1861441
Longitudinal multibunch feedback experiment with switched filter bank
Fast bunch to bunch feedback is necessary to control instabilities caused by coupled bunch oscillations in high intensity machines. A time domain active feedback scheme is discussed with focus on effective error detection using simple analog filters. Fast electronic switches direct each beam bunch signal from a beam pickup to a corresponding filter. The filters are excited at steady states. The output of the filters are steady sine waves tracking the phase and amplitude variations of individual bunches, allowing easy phase comparison with a reference rf signal. Amplitude detection of the signals yields valuable information of higher order beam oscillation modes. The beam motion information is processed and multiplexed to a fast phase or amplitude modulator that drives a wideband kicker. The feedback system can also be used to correct individual bunch oscillations caused by injection errors in larger machines filled by a number of booster cycles.
124338422
FIRST OBSERVATION OF A SNAKE DEPOLARIZING RESONANCE
Using a 104MeV stored polarized proton beam and a full Siberian snake, we recently found evidence for a so-called {open_quotes}snake{close_quotes} depolarizing resonance. A full Siberian snake forces the spin tune {nu}{sub s} to be a half integer. Thus, if the vertical betatron tune {nu}{sub y} is set near a quarter integer, then the {nu}{sub s}=n{plus_minus}2{nu}{sub y} second-order snake resonance can depolarize the beam. Indeed, with a full Siberian snake, we found a deep depolarization dip when {nu}{sub y} was equal to 4.756; moreover, when {nu}{sub y} was changed to 4.781, the deep dip disappeared and the polarization was preserved. {copyright} {ital 1997} {ital The American Physical Society}
120908048
Comment on “Quasiperiodic spin-orbit motion and spin tunes in storage rings”
96454816
Design and fabrication of a multi-purpose Panofsky magnet
A fast, flexible magnet system, consisting of a Panofsky style ferrite picture-frame magnet and pulsed power supply, has been developed. Magnet specifications are: 8 cm /spl times/8 cm aperture, 23 cm length, 500 A pulsed/l60 A DC, and 1 /spl mu/s risetime. Designed for general accelerator physics studies, the magnet may be quickly converted from dipole to quadrupole or sextupole and higher multipole configurations by easily changing winding end terminations. In the quadrupole configuration a field gradient of 0.5 T/m is achieved at 500 A. This magnet has become an important tool for nonlinear beam dynamics experiments at the IUCF Cooler Ring.<<ETX>>
117036088
Comparison of multipole expansion and exact form of the eddy current field of the AGS Booster
Studies are made on magnetic field representation using a multipole expansion as well as the exact form to calculate the magnetic field produced by eddy currents in the vacuum chamber of the AGS Booster as well as the field produced by three turn correction coils attached to the top and bottom of the vacuum chamber. The multiple representation of the chamber field does not converge to the next field when X > 30mm and limits the particle motion. When the exact form of the chamber field is used, initial amplitudes in the horizontal plane (measured at QF) can be nearly as large as the chamber half aperture. Use of three turn correction coils to compensate the eddy current fields seems to reduce rather than increase the acceptance. 6 figs., 3 tabs.
120417645
Snakes and spin rotators for high energy accelerators
Abstract A modification to the continuous family of snake and spin rotators, discovered by Steffen, is discussed. A compact snake configuration is found to have the advantages of requiring a smaller total integrated dipole magnet strength and a smaller transverse displacement for circulating particles. A split snake configuration has the advantage of allowing an entire experimental insertion region to be located between the two halves of the snake. Such configurations could serve as both a snake and a 90° spin rotator for experiments requiring different helicity states. General properties of these snake configurations are discussed.
123360724
Some test results of an anti-Cherenkov photomultiplier tube
Abstract We report on the beam test results of a photomultiplier tube (PMT) specially designed to suppress the signal due to Cherenkov light emitted by window glass when impacted by relativistic charged particles. This signal becomes a concern when it is comparable to the true PMT signal, especially in the case of calorimeters, where the response is at the level of a few photoelectrons per GeV. This design allows for placement of these PMTs behind the calorimeter without concern for hot spots from the Cherenkov background.
118443998
Quarkonium formation time in quark-gluon plasma
The quarkonium formation time in a quark-gluon plasma (QGP) is determined from the space-time correlator of heavy quark vector currents using the quarkonium in-medium mass and wave function obtained from heavy quark potentials extracted from the lattice QCD. It is found that the formation time of a quarkonium increases with the temperature of the QGP and diverges near its dissociation temperature. Also, the quarkonium formation time is longer if the heavy quark potential is taken to be the free energy from lattice calculations for a heavy quark pair, compared to that based on the more negative internal energy.
