A. Kreps

Calibration of a digital hadron calorimeter with muons

The calibration procedure of a finely granulated digital hadron calorimeter with Resistive Plate Chambers as active elements is described. Results obtained with a stack of nine layers exposed to muons from the Fermilab test beam are presented.The calibration procedure of a finely granulated digital hadron calorimeter with Resistive Plate Chambers as the active elements is described. Results obtained with a stack of nine layers exposed to muons from the Fermilab test beam are presented.

Production and commissioning of a large prototype Digital Hadron Calorimeter for future colliding beam experiments

A new detector technology is being developed for future colliding beam experiments that is based on the use of fine-grained calorimetry, to optimize the use of Particle Flow Algorithms (PFAs) in measuring hadronic jets. Instead of traditional tower geometry and energy summation from many sampling layers, the new approach measures energy deposition in 1 cm2 cells on each sampling layer using discriminators. Jets are reconstructed using hit patterns from each layer, combined with information from inner tracking and the electromagnetic calorimeter. We have built a 480,000 channel prototype detector that is based on Resistive Plate Chambers (RPCs) to demonstrate this concept. The development is part of the CALICE Collaboration. The readout system uses a 64-channel custom integrated circuit called DCAL to record hits from each cell and apply a global timestamp. The chips mount directly on sophisticated front-end boards that are not only an integral part of the charge collection of the detector chambers, but also incorporate digital signal transmission, clock and control, and power and ground. The readout of data is serial, multiplexed into high-speed serial streams and sent to a “back-end” VME system for time-sorting and higher-level triggering. The system can be operated with an external trigger or be self-triggered, and can produce trigger signals from the front-end chips. The construction, installation, and commissioning of this prototype system is now complete. We have begun a measurement program using a test beam at Fermilab. An overview of the system is described. Experiences in building this large prototype system are reported. Results from the test beam are presented.

A new detector for time-resolved small angle X-ray scattering studies

A new detector for time-resolved small-angle X-ray scattering has been designed and built for experiments at the Advanced Photon Source of Argonne National Laboratory. This detector is made from a 500 mum thick by 150 mm diameter ultra-high purity silicon wafer, which directly converts X-rays into electron-hole pairs. The electrodes are concentric rings that integrate the scattered X-rays over the azimuthal angle. The widths of the rings are optimized for the size of the X-ray beam and its energy spread. Only 128 rings, or channels, are needed to measure a scattering profile. The read-out electronics consist of preamplifiers with pulse-shaping, which are mounted on the detector, and 12-bit, 20 MHz digitizers. The resolving time of the electronics is 300 ns, which is sufficient to isolate a single pulse of scattered X-rays when the synchrotron is operated with a hybrid or asymmetric fill pattern. The data acquisition hardware can average a programmable number of digital samples, up to 64, every 3.68 mus (the period of the synchrotron) to provides a single 12-bit average of the voltage from the analog amplifier chain. The temporal range of the detector is 3.68 seconds or longer and may be controlled by the experimenter. An alpha source is used to calibrate the detector and electronics, and document their performance. Preliminary results obtained during the commissioning of the detector are presented

Design, Construction and Commissioning of the Digital Hadron Calorimeter - DHCAL

A novel hadron calorimeter is being developed for future lepton colliding beam detectors. The calorimeter is optimized for the application of Particle Flow Algorithms (PFAs) to the measurement of hadronic jets and features a very finely segmented readout with 1 × 1 cm2 cells. The active media of the calorimeter are Resistive Plate Chambers (RPCs) with a digital, i.e. one-bit, readout. To first order the energy of incident particles in this calorimeter is reconstructed as being proportional to the number of pads with a signal over a given threshold. A large-scale prototype calorimeter with approximately 500,000 readout channels has been built and underwent extensive testing in the Fermilab and CERN test beams. This paper reports on the design, construction, and commissioning of this prototype calorimeter.

