NEUTRAL PARTICLE-VELOCITY DISTRIBUTIONS OF LASER-IMPLODED MICROSHELLS

A new diagnostic method for studying the laser implosion of microshell targets based on time-of-flight and pinhole imagery of neutral atoms is described. Experiments have been conducted at the Rutherford Appleton Laboratory using the 12-beam laser facility "Vulcan" studying the implosion of high-aspect-ratio glass shell targets. Neutral particles originate by several different mechanisms which can he distinguished by the combination of time-of-flight (TOF) and imaging techniques. Theoretical analysis and numerical simulations of neutral atom velocity spectra support the interpretation of the experimental results. One group of atoms is shown to be characteristic of the imploded microshell and estimates of the imploded core parameters are possible using a simple analytic model. Results were obtained over a wide range of conditions using both tight-focus geometry and random-phase plates to obtain uniform irradiation. Marked changes in the neutral particle spectra between these two cases are observed.