Sensing the power
Friday, August 01, 2008
Talked to researcher Stephan Friedrich from Livermore the other day about a device his group’s developed to assist in the commissioning phase of the LCLS. Basically they’ve devised a sensor that will be placed directly in the X-ray beam to measure its full power. It’s the only sensor in the entire diagnostic suite of LCLS instrumentation to actually “touch” the beam. The idea is to measure the machine’s output through a range of settings and then use that to calibrate the primary sensors, which, when the LCLS is up and running, will not interfere with the beam.
Measuring beam power without touching the beam itself is a well understood technique at synchrotron labs. But the LCLS beam will carry so much more power than any other machine—about a one trillion watts per pulse, delivered in a quadrillionth of a second—that we don’t even really know the physics of how the beam will behave around traditional sensors. So the only way to know is to measure the beam power full-on and directly, and see what registers on the traditional sensors. What’s amazing to me, though, is that the new sensor itself is not destroyed by this abuse. Friedrich says that was part of the engineering challenge—to develop a sensor using just the right combination of materials so that we get the information we want without destroying the detection equipment in the process. Although a variety of sophisticated materials exist that could do the job, the team chose silicon (because it's easy to get) to absorb the beam's power, and a material called manganite that turns the heat generated in the silicon into a signal. Although custom instrumentation for physics experiments is nothing new, I think this case in particular illustrates exactly how “beyond the envelope” the LCLS really is. posted by Brad Plummer @ 12:00pm
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