121 research outputs found
Manipulation of charged particle beams through coherent interactions with crystals
In the last years, the field of channeling and related phenomena aimed to particle-beam
steering has received a tremendous impulse by the advent of a new generation of silicon
crystals, which resulted in significant performance increase and lead to the discovery of novel
phenomena.
The first key factor was the usage of silicon crystals exploiting secondary deformations,
which provide extremely uniform bending an optimal sample thickness across the beam.
Moreover, the holder to impart the primary curvature is designed to keep apart all the material
but silicon from the trajectory of the beam.
A second key factor which lead to performance improvement is the quality of the crystal
surfaces by using properly tailored chemical etchings. In particular, the entry face of the
crystal plays an important role, because it is the surface accepting incoming beam particles.
Lastly, significant contribution was due to the characterization of the samples with a
variety of techniques. A thorough characterization allows fine adjustment of the experimental
parameters for crystal fabrication and certification of its quality prior to installation in the
accelerator.
In this thesis it will be shown the procedures for manufacturing of crystal realized at
Sensors and Semiconductor Laboratory of Ferrara University. The fabrication methods, based
on revisitations of micromachining techniques, allow obtaining high quality crystals, which
lead to performance increase as well as to the discovery of new effects in the interaction with
positively and negatively charged particle beams at CERN facilities.
As it will be shown in this thesis, the geometry and the quality of the realized crystals
allowed attaining a record 83% efficiency when operated to deflect a 400 GeV proton beam at
the H8 line at CERN by means of planar channeling and contributed to the observation of
volume reflection.
The same crystal generation enabled to observe multiple volume reflection in both a
series and in a single crystal and to successfully achieve deflection of negatively charged
particle beams through either channeling or volume reflection.
Coherent phenomena in crystals may be the basis for halo collimation for current
hadron colliders (e.g. the LHC). An efficient collimation system is a necessary condition to
run the accelerator at its top luminosity and to prevent damage of its sophisticated
superconductive magnets. This smarted collimation scheme is currently being under
investigation in the pilot UA9 experiments, which investigate crystal-assisted schemes for
halo collimation in the CERN SPS through channeling of protons. The first and preliminary
results of UA9 experiment shows good perspectives on the possibility to collimate the LHC
beam by using bent crystals
Steering efficiency of a ultrarelativistic proton beam in a thin bent crystal
Crystals with small thickness along the beam exhibit top performance for
steering particle beams through planar channeling. For such crystals, the
effect of nuclear dechanneling plays an important role because it affects their
efficiency. We addressed the problem through experimental work carried out with
400 GeV/c protons at fixed-target facilities of CERN-SPS. The dependence of
efficiency vs. curvature radius has been investigated and compared favourably
to the results of modeling. A realistic estimate of the performance of a
crystal designed for LHC energy including nuclear dechanneling has been
achieved.Comment: 16 pages, 6 figure
Relaxation of axially confined 400 GeV/c protons to planar channeling in a bent crystal
An investigation on the mechanism of relaxation
of axially confined 400 GeV/c protons to planar channeling
in a bent crystal was carried out at the extracted line H8 from
CERN Super Proton Synchrotron. The experimental results
were critically compared to computer simulations, showing
a good agreement. We identified a necessary condition for
the exploitation of axial confinement or its relaxation for
particle beam manipulation in high-energy accelerators. We
introduce the idea of using a short bent crystal, aligned with
one of its main axis to the beam direction, as a beam steerer
or a beam splitter with adjustable intensity in the field of particle
accelerators. In particular, in the latter case, a complete
relaxation from axial confinement to planar channeling takes
place, resulting in beam splitting into the two strongest skew
planar channels.An investigation on the mechanism of relaxation of axially confined 400 GeV/c protons to planar channeling in a bent crystal was carried out at the extracted line H8 from CERN Super Proton Synchrotron. The experimental results were critically compared to computer simulations, showing a good agreement. We identified a necessary condition for the exploitation of axial confinement or its relaxation for particle beam manipulation in high-energy accelerators. We introduce the idea of using a short bent crystal, aligned with one of its main axis to the beam direction, as a beam steerer or a beam splitter with adjustable intensity in the field of particle accelerators. In particular, in the latter case, a complete relaxation from axial confinement to planar channeling takes place, resulting in beam splitting into the two strongest skew planar channels
Enhancement of the Inelastic Nuclear Interaction Rate in Crystals via Antichanneling
