1,624 research outputs found
A system for online beam emittance measurements and proton beam characterization
A system for online measurement of the transverse beam emittance was
developed. It is named PrOBaM (4-Profiler Online Beam
Emittance Measurement) and was conceived to measure the emittance in a fast and
efficient way using the multiple beam profiler method. The core of the system
is constituted by four consecutive UniBEaM profilers, which are based on silica
fibers passing across the beam. The PrOBaM system was
deployed for characterization studies of the 18~MeV proton beam produced by the
IBA Cyclone 18 MeV cyclotron at Bern University Hospital (Inselspital). The
machine serves daily radioisotope production and multi-disciplinary research,
which is carried out with a specifically conceived Beam Transport Line (BTL).
The transverse RMS beam emittance of the cyclotron was measured as a function
of several machine parameters, such as the magnetic field, RF peak voltage, and
azimuthal angle of the stripper. The beam emittance was also measured using the
method based on the quadrupole strength variation. The results obtained with
both techniques were compared and a good agreement was found. In order to
characterize the longitudinal dynamics, the proton energy distribution was
measured. For this purpose, a method was developed based on aluminum absorbers
of different thicknesses, a UniBEaM detector, and a Faraday cup. The results
were an input for a simulation of the BTL developed in the MAD-X software. This
tool allows machine parameters to be tuned online and the beam characteristics
to be optimized for specific applications.Comment: published in Journal of Instrumentatio
An adjustable focusing system for a 2 MeV H- ion beam line based on permanent magnet quadrupoles
A compact adjustable focusing system for a 2 MeV H- RFQ Linac is designed,
constructed and tested based on four permanent magnet quadrupoles (PMQ). A PMQ
model is realised using finite element simulations, providing an integrated
field gradient of 2.35 T with a maximal field gradient of 57 T/m. A prototype
is constructed and the magnetic field is measured, demonstrating good agreement
with the simulation. Particle track simulations provide initial values for the
quadrupole positions. Accordingly, four PMQs are constructed and assembled on
the beam line, their positions are then tuned to obtain a minimal beam spot
size of (1.2 x 2.2) mm^2 on target. This paper describes an adjustable PMQ beam
line for an external ion beam. The novel compact design based on commercially
available NdFeB magnets allows high flexibility for ion beam applications.Comment: published in JINST (4th Feb 2013
Significant enhancement of irreversibility field in clean-limit bulk MgB2
Low resistivity ("clean") MgB2 bulk samples annealed in Mg vapor show an
increase in upper critical field Hc2(T) and irreversibility field Hirr(T) by a
factor of 2 in both transport and magnetic measurements. The best sample
displayed Hirr above 14 T at 4.2 K and 6 T at 20 K. These changes were
accompanied by an increase of the 40 K resistivity from 1.0 to 18 microohm-cm
and a lowering of the resistivity ratio from 15 to 3, while the critical
temperature Tc decreased by only 1-2 K. These results point the way to make
prepare MgB2 attractive for magnet applications.Comment: 3 pages, 4 figures, submitted to Applied Physics Letter
Angular dependence of magnetoresistivity in c-oriented MgB2 thin film
The anisotropy of MgB2 is still under debate: its value, strongly dependent
on the sample and on the measuring method, ranges between 1.2 and 13. In this
work we present our results on a MgB2 c-oriented superconducting thin film. To
evaluate the anisotropy, we followed two different approaches. Firstly,
magnetoresistivity was measured as a function of temperature at selected
magnetic fields applied both parallel and perpendicular to the c-axis;
secondly, we measured magnetoresistivity at selected temperatures and magnetic
fields, varying the angle q between the magnetic field and the c-axis. The
anisotropy estimated from the ratio between the upper critical fields parallel
and perpendicular to the c-axis and the one obtained in the framework of the
scaling approach within the anisotropic Ginzburg-Landau theory are different
but show a similar trend in the temperature dependence. The obtained results
are compared and discussed in the light of the two-band nature of MgB2. A
comparison between critical fields in thin films and single crystal is also
performed.Comment: 13 pages, 4 figures, European Physical Journal B in pres
Critical Field of MGB2 : Crossover from Clean to Dirty Regimes
We have studied the upper critical field, Bc2, in poly-crystalline MgB2
samples in which disorder was varied in a controlled way to carry selectively p
and s bands from clean to dirty limit. We have found that the clean regime
survives when p bands are dirty and s bands are midway between clean and dirty.