A readout system utilizing the APV25 ASIC for the Forward GEM Tracker in STAR

We have developed a modular readout system for the 30,720 channel Forward GEM Tracker recently installed in the STAR Experiment at RHIC, BNL. The modular architecture is based on a passive compact PCI backplane running a custom protocol, not PCI, connecting 6 readout modules to a readout controller module. The readout modules provide all necessary functions, including isolated power supplies, to operate up to 24 APV25 chips per module with high-impedance ground isolation. The front-end boards contain a minimal set of components as they are located inside the STAR TPC inner field cage and are inaccessible except during long shutdown periods. The front-end boards connect to the readout modules with cables up to 24 m in length, carrying unbuffered analog readout signals from the APV25 as well as power, trigger, clock and control. The readout module digitizes the APV analog samples to 12 bits at 37.532 MHz, and zero suppresses and buffers the data. The readout controller distributes trigger and clock from the central trigger system, gathers the data over the backplane, and ships it to a linux PC via a 2.125 Gbps optical data link (Detector Data Link (DDL) from ALICE). The PC gathers data from multiple readout controllers and dispatches it to the STAR event builders. The readout modules, controllers, and backplanes are housed in a common crate together with the GEM HV bias power supplies.

A High-Speed One-Dimensional Detector for Time-Resolved Small-Angle X-Ray Scattering: Design and Characterization

A high-speed one-dimensional detector for time-resolved small-angle x-ray scattering has been designed and built for experiments at the Advanced Photon Source of Argonne National Laboratory. This detector is made from a 500-μm thick by 150-mm diameter ultra-high-purity n-type silicon wafer. The electrodes, which are a series of concentric rings that are deposited in the wafer, integrate the scattered x-rays over the azimuthal angle and, thereby, produce a one-dimensional detector. This design yields 128 rings, which allows parallel processing of the signal from each ring. The readout electronics consist of transimpedance front-end amplifiers, one for each ring, followed by active pulse-shaping filters. The amplifier signals are digitized using 12-bit analog-to-digital converters, one per ring, which operate at 20 MHz. The frame rate of the system is 271 kHz. Up to 220 - 1 scattering profiles may be stored on a random access memory chip and transferred to a data file at a rate of 16 × 103 profiles/sec. For X-ray energies between 3.5 and 13.2 keV the efficiency exceeds 80%. The resolving time of the electronics is 300 ns, which is sufficient to isolate electronically a single pulse of scattered x-rays when the synchrotron is operated in a hybrid or asymmetric fill pattern. Therefore, laser-pump/x-ray-probe experiments can be performed without a mechanical shutter. Examples of time-resolved speckle and the kinetics of the formation of sodium chloride particles are presented. This detector is capable of acquiring small-angle x-ray scattering profiles over multiple time scales, which are needed to characterize many chemical, physical, and biological processes. In addition, this detector may be tested and calibrated before experimental runs, without access to an intense beam of x-rays, with alpha particles from a radioactive source such as 241Am.

Field tests of a new high-speed pattern recognition trigger for ground-based gamma-ray telescope arrays

We have developed a three-stage, high-speed trigger for use in an array of imaging atmospheric Cherenkov telescopes (IACTs), which are used for the study of cosmic high-energy gamma-ray sources. This trigger has the ability to recognize patterns of Cherenkov light generated by gamma-ray initiated air showers in the atmosphere and correlate these patterns across multiple telescopes in the IACT array to form a stereoscopic realtime pattern recognition trigger. New hardware and firmware sampling at 400MHz with programmable coincidence recognition timing and programmable delay compensation over 500 pixel channels in an IACT camera has been produced which generates triggers from the coincidence of any three adjacent pixels within the camera. Reduction of the required coincidence time to 5 ns and the concomitant reduction in dead time from the faster logic allow operation at lower discriminator thresholds relative to existing systems, enabling studies of lower energy gamma-ray events. A successful field test of the first two stages of this pattern recognition hardware has been performed on one of the IACTs of the VERITAS array located in Southern Arizona. We present the results of these tests and compare them to the performance of the existing VERITAS trigger system. A subsequent field test where hardware is connected to multiple VERITAS telescopes to exercise the stereoscopic features is in the planning stages.

