JUNGFRAU: adJUstiNg Gain detector FoR the Aramis User station

JUNGFRAU is a novel, two-dimensional pixel detector for high performance photon science applications at free electron lasers (FEL) and synchrotron light sources. It has been developed primarily for the SwissFEL machine, which is now under commissioning at the Paul Scherrer Institute, Switzerland.

Design and Performance Characteristics

• Two-dimensional, modular/tilable, vacuum-compatible imaging detector
• 75 µm pixel size, comparable to photon counting detectors
• Single photon sensitivity
• High dynamic range with up to 10,000 12 keV photons/pulse/pixel
• Low noise over entire dynamic range
• Good linearity of detection over the full dynamic (non-linearity < 1%)
• Frame rates > 1.1kHz (>2 kHz with PCB revision)
• Energy range > 2 keV @ single photon sensitivity

Implementation
JUNGFRAU is a charge integrating detector, which will enable applications at high photon rates. JUNFRAU also features a three-stage, gain-switching preamplifier in each pixel, which automatically adjusts its gain to the amount of charge deposited on the pixel (similar to X-ray Free Electron Laser detectors like AGIPD or GOTTHARD). The automatic gain switching capability on the pixel level is motivated by the necessity to guarantee single photon sensitivity while covering a dynamic range of four orders of magnitude of input signal. Single photon detection at energies as low as 1.5keV has been obtained with short, XFEL compatible, exposure times.

Geometry
The final JUNGFRAU chip comprises 256 × 256 pixels of 75 µm × 75 µm each. Arrays of 2 × 4 chips are tiled to form modules of 4 cm × 8 cm, i.e. about 500 kPixels. The chips are coupled to 320 µm (450 µm are available on request) silicon sensors, which are in large part constructed in analogy to EIGER. Multi-module systems up to 16 Mpixels, i.e. consisting of 32 modules, are planned for various experimental setups at the two end stations of SwissFEL and synchrotron light sources.

Readout
The readout of JUNGFRAU is designed in analogy to the GOTTHARD strip detection system for XFEL applications. The system is fully modular, and the individual boards only require the 12V power input, a copper Ethernet connection for controls and a 10Gbit fiber link for data download. The system is compatible with vacuum, with the vacuum interface consisting of a slotted aluminum flange glued on the flat part of the readout board.
JUNGFRAU can be operated with rates from a few Hz up to 1.14 kHz (2.4kHz are anticipated with a revised PCB) with dead time free operation, which easily serves the readout requirements of SwissFEL but also enables high count rate synchrotron experiments with an extremely high linear count rate capability of >25 MHz/pixel (at 12keV photon energy, with 2.4kHz readout).

Cameras
Using single modules as building blocks, several detector cameras have been assembled. Single module, 1M and 1.5M systems with vertically stacked modules have been produced and are commonly used. A 4Mpixel camera has been designed and has to be assembled. A 4.5M linear module array for X-ray emission spectroscopy at the ALVRA SwissFEL endstation has been commissioned and successfully operated during the SwissFEL pilot experiment phase in Dec. 2017 (link to ALVRA pilot, link to BERNINA pilot). The 2 16Mpix camera for the BERNINA and ALVRA endstations have been designed and will be installed and commissioned in the first half of 2018.

• X-ray spectroscopy: X-ray absorption (XAS), X-ray emission (XES), resonant inelastic X-ray scattering (RIXS), X-ray diffuse scattering
• Nanocrystallography
• X-ray diffraction
• X-ray pump-probe <diffraction and scattering: time-resolved X-ray diffraction (trXRD), time-resolved resonant X-ray diffraction (trRXRD) and time-resolved resonant inelastic X-ray scattering (trRIXS)
• Protein crystallography, specifically high-rate applications