JUNGFRAU: adJUstiNg Gain detector FoR the Aramis User station

JUNGFRAU is a state-of-the-art, two-dimensional pixel detector designed for high-performance photon science applications at Free Electron Lasers (FEL) and synchrotron light sources. It was primarily developed for the SwissFEL machine at the Paul Scherrer Institute in Switzerland. JUNGFRAU is tailored to meet the stringent demands of these advanced facilities, offering exceptional performance in terms of dynamic range, noise reduction, and readout speed, making it ideal for cutting-edge experiments.

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
• High detection linearity over the full dynamic (non-linearity < 1%)
• Image rate > 2.2kHz continuous (up to 250 keV in burst mode)
• Energy range > 2 keV @ single photon sensitivity (with standard silicon sensors)

Implementation
JUNGFRAU is a charge-integrating detector designed to support applications involving high photon rates, making it particularly well-suited for high-intensity photon sources like X-ray Free Electron Lasers (XFEL) and synchrotron facilities. A key feature of JUNGFRAU is its three-stage gain-switching preamplifier embedded within each pixel, which dynamically adjusts the gain based on the amount of charge deposited. This mechanism, similar to that used in other advanced detectors like AGIPD and GOTTHARD, ensures single-photon sensitivity while maintaining a dynamic range spanning four orders of magnitude. JUNGFRAU has demonstrated single-photon detection down to energies as low as 1.5 keV under short, XFEL-compatible exposure times.

Geometry
The JUNGFRAU chip consists of 256 × 256 pixels, each measuring 75 µm × 75 µm. These chips are assembled into arrays of 2 × 4 to form modules measuring 4 cm × 8 cm, providing a total of approximately 500 kPixels per module. The chips are typically paired with 320 µm thick silicon sensors, although 450 µm sensors are available upon request, largely following the design principles of the EIGER detector. Multi-module systems, with up to 16 Mpixels (comprising 32 modules), are available for various experimental setups at SwissFEL’s end stations and at several synchrotron light sources.

Readout
The JUNGFRAU readout system is modeled after the GOTTHARD strip detector system, optimized for XFEL applications. It is fully modular, with individual boards requiring only a 12 V power supply, a copper Ethernet connection for controls, and a 10 Gbit fiber link for data transmission. The system is vacuum-compatible, using a slotted aluminum flange that is glued onto the flat part of the readout board for the vacuum interface. JUNGFRAU supports operation at frame rates ranging from a few Hz to 2.2 kHz with dead time-free performance, easily meeting readout demands of SwissFEL. Additionally, it enables high-rate synchrotron experiments with an exceptionally high linear count rate capability of over 25 MHz per pixel (at 12 keV photon energy with 2.2 kHz readout).

Cameras
Using single modules as building blocks, several detector cameras are available with customizable configurations. Single module (500 kPixels), 1 Mpixel, and 1.5 Mpixel systems with vertically stacked modules, as well as multiple 4 Mpixel and 9 Mpixel cameras have been produced and are commonly used at several synchrotron and FEL facilities. A 4.5 Mpixel 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 December 2017 (link to ALVRA pilot, link to BERNINA pilot). Two 16 Mpixel cameras for the BERNINA and ALVRA endstations were installed and commissioned in 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