1,947 research outputs found
Produção de gado de corte e acĂșmulo de matĂ©ria seca em sistemas de integração lavoura: pecuĂĄria em presença e ausĂȘncia de trevo branco e nitrogĂȘnio.
O trabalho foi conduzido com o objetivo de verificar a influĂȘncia da adubação nitrogenada em uma pastagem de azevĂ©m (Lolium multiflorium L.) e aveia (Avena strigosa Scherb) em presença e ausĂȘncia de trevo branco (Trifolium repens L.), conferida pelo acĂșmulo e produção de matĂ©ria seca, ganho mĂ©dio diĂĄrio, ganho de peso vivo e carga animal no sistema de integração lavoura-pecuĂĄria sob sistema de plantio direto. A cultura antecessora da pastagem foi a soja (Glycine Max L.). O delineamento experimental foi em blocos completos ao acaso, com parcelas subdivididas e trĂȘs repetiçÔes. Nas parcelas, foram testadas quatro doses de nitrogĂȘnio (0, 100, 200 e 300 kg.ha-1) e nas subparcelas, a combinação de presença e ausĂȘncia de trevo branco. A elevação das doses crescentes de N aumentaram de forma linear crescente o acĂșmulo e a produção de matĂ©ria seca da pastagem. A carga animal e o ganho de peso vivo por hectare de bovinos aumentaram com o incremento de nitrogĂȘnio. Os resultados demonstram o efeito da adubação nitrogenada no acĂșmulo diĂĄrio, na produção de matĂ©ria seca, carga animal e no ganho de peso vivo
Development of hollow electron beams for proton and ion collimation
Magnetically confined hollow electron beams for controlled halo removal in
high-energy colliders such as the Tevatron or the LHC may extend traditional
collimation systems beyond the intensity limits imposed by tolerable material
damage. They may also improve collimation performance by suppressing loss
spikes due to beam jitter and by increasing capture efficiency. A hollow
electron gun was designed and built. Its performance and stability were
measured at the Fermilab test stand. The gun will be installed in one of the
existing Tevatron electron lenses for preliminary tests of the hollow-beam
collimator concept, addressing critical issues such as alignment and
instabilities of the overlapping proton and electron beams.Comment: 3 pp. 1st International Particle Accelerator Conference: IPAC'10,
23-28 May 2010: Kyoto, Japa
Energy Deposition Studies for Possible Innovative Phase II Collimator Designs
Due to the known limitations of Phase I LHC collimators in stable physics conditions, the LHC collimation system will be complemented by additional 30 Phase II collimators. The Phase II collimation system is designed to improve cleaning efficiency and to minimize the collimator-induced impedance with the main function of protecting the Super Conducting (SC) magnets from quenching due to beam particle losses. To fulfil these requirements, different possible innovative collimation designs were taken in consideration. Advanced jaw materials, including new composite materials (e.g. CuâDiamond), jaw SiC insertions, coating foil, in-jaw instrumentation (e.g. BPM) and improved mechanical robustness of the jaw are the main features of these new promising Phase II collimator designs developed at CERN. The FLUKA Monte Carlo code is extensively used to evaluate the behavior of these collimators in the most radioactive areas of LHC, supporting the mechanical integration. These studies aim to identify the possible critical points along the IR7 line
Electron trapping and acceleration by the plasma wakefield of a self-modulating proton beam
It is shown that co-linear injection of electrons or positrons into the
wakefield of the self-modulating particle beam is possible and ensures high
energy gain. The witness beam must co-propagate with the tail part of the
driver, since the plasma wave phase velocity there can exceed the light
velocity, which is necessary for efficient acceleration. If the witness beam is
many wakefield periods long, then the trapped charge is limited by beam loading
effects. The initial trapping is better for positrons, but at the acceleration
stage a considerable fraction of positrons is lost from the wave. For efficient
trapping of electrons, the plasma boundary must be sharp, with the density
transition region shorter than several centimeters. Positrons are not
susceptible to the initial plasma density gradient.Comment: 9 pages, 9 figures, 1 table, 44 reference
Beam halo dynamics and control with hollow electron beams
Experimental measurements of beam halo diffusion dynamics with collimator
scans are reviewed. The concept of halo control with a hollow electron beam
collimator, its demonstration at the Tevatron, and its possible applications at
the LHC are discussed.Comment: 5 pages, 4 figures, in Proceedings of the 52nd ICFA Advanced Beam
Dynamics Workshop on High-Intensity and High-Brightness Hadron Beams
(HB2012), Beijing, China, 17-21 September 201
The UA9 experimental layout
The UA9 experimental equipment was installed in the CERN-SPS in March '09
with the aim of investigating crystal assisted collimation in coasting mode.
Its basic layout comprises silicon bent crystals acting as primary
collimators mounted inside two vacuum vessels. A movable 60 cm long block of
tungsten located downstream at about 90 degrees phase advance intercepts the
deflected beam.
Scintillators, Gas Electron Multiplier chambers and other beam loss monitors
measure nuclear loss rates induced by the interaction of the beam halo in the
crystal. Roman pots are installed in the path of the deflected particles and
are equipped with a Medipix detector to reconstruct the transverse distribution
of the impinging beam. Finally UA9 takes advantage of an LHC-collimator
prototype installed close to the Roman pot to help in setting the beam
conditions and to analyze the efficiency to deflect the beam. This paper
describes in details the hardware installed to study the crystal collimation
during 2010.Comment: 15pages, 11 figure, submitted to JINS
Beam Halo on the LHC TCDQ Diluter System and Thermal Load on the Downstream Superconducting Magnets
The moveable single-jawed graphite TCDQ diluter must be positioned very close to the circulating LHC beam in order to prevent damage to downstream components in the event of an unsynchronised beam abort. A two-jawed graphite TCS.IR6 collimator forms part of the TCDQ system. The requirement to place the jaws close to the beam means that the system can intercept a substantial beam halo load. Initial investigations indicated a worryingly high heat load on the Q4 coils. This paper presents the updated load cases, shielding and simulation geometry, and the results of simulations of the energy deposition in the TCDQ system and in the downstream superconducting Q4 magnet. The implications for the operation of the LHC are discussed
The super-LHC
We review here the prospects of a long-term upgrade programme for the Large
Hadron Collider (LHC), CERN laboratory's new proton-proton collider. The
super-LHC, which is currently under evaluation and design, is expected to
deliver of the order of ten times the statistics of the LHC. In addition to a
non-technical summary of the principal physics arguments for the upgrade, I
present a pedagogical introduction to the technological challenges on the
accelerator and experimental fronts, and a review of the current status of the
planning.Comment: To appear in Contemporary Physic
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