Measurements of the heat flux, inverse bremsstrahlung absorption and equilibration in an under-dense laser heated plasma

Abstract

A fully ionised hydrogen plasma of initial density approximately=5*1017 cm-3 and temperature approximately=12 eV is heated using a 1.053 mu m laser beam focussed to a spot of 200 mu m diameter with an irradiance of 5*1013 W cm-2. The resulting evolution of the plasma is monitored by Thomson scattering of a second laser beam at 5265 AA. Comparison with a one-dimensional two fluid hydrodynamic simulation shows that the inverse bremsstrahlung absorption coefficient should be modified to include the strong field correction and that the maximum heat flux is about 0.1 of the free streaming limit. The ratio of the electron mean free path to the temperature scale length is about 0.1 and Te/Ti approximately=5. The level of ion acoustic turbulence is observed to be small, close to thermal. The ion-electron equilibration rate is found to agree with the usual classical value.