“Like a thermometer or a camera, diagnostics can tell us if an experiment performed well, take a movie or snapshot of our experiment, and provide us with pieces of information that allow us to answer the important questions we are investigating.”
—David Martinez, NIF physicist and high energy density science researcher
Getting a grasp on the extreme physics that happens when NIF’s laser beams compress a fusion fuel capsule to the size of a pinpoint requires some of the most sophisticated measuring instruments ever made. Researchers often must examine conditions like those found at the center of stars and in exploding nuclear weapons—exceeding pressures of 100 billion atmospheres and temperatures of 100 million degrees Celsius.
NIF’s highly specialized instruments, called diagnostics, must not only operate in timescales of nanoseconds (billionths of a second) or shorter, but also detect interactions often below the submicron (millionth of a meter) level. Some diagnostics must function under the intense bombardment of both particle and electromagnetic radiation. In fact, it’s this radiation, such as neutrons and x rays, that many diagnostics are designed to detect to help researchers characterize NIF experiments.
Transformative diagnostics enable cutting-edge science. NIF makes nearly 120 diagnostics available to internal and external users; but as the boundaries of science are continually pushed, sometimes an experiment requires measuring capabilities that don’t yet exist. Every year, NIF and its partners develop about a dozen new diagnostics to meet these new challenges.
Plans for NIF diagnostics began in the mid-1990s, when a multi-laboratory Joint Central Diagnostic Team was formed to coordinate efforts to develop NIF diagnostics funded through the inertial confinement fusion (ICF) program at the various National Nuclear Security Administration laboratories. The resulting strategy called for a national effort to develop and implement a comprehensive suite of diagnostics on NIF. These diagnostics would be phased in over time and, when possible, multiple diagnostics would be available to measure key observables.
“The Nova Laser (NIF’s predecessor) was operated from 1984 to 1999,” said NIF Scientific Diagnostic Leader Joe Kilkenny, “becoming the best user facility of the era, with about 100 diagnostics to service its users. The initial NIF diagnostics were based on Nova diagnostics but were much better engineered for facility operations.
“More recent NIF diagnostics introduce many new optical, x-ray, and nuclear detector concepts and improve operational reliability to the present high 90 percent user satisfaction assessment,” he said. “A marvelous decade for diagnostic scientists, engineers and operations!”
NIF’s current diagnostic development benefits from those decades of experience and from the heavy involvement of organizations such as Los Alamos and Sandia national laboratories, the University of Rochester’s Laboratory for Laser Energetics, the Massachusetts Institute of Technology, General Atomics, National Security Technologies, LLC, and the atomic energy agencies in the UK and France.
NIF’s nuclear, optical, and x-ray diagnostics provide more than 650 channels for experimental data. Many diagnostics have multiple channels; for example, the Real-time Neutron Activation Detector (RT-NAD) system, a network of individual neutron detectors positioned at different angles around the Target Chamber, provides researchers with 48 data channels to reconstruct a 3D map of the fusion source and fuel. And each of NIF’s two DANTE soft x-ray power diagnostics has 18 data channels.
The need for multiple complementary and redundant diagnostics was recognized as an essential requirement since no single diagnostic makes a perfect measurement. Thermonuclear yield, for example, is measured by three absolute and independent diagnostics.
NIF diagnostics are either constructed and deployed to a fixed location in the Target Chamber/Target Bay or are fielded on diagnostic instrument manipulators (DIMs) or dual-purpose target and diagnostic manipulators known as TanDMs. DIMs and TanDMs are telescoping devices capable of inserting, retracting, positioning, and aligning diagnostic instruments in the Target Chamber, from the interior wall to Target Chamber center. They also provide a standard set of utilities and cables to support operation of all DIM- and TanDM-based diagnostic instruments.
Over the last 10 years, NIF’s diagnostics have improved in efficiency, resolution, and sensitivity. Instead of “seeing” a fusion target at a single point in time during compression in two dimensions (like a photograph), they have evolved to create images over three dimensions and at multiple times. Each new diagnostic capability enables researchers to gain more insight into the many forces at play every time the NIF lasers fire on a target.
“Icarus Camera Flies Close to NIF’s Sun—and Thrives!,” NIF & Photon Science News, August 12, 2020
“Nuclear Diagnostics Help Pave the Way to Ignition on NIF,” NIF & Photon Science News, March 6, 2020
“Discovery Science Inspires Novel Diagnostics for NIF,” NIF & Photon Science News, December, 2018
“A Time-Resolved High-Resolution X-ray Spectrometer for NIF,” NIF & Photon Science News, December, 2017
“Tracking NIF Implosions @ 200 Billion Frames a Second,” NIF & Photon Science News, August, 2014
Next Up: Efficiency Improvements