118032595
Progress on Analytical Modeling of Coherent Electron Cooling
We report recent progresses on analytical studies of Coherent Electron Cooling. The phase space electron beam distribution obtained from the 1D FEL amplifier is applied to an infinite electron plasma model and the electron density evolution inside the kicker is derived. We also investigate the velocity modulation in the modulator and obtain a closed form solution for the current density evolution for infinite homogeneous electron plasma.
117632548
Studies of beam dynamics for eRHIC
We present our studies on various aspects of the beam dynamics in 'racetrack' design of the first stage electron-ion collider at RHIC (eRHIC), including transverse beam break up instabilities, energy loss due to wakefields, electron beam emittance growth and energy loss due to synchrotron radiation, electron beam losses due to Touschek effects and residue gas scattering, beam-beam effects at the interaction region and emittance growth of ion beam due to electron bunch to bunch noises. For all effects considered above, no showstopper has been found.
115626894
Linear optics measurements and corrections using an AC dipole in RHIC
We report recent experimental results on linear optics measurements and corrections using ac dipole. In RHIC 2009 run, the concept of the SVD correction algorithm is tested at injection energy for both identifying the artificial gradient errors and correcting it using the trim quadrupoles. The measured phase beatings were reduced by 30% and 40% respectively for two dedicated experiments. In RHIC 2010 run, ac dipole is used to measure {beta}* and chromatic {beta} function. For the 0.65m {beta}* lattice, we observed a factor of 3 discrepancy between model and measured chromatic {beta} function in the yellow ring.
73519332
RHIC Performance for FY10 200 GeV Au+Au Heavy Ion Run
Since the last successful RHIC Au+Au run in 2007 (Run-7), the RHIC experiments have made numerous detector improvements and upgrades. In order to benefit from the enhanced detector capabilities and to increase the yield of rare events in the acquired heavy ion data a significant increase in luminosity is essential. In Run-7 RHIC achieved an average store luminosity of = 12 × 10 cm−2 s−1 by operating with 103 bunches (out of 111 possible), and by squeezing to β∗ = 0.85 m. This year, Run-10, we achieved = 20 × 10 cm−2 s−1, which put us an order of magnitude above the RHIC design luminosity. To reach these luminosity levels we decreased β∗ to 0.75 m, operated with 111 bunches per ring, and reduced longitudinal and transverse emittances by means of bunched-beam stochastic cooling. In addition we introduced a lattice to suppress intra-beam scattering (IBS) in both RHIC rings, upgraded the RF control system, and separated transition crossing times in the two rings. We present an overview of the changes and the results of Run-10 performance.
37012340
Status of R&D energy recovery LINAC at Brookhaven National Laboratory
In this paper we present status and plans for the 20- MeV R&D energy recovery linac (ERL), which is under construction at Collider Accelerator Department at BNL. The facility is based on high current (up to 0.5 A of average current) super-conducting 2.5 MeV RF gun,single-mode super-conducting 5-cell RF linac and about 20-m long return loop with very flexible lattice. The R&D ERL, which is planned for commissioning in early 2009, aims to address many outstanding questions relevant for high current, high brightness energy-recovery linacs.
118603199
Three-dimensional model of small signal free-electron lasers
Coherent electron cooling is an ultra-high-bandwidth form of stochastic cooling which utilizes the charge perturbation from Debye screening as a seed for a free-electron laser. The amplified and frequency-modulated signal that results from the free-electron laser process is then used to give an energy-dependent kick on the hadrons in a bunch. In this paper, we present a theoretical description of a high-gain free-electron laser with applications to a complete theoretical description of coherent electron cooling.
119180431
Empirical constraints on parton energy loss in nucleus–nucleus collisions at RHIC
Abstract We present empirical features of parton energy loss in nucleus–nucleus collisions at RHIC through studies of the spectra and nuclear modification factors ( R A A ) for charged hadrons, neutral pions ( π 0 ) and non-photonic electrons. The flat distribution of R A A at high transverse momentum ( p T ) for a given collision centrality is consistent with a scenario where parton energy loss Δ p T is proportional to p T . The centrality dependence of the parton energy loss indicates the absence of path length dependence in the magnitude of energy loss. The lack of strong path length dependence suggests a dynamical picture where the dense partonic medium undergoes rapid expansion and the density of the medium falls rapidly in the first a few Fermi interval, which may be much shorter than the full path length. Implications of the empirical constraints on the parton energy loss will also be discussed.
123025416
Bc DECAYS TO HEAVY-LIGHT ORBITALLY EXCITED MESONS
We calculate the exclusive semileptonic and nonleptonic decays of Bc meson to heavy-light orbitally excited states in the framework of the improved Bethe–Salpeter method. The hadronic matrix elements are calculated and expressed as overlap integrals of the relativistic Salpeter wave functions of corresponding mesons, decay rates of the semileptonic and nonleptonic Bc decays to , and are obtained. Some channels provide us sizable ratios, for examples, and , with such ratios, the missing scalar Bs0 may be detected though its cascade strong decays in the forthcoming LHC experiment.
120552860
The topological basis realization and the corresponding XXX spin chain
In this paper, it is shown that the XXX model can be constructed from the Temperley-Lieb algebra (TLA) generator. We find that the topological basis states are the two eigenstaes of a closed four-qubit Heisenberg XXX spin chain. Specifically, the spin single states and the energy single state of the system all fall on the topological basis states. It is worth mentioning that for the closed 2N-qubit (N=2, 3, 4, ...) Heisenberg XXX spin chain, all the topological basis states for 2N particles are the spin single states of the system. And the number of the topological basis states is equal to the number of the spin single states of the system, which is .
11542069
Observation of a critical gradient threshold for electron temperature fluctuations in the DIII-D Tokamak.
A critical gradient threshold has been observed for the first time in a systematic, controlled experiment for a locally measured turbulent quantity in the core of a confined high-temperature plasma. In an experiment in the DIII-D tokamak where L(T(e))(-1) = |∇T(e)|/T(e) and toroidal rotation were varied, long wavelength (k(θ)ρ(s) ≲ 0.4) electron temperature fluctuations exhibit a threshold in L(T(e))(-1): below, they change little; above, they steadily increase. The increase in δT(e)/T(e) is concurrent with increased electron heat flux and transport stiffness. Observations were insensitive to rotation. Accumulated evidence strongly enforces the identification of the experimentally observed threshold with ∇T(e)-driven trapped electron mode turbulence.
64627689
The progress of development of four kickers' bump system for injection in HLS ring
There are three kicker magnets to manipulate local bump orbit in Hefei storage ring, which could satisfy basically the commissioning and operations of General Purpose Light Source (GPLS) mode. In the Phase Two Project of HLS, four kicker magnets will be employed and installed in one straight section to form a ladder-shaped bump orbit. So the parameters of bump orbit are independent of the ring lattice. The new system also satisfies the multicycle and multiturn injection of High Brightness Light Source (HBLS) mode and other modes, and it expected to run stably for a long time. This paper presents the development of the new bump orbit system.