Cooling Tests of the NectarCAM camera for the Cherenkov Telescope Array

The NectarCAM is a camera proposed for the medium-sized telescopes in the framework of the Cherenkov Telescope Array (CTA), the next-generation observatory for very-high-energy gamma-ray astronomy. The cameras are designed to operate in an open environment and their mechanics must provide protection for all their components under the conditions defined for the CTA observatory. In order to operate in a stable environment and ensure the best physics performance, each NectarCAM will be enclosed in a slightly overpressurized, nearly air-tight, camera body, to prevent dust and water from entering. The total power dissipation will be ~7.7 kW for a 1855-pixel camera. The largest fraction is dissipated by the readout electronics in the modules. We present the design and implementation of the cooling system together with the test bench results obtained on the NectarCAM thermal demonstrator.Comment: In Proceedings of the 34th International Cosmic Ray Conference (ICRC2015), The Hague, The Netherlands. All CTA contributions at arXiv:1508.0589

SPIRAL II Project (electron option) - Preliminary Design Study

This document presents a Preliminary Design Study (PDS) of the electron option of the SPIRAL II project

NectarCAM : a camera for the medium size telescopes of the Cherenkov Telescope Array

NectarCAM is a camera proposed for the medium-sized telescopes of the Cherenkov Telescope Array (CTA) covering the central energy range of ~100 GeV to ~30 TeV. It has a modular design and is based on the NECTAr chip, at the heart of which is a GHz sampling Switched Capacitor Array and a 12-bit Analog to Digital converter. The camera will be equipped with 265 7-photomultiplier modules, covering a field of view of 8 degrees. Each module includes the photomultiplier bases, high voltage supply, pre-amplifier, trigger, readout and Ethernet transceiver. The recorded events last between a few nanoseconds and tens of nanoseconds. The camera trigger will be flexible so as to minimize the read-out dead-time of the NECTAr chips. NectarCAM is designed to sustain a data rate of more than 4 kHz with less than 5\% dead time. The camera concept, the design and tests of the various subcomponents and results of thermal and electrical prototypes are presented. The design includes the mechanical structure, cooling of the electronics, read-out, clock distribution, slow control, data-acquisition, triggering, monitoring and services.Comment: In Proceedings of the 34th International Cosmic Ray Conference (ICRC2015), The Hague, The Netherlands. All CTA contributions at arXiv:1508.0589

The DEMO magnet system – Status and future challenges

We present the pre-concept design of the European DEMO Magnet System, which has successfully passed the DEMO plant-level gate review in 2020. The main design input parameters originate from the so-called DEMO 2018 baseline, which was produced using the PROCESS systems code. It defines a major and minor radius of 9.1 m and 2.9 m, respectively, an on-axis magnetic field of 5.3 T resulting in a peak field on the toroidal field (TF) conductor of 12.0 T. Four variants, all based on low-temperature superconductors (LTS), have been designed for the 16 TF coils. Two of these concepts were selected to be further pursued during the Concept Design Phase (CDP): the first having many similarities to the ITER TF coil concept and the second being the most innovative one, based on react-and-wind (RW) Nb3Sn technology and winding the coils in layers. Two variants for the five Central Solenoid (CS) modules have been investigated: an LTS-only concept resembling to the ITER CS and a hybrid configuration, in which the innermost layers are made of high-temperature superconductors (HTS), which allows either to increase the magnetic flux or to reduce the outer radius of the CS coil. Issues related to fatigue lifetime which emerged in mechanical analyses will be addressed further in the CDP. Both variants proposed for the six poloidal field coils present a lower level of risk for future development. All magnet and conductor design studies included thermal-hydraulic and mechanical analyses, and were accompanied by experimental tests on both LTS and HTS prototype samples (i.e. DC and AC measurements, stability tests, quench evolution etc.). In addition, magnet structures and auxiliary systems, e.g. cryogenics and feeders, were designed at pre-concept level. Important lessons learnt during this first phase of the project were fed into the planning of the CDP. Key aspects to be addressed concern the demonstration and validation of critical technologies (e.g. industrial manufacturing of RW Nb3Sn and HTS long conductors, insulation of penetrations and joints), as well as the detailed design of the overall Magnet System and mechanical structures

Characterizing elastic properties of superconducting windings by simulations and experiments

