The X-Ray Flux Capacitor: A Low-Cost, Fail-Safe Monitor for Powerful X-Ray Lasers

What is it about?

High-power X-ray free-electron lasers (XFELs) generate extraordinarily intense beams that can rapidly melt through safety equipment if misaligned, endangering both delicate machinery and facility personnel. To prevent this, our team developed the X-Ray Flux Capacitor (XRFC), a new type of burn-through monitor (BTM) made using a standard multi-layer printed circuit board (PCB). Inside the board, alternating copper layers are connected to high voltage and ground, separated by a dielectric material. When a focused X-ray beam strikes the monitor, it quickly degrades this dielectric material, triggering a high-voltage electrical short. We tested 92 prototypes at the Linac Coherent Light Source and found that every single monitor successfully shorted and sent a fast detection signal before the beam could burn completely through the device.

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Photo by Winston Chen on Unsplash

Photo by Winston Chen on Unsplash

Why is it important?

As XFEL facilities upgrade to higher powers, older passive safety absorbers are no longer sufficient to contain stray beams. A fast, reliable way to detect that an X-ray beam has burned through its container is critical so the beam can be shut off immediately. Existing active solutions, like air-bladder or scintillator-based monitors, often have trouble balancing speed, cost, and reliability. The XRFC provides a low-cost, highly scalable, and fail-safe alternative. Because it relies on standard PCB manufacturing, it is inexpensive to produce and can be fabricated in almost any size or shape. Importantly, when the device shorts, it leaves a permanent, visible burn mark on the board, allowing personnel to verify that a real beam burn-through occurred and that it was not a false alarm.

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