Renzo Vaccarone

SAGACE : The spectroscopic active galaxies and clusters explorer

The SAGACE experiment consists of a mm/sub-mm telescope with a 3-m diameter primary mirror, coupled to a cryogenic multi-beam differential spectrometer. SAGACE explores the sky in the 100-760 GHz frequency range, using four diffraction-limited bolometer arrays. The instrument is designed to perform spectroscopic surveys of the Sunyaev- Zeldovich effects of thousands of galaxy clusters, of the spectral energy distribution of active galactic nuclei, and of the [CII] line of a thousand galaxies in the redshift desert. In 2008 a full phase-A study for a national small mission was completed and delivered to the Italian Space Agency (ASI). We have shown that taking advantage of the differential operation of the Fourier Transform Spectrometer, this ambitious instrument can operate from a Molniya orbit, and can be built and operated within the tight budget of a small mission. Copyright

A Study of the Excess Noise of Ir Transition Edge Sensors in the Frame of Statistical Models

Experiments on superconducting transition properties and power noise density experiments are performed in Ir-based transition edge sensors samples prepared by magnetron sputtering and by laser ablation techniques. The experimental temperature dependence of the resistive-superconducting transitions are compared and analyzed in terms of percolating models. Broad excess noise peak of low amplitude is detected close to the superconductive state and explained by the correlated avalanche theory.

A Numerical Simulation Of The Pulse Sequence Reconstruction in AC Biased TESs With a β Source

We study the response of micro‐calorimeters based on Ir/Au TESs biased by an AC voltage in the MHz range to the power input generated by beta emission in a Re source thermally connected to the calorimeter itself. The micro‐calorimeter is assumed to work at ‐80 mK, and the energy pulses corresponding to the beta emission have an energy distributed between zero and 2.58 KeV. In this numerical simulation the TES is inserted in a RLC resonating circuit, with a low quality factor. The thermal conductivities between the source and the calorimeter and that from the calorimeter to the heat sink are non‐linear. The superconducting to normal transition of the TES is described by a realistic non‐linear model. The AC current at the carrier frequency, modulated by the changing resistance of the TES, is demodulated and the output is filtered. The resulting signal is analyzed to deduce the attainable time resolution and the linearity of the response.

Spectroscopic active galaxies and clusters explorer

We present a concept for the payload SAGACE, the Spectroscopic Active Galaxies And Cluster Explorer, devoted to study the evolution of Universe structures using different observables, all of them in the mm∕submm wavelength. The SAGACE payload is made of a passively cooled 3 m telescope, a cryogenic Fourier Transform Spectrometer (FTS) and detector arrays to be operated at 0.3 K by a 3He fridge. The detectors are Ti∕Au Transition Edge Sensor (TES) bolometers with a NEP<10−17 W/Hz½. A phase‐A study has been recently completed for this experiment, in the framework of the call for small missions of the Italian Space Agency.

Characterization of the Superconducting Transition of Thin Ir Films for TES

We are currently producing iridium based TESs for a wide variety of applications such as single photon detection of the visible and infrared light, X-ray spectroscopy and low energy nuclear beta and electron capture spectroscopy for neutrino mass search experiment. We present a study of the TES performance related to the superconductivity properties of the Ir film as function of the production processes, that depend on substrate type: Si or SiN, and of the operating electrical parameters. Moreover we developed a finite element model of thin superconducting film, by which we obtain qualitative agreement between experimental and simulated data.

High Resolution Spectroscopy of the X‐Ray Emission of GRBs by IMBOSS on the ISS

The IMBOSS (Interstellar/Intergalactic Medium and gamma‐ray Burst Observatory and Spectroscopy Survey) is an experiment proposed to fly on the ISS (International Space Station), in order to perform an all‐sky survey to study the diffuse X‐ray emission and to measure the spectra of Gamma‐Ray Bursts (GRB) with high energy resolution in the 0.1–10 keV energy range. In a 3‐year mission, the experiment will detect about 20 to 40 GRBs. In several events, we can perform high resolution spectroscopy of the iron emission lines and absorption edges. Such components have been observed by BeppoSAX and Chandra. The measurements of these features would provide a direct diagnostic of the physical and kinematical state of the medium surrounding a GRB. Furthermore, they would supply information about the origin of the progenitors of the GRBs (probably a supernova explosion of massive stars) and their site formation (possibly a star‐forming region).

Measurement and numerical simulation of low field magnetization in laminated BSCCO

I present a simulation of the magnetic behaviour of a network of long Josephson junctions, with a statistical distribution of junction lengths and Josephson currents. To support the hypothesis of weak connectivity in laminar materials I measured the magnetization of Bi/Pb (2223) samples, at very low fields and low temperature. Hysteresis cycles were observed.