The objective of the present study is to identify the equivalent stiffness components of superconducting windings. First, a 3D multi-material finite element (FE) model was established to investigate the influence of the winding structural behavior on the identified equivalent stiffnesses. Then, the ideas resulting from this FE analysis were applied to the experiment. Four in-plane stiffnesses of the double pancake were retrieved successfully with the virtual fields method using the actual strain fields obtained from stereo image correlation

Applications of a new tool for fast stress recovery to DEMO TF coil system

DEMOnstration fusion reactor (DEMO) represents the second step in the EU fusion roadmap that has the objective to demonstrate the feasibility, from an economic point of view, to produce electric power using fusion reaction. The structural analyses of such a large machine represent a crucial issue for the design assessment. In fact a full detailed 3D model would require a huge mesh. In this work a novel procedure is presented, based on Radial Basis Functions interpolation, that allows to recover the stress state in a generic 3D section with low computational effort and significant time saving. This tool uses a mixed approach that allows to adjust the boundary shape and applies the magnetic loads to the local 3D model. To prove the Stress Recovery Tool (SRT) validity the results, obtained in a portion of the whole structure, have been compared to those of a high fidelity model. Once validated the SRT has been applied to a 2015 reference geometry

Dynamic effects on fracture toughness for ferritic steel in the ductile-to-brittle transition

International audienceDynamic loading effects on ferritic steel toughness havebeen evaluated in the brittle-to-ductile transition, consideringloading rates representative of object drops. To verify that thebrittle-to-ductile transition curve, initially defined from statictests, tends to shift to higher temperatures due to dynamiceffects even in the case of object drops, experiments on16MND5 steel have been performed.A three-point bending set-up and a thermal chamber havebeen designed in order to perform dynamic fracture tests onlarge Single Edge-notched Bending SE(B) specimen, at verylow temperature using a drop-shock machine. In a first step,considering that the reference temperature of the material(according to the master curve concept) is -122 °C, dynamictests at -120 °C have been performed. These tests haveconfirmed that the fracture mode is still brittle at thistemperature, when an impact speed of 4.85 m/s is used.Elastic-plastic or viscoplastic dynamic simulations of thetests, compared to classical static analysis, have demonstratedthat the effects of inertia and viscosity on fracture toughness arenegligible considering the very low values obtained on thesetests at -120 °C. These results also confirm the decrease offracture toughness due to dynamic loading compared toexperimental data from static tests. A further step will be tocomplete this demonstration with dynamic tests at highertemperatures in the brittle-to-ductile transition

Applications of a new tool for fast stress recovery to DEMO TF coil system

DEMOnstration fusion reactor (DEMO) represents the second step in the EU fusion roadmap that has the objective to demonstrate the feasibility, from an economic point of view, to produce electric power using fusion reaction. The structural analyses of such a large machine represent a crucial issue for the design assessment. In fact a full detailed 3D model would require a huge mesh. In this work a novel procedure is presented, based on Radial Basis Functions interpolation, that allows to recover the stress state in a generic 3D section with low computational effort and significant time saving. This tool uses a mixed approach that allows to adjust the boundary shape and applies the magnetic loads to the local 3D model. To prove the Stress Recovery Tool (SRT) validity the results, obtained in a portion of the whole structure, have been compared to those of a high fidelity model. Once validated the SRT has been applied to a 2015 reference geometry

Mechanical pre-dimensioning and pre-optimization of tokamaks’ toroidal coils featuring a winding pack layout

The structural integrity of superconducting magnets that are key elements of a fusion reactor must be ensured. At an early design stage relatively simple calculation tools can greatly facilitate design optimization. The main objective of this paper is the mechanical pre-dimensioning of the tokamak toroidal field coils by simple means prior to the global 3D numerical modeling. A semi-analytical calculation tool that reasonably estimates the static strength of the toroidal field coil under the electromagnetic forces at the critical location (inner leg equatorial plane) is described. The novelty of the approach is that it treats not only the massive coil casing but also the winding pack conductor jacket under an essentially 3D stress state. The calculation tool features pre-optimization of the coil winding for graded layered winding layouts. The minimum space (radial built) required for the coil inboard portion that is a key design parameter is defined after possible winding pre-optimization. The procedure has been successfully benchmarked against numerical solutions and has been used for pre-dimensioning the toroidal coils in the frame of the current 2015 DEMO activity