arXiv subjects

A. Simonetto

Publications and source records attributed to A. Simonetto.

10 recordsLinked to original sources

arXiv2024

Cross-Calibration and First Vertical ECE Measurement of Electron Energy Distribution in the TCV Tokamak

This paper describes the first Vertical Electron Cyclotron Emission (V-ECE) measurement of non-thermal electron distributions in the \textit{Tokamak \`a Configuration Variable}, TCV. These measurements were conducted in runaway electron scenarios and in the presence of Electron Cyclotron Current Drive. Measured intensities of linearly polarised X- and O-mode radiation from fast electrons allow the analysis of the energy distribution. The measurements were made possible through the creation of an operational regime for the diagnostic that is free of thermal background radiation, in relaxed electron density operations. This operational regime notably enables the cross-calibration of the diagnostic system, relying on thermal plasma measurements and modeling with the ray-tracing code SPECE.

physics.plasm-ph↗

arXiv2023

A Microwave Blackbody Target for Cosmic Microwave Background Spectral Measurements in the 10-20GHz range

The Tenerife Microwave Spectrometer (TMS) is a ground-based radio-spectrometer that will take absolute measurements of the sky between 10-20 GHz. To ensure the sensitivity and immunity to systematic errors of these measurements, TMS includes an internal calibration system optimised for the TMS band, and cooled down to 4 K. It consists of an Aluminium core, composed of a baseplate and a bed of pyramidal elements coated with an absorber material and a metallic shield. The absorber coating is made of a commercial resin ECCOSORB CR/MF 117. To achieve the high stability (+/- 1 mK/h), temperature homogeneity (thermal gradients {AT <= 25 mK), and emissivity (e>= 0.999) requirements of the reference unit, careful consideration has been given to the RF and thermal properties of the materials, as well as their geometry. In summary, this paper presents a comprehensive account of the design, characterisation, and test results of the TMS reference system.

astro-ph.IM↗

arXiv2010

Planck pre-launch status: calibration of the Low Frequency Instrument flight model radiometers

The Low Frequency Instrument (LFI) on-board the ESA Planck satellite carries eleven radiometer subsystems, called Radiometer Chain Assemblies (RCAs), each composed of a pair of pseudo-correlation receivers. We describe the on-ground calibration campaign performed to qualify the flight model RCAs and to measure their pre-launch performances. Each RCA was calibrated in a dedicated flight-like cryogenic environment with the radiometer front-end cooled to 20K and the back-end at 300K, and with an external input load cooled to 4K. A matched load simulating a blackbody at different temperatures was placed in front of the sky horn to derive basic radiometer properties such as noise temperature, gain, and noise performance, e.g. 1/f noise. The spectral response of each detector was measured as was their susceptibility to thermal variation. All eleven LFI RCAs were calibrated. Instrumental parameters measured in these tests, such as noise temperature, bandwidth, radiometer isolation, and linearity, provide essential inputs to the Planck-LFI data analysis.

astro-ph.IM↗

arXiv2010

Planck LFI flight model feed horns

this paper is part of the Prelaunch status LFI papers published on JINST: http://www.iop.org/EJ/journal/-page=extra.proc5/jinst The Low Frequency Instrument is optically interfaced with the ESA Planck telescope through 11 corrugated feed horns each connected to the Radiometer Chain Assembly (RCA). This paper describes the design, the manufacturing and the testing of the flight model feed horns. They have been designed to optimize the LFI optical interfaces taking into account the tight mechanical requirements imposed by the Planck focal plane layout. All the eleven units have been successfully tested and integrated with the Ortho Mode transducers.

astro-ph.IM↗

arXiv2010

The PLANCK LFI flight model ortho-mode transducers

The Low Frequency Instrument (LFI) of the ESA Planck CMB mission is an array of 22 ultra sensitive pseudocorrelation radiometers working at 30, 44, and 70 GHz. LFI has been calibrated and delivered for integration with the satellite to the European Space Agency on November 2006. The aim of Planck is to measure the anisotropy and polarization of the Cosmic Background Radiation with a sensitivity and angular resolution never reached before over the full sky. LFI is intrinsically sensitive to polarization thanks to the use of Ortho-Mode Transducers (OMT) located between the feedhorns and the pseudo-correlation radiometers. The OMTs are microwave passive components that divide the incoming radiation into two linear orthogonal components. A set of 11 OMTs (2 at 30 GHz, 3 at 44 GHz, and 6 at 70 GHz) were produced and tested. This work describes the design, development and performance of the eleven Flight Model OMTs of LFI. The final design was reached after several years of development. At first, Elegant Bread Board OMTs were produced to investigate the manufacturing technology and design requirements. Then, a set of 3 Qualification Model (QM) OMTs were designed, manufactured and tested in order to freeze the design and the manufacturing technology for the flight units. Finally, the Flight Models were produced and tested. It is shown that all the OMT units have been accepted for flight and the electromagnetic performance is at least marginally compliant with the requirements. Mechanically, the units passed all the thermoelastic qualification tests after a reworking necessary after the QM campaign.

