How do you measure what can't be seen? In the medical field, this is routine. Thermometers check temperatures and X-rays can show broken bones.
But what if you are trying to measure something hotter than the center of the sun that vanishes in 100 trillionths of a second? What if it's an experiment on Lawrence Livermore National Laboratory's National Ignition Facility (NIF)?
"We can't just stick a thermometer in our experiment because it's 200 million degrees. We can't use an X-ray machine because it's 50 times denser than lead," said experimental physicist Dave Schlossberg. "We had to develop clever, innovative techniques to take these measurements."
The answer is a very special suite of diagnostic tools, developed and improved over decades to record and measure what happens in lightning-quick NIF experiments - essentially becoming the eyes of the researchers. The latest episode of the Big Ideas Lab podcast tells this story: how LLNL scientists and engineers learned to turn events too fast, too hot and too dense to touch into knowledge. Listen on Apple and Spotify.
Over 120 diagnostic instruments are available to capture data from NIF experiments. They measure temperatures, densities, shape, pressure, fusion yield, structural composition, X-ray emission, particles, electromagnetic pulses and more. Most experiments use about 15 diagnostics that provide complementary and overlapping data.
This data is used to understand complex physics, validate computer models and design future experiments. NIF's primary mission is to provide the scientific basis for stockpile modernization. Since the end of underground nuclear testing, NIF experiments have recreated those harsh environments to ensure the safety, security and reliability of the U.S. nuclear arsenal.
"Diagnostics are both the scoreboard and the map," said Schlossberg. "They tell us what happened in an experiment and inform how we move forward."
NIF diagnostics are constantly evolving to give researchers both the most complete picture possible and the highest confidence in the data. One of the newest is FIDDLE, a time-resolved X-ray diffraction diagnostic that captures how atoms rearrange themselves in a material's phase transition under extreme pressure,
Hear from Schlossberg on his experience gathering diagnostic data from the first achievement of fusion ignition in late 2022 and experimental physicist Cara Vennari, who is leading development of FIDDLE. They'll share their insights, knowledge and what it's like to work on diagnostics for the world's most energetic laser. Listen on Spotify or Apple.
