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Construction of a Medium-Sized Schwarzschild-Couder Telescope for the Cherenkov Telescope Array: Implementation of the Cherenkov-Camera Data Acquisition System  [PDF]
M. Santander,J. Buckley,B. Humensky,R. Mukherjee,for the CTA Consortium
Physics , 2015,
Abstract: A medium-sized Schwarzchild-Couder Telescope (SCT) is being developed as a possible extension for the Cherenkov Telescope Array (CTA). The Cherenkov camera of the telescope is designed to have 11328 silicon photomultiplier pixels capable of capturing high-resolution images of air showers in the atmosphere. The combination of the large number of pixels and the high trigger rate (> 5 kHz) expected for this telescope results in a multi-Gbps data throughput. This sets challenging requirements on the design and performance of a data acquisition system for processing and storing this data. A prototype SCT (pSCT) with a partial camera containing 1600 pixels, covering a field of view of 2.5 x 2.5 square degrees, is being assembled at the F.L. Whipple Observatory. We present the design and current status of the SCT data acquisition system.
A Medium Sized Schwarzschild-Couder Cherenkov Telescope Mechanical Design Proposed for the Cherenkov Telescope Array  [PDF]
K. Byrum,T. B. Humensky,W. Benbow,R. Cameron,S. Criswell,M. Errando,V. Guarino,P. Kaaret,D. Kieda,R. Mukherjee,D. Naumann,D. Nieto,R. Northrop,A. Okumura,E. Roache,J. Rousselle,S. Schlenstedt,R. Sternberger,V. Vassiliev,S. Wakely,H. Zhao,for the CTA Consortium
Physics , 2015,
Abstract: The Cherenkov Telescope Array (CTA) is an international next-generation ground-based gamma-ray observatory. CTA will be implemented as southern and northern hemisphere arrays of tens of small, medium and large-sized imaging Cherenkov telescopes with the goal of improving the sensitivity over the current-generation experiments by an order of magnitude. CTA will provide energy coverage from ~20 GeV to more than 300 TeV. The Schwarzschild-Couder (SC) medium size (9.5m) telescopes will feature a novel aplanatic two-mirror optical design capable of accommodating a wide field-of-view with significantly improved angular resolution as compared to the traditional Davies-Cotton optical design. A full-scale prototype SC medium size telescope structure has been designed and will be constructed at the Fred Lawrence Whipple Observatory in southern Arizona during the fall of 2015. concentrate on the novel features of the design.
Layout design studies for medium-sized telescopes within the Cherenkov Telescope Array  [PDF]
T. Hassan,B. Humensky,D. Nieto,M. Wood,for the CTA Consortium
Physics , 2015,
Abstract: The Cherenkov Telescope Array (CTA) is an international project for a next-generation ground-based gamma-ray observatory. CTA, conceived as an array of tens of imaging atmospheric Cherenkov telescopes, comprising small, medium and large-size telescopes, is aiming to improve on the sensitivity of current-generation experiments by an order of magnitude and provide energy coverage from 20 GeV to more than 300 TeV. In this study we explore how the medium-sized telescopes layout design and composition impacts the overall CTA performance by analyzing Monte Carlo simulations including Davies-Cotton and Schwarzschild-Couder medium-sized telescopes.
FlashCam: a fully-digital camera for the medium-sized telescopes of the Cherenkov Telescope Array  [PDF]
G. Pühlhofer,C. Bauer,S. Bernhard,M. Capasso,S. Diebold,F. Eisenkolb,D. Florin,C. F?hr,S. Funk,A. Gadola,F. Garrecht,G. Hermann,I. Jung,O. Kalekin,C. Kalkuhl,J. Kasperek,T. Kihm,R. Lahmann,A. Manalaysay,A. Marszalek,M. Pfeifer,P. J. Rajda,O. Reimer,A. Santangelo,T. Schanz,T. Schwab,S. Steiner,U. Straumann,C. Tenzer,A. Vollhardt,Q. Weitzel,F. Werner,D. Wolf,K. Zietara,for the CTA consortium
Physics , 2015,
Abstract: The FlashCam group is currently preparing photomultiplier-tube based cameras proposed for the medium-sized telescopes (MST) of the Cherenkov Telescope Array (CTA). The cameras are designed around the FlashCam readout concept which is the first fully-digital readout system for Cherenkov cameras, based on commercial FADCs and FPGAs as key components for the front-end electronics modules and a high performance camera server as back-end. This contribution describes the progress of the full-scale FlashCam camera prototype currently under construction, as well as performance results also obtained with earlier demonstrator setups. Plans towards the production and implementation of FlashCams on site are also briefly presented.
