). The light is transported via a system of lenses and mirrors to the optical table where it is directed through a series of optical instruments. Finally, the light is subsequently captured by cameras who live stream the images via the internal network to a control center. To aid the development of the schematic and instrument selection, optical design simulations of the light transmission path were performed to ensure that the design could provide sufficient level of light itensity to the cameras at a defined trajectory. The selection of instruments, light transmission results, computer aided design- and simulation models of the optical table are presented in this report. While the selected components satisfied most criteria specified by its predefined system requirements, the project also serves as a foundation for future improvements of the optical table, including changes to any of the instruments, schematics, and optical design simulations.