be determined in close interaction with ASPERA (a group of European Research Area funding agencies which coordinates astroparticle physics in Europe). One of their main tasks is the “Implementation of new European-wide procedures for large infrastructures”. Regardless of the legal implementation, CTA management will be assisted by an in- ternational scientific and technical Advisory Board, and a Resource Board, composed of representatives of the national funding organisations supporting CTA.
Close contacts between CTA and the funding agencies (via the Resource Board) during all stages of the project are vital to secure sufficient and timely funding for the construction of the facility.
6.5. Time Schedule and Costs
CTA builds largely on proven technologies and Cherenkov telescopes of sizes similar to those needed for CTA have already been built or are in the advanced stages of construc- tion. Remaining challenges are: (a) optimisation of the cost of telescope components; (b) improvement of the reliability of telescope components, requiring extensive prototyping; (c) establishment of the formal framework for building and operating the instrument, and the selection and provision of sites; and (d) the funding of the infrastructure.
These challenges will be addressed during the Preparatory Phase (2010-2013) which will be supported by an FP7 grant of up to 5.2 Me from the European Community and by grants from various national funding agencies.
After a successful Preparatory Phase, and provided the funding has been secured, construction and deployment will then take from 2013 until 2018.
A detailed evaluation of the required construction and running costs is part of the Preparatory Phase studies. Current design efforts are conducted within an envelope of investment costs for the CTA construction and site infrastructure of 100 Me for the southern site, featuring full energy coverage, and 50 Me for the more specialised northern site (all in 2005 e). CTA aims to keep running costs below 10% of the total investment, in line with typical running costs for other astrophysical facilities.
Estimates for the costs of all major components of CTA are required for any optimi- sation of the array design. The current model makes the following assumptions:
• The investment required to construct CTA (according to European accounting schemes) is 100 Me for CTA-South and 50 Me for CTA-North.
• For both sites 20% of the budget is required for infrastructure and a central pro- cessing farm. Therefore, for example, telescope construction for CTA-South is an- ticipated to cost 80 Me.
• The construction of the telescope foundation, optical support structure, drive/safety system and camera masts will cost 450 ke for a 12 m telescope and the cost scales as dish area1.35.
• Mirrors, mounts and actuators will cost ≈ 1.7 ke/m2.
• Camera mechanics, photo-sensor and electronics costs will be 400 e/pixel, including lightcones, support structures and cooling systems.
6.5 Time Schedule and Costs 50
• Miscellaneous additional costs of about 20 ke/telescope will be incurred.
This cost model will evolve as the design work on the different components of CTA progresses.
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7. Monte Carlo Simulations and Layout Studies
The performance of an array of imaging atmospheric Cherenkov telescopes such as CTA depends on a large number of technical and design parameters. These include the general layout of the installation, with telescope sizes and locations, telescope optics, camera field-of-view and pixel size, signal shapes and trigger logic. In searching for the optimum configuration of a Cherenkov telescope array, one finds that most of these pa- rameters are intimately related, either technically or through constraints on the total cost. For many of these parameters there is experience from previous gamma-ray installations such as HEGRA, CAT, H.E.S.S., and MAGIC that provide reasonable starting points for the optimisation of CTA parameters. Whilst the full optimisation of CTA has not yet been completed, extensive simulation studies have been performed and demonstrate that an array of ≥60 Cherenkov telescopes can achieve the key performance targets for CTA, within the cost envelope described earlier. This section gives a summary of the most important simulation studies performed so far.
7.1. Simulation Tools
Only a modest number of candidate configurations has been simulated in full detail during the design study, but this still required the simulation of close to 1011 proton,
gamma, and electron induced showers, with full treatment of every interaction, tracking all the particles generated in these showers through the atmosphere, simulating emis- sion of Cherenkov light, propagating the light down to the telescopes, reflecting it on multi-faceted mirrors, entering photomultiplier tubes, generating pulses in complex trig- ger electronics, and having them registered in analogue-to-digital circuits. Simulations include not only Cherenkov photons but also NSB light resulting in the registration of photons at rates of ∼100 MHz in a typical photo-sensor.
Since the discrimination between γ-ray and hadron showers in CTA will surpass that of the best current instruments by a significant factor, huge numbers of background showers must be simulated before conclusions on the performance of a particular configuration can be drawn. Work is underway to reduce the CPU-time requirement by preferentially selecting proton showers early in their development if they are more likely to appear γ-
like. This should lead to a substantial speed improvement in future studies. Early results
from Toy models, which parametrize shower detection characteristics and are many orders of magnitude faster, are encouraging, but cannot yet be seen as adequate replacements for the detailed simulation process.
The air-shower simulation results presented here are based on the CORSIKA program [83], which is widely used in the community and very well tested. Cross-checks with the KASCADE-C++ air-shower code [84] have been performed as part of this study. Simula-
tions of the instrument response have been carried out with three codes. Two packages initially developed for H.E.S.S. (sim telarray [85] and SMASH [86]), and one for MAGIC simulations [87], were cross-checked using an initial benchmark arrays configurations.
The large volume of simulations, dominated by those of proton-induced showers needed for background estimations, has motivated the use of EGEE (Enabling Grids for E- sciencE) for the massive production of shower and detector simulations. A Virtual Or-