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This thesis examines theoretically the potential of the plasma confinement device known as a Stellarator as a fusion reactor. Chapter one contains a survey of the requirements for nuclear fusion to take place in a device employing magnetic confincment. The range of reactor parameters which are appropriate is- derived, both from the point of view of plasma physics and on the basis of a rather crude economic model. Chapter two begins with a discussion of the equilibrium of plasma in Stellarators. Solutions of the equilibrium equations are obtained, employing an Inverse aspect ratio axpansicn of the field quantities. Chapter three Indicates which macroscopic" instabilities are cause for concern in Stellarators without net longitudinal currant. A. stability criterion appropriate to Stellarators is evaluated, using the equilibrium fields found in the proceeding chapter. Chapter four is devoted to the study of the effects of particles which are localised in the ripple of the Stellarator masnetic field on transport. A random walk theory of their contribution to diffusion is given. Chapter five contains a description of the coil systems capable of generating fitellarator fields, and their properties. Specialising to "twisted" coils, geometrical scaling laws are sought, which describe the properties of the fields they produce. Chapter six is a brief indication as to how such coils may be incorporated into a reactor. Chapter seven considers the parameters of a Stellarator reactor based on "twisted" coils, and shows how they may be written in terms of the raajor and minor radii of the device. An economic model of the reactor is given, which allows us to optimise the reactor, to obtain the cheapest system at fixed total power output and wall loading. The result is shown Co be considerably less expensive than similar Tokamak designs.

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Human body motion capture systems based on inertial sensors (gyroscopes andaccelerometers) are able to track the relative motions in the body precisely, oftenwith the aid of supplementary sensors. The sensor measurements are combinedthrough a sensor fusion algorithm to create estimates of, among other parame-ters, position, velocity and orientation for each body segment. As this algorithmrequires integration of noisy measurements, some drift, especially in the positionestimate, is expected. Taking advantage of the knowledge about the tracked sub-ject, a human body, models have been developed that improve the estimates, butposition still displays drift over time.In this thesis, a GNSS receiver is added to the motion capture system to givea drift-free measurement of the position as well as a velocity measurement. Theinertial data and the GNSS data complements each other well, particularly interms of observability of global and relative motions. To enable the models of thehuman body at an early stage of the fusion of sensor data, an optimization basedmaximum a posteriori algorithm was used, which is also better suited for thenonlinear system tracked compared to the conventional method of using Kalmanfilters.One of the models that improves the position estimate greatly, without addingadditional sensing, is the contact detection, with which the velocity of a segmentis set to zero whenever it is considered stationary in comparison to the surround-ing environment, e.g. when a foot touches the ground. This thesis looks at botha scenario when this contact detection can be applied and a scenario where itcannot be applied, to see what possibilities an addition of GNSS sensor couldbring to the human body motion tracking case. The results display a notable im-provement in position, both with and without contact detection. Furthermore,the heading estimate is improved at a full-body scale and the solution makes theestimates depend less on acceleration bias estimation.These results show great potential for more accurate estimates outdoors andcould prove valuable for enabling motion tracking of scenarios where the contactdetection model cannot be used, such as e.g. biking.