6,081 research outputs found
Near-threshold production of , and at a fixed-target experiment at the future ultra-high-energy proton colliders
We outline the opportunities to study the production of the Standard Model
bosons, , and at "low" energies at fixed-target experiments
based at possible future ultra-high-energy proton colliders, \ie\ the
High-Energy LHC, the Super proton-proton Collider and the Future Circular
Collider -- hadron-hadron. These can be indeed made in conjunction with the
proposed future colliders designed to reach up to TeV by using
bent crystals to extract part of the halo of the beam which would then impinge
on a fixed target. Without disturbing the collider operation, this technique
allows for the extraction of a substantial amount of particles in addition to
serve for a beam-cleaning purpose. With this method, high-luminosity
fixed-target studies at centre-of-mass energies above the , and
masses, GeV, are possible. We also discuss the
possibility offered by an internal gas target, which can also be used as
luminosity monitor by studying the beam transverse shape
Gyrokinetic studies of the effect of beta on drift-wave stability in NCSX
The gyrokinetic turbulence code GS2 was used to investigate the effects of
plasma beta on linear, collisionless ion temperature gradient (ITG) modes and
trapped electron modes (TEM) in National Compact Stellarator Experiment (NCSX)
geometry. Plasma beta affects stability in two ways: through the equilibrium
and through magnetic fluctuations. The first was studied here by comparing ITG
and TEM stability in two NCSX equilibria of differing beta values, revealing
that the high beta equilibrium was marginally more stable than the low beta
equilibrium in the adiabatic-electron ITG mode case. However, the high beta
case had a lower kinetic-electron ITG mode critical gradient. Electrostatic and
electromagnetic ITG and TEM mode growth rate dependencies on temperature
gradient and density gradient were qualitatively similar. The second beta
effect is demonstrated via electromagnetic ITG growth rates' dependency on
GS2's beta input parameter. A linear benchmark with gyrokinetic codes GENE and
GKV-X is also presented.Comment: Submitted to Physics of Plasmas. 9 pages, 27 figure
Icing flight research: Aerodynamic effects of ice and ice shape documentation with stereo photography
Aircraft icing flight research was performed in natural icing conditions. A data base consisting of icing cloud measurements, ice shapes, and aerodynamic measurements is being developed. During research icing encounters the icing cloud was continuously measured. After the encounter, the ice accretion shapes on the wing were documented with a stereo camera system. The increase in wing section drag was measured with a wake survey probe. The overall aircraft performance loss in terms of lift and drag coefficient changes was obtained by steady level speed/power measurements. Selective deicing of the airframe components was performed to determine their contributions to the total drag increase. Engine out capability in terms of power available was analyzed for the iced aircraft. It was shown that the stereo photography system can be used to document ice shapes in flight and that the wake survey probe can measure increases in wing section drag caused by ice. On one flight, the wing section drag coefficient (c sub d) increased approximately 120 percent over the uniced baseline at an aircraft angle of attack of 6 deg. On another flight, the aircraft darg coefficient (c sub d) increased by 75 percent over the uniced baseline at an aircraft lift coefficient (C sub d) of 0.5
Optical alignment and polarization conversion of neutral exciton spin in individual InAs/GaAs quantum dots
We investigate exciton spin memory in individual InAs/GaAs self-assembled
quantum dots via optical alignment and conversion of exciton polarization in a
magnetic field. Quasiresonant phonon-assisted excitation is successfully
employed to define the initial spin polarization of neutral excitons. The
conservation of the linear polarization generated along the bright exciton
eigenaxes of up to 90% and the conversion from circular- to linear polarization
of up to 47% both demonstrate a very long spin relaxation time with respect to
the radiative lifetime. Results are quantitatively compared with a model of
pseudo-spin 1/2 including heavy-to-light hole mixing.Comment: 5 pages, 3 figure
An Enhanced Nonlinear Critical Gradient for Electron Turbulent Transport due to Reversed Magnetic Shear
The first nonlinear gyrokinetic simulations of electron internal transport
barriers (e-ITBs) in the National Spherical Torus Experiment show that reversed
magnetic shear can suppress thermal transport by increasing the nonlinear
critical gradient for electron-temperature-gradient-driven turbulence to three
times its linear critical value. An interesting feature of this turbulence is
nonlinearly driven off-midplane radial streamers. This work reinforces the
experimental observation that magnetic shear is likely an effective way of
triggering and sustaining e-ITBs in magnetic fusion devices.Comment: 4 pages, 5 figure
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