The first large-scale study of magnetically-confined plasma for the production of fusion energy is scheduled to begin this decade and will answer many questions. Two critical issues are: (1) how to control and prevent non-axisymmetric magnetic perturbations that may drive harmful current and plasma energy into the surrounding walls, and (2) how to understand the relationship between plasma rotation, plasma confinement, and plasma stability. To address both, this dissertation reports research with biasable electrode arrays in the HBT-EP tokamak. This work conducts systematic studies of driven current and achieves the first active control of plasma rotation and rotating magnetic instabilities with a toroidal electrode array. Electrode-driven current impacts the plasma in several ways. First, it can increase, decrease, and reverse plasma rotation as measured by Mach probes, which results in an altered radial electric field. By controlling the electrode voltage with an active feedback system, plasma rotation is controlled between 4 and 8 kHz. Second, by modulating the driven electrode current at fixed frequencies, spontaneous magnetic perturbations develop at the plasma’s edge. These distortions are field aligned, do not rotate, and match the magnetic helicity of the scrape-off-layer (SOL). Direct measurement of SOL current to collectors mounted on the wall, show that the SOL current is field-aligned with a filamentary structure. When a naturally-occurring rotating m=2 mode is present, magnetic measurements show that the two structures are superimposed with no obvious indication of coupling. Third, when the electrode current is driven at the natural frequency of rotating magnetic perturbations, the plasma’s proportional response increases, indicating a resonance at 9 kHz. Resonance is observed in the radial electric field, floating potential profile, plasma rotation, and magnetic measurements. Finally, when the electrode array is biased in quadrature and actively controlled, driven currents modify the rotation and amplitude of the long-wavelength rotating magnetic modes. When the quadrature electrode array is phase locked to the n=1 mode rotation, mode amplitudes are suppressed by as much as 50%. Suppression shows a clear dependence on a phase between the rotating mode and the driven current. These experiments show that the structure of SOL currents are field-aligned and demonstrate a clear relationship between biased-electrode driven current and the rotation and amplitude of helical magnetic perturbations.

The report shows the development during the last six months of the SMILE fluxgate magnetometer from a basic platform into a first generation magnetometer. The purpose of the SMILE project is to develop a miniaturized digital fluxgate magnetometer for the Nanospace project. The Nanospace project is collaboration by KTH and IRF Uppsala with the goal to develop a nano satellite platform. The FPGA programming has been improved to include a functional correlation loop, 13 bit DACs and a parallel and a serial interface with several output modes. The timing of the processes in the FPGA has been improved making it more robust. Some critical changes to the analogue parts has also been made. The LEMI sensors have been tested in a number of ways to increase the understanding of their characteristics. The magnetometer has also been calibrated at the Nurmijärvi geophysical observatory in Finland.

Fluxgate magnetometers have played a major role in space missions due to their stability, range of operation and low energy consumption. Their principle of operation is relatively simple and easy to implement, a nonlinear magnetic material is driven into saturation by an alternating excitation current inducing a voltage that is modulated by the external field intended to be measured. With the increasing use of nanosatellites the instruments and payload on board have been reduced considerably in size and weight. The Small Magnetometer in Low-Mass Experiment, SMILE, is a miniaturised triaxial fluxgate magnetometer with volume compensation incorporating efficient signal processing algorithms within a field programmable gate array (FPGA). SMILE was designed in collaboration between the Lviv Centre of Institute of Space Research in Ukraine where the sensor was developed and the Royal Institute of Technology (KTH) in Stockholm, Sweden where the electronics used to operate the instrument were designed and programmed. The characteristic dimensions of the SMILE magnetometer and geometry of its parts make impractical the task to find an analytical expression for the voltages induced in the pick-up coils to evaluate its performance. In this report, the results of numerical simulations of the SMILE magnetometer using a commercial finite element method (FEM) based software are presented. The results obtained are compared with the experimental data available and will serve as a first step to understand the behaviour of the nonlinear components that could lead to improvements of its design in a future.

Electrostatic waves in the form of Broadband Electrostatic Noise (BEN) have been observed in the Earth's auroral region associated with high geomagnetic activity. This broad frequency spectrum consists of three electrostatic modes, namely electron plasma, electron acoustic and beam-driven modes. These modes are excited in a plasma containing three electron components: hot, cool and beam electrons. A 1D Particle-in-Cell (PIC) simulation was developed to investigate the characteristics of the electrostatic waves found in such a plasma. Dispersion, phase space and spatial electric field diagrams were constructed from the output of the PIC simulation which were used to describe the wave dispersion and spatial field structures found in a plasma. The PIC code used a three electron component plasma with Maxwellian distributions to describe the electron velocity distributions. Beam-driven waves were found to dominate the frequency spectrum while electron plasma and electron acoustic waves are damped for a high beam velocity. Furthermore, for a high beam velocity, solitary waves are generated by electron holes (positive potentials), giving rise to a bipolar spatial electric fi eld structure moving in the direction of the beam. Increasing the beam temperature allows the beam electrons to mix more freely with the hot and cool electrons, which leads to electron plasma and electron acoustic waves being enhanced while beam-driven waves are damped. Decreasing the beam density and velocity leads to damping of beam-driven waves, while electron plasma and electron acoustic waves are enhanced. Measurements in Saturn's magnetosphere have found the co-existence of two electron (hot and cool) components. The electron velocities are best described by a kappa-distribution (instead of a Maxwellian) which has a high-energy tail. Using an adapted PIC simulation the study of electron plasma and electron acoustic waves was extended by using a kappa-distribution to describe the electron velocities with low indices. Electron acoustic waves are damped over most wave number ranges. Electron plasma waves are weakly damped at low wave numbers and damped for all other wave numbers. / <p>QC 20121205</p>

No description available.

No description available.

No description available.

No description available.

No description available.

No description available.