The interaction rate of a charged particle beam with the atomic nuclei of a target varies significantly if the target has a crystalline structure. In particular, under specific orientations of the target with respect to the incident beam, the probability of inelastic interaction with nuclei can be enhanced with respect to the unaligned case. This effect, which can be named antichanneling, can be advantageously used in the cases where the interaction between beam and target has to be maximized. Here we propose to use antichanneling to increase the radioisotope production yield via cyclotron. A dedicated set of experimental measurements was carried out at the INFN Legnaro Laboratories with the AN2000 and CN accelerators to prove the existence of the antichanneling effect. The variation of the interaction yield at hundreds of keV to MeV energies was observed by means of sapphire and indium phosphide crystals, achieving an enhancement of the interaction rate up to 73% and 25%, respectively. Such a result may pave the way to the development of a novel type of nozzle for the existing cyclotrons, which can exploit crystalline materials as targets for radioisotope production, especially to enhance the production rate for expensive prime materials with minor upgrades of the current instrumentation
FABRICATION OF CRYSTALS FOR CHANNELING OF PARTICLES IN ACCELERATOR
Abstract Channelling in bent crystals is technique with high potential to steer charged-particle beams for several applications in accelerators. Channeling and related techniques underwent significant progress in the last years. Distinctive features of performance increase was the availability of novel ideas other than new techniques to manufacture the crystal for channeling. We propose two methods to fabricate crystals through silicon micromachining techniques, i.e., isotropic or anisotropic silicon etchings. Characterization of the crystals accomplished for both methods to highlight that the crystals are free of lattice damage induced by the preparation. Crystals prepared by both kinds of methodologies were positively tested at the external line H8 of the SPS with 400 GeV protons for investigation on planar and axial channelings as well as on single and multiple volume reflection experiments by the H8-RD22 collaboration
Fabrication of Crystals for Channeling of Particles in Accelerators
Channelling in bent crystals is technique with high potential to steer charged-particle beams for several applications in accelerators. Channeling and related techniques underwent significant progress in the last years. Distinctive features of performance increase was the availability of novel ideas other than new techniques to manufacture the crystal for channeling. We propose two methods to fabricate crystals through silicon micromachining techniques, i.e., isotropic or anisotropic silicon etchings. Characterization of the crystals accomplished for both methods to highlight that the crystals are free of lattice damage induced by the preparation. Crystals prepared by both kinds of methodologies were positively tested at the external line H8 of the SPS with 400 GeV protons for investigation on planar and axial channelings as well as on single and multiple volume reflection experiments by the H8-RD22 collaboration
Near-infrared spectroscopy estimation of combined skeletal muscle oxidative capacity and O2 diffusion capacity in humans
The final steps of the O2 cascade during exercise depend on the product of the microvascular-tointramyocyte PO2 difference and muscle O2 diffusing capacity (DmO2). Non-invasive methods to determine DmO2 in humans are currently unavailable. Muscle oxygen uptake (mVO2) recovery rate constant (k), measured by near-infrared spectroscopy (NIRS) using intermittent arterial occlusions, is associated with muscle oxidative capacity in vivo. We reasoned that k would be limited by DmO2 when muscle oxygenation is low (kLOW), and hypothesized that: i) k in well-oxygenated muscle (kHIGH) is associated with maximal O2 flux in fiber bundles; and ii) Δk (kHIGH-kLOW) is associated with capillary density (CD). Vastus lateralis k was measured in 12 participants using NIRS after moderate exercise. The timing and duration of arterial occlusions were manipulated to maintain tissue saturation index (TSI) within a 10% range either below (LOW) or above (HIGH) half-maximal desaturation, assessed during sustained arterial occlusion. Maximal O2 flux in phosphorylating state was 37.7±10.6 pmol·s−1·mg−1 (~5.8 ml·min−1·100g−1). CD ranged 348 to 586 mm-2. kHIGH was greater than kLOW (3.15±0.45 vs 1.56±0.79 min-1, p\u3c0.001). Maximal O2 flux was correlated with kHIGH (r=0.80, p=0.002) but not kLOW (r=-0.10, p=0.755). Δk ranged -0.26 to -2.55 min-1, and correlated with CD (r=- 0.68, p=0.015). mVO2 k reflects muscle oxidative capacity only in well-oxygenated muscle. Δk, the difference in k between well- and poorly-oxygenated muscle, was associated with CD, a mediator of DmO2. Assessment of muscle k and Δk using NIRS provides a non-invasive window on muscle oxidative and O2 diffusing capacity
X-ray properties and obscured fraction of AGN in the J1030 Chandra field
The 500ks Chandra ACIS-I observation of the field around the quasar
SDSS J1030+0524 is currently the 5th deepest extragalactic X-ray survey. The
rich multi-band coverage of the field allowed for an effective identification
and redshift determination of the X-ray source counterparts: to date a catalog
of 243 extragalactic X-ray sources with either a spectroscopic or photometric
redshift estimate in the range is available over a 355 arcmin
area. Given its depth and the multi-band information, this catalog is an
excellent resource to investigate X-ray spectral properties of distant Active
Galactic Nuclei (AGN) and derive the redshift evolution of their obscuration.