53130301
Exact third-order density perturbation and one-loop power spectrum in general dark energy models
Abstract Under the standard perturbation theory (SPT), we obtain the fully consistent third-order density fluctuation and kernels for the general dark energy models without using the Einstein–de Sitter (EdS) universe assumption for the first time. We also show that even though the temporal and spatial components of the SPT solutions cannot be separable, one can find the exact solutions to any order in general dark energy models. With these exact solutions, we obtain the less than % error correction of one-loop matter power spectrum compared to that obtained from the EdS assumption for k = 0.1 h Mpc − 1 mode at z = 0 ( 1 , 1.5 ) . Thus, the EdS assumption works very well at this scale. However, if one considers the correction for P 13 , the error is about 6 (9, 11)% for the same mode at z = 0 ( 1 , 1.5 ) . One absorbs P 13 into the linear power spectrum in the renormalized perturbation theory (RPT) and thus one should use the exact solution instead of the approximation one. The error on the resummed propagator N of RPT is about 14 (8, 6)% at z = 0 ( 1 , 1.5 ) for k = 0.4 h Mpc − 1 . For k = 1 h Mpc − 1 , the error correction of the total matter power spectrum is about 3.6 (4.6, 4.5)% at z = 0 ( 1 , 1.5 ) . Upcoming observation is required to archive the sub-percent accuracy to provide the strong constraint on the dark energy and this consistent solution is prerequisite for the model comparison.
116349147
Cluster number counts in quintessence models
Abstract Even though the abundance and evolution of clusters have been used to study the cosmologicalparameters includingthe propertiesof darkenergy owing to their puredependenceon the geometryof the Universe and the power spectrum, it is necessary to pay particular attention to the eﬀectsof dark energy on the analysis. We obtain the explicit dark energy dependent rms linear massﬂuctuation σ 8 which is consistent with the CMB normalization with less than 2 % errors for generalconstant dark energy equation of state, ω Q . Thus, we do not have any degeneracy between σ 8 and the matter energy density contrast Ω 0m . When we use the correct value of the critical densitythreshold δ c = 1.58 obtained recently [30, 31] into the cluster number density n calculation in thePress-Schechter (PS) formalism, n increases as compared to the one obtained by using δ c = 1.69by about 60, 80, and 110 % at z = 0, 0.5, and 1, respectively. Thus, PS formalism predictsthe cluster number consistent with both simulation and observed data at the high mass region.We also introduce the improved coeﬃcients of Sheth-Tormen (ST) formalism, which is consistentwith the recently suggested mass function [36]. We found that changing ω
118595903
Astrophysical implications of a visible dark matter sector from a custodially warped GUT
We explore, within the warped extra dimensional framework, the possibility of finding antimatter signals in cosmic rays (CRs) from dark matter (DM) annihilation. We find that exchange of order 100 GeV radion, an integral part of this class of models, generically results in a sizable Sommerfeld enhancement of the annihilation rate for DM mass at the TeV scale. No ad hoc dark sector is required to obtain boosted annihilation cross sections and hence signals. Such a mild hierarchy between the radion and DM masses can be natural due to the pseudo-Goldstone boson nature of the radion. We study the implications of a Sommerfeld enhancement specifically in warped grand unified theory (GUT) models, where proton stability implies a DM candidate. We show, via a partially unified Pati-Salam group, how to incorporate a custodial symmetry for Z{yields}bb into the GUT framework such that a few TeV Kaluza-Klein (KK) mass scale is allowed by electroweak precision tests. Among such models, the one with the smallest SO(10) (fully unified) representation, with SU(5) hypercharge normalization, allows us to decouple the DM from the electroweak gauge bosons. Thus, a correct DM relic density can be obtained and direct detection bounds are satisfied. Looking at robust CRmore » observables, we find a possible future signal in the p/p flux ratio consistent with current constraints. Using a different choice of representations, we show how to embed in this GUT model a similar custodial symmetry for the right-handed tau, allowing it to be strongly coupled to KK particles. Such a scenario might lead to an observed signal in CR positrons; however, the DM candidate in this case cannot constitute all of the DM in the Universe. As an aside and independent of the GUT or DM model, the strong coupling between KK particles and tau's can lead to striking LHC signals.« less