astro-ph.IM↗

arXiv2010

The Planck-LFI flight model composite waveguides

The Low Frequency Instrument on board the PLANCK satellite is designed to give the most accurate map ever of the CMB anisotropy of the whole sky over a broad frequency band spanning 27 to 77 GHz. It is made of an array of 22 pseudo-correlation radiometers, composed of 11 actively cooled (20 K) Front End Modules (FEMs), and 11 Back End Modules (BEMs) at 300K. The connection between the two parts is made with rectangular Wave Guides. Considerations of different nature (thermal, electromagnetic and mechanical), imposed stringent requirements on the WGs characteristics and drove their design. From the thermal point of view, the WG should guarantee good insulation between the FEM and the BEM sections to avoid overloading the cryocooler. On the other hand it is essential that the signals do not undergo excessive attenuation through the WG. Finally, given the different positions of the FEM modules behind the focal surface and the mechanical constraints given by the surrounding structures, different mechanical designs were necessary. A composite configuration of Stainless Steel and Copper was selected to satisfy all the requirements. Given the complex shape and the considerable length (about 1.5-2 m), manufacturing and testing the WGs was a challenge. This work deals with the development of the LFI WGs, including the choice of the final configuration and of the fabrication process. It also describes the testing procedure adopted to fully characterize these components from the electromagnetic point of view and the space qualification process they underwent. Results obtained during the test campaign are reported and compared with the stringent requirements. The performance of the LFI WGs is in line with requirements, and the WGs were successfully space qualified.

astro-ph.IM↗

arXiv2010

Planck pre-launch status: Low Frequency Instrument calibration and expected scientific performance

We give the calibration and scientific performance parameters of the Planck Low Frequency Instrument (LFI) measured during the ground cryogenic test campaign. These parameters characterise the instrument response and constitute our best pre-launch knowledge of the LFI scientific performance. The LFI shows excellent $1/f$ stability and rejection of instrumental systematic effects; measured noise performance shows that LFI is the most sensitive instrument of its kind. The set of measured calibration parameters will be updated during flight operations through the end of the mission.

astro-ph.IM↗

arXiv2010

Planck pre-launch status: Design and description of the Low Frequency Instrument

In this paper we present the Low Frequency Instrument (LFI), designed and developed as part of the Planck space mission, the ESA program dedicated to precision imaging of the cosmic microwave background (CMB). Planck-LFI will observe the full sky in intensity and polarisation in three frequency bands centred at 30, 44 and 70 GHz, while higher frequencies (100-850 GHz) will be covered by the HFI instrument. The LFI is an array of microwave radiometers based on state-of-the-art Indium Phosphide cryogenic HEMT amplifiers implemented in a differential system using blackbody loads as reference signals. The front-end is cooled to 20K for optimal sensitivity and the reference loads are cooled to 4K to minimise low frequency noise. We provide an overview of the LFI, discuss the leading scientific requirements and describe the design solutions adopted for the various hardware subsystems. The main drivers of the radiometric, optical and thermal design are discussed, including the stringent requirements on sensitivity, stability, and rejection of systematic effects. Further details on the key instrument units and the results of ground calibration are provided in a set of companion papers.

astro-ph.IM↗

arXiv2003

The Low Frequency Instrument in the ESA Planck mission

Measurements of the cosmic microwave background (CMB) allow high precision observation of the cosmic plasma at redshift z~1100. After the success of the NASA satellite COBE, that in 1992 provided the first detection of the CMB anisotropy, results from many ground-based and balloon-borne experiments have showed a remarkable consistency between different results and provided quantitative estimates of fundamental cosmological properties. During the current year the team of the NASA WMAP satellite has released the first improved full-sky maps of the CMB since COBE, leading to a deeper insight in the origin and evolution of the Universe. The ESA satellite Planck, scheduled for launch in 2007, is designed to provide the ultimate measurement of the CMB temperature anisotropy over the full sky, with an accuracy that will be limited only by astrophysical foregrounds, and robust detection of polarisation anisotropy. Planck will observe the sky with two instruments over a wide spectral band (the Low Frequency Instrument, based on coherent radiometers, from 30 to 70 GHz and the High Frequency Instrument, based on bolometric detectors, from 100 to 857 GHz). The mission performances will improve dramatically the scientific return compared to WMAP. Furthermore the LFI radiometers (as well as some of the HFI bolometers) are intrinsically sensitive to polarisation so that by combining the data from different receivers it will be possible to measure accurately the E mode and to detect the B mode of the polarisation power spectrum. Planck sensitivity will offer also the possibility to detect the non-Gaussianities imprinted in the CMB.

astro-ph↗

arXiv2003

High Performances Corrugated Feed Horns for Space Applications at Millimetre Wavelengths

We report on the design, fabrication and testing of a set of high performance corrugated feed horns at 30 GHz, 70 GHz and 100 GHz, built as advanced prototypes for the Low Frequency Instrument (LFI) of the ESA Planck mission. The electromagnetic designs include linear (100 GHz) and dual shaped (30 and 70 GHz) profiles. Fabrication has been achieved by direct machining at 30 GHz, and by electro-formation at higher frequencies. The measured performances on side lobes and return loss meet the stringent Planck requirements over the large (20%) instrument bandwidth. Moreover, the advantage in terms of main lobe shape and side lobes levels of the dual profiled designs has been demonstrated.

astro-ph↗