AGIPD (Adaptive Gain Integrating Pixel Detector)

The AGIPD is a high speed detector intended for use at the European XFEL. It allows single pulse imaging at 4.5 MHz frame rate with a dynamic range allowing single photon detection and detection of more than 10.000 12.4 keV photons in the same image.

Fig. 1: Block diagram of the integrated circuitry to be used of the full scale (64x64) AGIPD chip. The typical signal path comprises charge generation and transport within the senor, charge collection and (amplified) charge to voltage conversion in the adaptive gain amplifier, Correlated Double Sampling (CDS) of the amplifier output voltage by the CDS stage, signal storage in the analog memory cells, readout of the storage cells and communication of the signal to the outside world via differential and LVDS lines.

Adaptive Gain Integrating Pixel Detector (AGIPD)
for the European X-ray Free Electron Laser in Hamburg


The European X-Ray Free Electron Laser (XFEL) [1,2] will provide ultra-short, highly coherent X-ray pulses which will revolutionize scientific experiments in a variety of disciplines spanning physics, chemistry, materials science, and biology.

One of the differences between the European XFEL and other free electron laser sources is the high pulse repetition frequency of 4.5 MHz. The European XFEL will provide pulse trains, consisting of up to 2700 pulses separated by 220 ns (600 µs in total) followed by an idle time of 99.4 ms, resulting in a supercycle of 10 Hz and 27000 pulses per second.

Dedicated fast 2D detectors are being developed, one of which is the Adaptive Gain Integrating Pixel Detector (AGIPD) [3, 5]. This development is a collaboration between DESY, the University of Hamburg, the University of Bonn (all in Germany) and the Paul Scherrer Institute (PSI) in Switzerland.

AGIPD is based on the hybrid pixel technology. The current design goals of the newly developed Application Specific Integrated Circuit (ASIC) with dynamic gain switching amplifier in each pixel are (for each pixel) a dynamic range of more than 104 12.4 keV photons in the lowest gain, single photon sensitivity in the highest gain, an analog memory capable of storing 352 images, and
operation at 4.5 MHz frame rate. An external veto signal can be provided to maximize the number of useful images by overwriting any image previously recorded during the pulse train. The data is read out and digitized in the 99.4 ms between pulse trains.

For most experiments using particle injection mechanisms the memory of AGIPD should be sufficient, as particle hit rates are usually below 10% (see [6] and references therein). The impact of the limited number of storage cell on X-ray Photon Correlation Spectroscopy (XPCS) as intended to be used on the MID station [7] depends on the properties of the sample and has been investigated elsewhere [8].

Due to the special pulse structure of the European XFEL, it is necessary to store the acquired images inside the pixel logic during the pulse train. A compromise had to be found between storing many images, requiring a large pixel area, and high spatial resolution, requiring small pixels sizes [3].

The AGIPD will feature p+-pixels of a size of (200 µm)2 fabricated on n-type silicon of 500 µm thickness. To minimize the effect of the large number of photons per pixel (plasma effect [9]) an operating voltage above 500 V is advisable. In order to achieve such a high operating voltage for X-ray radiation doses of up to 1 GGy required a special optimization [10].

Project Leader: Heinz Graafsma
References

[1] M. Altarelli et al., European X-ray Free Electron Laser. Technical Design Report, ISBN 978-3-935702-17-1 (2006).

[2] Th. Tschentscher et al., Layout of the X-Ray Systems at the European XFEL, TECHNICAL NOTE XFEL.EU TN-2011-001 (2011).

[3] B. Henrich et al., The adaptive gain integrating pixel detector AGIPD a detector for the European XFEL, Nucl. Instr. and Meth. A, DOI: 10.1016/j.nima.2010.06.107.

[5] G. Potdevin et al., Performance simulation of a detector for 4th generation photon sources: The AGIPD, Nucl. Instr. and Meth. A 607(1) 2009 51-54, DOI: 10.1016/j.nima.2009.03.121.

[6] A. Mancuso et al., Conceptual Design Report: Scientific Instrument SPB, 2011, TR-2011-007

[7] A. Madsen et al., Conceptual Design Report: Scientific Instrument MID, 2011, TR-2011-008

[8] J. Becker and H. Graafsma, Advantages of a logarithmic sampling scheme for XPCS experiments at the European XFEL using the AGIPD detector, 2012 JINST 7 P04012 doi:10.1088/1748-0221/7/04/P04012.

[9] J.Becker, D.Eckstein, R.Klanner and G.Steinbrück, Impact of plasma effects on the performance of silicon sensors at an X-ray FEL, Nucl. Inst. and Meth. A 615 (2010) 230-236, doi:10.1016/j.nima.2010.01.082.

[10] J Schwandt, E Fretwurst, R Klanner and J Zhang, Design of the AGIPD sensor for the European XFEL, 2013 JINST 8 C01015 doi:10.1088/1748-0221/8/01/C01015.