In this framework we can explain the anomalous behaviour of Al doped samples,
in which Bc2 decreases as doping increases.Comment: 11 pages, 2 figure
Ostracodes; witnesses of the Plio-Quaternary boundary in the North Eastern Atlantic preliminary results
Proceedings of the 1" R.C.A.N.S. Congress, Lisboa, October 1992The 2,4 MY crisis is an important event for the upper Neogene ofNorth Atlantic. A new climatic system occur and widespread during
the Quaternary and is characterized by glacial and interglacial alternance. To follow the different steps of this crisis, we have choosen a borehole situated in the Cotentin peninsula (Normandy, France) and used ostracodes such as markers. The interpretation of quantitative and qualitative data from the ostracode fauna analysis shows that bathymetry was around 40 and 60 meters with slight fluctuations, excepted during Praetiglian event where the zone was outofwater. The morphologicalvariability analysis offour species (the best represented in the core), show a low variability between the basement and 80 meters. Beyond this limit and after 10 meters, characterized by very low values, the variability increases to very high values to the top of the core. Present data; Abe et Choe, 1988;
Peypouquet et al, 1988; Carbonel et al., 1990 a, 1990 b; show that there is a close link between seasonal contrast intensity and ostracode
intraspecifical morphological variations. The carbonates balance at the interface water / sediment, were ostracodes live and moult, is related and reflects the intensity of the seasonal contrast. After the Praetiglian event, an increase of the seasonal contrast occurs during the Tiglian A and the lower Tiglian B
Study of the radioactivity induced in air by a 15-MeV proton beam
Radioactivity induced by a 15-MeV proton beam extracted into air was studied at the beam transport line of the 18-MeV cyclotron at the Bern University Hospital (Inselspital). The produced radioactivity was calculated and measured by means of proportional counters located at the main exhaust of the laboratory. These devices were designed for precise assessment of air contamination for radiation protection purposes. The main produced isotopes were 11C, 13N and 14O. Both measurements and calculations correspond to two different irradiation conditions. In the former, protons were allowed to travel for their full range in air. In the latter, they were stopped at the distance of 1.5 m by a beam dump. Radioactivity was measured continuously in the exhausted air starting from 2 min after the end of irradiation. For this reason, the short-lived 14O isotope gave a negligible contribution to the measured activity. Good agreement was found between the measurements and the calculations within the estimated uncertainties. Currents in the range of 120-370 nA were extracted in air for 10-30 s producing activities of 9-22 MBq of 11C and 13N. The total activities for 11C and 13N per beam current and irradiation time for the former and the latter irradiation conditions were measured to be (3.60 ± 0.48) × 10−3 MBq (nA s)−1 and (2.89 ± 0.37) × 10−3 MBq (nA s)−1, respectivel
A beam monitor detector based on doped silica and optical fibres
A beam monitor detector prototype based on doped silica fibres coupled to
optical fibres has been designed, constructed and tested, mainly for
accelerators used in medical applications. Scintillation light produced by Ce
and Sb doped silica fibres moving across the beam has been measured, giving
information on beam position, shape and intensity. Mostly based on commercial
components, the detector is easy to install, to operate and no electronic
components are located near the beam. Tests have been performed with a 2 MeV
proton pulsed beam at an average current of 0.8 {\mu}A. The response
characteristics of Sb doped silica fibres have been studied for the first time
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