17 research outputs found
The Influence of Longitudinal Space Charge Fields on the Modulation Process of Coherent Electron Cooling
The initial modulation in the scheme for Coherent electron Cooling (CeC)
rests on the screening of the ion charge by electrons. However, in a CeC system
with a bunched electron beam, inevitably, a long-range longitudinal space
charge force is introduced. For a relatively dense electron beam, its force can
be comparable to, or even greater than the attractive force from the ions.
Hence, the influence of the space charge field on the modulation process could
be important. If the 3-D Debye lengths are much smaller than the extension of
the electron bunch, the modulation induced by the ion happens locally. Then, in
that case, we can approximate the long-range longitudinal space charge field as
a uniform electric field across the region. As detailed in this paper, we
developed an analytical model to study the dynamics of ion shielding in the
presence of a uniform electric field. We solved the coupled Vlasov-Poisson
equation system for an infinite anisotropic electron plasma, and estimated the
influences of the longitudinal space charge field to the modulation process for
the experimental proof of the CeC principle at RHIC.Comment: 23 pages, 11 figures, single colum
High-precision geometry of a double-pole pulsar
High time resolution observations of PSR B0906-49 (or PSR J0908-4913) over a
wide range of frequencies have enabled us to determine the geometry and beam
shape of the pulsar. We have used the position angle traverse to determine
highly-constrained solutions to the rotating vector model which show
conclusively that PSR B0906-49 is an orthogonal rotator. The accuracy obtained
in measuring the geometry is unprecedented. This may allow tests of high-energy
emission models, should the pulsar be detected with GLAST. Although the impact
parameter, beta, appears to be frequency dependent, we have shown that this is
due to the effect of interstellar scattering. As a result, this pulsar provides
some of the strongest evidence yet that the position angle swing is indeed
related to a geometrical origin, at least for non-recycled pulsars. We show
that the beam structures of the main pulse and interpulse in PSR B0906-49 are
remarkably similar. The emission comes from a height of ~230 km and is
consistent with originating in a patchy cone located about half way to the last
open field lines. The rotation axis and direction of motion of the pulsar
appear to be aligned.Comment: accepted for publication in MNRAS, 7 pages, 4 figure
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
Status of Muon Collider Research and Development and Future Plans
The status of the research on muon colliders is discussed and plans are
outlined for future theoretical and experimental studies. Besides continued
work on the parameters of a 3-4 and 0.5 TeV center-of-mass (CoM) energy
collider, many studies are now concentrating on a machine near 0.1 TeV (CoM)
that could be a factory for the s-channel production of Higgs particles. We
discuss the research on the various components in such muon colliders, starting
from the proton accelerator needed to generate pions from a heavy-Z target and
proceeding through the phase rotation and decay ()
channel, muon cooling, acceleration, storage in a collider ring and the
collider detector. We also present theoretical and experimental R & D plans for
the next several years that should lead to a better understanding of the design
and feasibility issues for all of the components. This report is an update of
the progress on the R & D since the Feasibility Study of Muon Colliders
presented at the Snowmass'96 Workshop [R. B. Palmer, A. Sessler and A.
Tollestrup, Proceedings of the 1996 DPF/DPB Summer Study on High-Energy Physics
(Stanford Linear Accelerator Center, Menlo Park, CA, 1997)].Comment: 95 pages, 75 figures. Submitted to Physical Review Special Topics,
Accelerators and Beam
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Electron Cloud Mitigation in the Spallation Neutron Source Ring
The Spallation Neutron Source (SNS) accumulator ring is designed to accumulate, via H{sup -} injection, protons of 2 MW beam power at 1 GeV kinetic energy at a repetition rate of 60 Hz [1]. At such beam intensity, electron-cloud is expected to be one of the intensity-limiting mechanisms that complicate ring operations. This paper summarizes mitigation strategy adopted in the design, both in suppressing electron-cloud formation and in enhancing Landau damping, including tapered magnetic field and monitoring system for the collection of stripped electrons at injection, TiN coated beam chamber for suppression of the secondary yield, clearing electrodes dedicated for the injection region and parasitic on BPMs around the ring, solenoid windings in the collimation region, and planning of vacuum systems for beam scrubbing upon operation
Electric dipole moments and the search for new physics
Static electric dipole moments of nondegenerate systems probe mass scales for
physics beyond the Standard Model well beyond those reached directly at high
energy colliders. Discrimination between different physics models, however,
requires complementary searches in atomic-molecular-and-optical, nuclear and
particle physics. In this report, we discuss the current status and prospects
in the near future for a compelling suite of such experiments, along with
developments needed in the encompassing theoretical framework.Comment: Contribution to Snowmass 2021; updated with community edits and
endorsement
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VLHC accelerator physics
A six-month design study for a future high energy hadron collider was initiated by the Fermilab director in October 2000. The request was to study a staged approach where a large circumference tunnel is built that initially would house a low field ({approx}2 T) collider with center-of-mass energy greater than 30 TeV and a peak (initial) luminosity of 10{sup 34} cm{sup -2}s{sup -1}. The tunnel was to be scoped, however, to support a future upgrade to a center-of-mass energy greater than 150 TeV with a peak luminosity of 2 x 10{sup 34} cm{sup -2} sec{sup -1} using high field ({approx} 10 T) superconducting magnet technology. In a collaboration with Brookhaven National Laboratory and Lawrence Berkeley National Laboratory, a report of the Design Study was produced by Fermilab in June 2001. 1 The Design Study focused on a Stage 1, 20 x 20 TeV collider using a 2-in-1 transmission line magnet and leads to a Stage 2, 87.5 x 87.5 TeV collider using 10 T Nb{sub 3}Sn magnet technology. The article that follows is a compilation of accelerator physics designs and computational results which contributed to the Design Study. Many of the parameters found in this report evolved during the study, and thus slight differences between this text and the Design Study report can be found. The present text, however, presents the major accelerator physics issues of the Very Large Hadron Collider as examined by the Design Study collaboration and provides a basis for discussion and further studies of VLHC accelerator parameters and design philosophies
Two particle model for studying the effects of space-charge force on strong head-tail instabilities
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