7. Targets


A well-designed and precisely fabricated target is one of the keys to a successful experiment at NIF. While many targets are similar or identical to those previously fielded at NIF, some require the development of new materials, engineering techniques, fabrication and metrology approaches, and fielding strategies. Experimenters should discuss with target designers as early as possible (even before a shot date is determined) the design and type of target, its various components and materials, and its required specifications and tolerances, even if the design is only in the conceptual stage. Early consultation is critical because materials availability and target complexity may impact the fabrication timeline. Experimenters should also stay engaged throughout the target production process.

If the target will be fabricated by LLNL, a drawing of the target should be provided with sufficient information for NIF Target Fabrication to assess the cost and effort required for development, production, and fielding. The drawing should include dimensions and all materials to be used; it should specifically call out the use of any hazardous materials such as beryllium or radioactive elements. When a target requires new materials, target fabrication scientists with expertise in disciplines such as chemistry and materials science begin by developing the essential raw materials. Fabrication engineers then determine whether those materials, some of which may never have been used in targets before, can be shaped, machined, and assembled. If approved, components or an entire target will be assembled and tested. The effort and cost involved in making a new target is estimated by the program and target fabrication through an iterative process.

Targets are made using a number of different resources, depending on the type of target and its components or subassemblies. The majority of targets are made by the LLNL/General Atomics (GA, http://www.ga.com/energy-group ) Target Fabrication team, which has the capabilities and experience to build a wide variety of targets for investigating various areas of science on NIF. Both LLNL and GA have the infrastructure for making and characterizing precision components and assembling them into targets. Other vendors support the fabrication process. It is not necessary to procure targets from the LLNL/GA team; however, any target to be shot at NIF must be assembled with enough precision to be aligned in the target chamber, metrologized at LLNL (see Section 7.2.2), and approved for material compatibility (see Section 5.9) before use in the target chamber vacuum.

Depending on the target type and application, GA or LLNL may perform the various steps involved in making the target, although component assembly and characterization is typically performed on-site at LLNL by a combined team of LLNL, GA, and Schafer Corporation personnel. LLNL is also mainly responsible for the engineering design of targets, including facility interface–driven features, such as alignment ducials, unconverted light shields, and mass and debris requirements, as well as completion of the final metrology report as part of the requirements verification process (RVP).

This chapter summarizes the process involved in turning a sketch or idea for the target into a real, shootable target at NIF, including the timeframe involved, steps to be addressed, and interfaces to help the user with the process. It also provides a brief overview of the most commonly used target fabrication and metrology capabilities for NIF experiments.