Congratulations to Ellie Tubman who successfully defended her thesis at viva on 12 December 2016. Ellie’s thesis was entitled ‘Magnetic field generation in laser –plasma interactions’ and was supervised by Professor Nigel Woolsey. An abstract from Ellie’s thesis is shown below:
The primary focus of this thesis is understanding the production of magnetic fields during laser-plasma experiments. Each chapter investigates a different mechanism of producing magnetic fields. The first is from the by-product of launching asymmetric shocks which drive Biermann battery generated magnetic fields. The second looks at the reconnection of magnetic fields between two laser focal spots and the third is from fields produced around a current carrying loop target
Blast waves are investigated in the laboratory using a fast framing camera to capture multiple images on a single shot. In analysing the images, the blast wave trajectory is compared to a Sedov-Taylor solution and the coupling of the laser energy into the shock wave is calculated to be 0.5-2%. The evolution of the blast wave’s shape is characterised by fitting an ellipse to the outer edge and observed to progress into a more symmetrical shape. Calculations show that two shocks produced in the interaction cause the change in ellipticity.
We experimentally demonstrate that, when two laser spots are placed in close proximity reconnection occurs. Diagnostics, including proton radiography, X-ray detectors and an optical probe, record and diagnose the existence of a semi-collisional reconnection event. The experimental data and simulations show that both Nernst and anisotropic pressure effects needs to be taken into account for understanding and predicting the correct plasma dynamics observed.
Magnetic fields are produced driving a current through a loop attaching two plates where new measurements recording the voltages induced are presented. It is found that the predicted values for the resistance, capacitance and inductance do not match those extracted from the experimental data and reasons for these are presented. Ideas for furthering this research, to enhance our understanding in this area, are given.