High current cavity design at BNL
In order to meet the requirements of high average current accelerators, such as the Superconducting Proton Linac (SPL) at CERN and the electron–ion collider, (MeRHIC) at BNL, a high current 5-cell Nb superconducting cavity, called BNL3 cavity, was optimized and designed. The optimization process aimed at maximizing the R / Q of the fundamental mode and the geometry factor G under an acceptable RF field level of B peak / E acc or E peak / E acc . In addition, a pivotal consideration for the high current accelerators is efficient damping of dangerous Higher-Order Modes (HOM) to avoid inducing emittance degradation, cryogenic loading or Beam-Break-Up (BBU). To transport the HOMs out of the cavity, the BNL3 cavity employs a larger beam pipe, allowing the propagation of HOMs but not the fundamental mode. Moreover, concerning the BBU effect, the BNL3 cavity is aimed at low ( R / Q ) Q ext for dangerous modes, including dipole modes and quadrupole modes. This paper presents the design of the BNL3 cavity, including the optimization for the fundamental mode, and the BBU limitation for dipole and quadrupole modes. The BBU simulation results show that the designed cavity is qualified for high-current, multi-pass machines such as MeRHIC and by-product light source.

title: High Current SRF Cavity Design for SPL and eRHIC
abstract: A high current five-cell Nb superconducting cavity, called BNL3 cavity, was optimized and designed for the SPL and eRHIC. For the fundamental mode, the optimization process aimed at maximizing the R/Q of the fundamental mode and the geometry factor G under an acceptable RF field ratio level of B{sub peak}/E{sub acc} and E{sub peak}/E{sub acc}. For higher order modes, the optimization is to lower (R/Q)Q{sub ext} for dipole and quadrupole modes to suppress the beam-break-up (BBU). To extract the HOM power out of the cavity, the BNL3 cavity employs a larger beam pipe, allowing the propagation of HOMs, but not the fundamental mode. Six HOM couplers (three at each end) are used to extract large HOM power. To avoid the cross-talk between cavities, tapers are employed between the cavities. This paper presents the design of the BNL3 cavity, end groups and BBU simulation results.

title: Multipacting simulation and test results of BNL 704 MHz SRF gun
abstract: The BNL 704MHz SRF gun has a grooved choke joint to support the photo-cathode. Due to the distortion of grooves at the choke joint during the BCP for the choke joint, several multipacting barriers showed up when it was tested with Nb cathode stalk at JLab. We built a setup to use the spare large grain SRF cavity to test and condition the multipacting at BNL with various power sources up to 50kW. The test is carried out in three stages: testing the cavity performance without cathode, testing the cavity with the Nb cathode stalk that was used at Jlab, and testing the cavity with a copper cathode stalk that is based on the design for the SRF gun. This paper summarizes the results of multipacting simulation, and presents the large grain cavity test setup and the test results.

title: HOM identification by bead pulling in the Brookhaven ERL cavity
abstract: Exploratory measurements of the Brookhaven Energy Recovery Linac (ERL) cavity at superconducting temperature produced a long list of high order modes (HOMs). The niobium 5-cell cavity is terminated at each end with HOM ferrite dampers that successfully reduce the Q -factors to levels required to avoid beam break up (BBU) instabilities. However, a number of un-damped resonances with Q ≥10 6 were found at 4 K and their mode identification forms the focus of this paper. The approach taken here consists of bead pulling on a copper (Cu) replica of the ERL cavity with dampers involving various network analyzer measurements. Several different S 21 transmission measurements are used, including those taken from the fundamental input coupler to the pick-up probe across the cavity, others between beam-position monitor probes in the beam tubes, and also between probes placed into the cells. The bead pull technique suitable for HOM identification with a metallic needle or dielectric bead is detailed. This paper presents the results for HOMs in the first two dipole bands, the un-damped modes in the first quadrupole band, and the identification of several high- Q modes beyond.

