K. Nishimura

X‐ray detectors at the Linac Coherent Light Source

This paper offers an overview of area detectors developed for use at the Linac Coherent Light Source (LCLS) with particular emphasis on their impact on science. The experimental needs leading to the development of second-generation cameras for LCLS are discussed and the new detector prototypes are presented.

Detector Development for the Linac Coherent Light Source

Since it began operations in 2009, the Linac Coherent Light Source (LCLS) has opened a new and dynamic frontier in terms of light sources and their associated science [1, 2]. An increase in brightness by a factor of a billion over pre-existing synchrotrons, in combination with ultra-brief pulses of coherent X-rays, is ushering in a new era in the photon sciences. Pulses with durations of 50 fs under standard conditions and below 10 fs with a reduced energy per bunch are possible. Over 1013 or 1012 X-rays per pulse can be generated at the upper and lower ends of the X-ray energy range of 285 eV to 9600 eV. One of the unique machine parameters is its strobe-like time structure, where single ultra-brief pulses are delivered at a repetition rate of 120 Hz. The above characteristics represent a singular environment in which to operate detectors and demand the development of a new class of high-frame-rate camera systems.

Design of the SLAC RCE Platform: A general purpose ATCA based data acquisition system

The SLAC RCE platform is a general purpose clustered data acquisition system implemented on a custom ATCA compliant blade, called the Cluster On Board (COB). The core of the system is the Reconfigurable Cluster Element (RCE), which is a system-on-chip design based upon the Xilinx Zynq family of FPGAs, mounted on custom COB daughter-boards. The Zynq architecture couples a dual core ARM Cortex A9 based processor with a high performance 28nm FPGA. The RCE has 12 external general purpose bi-directional high speed links, each supporting serial rates of up to 12Gbps. 8 RCE nodes are included on a COB, each with a 10Gbps connection to an on-board 24-port Ethernet switch integrated circuit. The COB is designed to be used with a standard full-mesh ATCA backplane allowing multiple RCE nodes to be tightly interconnected with minimal interconnect latency. Multiple shelves can be clustered using the front panel 10-gbps connections. The COB also supports local and inter-blade timing and trigger distribution. An experiment specific Rear Transition Module adapts the 96 high speed serial links to specific experiments and allows an experiment-specific timing and busy feedback connection. This coupling of processors with a high performance FPGA fabric in a low latency, multiple node cluster allows high speed data processing that can be easily adapted to any physics experiment. RTEMS as well as Linux are ported to the module. The RCE has been used or is the baseline for several current and proposed experiments (LCLS, HPS, LSST, ATLAS-CSC, LBNE, DarkSide, ILC-SiD, etc).

Design and characterization of the ePix10k prototype: A high dynamic range integrating pixel ASIC for LCLS detectors

ePix10k is a variant of a novel class of integrating pixel ASICs architectures optimized for the processing of signals in second generation LINAC Coherent Light Source (LCLS) X-Ray cameras. The ASIC is optimized for high dynamic range application requiring high spatial resolution and fast frame rates. ePix ASICs are based on a common platform composed of a random access analog matrix of pixel with global shutter, fast parallel column readout, and dedicated sigma-delta analog to digital converters per column. The ePix10k variant has 100um×100um pixels arranged in a 176×192 matrix, a resolution of 140e- r.m.s. and a signal range of 3.5pC (10k photons at 8keV). In its final version it will be able to sustain a frame rate of 2kHz. A first prototype has been fabricated and characterized. In this paper the ASIC performance in terms of noise, linearity, uniformity and cross-talk are presented, together with preliminary measurements with bump bonded sensors.

ePix: A class of front-end ASICs for second generation LCLS integrating hybrid pixel detectors

ePix is a novel class of ASICs architectures based on a common platform optimized for the processing of signals in second generation LCLS cameras. The platform architecture is composed of a random access analog matrix of pixels with a global shutter, fast parallel column readout, and dedicated sigma-delta analog to digital converters per column. It also implements a dedicated control interface and all the required support electronics to perform configuration, calibration, and readout of the matrix. Based on this platform a class of front-end ASICs and several camera modules are under development, each utilizing specific pixel architectures, to meet varying requirements. This approach reduces development time and expands the possibility of integration of detector modules in size, shape or functionality as different modules could be assembled in the same camera. The ePix platform is currently under development together with two integrating pixel architectures: ePix100 optimized for ultra-low noise applications and ePix10k optimized instead for high dynamic range applications.