Performance of Silicon Photomultipliers for the Dual-Mirror Medium-Sized Telescopes of the Cherenkov Telescope Array  [PDF]
Jonathan Biteau,David Chinn,Dennis Dang,Kevin Doyle,Caitlin A. Johnson,David A. Williams,for the CTA Consortium
Physics , 2015,
Abstract: Gamma-ray observations in the very-high-energy domain (E > 30 GeV) can exploit the imaging of few-nanosecond Cherenkov flashes from atmospheric particle showers. Photomultipliers have been used as the primary photosensors to detect gamma-ray induced Cherenkov light for the past 25 years, but they are increasingly challenged by the swift progress of silicon photomultipliers (SiPMs). We are working to identify the optimal photosensors for medium-sized Schwarzschild-Couder telescopes (SCT), which are proposed to contribute a significant fraction of the sensitivity of the Cherenkov Telescope Array in its core energy range. We present the capabilities of the latest SiPMs from the Hamamatsu, SensL, and Excelitas companies that we have characterized in our laboratory, and compare them to the SiPMs equipping the prototype SCT camera that is under construction.
Construction of a medium-sized Schwarzschild-Couder telescope as a candidate for the Cherenkov Telescope Array: development of the optical alignment system  [PDF]
D. Nieto,S. Griffiths,B. Humensky,P. Kaaret,M. Limon,I. Mognet,A. Peck,A. Petrashyk,D. Ribeiro,J. Rousselle,B. Stevenson,V. Vassiliev,P. Yu,for the CTA Consortium
Physics , 2015,
Abstract: The Cherenkov Telescope Array (CTA) is an international project for a next-generation ground-based gamma-ray observatory. CTA, conceived as an array of tens of imaging atmospheric Cherenkov telescopes, comprising small, medium and large-size telescopes, is aiming to improve on the sensitivity of current-generation experiments by an order of magnitude and provide energy coverage from 20 GeV to more than 300 TeV. The Schwarzschild-Couder (SC) medium-size candidate telescope model features a novel aplanatic two-mirror optical design capable of a wide field-of-view with significantly improved imaging resolution as compared to the traditional Davis-Cotton optics design. Achieving this imaging resolution imposes strict alignment requirements to be accomplished by a dedicated alignment system. In this contribution we present the status of the development of the SC optical alignment system, soon to be materialized in a full-scale prototype SC medium-size telescope at the Fred Lawrence Whipple Observatory in southern Arizona.
Prototyping of Hexagonal Light Concentrators for the Large-Sized Telescopes of the Cherenkov Telescope Array  [PDF]
Akira Okumura,Sakiya Ono,Syunya Tanaka,Masaaki Hayashidad,Hideaki Katagiri,Tatsuo Yoshida
Physics , 2015,
Abstract: Reflective light concentrators with hexagonal entrance and exit apertures are frequently used at the focal plane of gamma-ray telescopes in order to reduce the size of the dead area caused by the geometries of the photodetectors, as well as to reduce the amount of stray light entering at large field angles. The focal plane of the large-sized telescopes (LSTs) of the Cherenkov Telescope Array (CTA) will also be covered by hexagonal light concentrators with an entrance diameter of 50 mm (side to side) to maximize the active area and the photon collection efficiency, enabling realization of a very low energy threshold of 20 GeV. We have developed a prototype of this LST light concentrator with an injection-molded plastic cone and a specular multilayer film. The shape of the plastic cone has been optimized with a cubic B\'{e}zier curve and a ray-tracing simulation. We have also developed a multilayer film with very high reflectance ($\gtrsim95$\%) along wide wavelength and angle coverage. The current status of the prototyping of these light concentrators is reported here.
Pointing Calibration for the Cherenkov Telescope Array Medium Size Telescope Prototype  [PDF]
Louise Oakes,Bagmeet Behera,Juergen Baehr,Sandra Gruenewald,Tobias Raeck,Stefan Schlenstedt,Anja Schubert,Ullrich Schwanke,for the CTA Consortium
Physics , 2013,
Abstract: Pointing calibration is an offline correction applied in order to obtain the true pointing direction of a telescope. The Cherenkov Telescope Array (CTA) aims to have the precision to determine the position of point-like as well as slightly extended sources, with the goal of systematic errors less than 7 arc seconds in space angle. This poster describes the pointing calibration concept being developed for the CTA Medium Size Telescope (MST) prototype at Berlin-Adlershof, showing test results and preliminary measurements. The MST pointing calibration method uses two CCD cameras, mounted on the telescope dish, to determine the true pointing of the telescope. The "Lid CCD" is aligned to the optical axis of the telescope, calibrated with LEDs on the dummy gamma-camera lid; the "Sky CCD" is pre-aligned to the Lid CCD and the transformation between the Sky and Lid CCD camera fields of view is precisely modelled with images from special pointing runs which are also used to determine the pointing model. During source tracking, the CCD cameras record images which are analysed offline using software tools including Astrometry.net to determine the true pointing coordinates.
