Diamond Annual Review 2021/22

114 115 D I A M O N D L I G H T S O U R C E A N N U A L R E V I E W 2 0 2 1 / 2 2 D I A M O N D L I G H T S O U R C E A N N U A L R E V I E W 2 0 2 1 / 2 2 results have been published to a conference 1 . Tristan10M has been scheduled to be used at I19 for several time resolved user experiments in 2022. It is worth reminding that Tristan time stamps events with a notional time accuracy of 1.56 ns (notional time resolution of the Timepix3 ASIC) and that it can acquire data continuously for a long time (up to 81 days) thanks to the extensions in the firmware developed by the Detector Group. The continuous acquisition with high accuracy time stamp enables to run experiments much more efficiently than running the same experiments by using gated detectors such as conventional photon counting detector systems. These characteristics were highly appreciated by a group who work on XPCS technique at MAX IV (Sweden). The Detector Group loaned a Tristan10M to MAX IV in May 2021 so that they could test the novel concept of data driven detector in an actual experiment. A research group from the University of Stockholm carried out an Detector Group Nicola Tartoni, Detector Group Leader L ast year's focus for the Detector Group was on the development of the Arc Detector for Diamond’s X-ray Pair Distribution Function (XPDF) beamline (I15-1). TheTristan10Mdetector delivered to theSmall-MoleculeSingle-Crystal DiffractionBeamline (I19)was further characterised and is ready to be used routinely for time resolved experiments on I19 in 2022. Finally, the Detector Group worked with the French synchrotron (SOLEIL) on new Ge detectors that may be useful for a number of beamlines. The Arc Detector The ARC detector project for I15-1 is the major development project which has been the main commitment of the Detector Group in the past 12 months. The ARC detector is devoted to the X-ray pair distribution function technique of beamline I15-1 and the detector system consists of an array of 24 sensors arranged in an arc geometry with a radius of 25 cm. In order to guarantee an acceptable detection efficiency at the photon energies of I15- 1 (40.05 keV, 65.40 keV, and 76.69 keV) the sensors are in CdTe. The sensors are pixelated with pixel pitch of 55 microns and each sensor is bonded to 3 Medipix3RX read-out chips. The sensors are mounted in a module, which include the electronics. Four modules are mounted in a supermodule which plugs into the mechanical structure of the detector system. The project is close to delivery and the detector head has been assembled and populated with 24 modules, which is the number of modules that had been planned when the project was launched. Figure 1 shows the detector head fully populated with six supermodules at the end of the assembly procedure. Figure 2 shows the detector head mounted at beamline I15-1. One peculiar aspect of this project is that the Schottky contact technology was chosen for the sensors instead of the most common ohmic one. Although Schottky sensors polarise more quickly than ohmic ones when they are exposed to radiation, they recover much faster when the bias voltage is removed and then applied again. A few seconds of voltage removal is enough to restore the sensors to the pristine condition which delivers a better duty cycle for this particular application. A comparison between Schottky and ohmic sensors, which was done a few years ago with a realistic test at I15-1, showed that the Schottky ones enabled a larger overall exposure time with respect to ohmic sensors. The additional advantage of Schottky sensors is that they can be biased with a voltage which is higher than the ohmic ones. This enables a faster charge collection and thus limits the charge diffusion and improves the spatial resolution. TheTristan10MDetector The Detector Group continued working on various aspects of the Tristan detectors. The Tristan10M, delivered to I19, was fully characterised and the experiment in June 2021 at the beamline NanoMAX at MAX IV. The experiment ran very smoothly and several datasets with a time resolution of 1microsecond were obtained. Figure 3 shows a plot of a dataset taken at MAX IV. Collaboration for new Ge detectors In addition to the two projects mentioned above, the Detector Group at Diamond is leading two activities to develop Ge detectors. Both activities aim to improve the throughput and compactness of monolithic multi-element Ge detectors. The first activity is a collaborationwith Synchrotron SOLEIL and it is in fact a continuation of the pioneering work already autonomously undertaken by the Detector Group to improve the segmentation and the speed of Ge detectors 2,3 . The ultimate goal of the collaboration with SOLEIL is to develop a detector with a large number of small elements to enhance the throughput. This system should make use of the Xspress4 pulse processor to reject the charge shared events electronically without the use of a collimator, like in the current versions of commercial detectors. The collaboration with SOLEIL is currently completing the phase 0 (the first of three phases) this year which is supposed to evaluate the detector technology from a particular vendor. Diamond and SOLEIL are also co-leader of work package 2 of the European project LEAPS-INNOV. This work package develops more compact Ge detectors for XAFS and XRF applications. Whilst the prototype currently being developed by LEAPS-INNOV is limited in the number of channels and therefore in its throughput, the innovative solutions adopted may be re-used for systems with larger number of channels as those envisaged by the collaboration between Diamond and SOLEIL. It is thought that detector systems with very high throughput will be indispensable for Diamond-II and therefore it could be a wise investment to progress to the other two phases (phase 1 and 2) of the collaboration with SOLEIL. References: 1. Z. Chen et al. Tristan10M detector: characterization of a large area detector for time resolved experiments based on Timepix3 chip. JINST , (pre-pub), 2022. 2. N. Tartoni et al . Hexagonal pad multichannel Ge X-Ray spectroscopy detector demonstrator: comprehensive characterization. IEEE Transactions on Nuclear Science 67, 1952-1961 (2020). DOI: 10.1109/ TNS.2020.3004923. 3. N. Tartoni et al. Monolithic multi-element HPGe detector equipped with CMOS preamplifiers: construction and characterization of a demonstrator . IEEE Transactions on Nuclear Science 62, 387-394 (2015) DOI: 10.1109/ TNS.2014.2381492. X-ray Technologies Figure 1: The detector head of the arc-detector on the mounting table. The detector is fully populated and the back side of the 6 supermodules can be noticed in the picture. Figure 2: The detector head closed and mounted on the beam line I15-1. Figure 3: XPCS data set of 100nm Si particles in water taken at the beam line NanoMAX at MAXIV with the Tristan1M detector (plot courtesy of Clemens Weninger (MaxIV)).