Transverse Beam Transfer Functions of Colliding Beams in RHIC

We use transverse beam transfer functions to measure tune distributions of colliding beams in RHIC. The tune has a distribution due to the beam-beam interaction, nonlinear magnetic fields - particularly in the interaction region magnets, and non-zero chromaticity in conjunction with momentum spread. The measured tune distributions are compared with calculations

Determination of the geometry of the PSR B1913+16 system by geodetic precession

New observations of the binary pulsar B1913+16 are presented. Since 1978 the leading component of the pulse profile has weakend dramatically by about 40%. For the first time, a decrease in component separation is observed, consistent with expectations of geodetic precession. Assuming the correctness of general relativity and a circular hollow-cone like beam, a fully consistent model for the system geometry is developed. The misalignment angle between pulsar spin and orbital momentum is determined giving direct evidence for an asymmetric kick during the second supernova explosion. It is argued that the orbital inclination angle is 132\fdg8 (rather than 47\fdg2). A prediction of this model is that PSR B1913+16 will not be observable anymore after the year 2025.Comment: 16 pages, incl. 5 figures, accepted for publication in Ap

Electron cloud instabilities in the Proton Storage Ring andSpallation Neutron Source

Electron cloud instabilities in the Los Alamos ProtonStorage Ring (PSR) and those foreseen forthe Oak Ridge SpallationNeutron Source (SNS) are examined theoretically, numerically, andexperimentally

Radio Emission by Particles due to Pulsar Spin

We present a relativistic model for the motion of charged particles in rotating magnetic field lines projected on to a plane perpendicular to the rotation axis. By making an approximation that the projected field lines are straight, an analytical expression is obtained for the particle trajectory. The motive behind developing this model is to elucidate some of the effects of rotation in pulsar profiles. There is a significant contribution to the curvature of particle trajectory due to the rotation of pulsar, which is in addition to the inherent curvature of the field lines. The asymmetry in the observed pulse shapes can be explained by considering the aberration-retardation effects. The single sign circular polarization that has been observed in many pulsars, might be due to the relative orientation of sight line with respect to the particle trajectory plane.Comment: 19 pages, 6 figues. Submitted to Astronomy and Astrophysic

Unusual profile variations in pulsar PSR J1022+1001 -- Evidence for magnetospheric "return currents"?

We report a detailed multi-frequency study of significant instabilities observed in the average pulse profile of the 16-millisecond pulsar PSR J1022+1001. These unusual profile variations which are seen as a function of time and of radio frequency are clearly different from classical profile mode-changing. We also note discrete jumps in the polarisation position angle curve of this pulsar which are remarkably coincident with the unstable profile component. We propose that these jumps, as well as the instability of the pulse profile, are due to magnetospheric return currents. This would allow us to measure the basic properties of the magnetospheric plasma for the very first time.Comment: Accepted for publication in Astronomy & Astrophysic

Dynamics of Charged Particles in the Radio Emission Region of Pulsar Magnetosphere

We consider the classical picture of three dimensional motion of charged particles in pulsar magnetosphere. We adopt a perturbative method to solve the equation of motion, and find the trajectory of particles as they move along the rotating dipolar magnetic field lines. Our aim is to study the influence of rotation on the pulsar radio emission by considering the constrained motion of particles along the open dipolar magnetic field lines. We find that the rotation induces a significant curvature into the particle trajectories. Our model predicts the intensity on leading side dominates over that of trailing side. We expect that if there is any curvature induced radio emission from the region close to the magnetic axis then it must be due to the rotation induced curvature. Our model predicts the radius--to--frequency mapping (RFM) in the core emissions.Comment: 16 pages, 11 figures, Accepted for publication in Astronomy and Astrophysics (2007

PSRs J0248+6021 and J2240+5832: Young Pulsars in the Northern Galactic Plane. Discovery, Timing, and Gamma-ray observations