2nd generation cameras for LCLS and the new challenges of high repetition rates at LCLS-II

With the experience of the first years of operation of the Linac Coherent Light Source (LCLS), SLAC developed a 2nd generation camera system with improved features and performance. The first camera to be deployed is the ePix-One, a compact camera which is a 155 mm long box with a quadratic front face of 52×52 mm2 which will feature 4 ASICs, either the ePIX100 or the ePIX10k, bump-bonded with a single sensor offering 35 × 38 mm2 active area. Combined with the ePIX100 hybrid pixel module which features 50 μm pixels and is targeted for X-ray Photon Correlation Spectroscopy and as a detector in wavelength dispersive spectrometer setups this will result in a 0.5Mpixel camera. Whereas the 100 μm pixels of ePIX10k, targeted towards protein crystallography, imaging and pump probe experiments, will provide a camera of 135kpixel. The camera uses simple Peltier/water cooling in combination with dry nitrogen purge against condensation. The compact housing and the simple interface (26pin cable & optical fiber) eases deployment and gives experimenters more flexibility in utilizing the camera where needed. The current ePix cameras support full frame readout faster than 120Hz and ROI modes which can be read at up to 1kHz rate. Next developments will target larger cameras and higher frame rates for the upcoming LCLS II.

Studies of the ePix100 low-noise x-ray camera at SLAC

A new hybrid pixel array detector, the ePix100, has been developed at SLAC for tender and hard x-ray experiments at the Linac Coherent Light Source (LCLS). It is intended for low noise and good spatial resolution applications, particularly X-ray Photon Correlation Spectroscopy (XPCS) and in combination with wavelength dispersive spectrometers. The detector has 50 μm pixel size and less than 100 e- r.m.s. noise over the range of tested operating conditions. A series of measurements to validate its performance with x-rays was carried out at the Stanford Synchrotron Radiation Lightsource (SSRL) and LCLS. Results are here reported and discussed.

ePix100 camera: Use and applications at LCLS

The ePix100 x-ray camera is a new system designed and built at SLAC for experiments at the Linac Coherent Light Source (LCLS). The camera is the first member of a family of detectors built around a single hardware and software platform, supporting a variety of front-end chips. With a readout speed of 120 Hz, matching the LCLS repetition rate, a noise lower than 80 e-rms and pixels of 50 µm × 50 µm, this camera offers a viable alternative to fast readout, direct conversion, scientific CCDs in imaging mode. The detector, designed for applications such as X-ray Photon Correlation Spectroscopy (XPCS) and wavelength dispersive X-ray Emission Spectroscopy (XES) in the energy range from 2 to 10 keV and above, comprises up to 0.5 Mpixels in a very compact form factor. In this paper, we report the performance of the camera during its first use at LCLS.

Design and characterization of the ePix10k: a high dynamic range integrating pixel ASIC for LCLS detectors

ePix10k is a variant of a novel class of integrating pixel ASICs architectures optimized for the processing of signals in second generation LINAC Coherent Light Source (LCLS) X-Ray cameras. The ASIC is optimized for high dynamic range application requiring high spatial resolution and fast frame rates. ePix ASICs are based on a common platform composed of a random access analog matrix of pixel with global shutter, fast parallel column readout, and dedicated sigma-delta analog to digital converters per column. The ePix10k variant has 100um×100um pixels arranged in a 176×192 matrix, a resolution of 140e- r.m.s. and a signal range of 3.5pC (10k photons at 8keV). In its final version it will be able to sustain a frame rate of 2kHz. A first prototype has been fabricated and characterized. Performance in terms of noise, linearity, uniformity, cross-talk, together with preliminary measurements with bump bonded sensors are reported here.

Design and characterization of the ePix100a: A low noise integrating pixel ASIC for LCLS detectors

ePix100 is the first variant of a novel class of integrating pixel ASICs architectures optimized for the processing of signals in second generation LINAC Coherent Light Source (LCLS) X-Ray cameras. ePix ASICs are based on a common platform composed of a random access analog matrix of pixel with global shutter, fast parallel column readout, and dedicated sigma-delta analog to digital converters per column. The ePix100 variant is optimized for low noise application requiring high spatial resolution and fast frame rates. The ASIC has pixels of 50×50 μm2 size arranged in a 352×384 array, a resolution of 50e- r.m.s., and a signal range of 35fC (100 photons at 8keV). In its final version it will be able to sustain a frame rate of 1 kHz. Currently a full-size analog version, ePix100a, has been fabricated in TSMC CMOS 0.25 μm technology. The ePix100a has been fully characterized and results are here reported.