1,378 research outputs found
Gravitational waveforms from unequal-mass binaries with arbitrary spins under leading order spin-orbit coupling
The paper generalizes the structure of gravitational waves from orbiting
spinning binaries under leading order spin-orbit coupling, as given in the work
by K\"onigsd\"orffer and Gopakumar [PRD 71, 024039 (2005)] for single-spin and
equal-mass binaries, to unequal-mass binaries and arbitrary spin
configurations. The orbital motion is taken to be quasi-circular and the
fractional mass difference is assumed to be small against one. The emitted
gravitational waveforms are given in analytic form.Comment: 13 pages, 2 figures, submitted to PRD on 11 Sep. 200
Vacuum system
The vacuum system of a particle accelerator must provide the necessary conditions for the high energy beam to avoid loss of particles and deterioration of the beam quality. In this talk we will review basic design concepts, vacuum components and procedures required for an accelerator vacuum system
LHC vacuum system
The Large Hadron Collider (LHC) project, now in the advanced construction phase at CERN, comprises two proton storage rings with colliding beams of 7-TeV energy. The machine is housed in the existing LEP tunnel with a circumference of 26.7 km and requires a bending magnetic field of 8.4 T with 14-m long superconducting magnets. The beam vacuum chambers comprise the inner 'cold bore' walls of the magnets. These magnets operate at 1.9 K, and thus serve as very good cryo-pumps. In order to reduce the cryogenic power consumption, both the heat load from synchrotron radiation emitted by the proton beams and the resistive power dissipation by the beam image currents have to be absorbed on a 'beam screen', which operates between 5 and 20 K and is inserted inside the vacuum chamber. The design of this beam screen represents a technological challenge in view of the numerous and often conflicting requirements and the very tight mechanical tolerances imposed. The synchrotron radiation produces strong outgassing from the walls. The design pressure necessary for operation must provide a beam lifetime of several days. An additional stringent requirement comes from the power deposition in the superconducting magnet coils due to protons scattered on the residual gas, which could lead to a magnet quench and interrupt the machine operation. Cryopumping of gas on the cold surfaces provides the necessary low gas densities but it must be ensured that the vapour pressure of cryosorbed molecules, of which H/sub 2/ and He are the most critical species, remains within acceptable limits. In the warm straight sections of the LHC the pumping speed requirement is determined by ion induced desorption and the resulting vacuum stability criterion. (27 refs)
Beam Induced Multipacting
Beam induced multipacting driven by the electric field of successive bunches, as first observed in the ISR proton-proton storage ring [1] may arise from a resonance motion of a cloud of secondary electrons bouncing back and forth between opposite walls of the vacuum chamber. Under conditions where the average secondary electron yield of this process exceeds unity, the electron cloud may increase exponentially. A consequence for the vacuum system is strong electron stimulated gas desorption and the associated pressure increase which may affect the beam lifetime. A simple criterion for the onset of multipacting and an estimate of the average secondary electron yield is derived and will be applied to typical vacuum chambers and to the specific conditions found in the LHC
The LHC Vacuum System
The Large Hadron Collider (LHC) at CERN, involves two proton storage rings with colliding beams of 7 TeV. The machine will be housed in the existing LEP tunnel and requires 16 m long superconducting b ending magnets. The vacuum chamber will be the inner wall of the cryostat and hence at the temperature of the magnet cold bore, i.e. at 1.9 K and therefore a very good cryopump. To reduce the cryogeni c power consumption, the heat load from synchrotron radiation and from the image currents in the vacuum chamber will be absorbed on a 'beam screen', which operates between 5 and 20 K, inserted in the magnet cold bore. The design pressure necessary for operation must provide a lifetime of several days and a further stringent requirement comes from the power deposition in the superconducting magnet coils due to protons scattered on the residual gas which could lead to a magnet quench. Cryopumping of gas on the cold surfaces provides the necessary low gas densities but it must be ensured that the vapour pressure of cryosorbed molecules, of which H2 and He would be the most critical species, remains within acceptable limits. In the room temperature sections of the LHC, specifically in the exper iments, the vacuum must be stable against ion induced desorption and ISR-type 'pressure bumps'
Binary black hole mergers in AGN accretion discs: gravitational wave rate density estimates
The majority of gravitational wave (GW) events detected so far by LIGO/Virgo
originate from binary black hole (BBH) mergers. Among the different binary
evolution paths, the merger of BBHs in accretion discs of active galactic
nuclei (AGNs) is a possible source of GW detections. We consider an idealised
analytical model of the orbital evolution of BBHs embedded in an AGN accretion
disc. In this framework, the disc-binary interaction increases the orbital
eccentricity and decreases the orbital separation, driving the BBH into a
regime where GW emission eventually leads to coalescence. We compute the
resulting GW merger rate density from this channel based on a weighted average
of the merger timescales of a population of BBHs radially distributed within
the AGN accretion disc. The predicted merger rates broadly lie in the range
. We analyse the
dependence of the merger rate density on both the accretion disc and binary
orbital parameters, emphasising the important role of the orbital eccentricity.
We discuss the astrophysical implications of this particular BBH-in-AGN
formation channel in the broader context of binary evolution scenarios.Comment: accepted for publication in A&
Ultrarelativistic boost of the black ring
We investigate the ultrarelativistic boost of the five-dimensional
Emparan-Reall non-rotating black ring. Following the classical method of
Aichelburg and Sexl, we determine the gravitational field generated by a black
ring moving ``with the speed of light'' in an arbitrary direction. In
particular, we study in detail two different boosts along axes orthogonal and
parallel to the plane of the ring circle, respectively. In both cases, after
the limit one obtains a five-dimensional impulsive pp-wave propagating in
Minkowski spacetime. The curvature singularity of the original static spacetime
becomes a singular source within the wave front, in the shape of a ring or a
rod according to the direction of the boost. In the case of an orthogonal
boost, the wave front contains also a remnant of the original disk-shaped
membrane as a component of the Ricci tensor (which is everywhere else
vanishing). We also analyze the asymptotic properties of the boosted black ring
at large spatial distances from the singularity, and its behaviour near the
sources. In the limit when the singularity shrinks to a point, one recovers the
well known five-dimensional analogue of the Aichelburg-Sexl ``monopole''
solution.Comment: 10 pages, 2 figures, REVTeX 4. v2: added boost in an arbitrary
direction, one new figure, one new reference. To appear in Phys. Rev.
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