108668588
FODO-Supercell Based Compact Ring Design with Tunable Momentum Compaction and Optimized Dynamic Aperture
A storage ring with tunable momentum compaction has the advantage in achieving different RMS bunch length with similar RF capacity, which is potentially useful for many applications, such as linear collider damping ring and pre-damping ring where injected beam has a large energy spread and a large transverse emittance. A tunable bunch length also makes the commissioning and fine tuning easier in manipulating the single bunch instabilities. In this paper, a compact ring design based on a supercell is presented, which achieves a tunable momentum compaction while maintaining a large dynamic aperture.
119471625
Crab dispersion and its impact on the CERN Large Hadron Collider collimation
European Organization for Nuclear Research (CERN), Geneva, Switzerland(Received 19 October 2009; published 12 March 2010)Crab cavities are proposed to be used for a luminosity upgrade of the Large Hadron Collider (LHC).Crab cavities are rf cavities operated in a transverse dipole mode, which imparts on the beam particles atransverse kick that varies with the longitudinal position along the bunch. The crab cavity introducesanother kind of dispersion to the particles which is z dependent, and thus could complicate the beamdynamics and have an impact on the LHC collimation system. As for LHC, the off-momentum beta-beatand dispersion-beat already compromise the performance of the collimation system; the crab dispersionintroduced by global crab cavities might do the same, and should be carefully evaluated. In this paper, wepresent a deﬁnition for the crab dispersion, and study its impact on the LHC collimation system.
55348092
Beam dynamics aspects of crab cavities in the CERN Large Hadron Collider
Modern colliders bring into collision a large number of bunches to achieve a high luminosity. The long-range beam-beam effects arising from parasitic encounters at such colliders are mitigated by introducing a crossing angle. Under these conditions, crab cavities (CC) can be used to restore effective head-on collisions and thereby to increase the geometric luminosity. Such crab cavities have been proposed for both linear and circular colliders. The crab cavities are rf cavities operated in a transverse dipole mode, which imparts on the beam particles a transverse kick that varies with the longitudinal position along the bunch. The use of crab cavities in the Large Hadron Collider (LHC) may not only raise the luminosity, but it could also complicate the beam dynamics, e.g., crab cavities might not only cancel synchrobetatron resonances excited by the crossing angle but they could also excite new ones, they could reduce the dynamic aperture for off-momentum particles, they could influence the aperture and orbit, also degrade the collimation cleaning efficiency, and so on. In this paper, we explore the principal feasibility of LHC crab cavities from a beam dynamics point of view. The implications of the crab cavities for the LHC optics, analytical and numerical luminositymore » studies, dynamic aperture, aperture and beta beating, emittance growth, beam-beam tune shift, long-range collisions, and synchrobetatron resonances, crab dispersion, and collimation efficiency will be discussed.« less
15369403
A Compact Ring Design with Tunable Momentum Compaction
A storage ring with tunable momentum compaction has the advantage of allowing different RMS bunch lengths to be achieved with similar RF capacity. This is potentially useful for many applications, such as a linear collider damping ring and pre-damping ring where the injected beam has a large energy spread and a large transverse emittance. A tunable bunch length also makes it easier to manipulate single bunch instabilities in commissioning and fine tuning. This paper presents a compact ring design based on a supercell that achieves momentum compaction tunability while maintaining a large dynamic aperture.
17071903
Preliminary study on emittance growth in the LHEC recirculating LINAC
In this paper, we estimate the emittance growth in the LHeC recirculating Linac, the lattice design of which is presented in another paper of IPAC10 proceedings. The possible sources for emittance growth included here are: energy spread from RF acceleration in the SRF (superconducting RF) linac together with large chromatic effects from the lattice, and synchrotron radiation (SR) fluctuations in the recirculating arcs. 6-D multi-particle tracking is launched to calculate the emittance from the statistical point of view. The simulation results are also compared with a theoretical estimation.
18941502
Emittance Growth in the NLCTA First Chicane
In this paper, the emittance growth in the NLCTA (Next Linear Collider Test Accelerator) first chicane region is evaluated by simulation studies. It is demonstrated that the higher order fields of the chicane dipole magnet and the dipole corrector magnet (which is attached on the quadrupoles) are the main contributions for the emittance growth, especially for the case with a large initial emittance ({gamma}{epsilon}{sub 0} = 5 {micro}m for instance). These simulation results agree with the experimental observations.