Development of the photomultiplier tube readout system for the first Large-Sized Telescope of the Cherenkov Telescope Array  [PDF]
Shu Masuda,Yusuke Konno,Juan Abel Barrio,Oscar Blanch Bigas,Carlos Delgado,Lluís Freixas Coromina,Shuichi Gunji,Daniela Hadasch,Kenichiro Hatanaka,Masahiro Ikeno,Jose Maria Illa Laguna,Yusuke Inome,Kazuma Ishio,Hideaki Katagiri,Hidetoshi Kubo,Gustavo Martínez,Daniel Mazin,Daisuke Nakajima,Takeshi Nakamori,Hideyuki Ohoka,Riccardo Paoletti,Stefan Ritt,Andrea Rugliancich,Takayuki Saito,Karl-Heinz Sulanke,Junki Takeda,Manobu Tanaka,Shunsuke Tanigawa,Luis ángel Tejedor,Masahiro Teshima,Yugo Tsuchiya,Tomohisa Uchida,Tokonatsu Yamamoto,the LST team,for the CTA Consortium
Physics , 2015,
Abstract: The Cherenkov Telescope Array (CTA) is the next generation ground-based very high energy gamma-ray observatory. The Large-Sized Telescope (LST) of CTA targets 20 GeV -- 1 TeV gamma rays and has 1855 photomultiplier tubes (PMTs) installed in the focal plane camera. With the 23 m mirror dish, the night sky background (NSB) rate amounts to several hundreds MHz per pixel. In order to record clean images of gamma-ray showers with minimal NSB contamination, a fast sampling of the signal waveform is required so that the signal integration time can be as short as the Cherenkov light flash duration (a few ns). We have developed a readout board which samples waveforms of seven PMTs per board at a GHz rate. Since a GHz FADC has a high power consumption, leading to large heat dissipation, we adopted the analog memory ASIC "DRS4". The sampler has 1024 capacitors per channel and can sample the waveform at a GHz rate. Four channels of a chip are cascaded to obtain deeper sampling depth with 4096 capacitors. After a trigger is generated in a mezzanine on the board, the waveform stored in the capacitor array is subsequently digitized with a low speed (33 MHz) ADC and transferred via the FPGA-based Gigabit Ethernet to a data acquisition system. Both a low power consumption (2.64 W per channel) and high speed sampling with a bandwidth of $>$300 MHz have been achieved. In addition, in order to increase the dynamic range of the readout we adopted a two gain system achieving from 0.2 up to 2000 photoelectrons in total. We finalized the board design for the first LST and proceeded to mass production. Performance of produced boards are being checked with a series of quality control (QC) tests. We report the readout board specifications and QC results.
Monte Carlo Studies of medium-size telescope designs for the Cherenkov Telescope Array  [PDF]
M. Wood,T. Jogler,J. Dumm,S. Funk
Physics , 2015, DOI: 10.1016/j.astropartphys.2015.04.008
Abstract: We present studies for optimizing the next generation of ground-based imaging atmospheric Cherenkov telescopes (IACTs). Results focus on mid-sized telescopes (MSTs) for CTA, detecting very high energy gamma rays in the energy range from a few hundred GeV to a few tens of TeV. We describe a novel, flexible detector Monte Carlo package, FAST (FAst Simulation for imaging air cherenkov Telescopes), that we use to simulate different array and telescope designs. The simulation is somewhat simplified to allow for efficient exploration over a large telescope design parameter space. We investigate a wide range of telescope performance parameters including optical resolution, camera pixel size, and light collection area. In order to ensure a comparison of the arrays at their maximum sensitivity, we analyze the simulations with the most sensitive techniques used in the field, such as maximum likelihood template reconstruction and boosted decision trees for background rejection. Choosing telescope design parameters representative of the proposed Davies-Cotton (DC) and Schwarzchild-Couder (SC) MST designs, we compare the performance of the arrays by examining the gamma-ray angular resolution and differential point-source sensitivity. We further investigate the array performance under a wide range of conditions, determining the impact of the number of telescopes, telescope separation, night sky background, and geomagnetic field. We find a 30-40% improvement in the gamma-ray angular resolution at all energies when comparing arrays with an equal number of SC and DC telescopes, significantly enhancing point-source sensitivity in the MST energy range. We attribute the increase in point-source sensitivity to the improved optical point-spread function and smaller pixel size of the SC telescope design.
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