Pulsars PSR J0248+6021 (rotation period P=217 ms and spin-down power Edot = 2.13E35 erg/s) and PSR J2240+5832 (P=140 ms, Edot = 2.12E35 erg/s) were discovered in 1997 with the Nancay radio telescope during a northern Galactic plane survey, using the Navy-Berkeley Pulsar Processor (NBPP) filter bank. GeV gamma-ray pulsations from both were discovered using the Fermi Large Area Telescope. Twelve years of radio and polarization data allow detailed investigations. The two pulsars resemble each other both in radio and in gamma-ray data. Both are rare in having a single gamma-ray pulse offset far from the radio peak. The high dispersion measure for PSR J0248+6021 (DM = 370 pc cm^-3) is most likely due to its being within the dense, giant HII region W5 in the Perseus arm at a distance of 2 kpc, not beyond the edge of the Galaxy as obtained from models of average electron distributions. Its high transverse velocity and the low magnetic field along the line-of-sight favor this small distance. Neither gamma-ray, X-ray, nor optical data yield evidence for a pulsar wind nebula surrounding PSR J0248+6021. The gamma-ray luminosity for PSR J0248+6021 is L_ gamma = (1.4 \pm 0.3)\times 10^34 erg/s. For PSR J2240+5832, we find either L_gamma = (7.9 \pm 5.2) \times 10^34 erg/s if the pulsar is in the Outer arm, or L_gamma = (2.2 \pm 1.7) \times 10^34 erg/s for the Perseus arm. These luminosities are consistent with an L_gamma ~ sqrt(Edot) rule. Comparison of the gamma-ray pulse profiles with model predictions, including the constraints obtained from radio polarization data, favor emission in the far magnetosphere. These two pulsars differ mainly in their inclination angles and acceleration gap widths, which in turn explains the observed differences in the gamma-ray peak widths.Comment: 13 pages, Accepted to Astronomy & Astrophysic

Recent RHIC in-situ coating technology developments

To rectify the problems of electron clouds observed in RHIC and unacceptable ohmic heating for superconducting magnets that can limit future machine upgrades, we started developing a robotic plasma deposition technique for $in-situ$ coating of the RHIC 316LN stainless steel cold bore tubes based on staged magnetrons mounted on a mobile mole for deposition of Cu followed by amorphous carbon (a-C) coating. The Cu coating reduces wall resistivity, while a-C has low SEY that suppresses electron cloud formation. Recent RF resistivity computations indicate that 10 {\mu}m of Cu coating thickness is needed. But, Cu coatings thicker than 2 {\mu}m can have grain structures that might have lower SEY like gold black. A 15-cm Cu cathode magnetron was designed and fabricated, after which, 30 cm long samples of RHIC cold bore tubes were coated with various OFHC copper thicknesses; room temperature RF resistivity measured. Rectangular stainless steel and SS discs were Cu coated. SEY of rectangular samples were measured at room; and, SEY of a disc sample was measured at cryogenic temperatures.Comment: 8 pages, contribution to the Joint INFN-CERN-EuCARD-AccNet Workshop on Electron-Cloud Effects: ECLOUD'12; 5-9 Jun 2012, La Biodola, Isola d'Elba, Ital

A new technique for timing the double pulsar system

In 2004, McLaughlin et al. discovered a phenomenon in the radio emission of PSR J0737-3039B (B) that resembles drifting sub-pulses. The repeat rate of the sub-pulses is equal to the spin frequency of PSR J0737-3039A (A); this led to the suggestion that they are caused by incidence upon B's magnetosphere of electromagnetic radiation from A. Here we describe a geometrical model which predicts the delay of B's sub-pulses relative to A's radio pulses. We show that measuring these delays is equivalent to tracking A's rotation from the point of view of an hypothetical observer located near B. This has three main astrophysical applications: (a) to determine the sense of rotation of A relative to its orbital plane; (b) to estimate where in B's magnetosphere the radio sub-pulses are modulated and (c) to provide an independent estimate of the mass ratio of A and B. The latter might improve existing tests of gravitational theories using this system.Comment: Accepted for publication in MNRAS. 9 pages in emulated MNRAS format, 3 figure