175 research outputs found
Rad-hard vertical JFET switch for the HV-MUX system of the ATLAS upgrade Inner Tracker
This work presents a new silicon vertical JFET (V-JFET) device, based on the
trenched 3D-detector technology developed at IMB-CNM, to be used as switches
for the High-Voltage powering scheme of the ATLAS upgrade Inner Tracker. The
optimization of the device characteristics is performed by 2D and 3D TCAD
simulations. Special attention has been paid to the on-resistance and the
switch-off and breakdown voltages to meet the specific requirements of the
system. In addition, a set of parameter values has been extracted from the
simulated curves to implement a SPICE model of the proposed V-JFET transistor.
As these devices are expected to operate under very high radiation conditions
during the whole experiment life-time, a study of the radiation damage effects
and the expected degradation on the device performance is also presented at the
end of the paper.Comment: KEYWORDS: Radiation-hard electronics; Voltage distributions; Large
detector systems for particle and astroparticle physics. 9 Pages, 7 Figure
New two-colour light curves of Q0957+561: time delays and the origin of intrinsic variations
We extend the gr-band time coverage of the gravitationally lensed double
quasar Q0957+561. New gr light curves permit us to detect significant intrinsic
fluctuations, to determine new time delays, and thus to gain perspective on the
mechanism of intrinsic variability in Q0957+561. We use new optical frames of
Q0957+561 in the g and r passbands from January 2005 to July 2007. These frames
are part of an ongoing long-term monitoring with the Liverpool robotic
telescope. We also introduce two photometric pipelines that are applied to the
new gr frames of Q0957+561. The transformation pipeline incorporates
zero-point, colour, and inhomogeneity corrections to the instrumental
magnitudes, so final photometry to the 1-2% level is achieved for both quasar
components. The two-colour final records are then used to measure time delays.
The gr light curves of Q0957+561 show several prominent events and gradients,
and some of them (in the g band) lead to a time delay between components of 417
+/- 2 d (1 sigma). We do not find evidence of extrinsic variability in the
light curves of Q0957+561. We also explore the possibility of a delay between a
large event in the g band and the corresponding event in the r band. The gr
cross-correlation reveals a time lag of 4.0 +/- 2.0 d (1 sigma; the g-band
event is leading) that confirms a previous claim of the existence of a delay
between the g and r band in this lensed quasar. The time delays (between quasar
components and between optical bands) from the new records and previous ones in
similar bands indicate that most observed variations in Q0957+561 (amplitudes
of about 100 mmag and timescales of about 100 d) are very probably due to
reverberation within the gas disc around the supermassive black hole.Comment: 13 pages, 9 figures. Accepted for publication in A&
Employing a 2D surface grating to improve light out coupling of a substrate emitting organic LED. - art. no. 64860H
The dark halo of the main lens galaxy in QSO 0957+561
We present an analysis of infrared/optical/ultraviolet spectra of the two
images of the first gravitationally lensed quasar Q0957+561A, B. The Hubble
Space Telescope observations of Q0957+561A and Q0957+561B are separated in time
by the known time delay in this system, so we can directly deduce the flux
ratios. These flux ratios of images lead to important information on the dark
halo of the main lens galaxy (a giant elliptical at redshift z = 0.36). Our
measurements for the continuum are in good agreement with extinction in the
elliptical galaxy and a small fraction of mass in collapsed objects (no need
for gravitational microlensing). From the continuum and emission line ratios,
we also show evidence in favour of the existence of a network of compact dusty
clouds.Comment: 5 pages, 2 figures + 1 table, accepted for publication in MNRAS
Letters (more details at http://grupos.unican.es/glendama/
Thermal and hydrodynamic studies for micro-channel cooling for large area silicon sensors in high energy physics experiments
Micro-channel cooling initially aiming at small-sized high-power integrated
circuits is being transferred to the field of high energy physics. Today`s
prospects of micro-fabricating silicon opens a door to a more direct cooling of
detector modules. The challenge in high energy physics is to save material in
the detector construction and to cool large areas. In this paper, we are
investigating micro-channel cooling as a candidate for a future cooling system
for silicon detectors in a generic research and development approach. The work
presented in this paper includes the production and the hydrodynamic and
thermal testing of a micro-channel equipped prototype optimized to achieve a
homogeneous flow distribution. Furthermore, the device was simulated using
finite element methods.Comment: 10 pages, submitted to NIMA (accepted
New VR magnification ratios of QSO 0957+561
We present VR magnification ratios of QSO 0957+561, which are inferred from
the GLITP light curves of Q0957+561A and new frames taken with the 2.56m Nordic
Optical Telescope about 14 months after the GLITP monitoring. From two
photometric approaches and a reasonable range for the time delay in the system
(415-430 days), we do not obtain achromatic optical continuum ratios, but
ratios depending on the wavelength. These new measurements are consistent with
differential extinction in the lens galaxy, the Lyman limit system, the damped
Ly-alpha system, or the host galaxy of the QSO. The possible values for the
differential extinction and the ratio of total to selective extinction in the V
band are reasonable. Moreover, crude probability arguments suggest that the ray
paths of the two components cross a similar dusty environment, including a
network of compact dust clouds and compact dust voids. As an alternative (in
fact, the usual interpretation of the old ratios), we also try to explain the
new ratios as caused by gravitational microlensing in the deflector. From
magnification maps for each of the gravitationally lensed images, using
different fractions of the surface mass density represented by the microlenses,
as well as different sizes and profiles of the V-band and R-band sources,
several synthetic distributions of V-band and R-band ratios are derived. In
some gravitational scenarios, there is an apparent disagreement between the
observed pair of ratios and the simulated distributions. However, several
microlensing pictures work well. To decide between either extinction, or
microlensing, or a mixed scenario (extinction + microlensing), new
observational and interpretation efforts are required.Comment: PS and PDF versions are created from the LaTeX file and 5 EPS
figures, two additional figues (Figs. 6 and 7) in JPEG format, scheduled for
the ApJ 20 January 2005 issu
Lithium ion-induced damage in silicon detectors
Silicon diodes processed by CNM on standard and oxygenated silicon substrates have been irradiated by 58 MeV lithium ions. The radiation-induced effects are very similar to the one observed after proton irradiation: substrate space charge sign inversion (SCSI), lower increase of the effective substrate doping concentration after SCSI for the oxygenated devices. The experimental radiation hardness factor has been determined to be 45.01, within 8.2% with the expected value. These results suggest that 58 MeV Li ions are a suitable radiation source for radiation hardness studies by ions heavier than protons for the future very high luminosity hadron colliders
New evidence of dominant processing effects in standard and oxygenated silicon diodes after neutron irradiation
Abstract Silicon diodes processed on standard and oxygenated silicon substrates by three different manufacturers have been irradiated by neutrons in a nuclear reactor. The leakage current density ( J D ) increase is linear with the neutron fluence. J D and its annealing curve at 80°C do not present any sizeable dependence on substrate oxygenation and/or manufacturing process. The acceptor introduction rate ( ÎČ ) of the effective substrate doping concentration ( N eff ) is independent from the oxygen concentration when standard and oxygenated devices from the same manufacturer are considered. On the contrary, ÎČ significantly varies from one manufacturer to another showing that the ÎČ dependence on the particular process can be important, overtaking the small substrate oxygenation effect. Finally, the average saturation value of the N eff reverse annealing is slightly lower for the oxygenated samples, pointing out a positive effect of the substrate oxygenation even for devices irradiated by neutrons
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