A new high-speed pattern recognition trigger for ground-based telescope arrays used in gamma ray astronomy

Modern imaging atmospheric Cerenkov telescopes (IACTs) are often configured as an array of individual telescopes, each having 500 pixels or more, where stereoscopic views of gamma ray air showers using two or more telescopes operating in unison improve the measurement of the location of the source in the night sky. The gamma-ray showers of interest have significant backgrounds, including cosmic-ray showers from protons and heavier elements, muons, and fluctuations in the night sky background that generate noise events in the photo-detectors. It is desirable to lower the thresholds on individual pixels, as this reduces the energy threshold of the instrument and facilitates observation of more distant cosmological objects. However, lowering the threshold also increases the noise and background rates. System aspects ultimately determine how low the threshold can be, including the depth of memory in the front end electronics, the speed of the data acquisition, and the sophistication of the trigger. Gamma-ray showers have a distinct but not unique signature compared to the background signals. We have developed a three-stage, high-speed trigger that can recognize patterns from gamma-ray showers and correlate them across all telescopes in the array to form a stereoscopic real-time pattern recognition trigger. Our goal is to process the ∼10 MHz individual pixel rate on 500+ channels of each telescope (Level 1), and produce a camera trigger rate of 10 MHz (Level 2), and an array trigger rate of less than1 KHz (Level 3). This is a significant increase in performance over current IACTs that operate typically at a 1 KHz Level–2 and at 300∼Hz event acceptance rate. We describe the architecture of this new sophisticated trigger, present first measurements of the prototype system, and describe plans to test this system in an existing IACT as a proof of principle for a future IACT array that might consist of hundreds of telescopes.

2-D scintillation position-sensitive neutron detector

A new 2-dimensional scintillation position-sensitive neutron detector (PSND) with an active area of 155times155 mm2 was developed for use on the single crystal diffractometer at the intense pulsed neutron source at Argonne National Laboratory. The detector is based on the well-proven Anger camera technique and uses a 6Li glass scintillator as the neutron converter. This PSND incorporates a 6times6 PMT array with 29.6 mm pitch and optimized optics to achieve an average spatial resolution of 1.75 mm full width at half maximum. The detector read-out has separate electronics for each PMT and the neutron position is calculated by a microprocessor during acquisition. A newly developed position extraction algorithm makes use of an analytical calculation to determine the event position. This new method improves the linearity of the calculated position, provides a slight improvement in resolution, and in principle allows for the correct determination of position to the edge of the scintillator. The design of the detector enclosure allows multiple detectors to be tiled with minimal dead space between them. In addition, the design incorporates a means of attaching external shielding plates that minimizes the shielding surface area required

Commissioning and performance of a fast level-2 trigger system at VERITAS

We have built a new three-stage FPGA-based high-speed trigger for VERITAS, an array of ground-based imaging atmospheric Cherenkov telescopes (IACTs) located in Arizona. This trigger has the ability to recognize patterns of Cherenkov light generated by atmospheric air showers initiated by incident extra-terrestrial gamma rays. The new trigger has programmable coincidence recognition timing and programmable delay compensation over 499 pixel channels in an IACT camera. Measurement of and compensation for systemic variations is achieved through the use of an FPGA-based time-to-digital converter (TDC) and FPGA-based programmable delay elements. The trigger pattern is the coincidence of any three adjacent pixels within the camera. The minimum coincidence window of 3ns with low dead time provides sensitivity at lower energies than were achieved previously. The new trigger has now been successfully installed on all four of the IACTs of VERITAS, replacing the previous system. We present measurements of the performance of this new trigger in comparison with that of the previous system and of the effect of the new trigger upon overall array performance.