2,274 research outputs found
Measurement and Compensation of Horizontal Crabbing at the Cornell Electron Storage Ring Test Accelerator
In storage rings, horizontal dispersion in the rf cavities introduces
horizontal-longitudinal (xz) coupling, contributing to beam tilt in the xz
plane. This coupling can be characterized by a "crabbing" dispersion term
{\zeta}a that appears in the normal mode decomposition of the 1-turn transfer
matrix. {\zeta}a is proportional to the rf cavity voltage and the horizontal
dispersion in the cavity. We report experiments at the Cornell Electron Storage
Ring Test Accelerator (CesrTA) where xz coupling was explored using three
lattices with distinct crabbing properties. We characterize the xz coupling for
each case by measuring the horizontal projection of the beam with a beam size
monitor. The three lattice configurations correspond to a) 16 mrad xz tilt at
the beam size monitor source point, b) compensation of the {\zeta}a introduced
by one of two pairs of RF cavities with the second, and c) zero dispersion in
RF cavities, eliminating {\zeta}a entirely. Additionally, intrabeam scattering
(IBS) is evident in our measurements of beam size vs. rf voltage.Comment: 5 figures, 10 page
Measurement of Electron Trapping in the CESR Storage Ring
The buildup of low-energy electrons has been shown to affect the performance
of a wide variety of particle accelerators. Of particular concern is the
persistence of the cloud between beam bunch passages, which can impose
limitations on the stability of operation at high beam current. We have
obtained measurements of long-lived electron clouds trapped in the field of a
quadrupole magnet in a positron storage ring, with lifetimes much longer than
the revolution period. Based on modeling, we estimate that about 7% of the
electrons in the cloud generated by a 20-bunch train of 5.3 GeV positrons with
16-ns spacing and population survive longer than 2.3 s in a
quadrupole field of gradient 7.4 T/m. We have observed a non-monotonic
dependence of the trapping effect on the bunch spacing. The effect of a witness
bunch on the measured signal provides direct evidence for the existence of
trapped electrons. The witness bunch is also observed to clear the cloud,
demonstrating its effectiveness as a mitigation technique.Comment: 6 pages, 9 figures, 28 citation
Beam test of a superconducting cavity for the Fermilab high-brightness electron photo-injector
Aligned Spins: Orbital Elements, Decaying Orbits, and Last Stable Circular Orbit to high post-Newtonian Orders
In this article the quasi-Keplerian parameterisation for the case that spins
and orbital angular momentum in a compact binary system are aligned or
anti-aligned with the orbital angular momentum vector is extended to 3PN
point-mass, next-to-next-to-leading order spin-orbit, next-to-next-to-leading
order spin(1)-spin(2), and next-to-leading order spin-squared dynamics in the
conservative regime. In a further step, we use the expressions for the
radiative multipole moments with spin to leading order linear and quadratic in
both spins to compute radiation losses of the orbital binding energy and
angular momentum. Orbital averaged expressions for the decay of energy and
eccentricity are provided. An expression for the last stable circular orbit is
given in terms of the angular velocity type variable .Comment: 30 pages, 2 figures, v2: update to match published versio
Motion and gravitational wave forms of eccentric compact binaries with orbital-angular-momentum-aligned spins under next-to-leading order in spin-orbit and leading order in spin(1)-spin(2) and spin-squared couplings
A quasi-Keplerian parameterisation for the solutions of second post-Newtonian
(PN) accurate equations of motion for spinning compact binaries is obtained
including leading order spin-spin and next-to-leading order spin-orbit
interactions. Rotational deformation of the compact objects is incorporated.
For arbitrary mass ratios the spin orientations are taken to be parallel or
anti-parallel to the orbital angular momentum vector. The emitted gravitational
wave forms are given in analytic form up to 2PN point particle, 1.5PN spin
orbit and 1PN spin-spin contributions, where the spins are counted of 0PN
order.Comment: 26 pages, 1 figure, published in CQG. Current version: we removed a
remark and clarified the derivation of the orbital element \e_ph
Pharmacological management of spasticity in multiple sclerosis: Systematic review and consensus paper
BACKGROUND AND OBJECTIVES: Treatment of spasticity poses a major challenge given the complex clinical presentation and variable efficacy and safety profiles of available drugs. We present a systematic review of the pharmacological treatment of spasticity in multiple sclerosis (MS) patients. METHODS: Controlled trials and observational studies were identified. Scientific evidence was evaluated according to pre-specified levels of certainty. RESULTS: The evidence supports the use of baclofen, tizanidine and gabapentin as first-line options. Diazepam or dantrolene could be considered if no clinical improvement is seen with the previous drugs. Nabiximols has a positive effect when used as add-on therapy in patients with poor response and/or tolerance to first-line oral treatments. Despite limited evidence, intrathecal baclofen and intrathecal phenol show a positive effect in severe spasticity and suboptimal response to oral drugs. CONCLUSION: The available studies on spasticity treatment offer some insight to guide clinical practice but are of variable methodological quality. Large, well-designed trials are needed to confirm the effectiveness of antispasticity agents and to produce evidence-based treatment algorithms
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