Diagnostics

Inertial confinement fusion (ICF) uses powerful lasers to compress and heat a mixture of deuterium and tritium – the two heavy isotopes of hydrogen – to temperatures of up to 100 million degrees Celsius. During this implosion, the inertia of the fuel capsule itself confines the reaction long enough for fusion to occur. But these reactions begin and end over extremely short periods of time, lasting no more than a few nanoseconds. That means that recovering useful data from these experiments requires instruments that can record images even faster, into the tens of picoseconds (ps; one trillionth of a second).

Working with Kentech Instruments, Lawrence Livermore National Laboratory and Sandia National Laboratories, General Atomics has developed a cutting edge line of high-speed imaging diagnostics. These include the DIXI (Dilation X-ray Imager) installed at the National Ignition Facility (NIF) at LLNL. DIXI is a high-speed x-ray framing camera that uses the pulse-dilation technique to achieve a temporal resolution (shutter speed) of less than 10 ps.

The most recent innovation is a single-line-of-sight (SLOS) imager developed with Kentech, LLNL, Sandia, and the Laboratory for Laser Energetics (LLE) at the University of Rochester. SLOS can capture multiple images with a shutter speed of 25 ps, roughly 100 times faster than previous technology. By capturing multiple images along a single line of sight, the imager allows greatly improved accuracy in radiographs of implosion experiments by eliminating the parallax that exists when taking two images from different angles – previously the only way in which such images could be taken so close together in time.

At left, this image from the DIXI instrument depicts x-ray self-emission from an imploded NIF capsule. There are four active strips on the detector, and time runs vertically along the strips from bottom to top and right to left, with the images separated by 20 ps along the vertical direction. At center and right, these two x-ray images of two laser pulses were taken 100 ps apart using the prototype SLOS imager.

GA has delivered two versions of the SLOS instrument so far. The SLOS-CBI (Crystal Beam Imager) was delivered to LLNL in 2017 and, like DIXI, is in use at the NIF. It began operations in September. SLOS-TRXI (Time Resolved X-ray Imager) was delivered to LLE, and is now operating as part of the OMEGA laser facility.

Images courtesy LLNL.