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.
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.
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.
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.
119539356
The PEP II injection kicker system
PEP II or the B-Factory consists of two asymmetric storage rings. The injection energy for electrons is 9 GeV, while that for positrons is 3.1 GeV. The bend angle into the high energy ring (HER) is 0.35 m-rad, and the angle into the low energy ring (LER) is 0.575 m-rad. The magnetic length for the HER kicker is 0.85 m, and 0.55 m for the LER kicker. The field produced by the magnet is therefore 123.5 G for the HER, and 132 G for the LER. Each ring has a kicker magnet upstream of the injection line which is used to distort the orbit of the stored beam. An identical magnet downstream of the injection line is used to restore the orbit of the stored beam and inject the incoming beam. The two magnets are driven in parallel by the modulator. The aperture of the magnets is 3.86/spl times/3.46 cm (H/spl times/V). Therefore the current required to drive the HER is 863 A, while for the LER it is 756 A. The inductance of the magnet is approximately 1.4 /spl mu/H/m. The current pulse is a critically damped sinusoid with a rise time of less than 300 ns. A kicker system has been designed which can be used for injection of both beams by varying the charge voltage. The modulator uses a conjugate circuit to match the impedance of the magnet, and coupling to the beam chamber.
1690982
Gate drive for high speed, high power IGBTs
A new gate drive for high-voltage, high-power IGBT has been developed for the SLAC NLC (Next Linear Collider) Solid State Induction Modulator. This paper describes the design and implementation of a driver that allows an IGBT module rated at 800 A/3300 V to switch up to 3000 A at 2200 V in 3 /spl mu/s with a rate of current rise of more than 10000 A//spl mu/s, while still being short circuit protected. Issues regarding fast turn on, high de-saturation voltage detection, and low short circuit peak current are presented. A novel approach is also used to counter the effect of unequal current sharing between parallel chips inside most high-power IGBT modules. It effectively reduces the collector-emitter peak currents and thus protects the IGBT from being destroyed during soft short circuit conditions at high di/dt.
56475409
The injection kicker system for the muon g-2 experiment
The muon g-2 experiment is designed to measure the anomalous magnetic moment of the muon to an accuracy of 0.35 ppm by measuring the difference between the spin precession frequency and the cyclotron frequency of the particle in a known magnetic field. The injection kicker is designed to deflect 3.094 GeV/c muons by an angle of 10 mrad into a storage ring with a radius of 7.112 m. No magnetic materials can be used in or near the beam line because of the high precision with which the field of the main dipole magnets must be known. Eddy currents induced in the vacuum chamber by the fast kicker pulse, and their effect on the main dipole field must also be considered. An air core magnet which is driven by an underdamped capacitor discharge modulator using a spark gap switch has been designed. This design, as well as test data, will be presented.
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.