Debris mitigation techniques for petawatt-class lasers in high debris environments

Sandia National Laboratories, P.O. Box 5800, Albuquerque, New Mexico 87185-1193, USA(Received 13 November 2009; published 20 April 2010)This paper addresses debris mitigation techniques for two different kinds of debris sources that arefoundinthehigh-energydensitycommunity.Thefirstdebrissourcestemsfromthelaser-targetinteractionand this debris can be mitigated by avoiding a direct line of sight to the debris source (e.g. by using asacrificial fold mirror) or by inserting a thin debris shield. Several thin film debris shields have beeninvestigated and nitrocellulose was found to be the best suited. The second debris source originates froman external high-energy density driver or experiment. In our specific case, this is the Z accelerator, aZ-pinch machine that generates 2 MJ of x rays at 300 TW. The center section of the Z accelerator is anextremely violent environment which requires the development of novel debris mitigation approaches forbacklighting with petawatt lasers. Two such approaches are presented in this paper. First, a self-closingfocusing cone. In our facility, the focused beam on target is fully enclosed inside a solid focusing cone. Inthe first debris mitigation scenario, the last part of the cone has a ‘‘flapper’’ that should seal the conewhenthe pressure wave from the Z-pinch explosion hits it. In the second scenario, an enclosed target assemblyis used, with the last part of the focusing cone connected to a ‘‘target can’’ which houses the laser target.The laser produced x rays for backlighting escape through a 3 mm diameter hole that is protected by anx-ray filter stack. Both techniques are discussed in detail and have been successfully tested on the Zaccelerator.