X-ray lasing as a result of an induced instability in an ablative capillary discharge
Résumé
We report lasing of the CVI Balmer-α line at 18.22 nm using the new technique of an induced MHD instability in an ablative capillary discharge. A large spike of this line during the second half-cycle of the discharge is observed. The spike is identified as amplified spontaneous emission (ASE), and enhancements are derived for capillaries of lengths between 15 and 50 mm. We explain the ASE as a result of charge exchange processes which occur between ions produced in the neck of the MHD instability and low temperature ions present in the same plasma column. To emphasize this instability, we implemented a new method by using a straight capillary with a waved structure imprinted inside. The results are encouraging and an exponential gain length is achieved with GL =4.5 for a 40 mm length capillary. Other evidence to support the observation is realised when a plane multilayer mirror with reflectivity <30% is introduced resulting in amplification.