Digital Complex Correlator for a C-band Polarimetry survey

The international Galactic Emission Mapping project aims to map and characterize the polarization field of the Milky Way. In Portugal it will cartograph the C-band sky polarized emission of the Northern Hemisphere and provide templates for map calibration and foreground control of microwave space probes like ESA Planck Surveyor mission. The receiver system is equipped with a novel receiver with a full digital back-end using an Altera Field Programmable Gate Array, having a very favorable cost/performance relation. This new digital backend comprises a base-band complex cross-correlator outputting the four Stokes parameters of the incoming polarized radiation. In this document we describe the design and implementation of the complex correlator using COTS components and a processing FPGA, detailing the method applied in the several algorithm stages and suitable for large sky area surveys.Comment: 15 pages, 10 figures; submitted to Experimental Astronomy, Springe

Site Evaluation and RFI spectrum measurements in Portugal at the frequency range 0.408-10 GHz for a GEM polarized galactic radio emission experiment

We probed for Radio Frequency Interference (RFI) for the three potential Galactic Emission Mapping Experiment (GEM) sites at Portugal using custom made omnidirectional disconic antennas. For the installation of a 10-meter dish dedicated to the mapping of Polarized Galactic Emission foreground planned for 2005-2007 in the 5-10 GHz band, the three sites chosen as suitable to host the antenna were surveyed for local radio pollution in the frequency range [0.01-10] GHz. Tests were done to look for radio broadcasting and mobile phone emission lines in the radio spectrum. The results show one of the sites to be almost entirely RFI clean and showing good conditions to host the experiment.Comment: 9 pages, 6 figures, submitted to New Astronom

The Comet Interceptor Mission

Here we describe the novel, multi-point Comet Interceptor mission. It is dedicated to the exploration of a little-processed long-period comet, possibly entering the inner Solar System for the first time, or to encounter an interstellar object originating at another star. The objectives of the mission are to address the following questions: What are the surface composition, shape, morphology, and structure of the target object? What is the composition of the gas and dust in the coma, its connection to the nucleus, and the nature of its interaction with the solar wind? The mission was proposed to the European Space Agency in 2018, and formally adopted by the agency in June 2022, for launch in 2029 together with the Ariel mission. Comet Interceptor will take advantage of the opportunity presented by ESA’s F-Class call for fast, flexible, low-cost missions to which it was proposed. The call required a launch to a halo orbit around the Sun-Earth L2 point. The mission can take advantage of this placement to wait for the discovery of a suitable comet reachable with its minimum ΔV capability of 600 ms−1. Comet Interceptor will be unique in encountering and studying, at a nominal closest approach distance of 1000 km, a comet that represents a near-pristine sample of material from the formation of the Solar System. It will also add a capability that no previous cometary mission has had, which is to deploy two sub-probes – B1, provided by the Japanese space agency, JAXA, and B2 – that will follow different trajectories through the coma. While the main probe passes at a nominal 1000 km distance, probes B1 and B2 will follow different chords through the coma at distances of 850 km and 400 km, respectively. The result will be unique, simultaneous, spatially resolved information of the 3-dimensional properties of the target comet and its interaction with the space environment. We present the mission’s science background leading to these objectives, as well as an overview of the scientific instruments, mission design, and schedule

Reflectometo de micro-ondas para o diversor do tokamak JET

The microwaves provide a powerful mean for plasma fusion diagnostics. Microwave reflectometry is one of the emerging techniques for density measurements of fusion plasmas. This work presents a reflectometry system, Installed in the divertor of the JET tokamak. Several system configurations where addresed in order to cope with the divertor specifications and provide density measurements. The electronic and microwave design is presented along with some implementation details. The system is composed of eight channels of operating in the ordinary mode of propagation in the range 50 to 100 GHz, that corresponds to densities between 3.1x10"1"9m-"3 and 12.1x10"1"9m-"3. Results of the laboratory tests and also the first results with plasma are presented. These presuits to conclude that reflectometry has the potential for disgnosing large tokamak divertors such as in ITERAvailable from Fundacao para a Ciencia e a Tecnologia, Servico de Informacao e Documentacao, Av. D. Carlos I, 126, 1200 Lisboa / FCT - Fundação para o Ciência e a TecnologiaSIGLEPTPortuga

A large memory, high transfer rate VME data acquisition system for the JET correlation reflectometer

The current paper presents a large memory giving special emphasis to the architecture and suitability of the Linux OS for this type of applications. The system will be used on the joint european torus new correlation reflectometers composed by four microwave channels with four analogue signals each. All sixteen signals will be acquired by 12-bit VME fast acquisition channels at 2 Msamples/s achieving a total data rate of 60MB/s. Slower VME acquisition channels, with 16-bit resolution and sampling rates up to 250 ksamples/s, can also acquire these 16 signals. Two dedicated digital signal processors run an algorithm over this acquired data to avoid the use of the old KG8B root mean square analogue circuits as well as to control and to generate all the timing and acquisition clocks needed by the system.http://www.sciencedirect.com/science/article/B6V3C-45CNCVD-4/1/192edf0549f525a800b501563b54de1