The smooth blue sphere of the National Ignition Facility’s (NIF) target chamber bristles with diagnostics—nuclear, optical and X-ray instruments that together provide some 300 channels for experimental data. These diagnostics provide vital information to help NIF scientists understand how well an experiment performed.
Two of these diagnostics, known as Dante 1 and Dante 2, are pressed into service for nearly every shot. These broadband, time-resolved X-ray spectrometers measure the time-dependent soft X-ray power produced by the NIF lasers interacting with the hohlraum—the small gold cylinder that holds the NIF target capsule. The X-rays heat and ablate the outer surface of the capsule and drive the capsule’s rocket-like implosion. The resulting data are used to calculate the radiation spectrum and infer the temperature of the radiation field inside the hohlraum. This information can be directly compared to hohlraum simulations to determine if the hohlraum and laser pulse are performing as designed.
“Dante is one of the workhorse diagnostics of NIF—it participates in almost every shot,” said Alastair Moore, responsible scientist for Dante. “Even when a hohlraum is not used, it is one of the few absolutely calibrated soft X-ray diagnostics that can provide absolute measurements of the conversion efficiency of laser light into X- rays.”
Each Dante diagnostic measures the voltage produced by 18 filtered X-ray diodes. Each diode is filtered to record the X-ray power in a specific part of the spectrum. Spectral ranges are controlled by filters, metallic mirrors and X-ray diode material. Dante 1 has five channels with mirrors, and Dante 2 has eight mirrored channels.