1,217 research outputs found
Status of high temperature superconductor based magnets and the conductors they depend upon
This paper reviews the status of high temperature superconductors for high
field magnets for future devices such as a high energy LHC or a muon collider.
Some of the primary challenges faced for the implementation of systems are
discussed. Two conductor technologies, BiSrCaCuO and
YBaCuO, have emerged as high field conductor options, but
their relative advantages and disadvantages for high field magnets are quite
different. These are reviewed from an engineering perspective, including coil
manufacturing, electromechanical behaviour and quench behaviour. Lastly, the
important roles of "system pull" upon conductor and magnet technology
development, and of interactions between the materials and magnet communities
for accelerating development, are discussed.Comment: 11 pages, contribution to the EuCARD-AccNet-EuroLumi Workshop: The
High-Energy Large Hadron Collider, Malta, 14 -- 16 Oct 2010; CERN Yellow
Report CERN-2011-003, pp. 59-6
The Knee of the Cosmic Hydrogen and Helium Spectrum below 1 PeV Measured by ARGO-YBJ and a Cherenkov Telescope of LHAASO
The measurement of cosmic ray energy spectra, in particular for individual
species, is an essential approach in finding their origin. Locating the "knees"
of the spectra is an important part of the approach and has yet to be achieved.
Here we report a measurement of the mixed Hydrogen and Helium spectrum using
the combination of the ARGO-YBJ experiment and of a prototype Cherenkov
telescope for the LHAASO experiment. A knee feature at 640+/-87 TeV, with a
clear steepening of the spectrum, is observed. This gives fundamental inputs to
galactic cosmic ray acceleration models
Gamma ray flares from Mrk421 in 2008 observed with the ARGO-YBJ detector
In 2008 the blazar Markarian 421 entered a very active phase and was one of
the brightest sources in the sky at TeV energies, showing frequent flaring
episodes. Using the data of ARGO-YBJ, a full coverage air shower detector
located at Yangbajing (4300 m a.s.l., Tibet, China), we monitored the source at
gamma ray energies E > 0.3 TeV during the whole year. The observed flux was
variable, with the strongest flares in March and June, in correlation with
X-ray enhanced activity. While during specific episodes the TeV flux could be
several times larger than the Crab Nebula one, the average emission from day 41
to 180 was almost twice the Crab level, with an integral flux of (3.6 +-0.6)
10^-11 photons cm^-2 s^-1 for energies E > 1 TeV, and decreased afterwards.
This paper concentrates on the flares occurred in the first half of June.
This period has been deeply studied from optical to 100 MeV gamma rays, and
partially up to TeV energies, since the moonlight hampered the Cherenkov
telescope observations during the most intense part of the emission. Our data
complete these observations, with the detection of a signal with a statistical
significance of 3.8 standard deviations on June 11-13, corresponding to a gamma
ray flux about 6 times larger than the Crab one above 1 TeV. The reconstructed
differential spectrum, corrected for the intergalactic absorption, can be
represented by a power law with an index alpha = -2.1 extending up to several
TeV. The spectrum slope is fully consistent with previous observations
reporting a correlation between the flux and the spectral index, suggesting
that this property is maintained in different epochs and characterizes the
source emission processes.Comment: Accepted for publication on ApJ
Mean Interplanetary Magnetic Field Measurement Using the ARGO-YBJ Experiment
The sun blocks cosmic ray particles from outside the solar system, forming a
detectable shadow in the sky map of cosmic rays detected by the ARGO-YBJ
experiment in Tibet. Because the cosmic ray particles are positive charged, the
magnetic field between the sun and the earth deflects them from straight
trajectories and results in a shift of the shadow from the true location of the
sun. Here we show that the shift measures the intensity of the field which is
transported by the solar wind from the sun to the earth.Comment: 6 papges,3 figure
Transpolar arc observation after solar wind entry into the high-latitude magnetosphere
Recently, Cluster observations have revealed the presence of new regions of solar wind plasma entry at the high-latitude magnetospheric lobes tailward of the cusp region, mostly during periods of northward interplanetary magnetic field. In this study, observations from the Global Ultraviolet Imager (GUVI) experiment on board the TIMED spacecraft and Wideband Imaging Camera imager on board the IMAGE satellite are used to investigate a possible link between solar wind entry and the formation of transpolar arcs in the polar cap. We focus on a case when transpolar arc formation was observed twice right after the two solar wind entry events were detected by the Cluster spacecraft. In addition, GUVI and IMAGE observations show a simultaneous occurrence of auroral activity at low and high latitudes after the second entry event, possibly indicating a two-part structure of the continuous band of the transpolar arc
Study of the diffuse gamma-ray emission from the Galactic plane with ARGO-YBJ
The events recorded by ARGO-YBJ in more than five years of data collection
have been analyzed to determine the diffuse gamma-ray emission in the Galactic
plane at Galactic longitudes 25{\deg} < l < 100{\deg} and Galactic latitudes .
The energy range covered by this analysis, from ~350 GeV to ~2 TeV, allows the
connection of the region explored by Fermi with the multi-TeV measurements
carried out by Milagro. Our analysis has been focused on two selected regions
of the Galactic plane, i.e., 40{\deg} < l < 100{\deg} and 65{\deg} < l <
85{\deg} (the Cygnus region), where Milagro observed an excess with respect to
the predictions of current models. Great care has been taken in order to mask
the most intense gamma-ray sources, including the TeV counterpart of the Cygnus
cocoon recently identified by ARGO-YBJ, and to remove residual contributions.
