Search

The Cherenkov Telescope Array (CTA) project is an initiative to build two large arrays of Cherenkov gamma- ray telescopes. CTA will be deployed as two installations, one in the northern and the other in the southern hemisphere, containing dozens of telescopes of different sizes. CTA is a big step forward in the field of ground- based gamma-ray astronomy, not only because of the expected scientific return, but also due to the order-of- magnitude larger scale of the instrument to be controlled. The performance requirements associated with such a large and distributed astronomical installation require a thoughtful analysis to determine the best software solutions. The array control and data acquisition (ACTL) work-package within the CTA initiative will deliver the software to control and acquire the data from the CTA instrumentation. In this contribution we present the current status of the formal ACTL system decomposition into software building blocks and the relationships among them. The system is modelled via the Systems Modelling Language (SysML) formalism. To cope with the complexity of the system, this architecture model is sub-divided into different perspectives. The relationships with the stakeholders and external systems are used to create the first perspective, the context of the ACTL software system. Use cases are employed to describe the interaction of those external elements with the ACTL system and are traced to a hierarchy of functionalities (abstract system functions) describing the internal structure of the ACTL system. These functions are then traced to fully specified logical elements (software components), the deployment of which as technical elements, is also described. This modelling approach allows us to decompose the ACTL software in elements to be created and the ow of information within the system, providing us with a clear way to identify sub-system interdependencies. This architectural approach allows us to build the ACTL system model and trace requirements to deliverables (source code, documentation, etc.), and permits the implementation of a flexible use-case driven software development approach thanks to the traceability from use cases to the logical software elements. The Alma Common Software (ACS) container/component framework, used for the control of the Atacama Large Millimeter/submillimeter Array (ALMA) is the basis for the ACTL software and as such it is considered as an integral part of the software architecture.

The Cherenkov Telescope Array (CTA) is an international initiative to build the next generation ground-based gamma-ray instrument. CTA will allow studying the Universe in the very-high-energy gamma-ray domain with energies ranging from a few tens of GeV to more than a hundred TeV. It will extend the currently accessible energy band, while increasing the sensitivity by a factor of 10 with respect to existing Cherenkov facilities. Furthermore, CTA will enhance other important aspects like angular and energy resolution. CTA will comprise two arrays, one in the Northern hemisphere and one in the Southern hemisphere, of in total more than one hundred of telescopes of three different sizes. The CTA performance requirements and the increased complexity in operation, control and monitoring of such a large distributed multi-telescope array leads to new challenges in designing and developing the CTA control software system. Indeed, the control software system must be flexible enough to allow for the simultaneous operation of multiple sub-arrays of different types of telescopes, to be ready to react in short timescales to changing weather conditions or to automatic alarms for transient phenomena, to be able to operate the observatory with a minimum personal effort on site, to cope with the malfunctioning of single telescopes or sub-arrays of telescopes, and to readout and control a large and heterogeneous set of devices. This report describes the preliminary architectural design concept for the CTA control software system that will be responsible to manage all the functionality of the CTA array, thereby enabling CTA to reach its scientific goals.

The Cherenkov Telescope Array (CTA) will be the next generation ground-based very-high energy -ray observatory. CTA will consist of two arrays: one in the Northern hemisphere composed of about 20 telescopes, and the other one in the Southern hemisphere composed of about 100 telescopes, both arrays containing telescopes of different sizes and types and in addition numerous auxiliary devices. In order to provide a test-ground for the CTA array control, the steering software of the 12-m medium size telescope (MST) prototype deployed in Berlin has been implemented using the tools and design concepts under consideration to be used for the control of the CTA array. The prototype control system is implemented based on the Atacama Large Millimeter/submillimeter Array (ALMA) Common Software (ACS) control middleware, with components implemented in Java, C++ and Python. The interfacing to the hardware is standardized via the Object Linking and Embedding for Process Control Unified Architecture (OPC UA). In order to access the OPC UA servers from the ACS framework in a common way, a library has been developed that allows to tie the OPC UA server nodes, methods and events to the equivalents in ACS components. The front-end of the archive system is able to identify the deployed components and to perform the sampling of the monitoring points of each component following time and value change triggers according to the selected configurations. The back-end of the archive system of the prototype is composed by two different databases: MySQL and MongoDB. MySQL has been selected as storage of the system configurations, while MongoDB is used to have an efficient storage of device monitoring data, CCD images, logging and alarm information. In this contribution, the details and conclusions on the implementation of the control software of the MST prototype are presented.

The Cherenkov Telescope Array (CTA) is designed to make a maj or improvement in the sensitivity of ground basedVHE (Very High Energy, den ed as > 20GeV to 100s of TeV) gamma-ray telescopes. Not only will the di erential-u xsensitivitybeanorderofmagnitudebetterthanthoseofthe currentlyoperatingCherenkovtelescopes,buttherewilla lsobesignic ant improvementsin the energy, spectral and angula r resolution. Delivering these features cost-e ectively requiresseveral telescope sizes and designs - a few large size telesc opes (23m diameter) are designed for the lowest energies, alarge number of small size telescopes (4–7m diameter) to inc rease the overall collection area which helps at the highestenergies and a number of Medium Size Telescopes (MST, 9 :5m or 12m diameter, depending on the mirror design) toprovidethe greatest sensitivity at 1TeV. To providecomplete sky coverage,CTA will have both a N orthern Hemisphereand a Southern Hemisphere site.A prototype for an MST design (currently under development) will be build in Berlin by 2012. This MST prototypehas a modie dDavies-Cottondesignwith a tessellated mirro r,with individualfacets of 1:2m in diameter. The facets arethree-pointmountedon the optical supportstructure, havi ngtwo poweredactuators for alignmentadjustments. In addi tiona number of CCD cameras will be mounted at various positions o n the dish and will be used for calibration. Here wepresent the various optical calibration tasks - optimizati on of the optical point-spread-function (PSF) and the point ing ofthis MST prototype,along with initial results.Keywords: CTA, Cherenkov,Telescope, Array,MST prototype,optical, calibration, PSF