We performed a thorough X-ray spectral analysis for each object in the sample,
measuring its nuclear column density and intrinsic (de-absorbed)
2-10 keV rest-frame luminosity, . Whenever possible, we also used the
presence of the Fe K emission line to improve the photometric redshift
estimates. We measured the fractions of AGN hidden by column densities in
excess of and cm ( and ,
respectively) as a function of and redshift, and corrected for
selection effects to recover the intrinsic obscured fractions. At ,
we found and , respectively, in broad
agreement with the results from other X-ray surveys. No significant variations
with X-ray luminosity were found within the limited luminosity range probed by
our sample (log). When focusing on luminous AGN with
log to maximize the sample completeness up to large
cosmological distances, we did not observe any significant change in
or over the redshift range . Nonetheless, the obscured
fractions we measure are significantly higher than ...Comment: A&A, in pres
LBT-MODS spectroscopy of high-redshift candidates in the Chandra J1030 field. A newly discovered z2.8 large scale structure
We present the results of a spectroscopic campaign with the Multi-Object
Double Spectrograph (MODS) instrument mounted on the Large Binocular Telescope
(LBT), aimed at obtaining a spectroscopic redshift for seven Chandra J1030
sources with a photometric redshift >=2.7 and optical magnitude
r_AB=[24.5-26.5]. We obtained a spectroscopic redshift for five out of seven
targets: all of them have z_spec>=2.5, thus probing the reliability of the
Chandra J1030 photometric redshifts. The spectroscopic campaign led to the
serendipitous discovery of a z~2.78 large scale structure (LSS) in the J1030
field: the structure contains four X-ray sources (three of which were targeted
in the LBT-MODS campaign) and two non-X-ray detected galaxies for which a
VLT-MUSE spectrum was already available. The X-ray members of the LSS are
hosted in galaxies that are significantly more massive
(log(M_*/M_sun)=[10.0-11.1]) than those hosting the two MUSE-detected sources
(log(M_*/M_sun)<10). Both observations and simulations show that massive
galaxies, and particularly objects having log(M_*/M_sun)>10, are among the best
tracers of large scale structures and filaments in the cosmic web.
Consequently, our result can explain why X-ray-detected AGN have also been
shown to be efficient tracers of large scale structures.Comment: 16 pages, 9 Figures. Accepted for publication in Astronomy and
Astrophysic
Next-generation ultra-compact calorimeters based on oriented crystals
Calorimeters based on oriented crystals provide unparalleled compactness and resolution in measuring the energy of electromagnetic particles. Recent experiments performed at CERN and DESY beamlines by the AXIAL/ELIOT experiments demonstrated a significant reduction in the radiation length inside tungsten and PbWO4, the latter being the scintillator used for the CMS ECAL, observed when the incident particle trajectory is aligned with a lattice axis within ∼1∘. This remarkable effect, being observed over the wide energy range from a few GeV to 1 TeV or higher, paves the way for the development of innovative calorimeters based on oriented crystals, featuring a design significantly more compact than currently achievable while rivaling the current state of the art in terms of energy resolution in the range of interest for present and future forward detectors (such as the KLEVER Small Angle Calorimeter at CERN SPS) and source-pointing space-borne γ-ray telescopes
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