When the stadium-size National Ignition Facility (NIF) is fully operational at the Lawrence Livermore National Laboratory (LLNL), its 192 laser beams will deliver 1.8 megajoules (500 terawatts) of energy onto a target to create extremely high temperatures and pressures for inertial confinement fusion research as part of the Stockpile Stewardship Program. Due to the performance threshold and requirements of the NIF optical components, the optics and their surrounding beampath as well as the supporting utility systems must be fabricated, cleaned, assembled, and commissioned for precision cleanliness. This paper will provide an overview of the NIF cleanliness requirements, the Clean Construction Protocol (CCP) specifications for the beampath and clean utilities, and techniques for verifying the CCP specifications.
The NIF cleanliness requirements define limits for molecular and particulate contamination. The goal of these limits is to prevent contamination of optical components. To prevent laser-induced damage and poor laser quality in the optical components, requirements for cleaning, assembly, installation, and commissioning in terms of particle and nonvolatile residue (NVR) levels are defined. The airborne cleanliness requirements in the interior of the beampath are Class 1 (ISO Class 3) particulate levels and a few parts-per-billion (ppb) airborne molecular contamination (AMC) (SEMI F21-95 MC-1,000).
To achieve the cleanliness requirements for the beampath interior, a graded CCP approach is used as the NIF beampath and utilities are being constructed by a partnership between LLNL and the construction contractor, Jacobs Facilities Inc. (JFI) in a stadium-size Class 100,000 (ISO Class 8) building. Installation of the beampath components utilizes localized mini-environments of Class 100 (ISO Class 5) or better, with budgets of cleanliness exposure or "class-hours" for each clean connection. Garment, equipment, and operational considerations are evaluated with process verification.
Verification of the beampath and utility cleanliness is performed with cleanliness exposure monitoring, evaluating particulates with "swipes" and the LLNL-developed Precision Cleanliness Verification System (PCVS), and measuring nonvolatile residues (NVRs) and AMCs with analytical chemistry techniques. Cleanliness verification results demonstrate that the CCP specifications are achieving the NIF cleanliness requirements for the beampath and clean utilities.