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A 56 MHz superconducting rf cavity was designed and installed in the Relativistic Heavy Ion Collider (RHIC). It is the first superconducting quarter wave resonator (QWR) operating in a high-energy storage ring. We discuss herein a design of the cavity and its key components and the cavity operation withAu+Aucollisions, and with asymmetricalAu+He3collisions. The cavity is a storage cavity, meaning that it becomes active only at the energy of the experiment, after the acceleration cycle is completed. Without beam, the cavity reached 1.93 MV and aQ0of3.0×108after helium conditioning. The cavity voltage was limited at 300 kV with beam operation due to heating in the Higher Order Mode (HOM) coupler. With the cavity operating at 300 kV, an improvement in luminosity was detected from direct measurements, and the bunch length has been reduced. The uniqueness of the QWR necessitated development of an innovative design of the higher order mode dampers with high-pass filters, and a distinctive fundamental mode damper that enables the cavity to be transparent to the beam during acceleration.

Effects of the chromaticity on head-tail instabilities for broadband impedances are comprehensively studied, using the two particle model, the Vlasov analysis and computer simulations. We show both in the two particle model and the Vlasov analysis with the trapezoidal (semiconstant) wake model that we can derive universal contour plots for the growth factor as a function of the two dimensionless parameters: the wakefield strength, ϒ , and the difference of the betatron phase advances between the head and the tail, χ . They reveal how the chromaticity affects strong head-tail instabilities and excites head-tail instabilities. We also apply the LEP (Large Electron-Positron Collider) broadband resonator model to the Vlasov approach and find that the results are in very good agreement with those of the trapezoidal wake model. The theoretical findings are also reinforced by the simulation results. The trapezoidal wake model turns out to be a very useful tool since it significantly simplifies the time domain analysis and provides well-behaved impedance at the same time.

In this paper, we present a new two particle model for studying the strong head-tail instabilities in the presence of the space-charge force. It is a simple expansion of the well-known two particle model for strong head-tail instability and is still analytically solvable. No chromaticity effect is included. It leads to a formula for the growth rate as a function of the two dimensionless parameters: the space-charge tune shift parameter (normalized by the synchrotron tune) and the wakefield strength, ϒ . The three-dimensional contour plot of the growth rate as a function of those two dimensionless parameters reveals stopband structures. Many simulation results generally indicate that a strong head-tail instability can be damped by a weak space-charge force, but the beam becomes unstable again when the space-charge force is further increased. The new two particle model indicates a similar behavior. In weak space-charge regions, additional tune shifts by the space-charge force dissolve the mode coupling. As the space-charge force is increased, they conversely restore the mode coupling, but then a further increase of the space-charge force decouples the modes again. This mode coupling/decoupling behavior creates the stopband structures.

The Electron-Ion Collider (EIC) will use swap-out injection scheme for the Electron Storage Ring (ESR) to overcome limitations in polarization lifetime. However, the pursuit of highest luminosity with the required 28 nC electron bunches encounters stability challenges in the Rapid Cycling Synchrotron (RCS). One method is to inject multiple RCS bunches into a same ESR bucket. In this paper we perform simulation studies investigating proton emittance growth and electron emittance blowup in this injection scheme. Mitigation strategies are explored. These findings promise enhanced EIC stability and performance, shaping potential future operational improvements.

Flat hadron beam collisions, though expected to enhance peak luminosity by about an order of magnitude, have not yet been demonstrated. Our study reveals a critical limitation: realistic fluctuations, when amplified by synchro-betatron resonance, lead to transverse emittance transfer in flat-beam collisions. Using beam-beam simulations based on Electron-Ion Collider design parameters, we show that this effect leads to vertical emittance growth, which can distort the flat-beam profile and degrade luminosity. We propose a dynamic focusing scheme that combines sextupoles with crab cavities to suppress the hourglass-induced resonance. This approach increases tolerance to fluctuations and improves the robustness of flat-beam collisions. This practical mitigation facilitates the adoption of flat-beam collisions in next-generation lepton-hadron colliders.

