397875
Revising the multipole moments of numerical spacetimes and its consequences.
Identifying the relativistic multipole moments of a spacetime of an astrophysical object that has been constructed numerically is of major interest, both because the multipole moments are intimately related to the internal structure of the object, and because the construction of a suitable analytic metric that mimics a numerical metric should be based on the multipole moments of the latter one in order to yield a reliable representation. In this Letter, we show that there has been a widespread delusion in the way the multipole moments of a numerical metric are read from the asymptotic expansion of the metric functions. We show how one should read correctly the first few multipole moments (starting from the quadrupole mass moment) and how these corrected moments improve the efficiency of describing the metric functions with analytic metrics that have already been used in the literature, as well as other consequences of using the correct moments.
22467228
Effectively universal behavior of rotating neutron stars in general relativity makes them even simpler than their Newtonian counterparts.
Recently, it was shown that slowly rotating neutron stars exhibit an interesting correlation between their moment of inertia I, their quadrupole moment Q, and their tidal deformation Love number λ (the I-Love-Q relations), independently of the equation of state of the compact object. In the present Letter a similar, more general, universality is shown to hold true for all rotating neutron stars within general relativity; the first four multipole moments of the neutron star are related in a way independent of the nuclear matter equation of state we assume. By exploiting this relation, we can describe quite accurately the geometry around a neutron star with fewer parameters, even if we don't know precisely the equation of state. Furthermore, this universal behavior displayed by neutron stars could promote them to a more promising class of candidates (next to black holes) for testing theories of gravity.
73697159
An all-purpose metric for the exterior of any kind of rotating neutron star
We have tested the appropriateness of two-soliton analytic metric to describe the exterior of all types of neutron stars, no matter what their equation of state or rotation rate is. The particular analytic solution of the vacuum Einstein equations proved quite adjustable to mimic the metric functions of all numerically constructed neutron star models that we used as a testbed. The neutron star models covered a wide range of stiffness, with regard to the equation of state of their interior, and all rotation rates up to the maximum possible rotation rate allowed for each such star. Apart from the metric functions themselves, we have compared the radius of the innermost stable circular orbit RISCO, the orbital frequency � ≡ dφ dt of circular geodesics, and their epicyclic frequencies � ρ, � z, as well as the change of the energy of circular orbits per logarithmic change of orbital frequency � ˜ E. All these quantities, calculated by means of the two-soliton analytic metric, fitted with good accuracy the corresponding numerical ones as in previous analogous comparisons (although previous attempts were restricted to neutron star models with either high or low rotation rates). We believe that this particular analytic solution could be considered as an analytic faithful representation of the gravitation field of any rotating neutron star with such accuracy, that one could explore the interior structure of a neutron star by using this space–time to interpret observations of astrophysical processes that take place around it.
117876454
Multipole Moments of numerical spacetimes
In this article we present some recent results on identifying correctly the relativistic multipole moments of numerically constructed spacetimes, and the consequences that this correction has on searching for appropriate analytic spacetimes that can approximate well the previously mentioned numerical spacetimes. We also present expressions that give the quadrupole and the spin octupole as functions of the spin parameter of a neutron star for various equations of state and in a range of masses for every equation of state used. These results are relevant for describing the exterior spacetime of rotating neutron stars that are made up of matter obeying realistic equations of state.
119297500
Effective No-Hair Relations for Neutron Stars and Quark Stars: Relativistic Results
Astrophysical charge-free black holes are known to satisfy no-hair relations through which all multipole moments can be specified in terms of just their mass and spin angular momentum. We here investigate the possible existence of no-hair-like relations among multipole moments for neutron stars and quark stars that are independent of their equation of state. We calculate the multipole moments of these stars up to hexadecapole order by constructing uniformly-rotating and unmagnetized stellar solutions to the Einstein equations. For slowly-rotating stars, we construct stellar solutions to quartic order in spin in a slow-rotation expansion, while for rapidly-rotating stars, we solve the Einstein equations numerically with the LORENE and RNS codes. We find that the multipole moments extracted from these numerical solutions are consistent with each other. We confirm that the current-dipole is related to the mass-quadrupole in an approximately equation of state independent fashion, which does not break for rapidly rotating neutron stars or quark stars. We further find that the current-octupole and the mass-hexadecapole moments are related to the mass-quadrupole in an approximately equation of state independent way to $\sim 10%$, worsening in the hexadecapole case. All of our findings are in good agreement with previous work that considered stellar solutions to leading-order in a weak-field expansion. The quartic in spin, slowly-rotating solutions found here allow us to estimate the systematic errors in the measurement of the neutron star's mass and radius with future X-ray observations, such as NICER and LOFT. We find that the effect of these quartic-in-spin terms on the quadrupole and hexadecapole moments and stellar eccentricity may dominate the error budget for very rapidly-rotating neutron stars. The new universal relations found here should help to reduce such systematic errors.