title: High-energy high-luminosity electron-ion collider eRHIC
abstract: Joanne Beebe-Wang, Sergey Belomestnykh, Michael M. Blaskiewicz, Rama Calaga, XiangyunChang, Alexei Fedotov, David Gassner, Harald Hahn, Ping He, William Jackson, Animesh Jain,Elliott C.Johnson, Dmitry Kayran, Jorg Kewisch, Yun Luo, George Mahler, Gary McIntyre, WuzhengMeng, Michiko Minty, Brett Parker, Alexander Pikin, Vadim Ptitsyn, Triveni Rao, Thomas Roser, JohnSkaritka, Brian Sheehy, Steven Tepikian, Yatming Than, Dejan Trbojevic, Nicholaos Tsoupas, JosephTuozzolo, Gang Wang, Qiong Wu, Wencan Xu, and Anatoly Zelenski

title: BNl 703 MHz superconducting RF cavity testing
abstract: The BNL 5-cell, 703 MHz superconducting accelerating cavity has been installed in the high-current ERL experiment. This experiment will function as a proving ground for the development of high-current machines in general and is particularly targeted at beam development for an electron-ion collider (eRHIC). The cavity performed well in vertical tests, demonstrating gradients of 20 MV/m and a Q{sub 0} of 1e10. Here we will present its performance in the horizontal tests, and discuss technical issues involved in its implementation in the ERL.

title: Energy and system-size dependence of two- and four-particle $v_2$ measurements in heavy-ion collisions at RHIC and their implications on flow fluctuations and nonflow
abstract: We present STAR measurements of azimuthal anisotropy by means of the two- and four-particle cumulants $v_2$ ($v_2\{2\}$ and $v_2\{4\}$) for Au+Au and Cu+Cu collisions at center of mass energies $\sqrt{s_{_{\mathrm{NN}}}} = 62.4$ and 200 GeV. The difference between $v_2\{2\}^2$ and $v_2\{4\}^2$ is related to $v_{2}$ fluctuations ($\sigma_{v_2}$) and nonflow $(\delta_{2})$. We present an upper limit to $\sigma_{v_2}/v_{2}$. Following the assumption that eccentricity fluctuations $\sigma_{\epsilon}$ dominate $v_2$ fluctuations $\frac{\sigma_{v_2}}{v_2} \approx \frac{\sigma_{\epsilon}}{\epsilon}$ we deduce the nonflow implied for several models of eccentricity fluctuations that would be required for consistency with $v_2\{2\}$ and $v_2\{4\}$. We also present results on the ratio of $v_2$ to eccentricity.

title: The high transverse momentum non-photonic electron measurements in Au + Au collisions at sNN = 200 GeV at RHIC
abstract: We present preliminary results of Non-Photonic Electron (NPE) production, NPE-hadron azimuthal correlation as well as NPE elliptic flow studies at midrapidity using a data set with high statistics and low photon conversion background from Au + Au collisions at sNN = 200 GeV collected at RHIC in Run 2010.

title: Three-particle coincidence of the long range pseudorapidity correlation in high energy nucleus-nucleus collisions.
abstract: We report the first three-particle coincidence measurement in pseudorapidity (Δη) between a high transverse momentum (p⊥) trigger particle and two lower p⊥ associated particles within azimuth |Δϕ|<0.7 in square root of s(NN)=200 GeV d+Au and Au+Au collisions. Charge ordering properties are exploited to separate the jetlike component and the ridge (long range Δη correlation). The results indicate that the correlation of ridge particles are uniform not only with respect to the trigger particle but also between themselves event by event in our measured Δη. In addition, the production of the ridge appears to be uncorrelated to the presence of the narrow jetlike component.

title: Accelerating BTZ spacetime
abstract: An exact solution of (2 + 1)-dimensional Einstein gravity with a cosmological constant is studied. The corresponding spacetime is interpreted as an accelerating BTZ spacetime. The proper acceleration, horizon structure, temperature and entropy are presented in detail. The metric being studied is very similar to the one studied by Astorino (2011 ) but the range of parameters is different which results in significant changes in the causal structures.

title: New class of rotating perfect fluid black holes in three dimensional gravity
abstract: We obtain a new class of rotating black holes for Einstein theory with perfect fluid source in $$(2+1)$$(2+1) dimensions. We conclude that these black hole solutions only depend on the variable of the angular velocity $$m(r)$$m(r). Some examples of these black holes are given explicitly. In particular, an unknown static black hole in this special background is obtained. In addition, the general properties including the horizon structure, energy conditions and equation of state, mass, and angular momentum are explained in detail.