123608448
Experience of BESIII data production with local cluster and distributed computing model
The BES III detector is a new spectrometer which works on the upgraded high-luminosity collider, BEPCII. The BES III experiment studies physics in the tau-charm energy region from 2 GeV to 4.6 GeV . From 2009 to 2011, BEPCII has produced 106M ψ(2S) events, 225M J/ψ events, 2.8 fb−1 ψ(3770) data, and 500 pb−1 data at 4.01 GeV. All the data samples were processed successfully and many important physics results have been achieved based on these samples. Doing data production correctly and efficiently with limited CPU and storage resources is a big challenge. This paper will describe the implementation of the experiment-specific data production for BESIII in detail, including data calibration with event-level parallel computing model, data reconstruction, inclusive Monte Carlo generation, random trigger background mixing and multi-stream data skimming. Now, with the data sample increasing rapidly, there is a growing demand to move from solely using a local cluster to a more distributed computing model. A distributed computing environment is being set up and expected to go into production use in 2012. The experience of BESIII data production, both with a local cluster and with a distributed computing model, is presented here.
54683815
The optimization of a DC injector for the Energy Recovery Linac upgrade to APS
An energy recovery linac based light source is a potential revolutionary upgrade to the Advanced Photon Source (APS) at Argonne National Laboratory. The concept relies on several key research areas, one of which is the generation of ultra-low emittance, high-average-current electron beams. In this paper, we present our investigation of a dc-gun-based system for ultra-low emittance bunches in the 20 pC range. A parallel multi-objective numerical optimization is performed in multi-parameter space. Parameters varied include experimentally feasible drive-laser shapes, the DC gun voltage, the thermal energy of the emitted photo-electrons and other electric or magnetic field strengths, RF cavity phase etc. Our goal is to deliver a {approx}10 MeV, 20 pC bunch at the entrance of the linac with an emittance of 0.1 {micro}m or lower, rms bunch length of 2 {approx} 3 ps, and energy spread no larger than 140 keV. We present the machine parameters needed to generate such an injector beam, albeit without a merger.
7518066
First observation of the exchange of transverse and longitudinal emittances.
An experimental program to demonstrate a novel phase-space manipulation in which the horizontal and longitudinal emittances of a particle beam are exchanged has been completed at the Fermilab A0 Photoinjector. A new beam line, consisting of a TM(110) deflecting mode cavity flanked by two horizontally dispersive doglegs has been installed. We report on the first direct observation of transverse and longitudinal emittance exchange.
119301218
Electric-magnetic duality of Abelian gauge theory on the four-torus, from the fivebrane on T2 × T4, via their partition functions
A bstractWe compute the partition function of four-dimensional abelian gauge theory on a general four-torus T4 with flat metric using Dirac quantization. In addition to an SL4,Z$$ \mathrm{S}\mathrm{L}\left(4,\;\mathcal{Z}\right) $$ symmetry, it possesses SL2,Z$$ \mathrm{S}\mathrm{L}\left(2,\;\mathcal{Z}\right) $$ symmetry that is electromagnetic S-duality. We show explicitly how this SL2,Z$$ \mathrm{S}\mathrm{L}\left(2,\;\mathcal{Z}\right) $$ S-duality of the 4d abelian gauge theory has its origin in symmetries of the 6d (2, 0) tensor theory, by computing the partition function of a single fivebrane compactified on T2 times T4, which has SL2,Z×SL4,Z$$ \mathrm{S}\mathrm{L}\left(2,\;\mathcal{Z}\right)\times \mathrm{S}\mathrm{L}\left(4,\;\mathcal{Z}\right) $$ symmetry. If we identify the couplings of the abelian gauge theory τ=θ2π+i4πe2$$ \tau =\frac{\theta }{2\pi }+i\frac{4\pi }{e^2} $$ with the complex modulus of the T2 torus τ=β2+iR1R2$$ \tau ={\beta}^2+i\frac{R_1}{R_2} $$, then in the small T2 limit, the partition function of the fivebrane tensor field can be factorized, and contains the partition function of the 4d gauge theory. In this way the SL2,Z$$ \mathrm{S}\mathrm{L}\left(2,\;\mathcal{Z}\right) $$ symmetry of the 6d tensor partition function is identified with the S-duality symmetry of the 4d gauge partition function. Each partition function is the product of zero mode and oscillator contributions, where the SL2,Z$$ \mathrm{S}\mathrm{L}\left(2,\;\mathcal{Z}\right) $$ acts suitably. For the 4d gauge theory, which has a Lagrangian, this product redistributes when using path integral quantization.
56322128
Ugrades of beam diagnostics in support of emittance-exchange experiments at the Fermilab A0 photoinjector
The possibility of using electron beam phase space manipulations to support a free-electron laser accelerator design optimization has motivated our research. An ongoing program demonstrating the exchange of transverse horizontal and longitudinal emittances at the Fermilab A0 photoinjector has benefited recently from the upgrade of several of the key diagnostics stations. Accurate measurements of these properties upstream and downstream of the exchanger beamline are needed. Improvements in the screen resolution term and reduced impact of the optical system's depth-of-focus by using YAG:Ce single crystals normal to the beam direction will be described. The requirement to measure small energy spreads (<10 keV) in the spectrometer and the exchange process which resulted in bunch lengths less than 500 fs led to other diagnostics performance adjustments and upgrades as well. A longitudinal to transverse exchange example is also reported.