NIF diagnostic damage and design issues

The NIF target environment is evaluated with respect to target and diagnostic debris and with respect to instrument survivability in the presence of target debris and radiation. Quantitative estimates are arrived at by extrapolating from Nova and Omega experience using simple scaling arguments. Specifically, we evaluate the closest distance of approach of various components of DIM-based diagnostics such as target mounted pinhole arrays, open detectors, filters, x-ray optics, and spectrometers. We also include constraints on achieving adequate signal-to-noise on x-ray diagnostics. Four of the most important conclusions are as follows: (1) The required full NIF stand-off distance for heavily filtered detectors (e.g. multi-keV x-ray and particle detectors) as determined by concerns of diagnostic debris and diagnostic survivability to debris and radiation is no more than 100 cm. (2) Target mounted pinhole arrays and slits mounted a few cm from chamber center at NIF will survive long enough to record data and should be an acceptable source of shrapnel debris. (3) DIM-based instrument stand-off distances are compatible with achieving the same photon statistics (or better with ongoing improvements in detector resolution and noise) than available with current Nova and Omega SIM- or TIM-based instrumentation. Section II reviews target and diagnostic debris with respect to final optics. Section III reviews debris and radiation with respect to all diagnostic components. The following laser scaling between Nova/Omega and NIF is used throughout unless otherwise specified: laser energy E = 100x, drive duration {tau} = 6x and hence for a given laser intensity or hohlraum temperature, target size r {approximately} {radical}(E/{tau}) = 4x. The 100x increase in E accounts for the fact that many Nova shots were performed with only 20 kJ and all LLNL Omega shots were performed with only 15 kJ.