Browsing by Author "Cole, Elizabeth"

Thermal instability (hereafter TI) is investigated in numerical simulations to determine its effect on the growth and efficiency of the dynamo processes. The setup used is a three-dimensional periodic cube of a size several times the correlation length of the interstellar turbulence. The simulations are designed to model the interstellar medium without any shear or rotation, to isolate the effect of TI. Hydrodynamical and nonhelical simulations are run for comparison to determine the effects the magnetic field has upon the gas itself. Turbulence is simulated by external helical forcing of varying strength, which is known to create a large-scale dynamo of alpha squared-type. The nonhelical cases are also explored in an attempt to create a small-scale dynamo at high Rm, but no dynamo action could be detected in the range of Rm ~ 30 – 150. The hydrodynamical simulations reproduce the tendency of the gas to separate into two phases if an unstable cooling function is present. The critical magnetic Reynolds number of the large-scale dynamo was observed to be almost twice as large for the unstable versus stable cooling function, indicating that the dynamo is harder to excite when TI is present. The efficiency of the dynamo as measured by the ratio of magnetic to kinetic energy was found to increase for the unstable case at higher forcing. The results of the runs from this thesis are part of a larger project studying dynamo action in interstellar flows.