Synchrotron Innovation Award for Heinz Graafsma

This year's European Innovation Award on Synchrotron Radiation goes to CFEL physicist Heinz Graafsma together with Aldo Mozzanica and Bernd Schmitt from the Paul Scherrer Institute in Switzerland. The scientists had jointly developed an innovative ultrafast X-ray camera. The detector, called AGIPD (Adaptive Gain Integrating Pixel Detector), takes the fastest X-ray series images in the world and is already being used at the European X-ray laser European XFEL. The Innovation Award on Synchrotron Radiation is endowed with 3000 Euro and sponsored by SPECS GmbH and BESTEC GmbH. It was delivered at the users' meeting of Helmholtz-Zentrum Berlin (HZB) by Friends of HZB.

The prize for innovations in synchrotron research went to PSI researchers Dr. Aldo Mozzanica (2nd from left), Dr. Bernd Schmitt (3rd from left) and DESY scientist Prof. Dr. Heinz Graafsma (4th from left). It was presented by Prof. Dr. Mathias Richter (5.f.l.) from the circle of friends of the HZB. The laudatio was held by Prof. Dr. Edgar Weckert, DESY (1st from left). Credit: HZB,M. Setzpfand

For experiments on storage rings, so-called photon counting pixel detectors are usually used, since the photons arrive one after the other in each pixel, and the signal of each photon is processed individually per pixel. For free-electron lasers (FELs) such as the European XFEL, this is not an option, since many photons arrive at the detector in a single X-ray pulse that is only 0.1 trillionth of a second (100 femtoseconds) short. That is much too short to process them individually. This means that for FELs so-called integrating detectors have to be used. However, in some pixels arrive so many photons that it overflows, leading to the loss of important information.

“So far one had to choose: Either make the integrating detector very sensitive, in other words having a high gain, in order to be able to detect signals generated by a single photon, or make the integrating detector not very sensitive, in other words having a low gain, in order to be able to cope with signals generated by a large number of photons. But one could not have both,” explains Graafsma.

To solve this problem, Graafsma's team developed and built an integrating detector in which the gain for each individual pixel is automatically adjusted according to the strength of the input signal. Hence the name Adaptive Gain Integrating Pixel Detector. This allows the detector to exploit its full dynamic range in each individual pixel, leading to significantly improved data quality and thus to better scientific results.

For the use at the European XFEL, there was an additional challenge: It has an extremely high pulse rate of up to 4.5 megahertz. This means that two flashes of the X-ray laser follow each other at an interval of only 220 nanoseconds (billionths of a second). This is about a thousand times faster than at all other such systems. In order to keep up with this fast pulse rate, a buffer memory for 352 images was implemented in each pixel. “This makes AGIPD the world's fastest X-ray camera with a high dynamic range,” emphasizes Graafsma.