Soft-X ray 2-D imaging on ITER is not considered yet. We propose a new approach, based on a gas detector with a gas electron multiplier (GEM) as amplifying structure and with a two-dimensional ...readout fully integrated with the front end electronics, through an ASIC developed on purpose. The concept has been already tested by means of a prototype, with 128 pixels, carried out in Frascati in collaboration with INFN-Pisa and tested on FTU in 2001 and NSTX in 2002-2004. Thanks to the photon counting mode, it provides 2-D imaging with high time resolution (sub millisecond), high sensitivity and signal to noise ratio. Its capability of energy discrimination allows the acquisition of pictures in X-ray energy bands or to perform a spectral scan in the full energy interval. We propose the realisation of such kind a detector with a readout microchip (ASIC) equipped with 105600 hexagonal pixels arranged at 70 mum pitch in a 300X352 honeycomb matrix, corresponding to an active area of 2.1X2.1 cm2, with a pixel density of 240 pixels/ mm2. Each pixel is connected to a charge sensitive amplifier followed by a discriminator of pulse amplitude and counter. The chip integrates more than 16.5 million transistors and it is subdivided in 64 identical clusters, to be read independently each other. An important part of the work will be also the design of the whole detector to fulfil all the constraints and requirements as plasma diagnostic in a tokamak machine. Since the detector has high and controllable intrinsic gain, it works well even at very low photon energy, ranging from 0.2 keV to 10 keV (X-VUV region). This range appears therefore particularly suitable for ITER to monitor the outer part of the plasma. In particular pedestal physics, edge modes, localization and effects of additional heating, boundary plasma control etc. The capability of this proposed detector to work in this energy range is further valuable because solid state detectors are not favorite at low energy because of the lack of intrinsic gain.
A unique electronics system has been built and tested for reading signals from the silicon-strip detectors of the Gamma-ray Large Area Space Telescope mission. The system amplifies and processes ...signals from 884 736 36-cm long silicon strips in a 4times4 array of tower modules. An aggressive mechanical design fits the readout electronics in narrow spaces between the tower modules, to minimize dead area. This design and the resulting departures from conventional electronics packaging led to several fabrication challenges and lessons learned. This paper describes the fabrication processes and how the problems peculiar to this design were overcome
The WELL detector Bellazzini, R; Bozzo, M; Brez, A ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
02/1999, Volume:
423, Issue:
1
Journal Article
Peer reviewed
Open access
We introduce the WELL detector, a new type of position-sensitive gas proportional counter produced using advanced Printed Circuit Board (PCB) technology. The WELL is based on a thin kapton foil, ...copper-clad on both sides. Charge amplifying micro-wells are etched into the first metal and kapton layers. These end on a micro-strip pattern which is defined on the second metal plane. The array of micro-strips is used for read-out to obtain 1-D positional information. First results from our systematic assessment of this device are reported.
What is the real gas gain of a standard GEM? Bellazzini, R.; Brez, A.; Gariano, G. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
12/1998, Volume:
419, Issue:
2-3
Journal Article
Peer reviewed
Open access
We have observed very high gains (up to 7000) from GEMs with ‘standard’ parameters (kapton thickness 50μm, pitch 120μm, copper hole diameter 65μm, kapton hole diameter 30μm). This was achieved using ...GEMs coupled to a simple array of copper read-out strips. From the measurements of the current on all the electrodes, we conclude that the high observed gains are fully attributable to electron multiplication in the holes of the mesh, and not to electronics related effects as had been previously suggested. Furthermore, we report that this large gain may only be fully exploited when the field in the second GEM gap is high. The effect on the gain of coupling a GEM to another charge amplifying device was investigated using a GEM–PMGC combination.
Purpose:
Detectors with hexagonal pixels require resampling to square pixels for distortion‐free display of acquired images. In this work, the presampling modulation transfer function (MTF) of a ...hexagonal pixel array photon‐counting CdTe detector for region‐of‐interest fluoroscopy was measured and the optimal square pixel size for resampling was determined.
Methods:
A 0.65mm thick CdTe Schottky sensor capable of concurrently acquiring up to 3 energy‐windowed images was operated in a single energy‐window mode to include ≥10 KeV photons. The detector had hexagonal pixels with apothem of 30 microns resulting in pixel spacing of 60 and 51.96 microns along the two orthogonal directions. Images of a tungsten edge test device acquired under IEC RQA5 conditions were double Hough transformed to identify the edge and numerically differentiated. The presampling MTF was determined from the finely sampled line spread function that accounted for the hexagonal sampling. The optimal square pixel size was determined in two ways; the square pixel size for which the aperture function evaluated at the Nyquist frequencies along the two orthogonal directions matched that from the hexagonal pixel aperture functions, and the square pixel size for which the mean absolute difference between the square and hexagonal aperture functions was minimized over all frequencies up to the Nyquist limit.
Results:
Evaluation of the aperture functions over the entire frequency range resulted in square pixel size of 53 microns with less than 2% difference from the hexagonal pixel. Evaluation of the aperture functions at Nyquist frequencies alone resulted in 54 microns square pixels. For the photon‐counting CdTe detector and after resampling to 53 microns square pixels using quadratic interpolation, the presampling MTF at Nyquist frequency of 9.434 cycles/mm along the two directions were 0.501 and 0.507.
Conclusion:
Hexagonal pixel array photon‐counting CdTe detector after resampling to square pixels provides high‐resolution imaging suitable for fluoroscopy.
A sealed Gas Pixel Detector for X-ray astronomy Bellazzini, R.; Spandre, G.; Minuti, M. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
09/2007, Volume:
579, Issue:
2
Journal Article
Peer reviewed
We report on the results of a new, sealed Gas Pixel Detector. The very compact design and the absence of the gas flow system make this detector substantially ready for use as focal plane detector for ...future X-ray space telescopes. The instrument brings high sensitivity to X-ray polarimetry, which is the last unexplored field of X-ray astronomy. It derives the polarization information from the track of the photoelectrons that are imaged by a high-gain (>1000), fine pitch GEM that matches the pitch of a pixel ASIC which is the collecting anode of the GPD (105k, 50
μm wide, hexagonal cells). The device is able to simultaneously perform good imaging (50–60
μm), moderate spectroscopy (∼15% at 6
keV) as well as fast, high-rate timing in the 1–10
keV range. Moreover, being truly 2D, it is non-dispersive and does not require any rotation. The great improvement of sensitivity, at least two orders of magnitude with respect to traditional polarimeters (based on Bragg crystals or Thomson scattering), will allow the direct exploration of the most dramatic objects of the X-ray sky. At the focus of the large mirror area of the XEUS telescope it will be decisive in reaching many of the scientific goals of the mission. With integration times of the order of 1 day, polarimetry of Active Galactic Nuclei at the percent level will be possible, making for a real breakthrough in high-energy astrophysics.
Construction strategy of the GLAST tracker Brez, Alessandro
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
09/2005, Volume:
549, Issue:
1
Journal Article
Peer reviewed
The GLAST observatory is an astroparticle mission that will study γ-rays emissions from a wide range of cosmological sources in the 20
MeV–300
GeV energy band. The tracker is the largest (80
m
2) ...silicon detector ever built for a space mission. Its construction is a major technological challenge which has required close collaboration of INFN with space qualified industries, in order to meet the requirements of reliability, high yield and large volume production.
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