In this paper, we describe a future electron-ion collider (EIC), based on the existing Relativistic Heavy Ion Collider (RHIC) hadron facility, with two intersecting superconducting rings, each 3.8 km in circumference. A new ERL accelerator, which provide 5-30 GeV electron beam, will ensure 10^33 to 10^34 cm^-2 s^-1 level luminosity.

Abstract BACKGROUND Deciding where to end a long-segment fusion for adult spinal deformity (ASD) may be a challenge, particularly in the absence of an abnormality at L5/S1. Some suggest prophylactic extension of the construct to the sacrum and/or ilium (S/I) to protect against distal junctional failure, while others support terminating in the lower lumbar spine to preserve motion. OBJECTIVE To compare the risk of re-operation after long-segment fusions for ASD that ends at L4 or L5 (L4/5) vs S/I. METHODS A multicenter database of patients treated for ASD by circumferential minimally invasive surgery or hybrid surgical technique was screened for individuals with long fusions (≥4 vertebral levels) ending at L4 or below and with at least 2 yr of follow-up. Multivariate regression modeling was used to compare surgical morbidity between the L4/5 and S/I groups, and Cox proportional hazard modeling was used to compare risk of re-operation. RESULTS There were 45 subjects with fusion to L4/5 and 71 to S/I. Over a 32-mo median follow-up, 41 re-operations were performed; 6 were for distal junctional failure. In those with normal or mild degeneration at L5/S1, fusion to S/I afforded no significant change in re-operative risk (hazard ratio = 1.18 [95% confidence interval: 0.53-2.62], P = .682). In those undergoing circumferential minimally invasive surgery correction, fusion to S/I was associated with significantly greater blood loss (499.6 cc, P < .001) and surgical time (97.5 min, P = .04). CONCLUSION In the setting of a normal or mildly degenerated L5/S1 disc space, fusion to the sacrum/ilium did not significantly change the risk of requiring a re-operation after a long-segment fusion for ASD.

The Proton EDM Experiment (pEDM) is the first direct search for the proton electric dipole moment (EDM) with the aim of being the first experiment to probe the Standard Model (SM) prediction of any particle EDM. Phase-I of pEDM will achieve \\(10^{-29} e\\cdot\\)cm, improving current indirect limits by four orders of magnitude. This will establish a new standard of precision in nucleon EDM searches and offer a unique sensitivity to better understand the Strong CP problem. The experiment is ideally positioned to explore physics beyond the Standard Model (BSM), with sensitivity to axionic dark matter via the signal of an oscillating proton EDM and across a wide mass range of BSM models from \\(\\mathcal{O}(1\\text{GeV})\\) to \\(\\mathcal{O}(10^3\\text{TeV})\\). Utilizing the frozen-spin technique in a highly symmetric storage ring that leverages existing infrastructure at Brookhaven National Laboratory (BNL), pEDM builds upon the technological foundation and experimental expertise of the highly successful Muon $g$$-$$2$ Experiments. With significant R\\&D and prototyping already underway, pEDM is preparing a conceptual design report (CDR) to offer a cost-effective, high-impact path to discovering new sources of CP violation and advancing our understanding of fundamental physics. It will play a vital role in complementing the physics goals of the next-generation collider while simultaneously contributing to sustaining particle physics research and training early-career researchers during gaps between major collider operations.

We describe a proposal to search for an intrinsic electric dipole moment (EDM) of the proton with a sensitivity of \\targetsens, based on the vertical rotation of the polarization of a stored proton beam. The New Physics reach is of order \\(10^~3\\)TeV mass scale. Observation of the proton EDM provides the best probe of CP-violation in the Higgs sector, at a level of sensitivity that may be inaccessible to electron-EDM experiments. The improvement in the sensitivity to \\(\\theta_{QCD}\\), a parameter crucial in axion and axion dark matter physics, is about three orders of magnitude.