109002909
Preliminary testing of the LEB to MEB transfer kicker modulator prototype
The extraction kicker for the Low Energy Booster (LEB) is used to deflect a 12 GeV/c proton beam from the synchrotron into a transfer line. A kicker system of similar design is used to inject the beam from the transfer line into the Medium Energy Booster (MEB). The modulator requirements for these kicker systems are to deliver a pulse train of seven 1.6 kA, 2.5 /spl mu/s pulses at a pulse-repetition frequency of 10 pps, every seven seconds for one hour. The impedance of the modulator is 12.5 /spl Omega/ resulting in a charge voltage of 40 kV. The 10-90% rise time of the pulses is 20 ns, and the 1-99% fall time is 2 /spl mu/s. The allowable pulse ripple is /spl plusmn/1% of the peak current during the pulse, and /spl plusmn/0.3% from pulse to pulse. The shot to-shot timing jitter requirement is less than 2ns. This paper describes the design and performance of the prototype modulator which was fabricated to meet these specifications.<<ETX>>
109841692
A solid state induction modulator for SLAC NLC
The Next Linear Collider accelerator proposal at SLAC requires a high efficiency, highly reliable, and low cost pulsed-power modulator to drive the 500 KV, 260A X band klystrons. With a pulse width of less than 1.5 microseconds, it is difficult for the present SLAC type modulator with conventional pulse transformer to have a high efficiency due primarily to the inherently slow rise and fall time of the video pulse. The proposed induction modulator utilises a pulse transformer similar to an induction accelerator driven by solid state high voltage IGBTs. The performance of the IGBTs, induction cores and a low voltage model will be discussed as well as the design and construction of a prototype modulator capable of driving up to 8 of the X band klystrons.
107741742
Kicker magnet systems for injector synchrotrons
A kicker magnet is a device capable of producing a pulsed magnetic field for the purpose of deflecting charged particle beams out of their defined orbit. The kicker magnets at the Superconducting Super Collider (SSC) Laboratory are designed to transfer beam bunches from a series of three booster stages into a counter-rotating 20 TeV collider ring. The required kicker magnetic field is the result of factors such as bunch spacing, maximum allowable lost bunches, required angular deflection, and other characteristics of synchrotron operation.
15700414
Diagnosing the PEP-II Injection System
The injection of beam into the PEP-II B-Factory, especially into the High Energy Ring (HER) has some challenges. A high background level in the BaBar detector has for a while inhibited us from trickling charge into the HER similar to the Low Energy Ring (LER). Analyzing the injection system has revealed many issues which could be improved. The injection bump between two kickers was not closed, mainly because the phase advance wasn't exactly 180{sup o} and the two kicker strengths were not balanced. Additionally we found reflections which kick the stored beam after the main kick and cause the average luminosity to drop about 3% for a 10 Hz injection rate. The strength of the overall kick is nearly twice as high as the design, indicating a much bigger effective septum thickness. Compared with single beam the background is worse when the HER beam is colliding with the LER beam. This hints that the beam-beam force and the observed vertical blow-up in the HER pushes the beam and especially the injected beam further out to the edge of the dynamic aperture or beyond.
56510022
The RHIC injection fast kicker
The purpose of the injection kicker is to provide the ultimate deflection to the incoming beam from the Alternating Gradient Synchrotron (AGS) into the Relativistic Heavy Ion Collider (RHIC). The beam is kicked in the vertical direction to place it on the equilibrium orbit of RHIC. Each bunch in the AGS is transferred separately, and stacked box-car fashion in the appropriate RHIC RF bucket. In order to achieve the required deflection angle four magnets powered by four pulsers will be used for each ring of RHIC. When the bunches are stacked in RHIC the last few RF buckets are left unfilled in order to provide a gap in the beam to facilitate the ejection or beam abort process. This also means there is not a severe constraint on the fall-time of the injection kicker. One prototype pulser has been built and tested. Much of the development effort has gone into the magnet design. Although lumped ferrite magnets are simpler to build and require less power to reach full field a transmission line magnet was developed because of the very fast rise-time requirement and the tolerances imposed on the field variation and ripple.