A new technology at the service of radiographic imaging


image: Barrel-shaped Febetrons are powered by capacitor modules, a technology that hadn’t seen a design update in over 40 years.
to see Continued

Credit: Los Alamos National Laboratory

In cutting-edge national security science, where a rapidly evolving understanding of materials and physical processes is critical to applications, middle-aged technology is at the center of the action. About the size of a small sport utility vehicle and shaped like a barrel, devices called Febetron generate X-rays to photograph objects that are moving at extremely high speeds as part of a detonation and can measure their position, their speed, shape and internal structure. density profiles. Febetrons are powered by capacitor modules, a technology that hadn’t seen a design update in over 40 years, until a research team at Los Alamos National Laboratory developed a new device. “K-module”.

“The capacitor modules are like the automotive motors in these Febetron devices,” said Kalpak Dighe, project leader in the pulsed power systems team. “This means the Febetron user community is forced to ride with an engine that hasn’t changed in four decades. What we’ve done is completely redesign the engine, with all the up-to-date performance, reliability and efficiency benefits.

X-ray devices also have civilian uses, and the new capacitor module technology could be suitable for medical imaging devices, as well as applications in the petrochemical, energy and aerospace sectors. . But technology is especially essential for national security missions. As a result, about three-quarters of flash X-ray users are Department of Defense and Department of Energy labs. X-ray data and images are used to constrain computer models for the behavior of materials in high temperature and high pressure regimes.

When stacked horizontally in a capacitor bank (also called a Marx battery) inside a Febetron, the disc-shaped capacitor modules store and deliver pulsed power to an anode-cathode (AK) space for produce an X-ray. The 80-module-long bank multiplies voltage as the charge accelerates through the stack, travels towards the AK gap and releases X-rays. Aimed and timed with a detonation, X-rays can image the processes occurring during the explosion – essential information for understanding and improving the mechanisms of weapons. The more powerful the x-rays, the deeper they can penetrate the detonation activity to “see” the details of the materials.

Beginning design work two years ago, Dighe and his team worked on several prototypes to revamp and optimize the design of the modules. Research technologist Robert Sedillo was instrumental in assembling the K modules with next-generation components such as high-voltage capacitors and resistors capable of withstanding high-energy pulses, helping to improve performance and reliability. The ladder design of the circuit switches – as opposed to the side-by-side design of the current modules – contributes to the increased efficiency of current flow through the capacitor bank during discharge. Redesigned robust electrical connections between adjacent modules prevent arcing. Technicians Timothy Byers and John Wilson helped Dighe plan and execute lab tests to validate the performance of the K modules.

Compared to current modules, which generate approximately 2 million volts, K modules significantly increase the output voltage and power of flash X-ray devices. The newly designed K modules are expected to generate approximately 3.3 million volts and 10,000 amps, which will translate to 33 gigawatts of peak power for 20 nanoseconds. This increase in output voltage will also increase the X-ray spectra, in other words, the energy of the accelerated photons, allowing the X-rays to penetrate further through the material and provide better contrast, thus a better clarity, in x-rays. These capabilities are particularly valuable for imaging high-Z elements, elements with a high atomic (Z) number of protons in the nucleus. K modules will also increase the flow of electrons to the target when installed in electron beam devices. Febetrons that generate electron beams are used to characterize the effects of radiation on high-value electronic circuits such as missile guidance systems, space vehicles and satellite payloads.

In addition to performance constraints, the reliability of current-generation capacitor modules is limited – imagine an early 1980s vehicle that, four decades later, still can’t be trusted to get from point A to point B. Los Alamos lab, Dighe can point to a current tech module that only lasted 39 shots instead of the 3,000 that should be its lifespan. With epoxy-coated circuitry inside a plastic shell, the current-generating modules are vulnerable to internal damage from potential arc flash. In initial field tests over the past two years, over approximately 400 shots, the K-Mods have retained their effectiveness and continue to operate reliably.

There are no patches for a current generation module; even a pinhole defect means the end of the road for him. Ordering a replacement can result in a delay of months or even a year, posing a constant threat to experiment schedules and the significant investment of time and resources associated with those schedules. In contrast, K-modules are user-repairable. Off-the-shelf components are accessible and can be easily replaced, making repair a viable option over disposing of a module. In addition, the majority of the components of the K module are recyclable.

K modules have been developed specifically for Febetron and can find immediate application in these machines. But pulsed power capacitor module technology could also be used in X-ray machines for sterilization of medical devices, healthcare products (such as syringes, gloves, oxygen tubes, etc.) and pharmaceutical products. K modules may find applications in portable X-ray devices used in the aerospace and oil and gas industries for the detection of structural defects or fractures. Similarly, K modules could find applications in electron beam devices used in the food packaging industry to kill microorganisms such as E. coli and salmonella. Applications of electromagnetic pulses could also be viable, for example, for testing radiation hardening of military targets, or using devices to calibrate sophisticated but remote equipment, such as satellites.

The customizable manufacture of the K modules leaves the door open to many possible applications – there are, after all, many cars on the road. Now they finally have a choice of engine.
LA-UR-22-22704


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