The ARGO-YBJ results do not show any excess at sub-TeV energies corresponding
to the excess found by Milagro, and are consistent with the predictions of the
Fermi model for the diffuse Galactic emission. From the measured energy
distribution we derive spectral indices and the differential flux at 1 TeV of
the diffuse gamma-ray emission in the sky regions investigated.Comment: 11 pages, 6 figures, published in AP
The cosmic ray proton plus helium energy spectrum measured by the ARGO-YBJ experiment in the energy range 3-300 TeV
The ARGO-YBJ experiment is a full-coverage air shower detector located at the
Yangbajing Cosmic Ray Observatory (Tibet, People's Republic of China, 4300 m
a.s.l.). The high altitude, combined with the full-coverage technique, allows
the detection of extensive air showers in a wide energy range and offer the
possibility of measuring the cosmic ray proton plus helium spectrum down to the
TeV region, where direct balloon/space-borne measurements are available. The
detector has been in stable data taking in its full configuration from November
2007 to February 2013. In this paper the measurement of the cosmic ray proton
plus helium energy spectrum is presented in the region 3-300 TeV by analyzing
the full collected data sample. The resulting spectral index is . These results demonstrate the possibility of performing an accurate
measurement of the spectrum of light elements with a ground based air shower
detector.Comment: 18 pages, 8 figures, preprint submitted to Phys. Rev.
4.5 years multi-wavelength observations of Mrk 421 during the ARGO-YBJ and Fermi common operation time
We report on the extensive multi-wavelength observations of the blazar
Markarian 421 (Mrk 421) covering radio to gamma-rays, during the 4.5 year
period of ARGO-YBJ and Fermi common operation time, from August 2008 to
February 2013. In particular, thanks to the ARGO-YBJ and Fermi data, the whole
energy range from 100 MeV to 10 TeV is covered without any gap. In the
observation period, Mrk 421 showed both low and high activity states at all
wavebands. The correlations among flux variations in different wavebands were
analyzed. Seven large flares, including five X-ray flares and two GeV gamma-ray
flares with variable durations (3-58 days), and one X-ray outburst phase were
identified and used to investigate the variation of the spectral energy
distribution with respect to a relative quiescent phase. During the outburst
phase and the seven flaring episodes, the peak energy in X-rays is observed to
increase from sub-keV to few keV. The TeV gamma-ray flux increases up to
0.9-7.2 times the flux of the Crab Nebula. The behavior of GeV gamma-rays is
found to vary depending on the flare, a feature that leads us to classify
flares into three groups according to the GeV flux variation. Finally, the
one-zone synchrotron self-Compton model was adopted to describe the emission
spectra. Two out of three groups can be satisfactorily described using injected
electrons with a power-law spectral index around 2.2, as expected from
relativistic diffuse shock acceleration, whereas the remaining group requires a
harder injected spectrum. The underlying physical mechanisms responsible for
different groups may be related to the acceleration process or to the
environment properties.Comment: 17 pages, 9 figures, 5 tables, Accepted for publication in ApJ
Observation of TeV gamma rays from the Cygnus region with the ARGO-YBJ experiment
We report the observation of TeV gamma-rays from the Cygnus region using the
ARGO-YBJ data collected from 2007 November to 2011 August. Several TeV sources
are located in this region including the two bright extended MGRO J2019+37 and
MGRO J2031+41. According to the Milagro data set, at 20 TeV MGRO J2019+37 is
the most significant source apart from the Crab Nebula. No signal from MGRO
J2019+37 is detected by the ARGO-YBJ experiment, and the derived flux upper
limits at 90% confidence level for all the events above 600 GeV with medium
energy of 3 TeV are lower than the Milagro flux, implying that the source might
be variable and hard to be identified as a pulsar wind nebula. The only
statistically significant (6.4 standard deviations) gamma-ray signal is found
from MGRO J2031+41, with a flux consistent with the measurement by Milagro.Comment: 14 pages, 4 figure
Observation of TeV gamma-rays from the unidentified source HESS J1841-055 with the ARGO-YBJ experiment
We report the observation of a very high energy \gamma-ray source, whose
position is coincident with HESS J1841-055. This source has been observed for
4.5 years by the ARGO-YBJ experiment from November 2007 to July 2012. Its
emission is detected with a statistical significance of 5.3 standard
deviations. Parameterizing the source shape with a two-dimensional Gaussian
function we estimate an extension \sigma=(0.40(+0.32,-0.22}) degree, consistent
with the HESS measurement. The observed energy spectrum is dN/dE =(9.0-+1.6) x
10^{-13}(E/5 TeV)^{-2.32-+0.23} photons cm^{-2} s^{-1} TeV^{-1}, in the energy
range 0.9-50 TeV. The integral \gamma-ray flux above 1 TeV is 1.3-+0.4 Crab
units, which is 3.2-+1.0 times the flux derived by HESS. The differences in the
flux determination between HESS and ARGO-YBJ, and possible counterparts at
other wavelengths are discussed.Comment: 17 pages, 4 figures, have been accepted for publication in Ap
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