686 research outputs found
Beam-Induced Electron Loading Effects in High Pressure Cavities for a Muon Collider
Ionization cooling is a critical building block for the realization of a muon collider. To suppress breakdown in the presence of the external magnetic field, an idea of using an RF cavity filled with high pressure hydrogen gas is being considered for the cooling channel design. One possible problem expected in the high pressure RF cavity is, however, the dissipation of significant RF power through the beam-induced electrons accumulated inside the cavity. To characterize this detrimental loading effect, we develop a simplified model that relates the electron density evolution and the observed pickup voltage signal in the cavity, with consideration of several key molecular processes such as the formation of the polyatomic molecules, recombination and attachment. This model is expected to be compared with the actual beam test of the cavity in the MuCool Test Area (MTA) of Fermilab
Trends in early childhood obesity in a large, urban school district in the Southwest from 2007 to 2014.
Presented at: Experimental Biology 2016; April 2-6, 2016; San Diego, CA.https://digitalrepository.unm.edu/prc-posters-presentations/1022/thumbnail.jp
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Beam Test of a High Pressure Cavity for a Muon Collider
To demonstrate the feasibility of a high pressure RF cavity for use in the cooling channel of a muon collider, an experimental setup that utilizes 400-MeV Fermilab linac proton beam has been developed. In this paper, we describe the beam diagnostics and the collimator system for the experiment, and report the initial results of the beam commissioning. The transient response of the cavity to the beam is measured by the electric and magnetic pickup probes, and the beam-gas interaction is monitored by the optical diagnostic system composed of a spectrometer and two PMTs
π0 and ρ0 photoproduction from 6 to 18 GeV
Differential cross sections for π0 and ρ0 photoproduction from protons have been measured at photon energies 6, 12, and 18 GeV and momentum transfers 0.5 to 3 (GeV/c)^2
Pressurized H-2 rf Cavities in Ionizing Beams and Magnetic Fields
A major technological challenge in building a muon cooling channel is operating rf cavities in multitesla external magnetic fields. We report the first proof-of-principle experiment of a high pressure gas-filled rf cavity for use with intense ionizing beams and strong external magnetic fields. rf power consumption by beam-induced plasma is investigated with hydrogen and deuterium gases with pressures between 20 and 100 atm and peak rf gradients between 5 and 50 MV/m. The low pressure case agrees well with an analytical model based on electron and ion mobilities. Varying concentrations of oxygen gas are investigated to remove free electrons from the cavity and reduce the rf power consumption. Measurements of the electron attachment time to oxygen and rate of ion-ion recombination are also made. Additionally, we demonstrate the operation of the gas-filled rf cavity in a solenoidal field of up to 3 T, finding no major magnetic field dependence. All these results indicate that a high pressure gas-filled cavity is a viable technology for muon ionization cooling.open1
Synchronous Optical and Radio Polarization Variability in the Blazar OJ287
We explore the variability and cross-frequency correlation of the flux
density and polarization of the blazar OJ287, using imaging at 43 GHz with the
Very Long Baseline Array, as well as optical and near-infrared polarimetry. The
polarization and flux density in both the optical waveband and the 43 GHz
compact core increased by a small amount in late 2005, and increased
significantly along with the near-IR polarization and flux density over the
course of 10 days in early 2006. Furthermore, the values of the electric vector
position angle (EVPA) at the three wavebands are similar. At 43 GHz, the EVPA
of the blazar core is perpendicular to the flow of the jet, while the EVPAs of
emerging superluminal knots are aligned parallel to the jet axis. The core
polarization is that expected if shear aligns the magnetic field at the
boundary between flows of disparate velocities within the jet. Using variations
in flux density, percentage polarization, and EVPA, we model the inner jet as a
spine-sheath system. The model jet contains a turbulent spine of half-width 1.2
degrees and maximum Lorentz factor of 16.5, a turbulent sheath with Lorentz
factor of 5, and a boundary region of sheared field between the spine and
sheath. Transverse shocks propagating along the fast, turbulent spine can
explain the superluminal knots. The observed flux density and polarization
variations are then compatible with changes in the direction of the inner jet
caused by a temporary change in the position of the core if the spine contains
wiggles owing to an instability. In addition, we can explain a stable offset of
optical and near-IR percentage polarization by a steepening of spectral index
with frequency, as supported by the data.Comment: 34 pages, 12 figures; To be published in Astrophysical Journal,
accepted 03/200
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