44445173
Beam-Beam Effects in the Ring-Ring Version of eRHIC
Beam-beam effects in the ring-ring version of eRHIC was studied with a self-consistent beam-beam simulation by using the particle-in-cell method. Beam-beam limits of the two beams were examined as the thresholds of the onset of the coherent beam-beam instability. For the proposed luminosity, the bunch intensities optimized in consideration of the beam-beam effect were discussed. As the beam-beam interaction in the eRHIC is traditionally considered as a strong-weak case, this represents an example of the coherent beam-beam effect in the strong-weak case of beam-beam interactions.
15136170
Structural Basis of Transcription: Role of the Trigger Loop in Substrate Specificity and Catalysis
New structures of RNA polymerase II (pol II) transcribing complexes reveal a likely key to transcription. The trigger loop swings beneath a correct nucleoside triphosphate (NTP) in the nucleotide addition site, closing off the active center and forming an extensive network of interactions with the NTP base, sugar, phosphates, and additional pol II residues. A histidine side chain in the trigger loop, precisely positioned by these interactions, may literally "trigger" phosphodiester bond formation. Recognition and catalysis are thus coupled, ensuring the fidelity of transcription.
92986025
COMMISSIONING OF THE SSRF BOOSTER
The SSRF Booster, designed to accelerate the electrons from 150MeV to 3.5GeV, is a FODO structure synchrotron with 180m circumference and 2Hz repetition rate. The commissioning of the SSRF booster from the LTB transfer line started on Sept. 30th evening, 2007, the first turns of beam in the booster was obtained in 20 hours. With about 60 hours effective commissioning effort, the electrons were accelerated to 3.5GeV on October 5th morning, 2007. And then the first 3.5GeV beam was extracted to BTS transfer line on October 30th, 2007. In this paper, the SSRF booster is introduced and its commissioning results are presented. INTRODUCTION Shanghai Synchrotron Radiation Facility (SSRF) is a 3rd generation light source, which consists of a 150MeV LINAC, a full energy booster synchrotron and a 20-DBA storage ring. It will provide 4nm·rad nature emittance electron beam at 3.5GeV [1][2]. SSRF booster is used to accelerate the electron beam from 150MeV to 3.5GeV. It is composed with 2 super periods, 28 standard FODO cells and 180m circumferences. The curvature radius of dipole is 14.515m, which can reduce the eddy currents effectively during the energy ramping. There are also eight 2.9m straight sections, which used for the installation of injection, extraction and radio frequency systems [3]. BOOSTER PARAMETERS Fig.1 shows layout of one standard booster cell. Fig.2 shows lattice functions in one quarter of the ring. Figure1: Layout of one standard booster cell. Figure 2: Twiss parameters of SSRF booster synchrotron. (One fourth of the ring is shown.). There are two modes, single bunch and multi bunch, designed for booster commissioning, which can satisfy both the accumulative rate and the top-up injection requirements of the storage ring. The main parameters of the booster are shown in Table 1. Table 1: Main Parameters of the Booster Parameters Value Energy range (GeV) 0.15~3.5 Single bunch 2 Current (mA) Multi bunch 15 Repetition rate (Hz) 2 Cell length (m) 6.4286 Length of long straight (m) 2.904 RF frequency (MHz) 499.654 Harmonic number 300 Nature emittance (nm·rad) 104 Tune, νH /νV 8.181/5.229 Natural chromaticity, ξH/ξV -9.91/-7.45 Nature energy spread 7.799×10 Momentum compaction, αP 0.01849 Damping time, τH,V,L (ms) 4.77/4.60/2.26 Longitudinal tune, νs 0.019 Bunch length (mm) 21.4 0 5 10 15 20 25 30 35 40 45 -5 0 5 10 15 20 25 30 s [m] β x ,y [m ] Twiss Parameters 0 5 10 15 20 25 30 35 40 45 0 0.2 0.4 0.6 0.8 1
55429266
STUDY OF THE ENERGY CHIRP EFFECTS ON SEEDED FEL SCHEMES AT SDUV-FEL
In this paper, theoretical and simulation study of the energy chirp effects on the HGHG and EEHG schemes are present. It is found that the central wavelength and output bandwidth of EEHG can be nearly immune to the beam energy chirp by properly setting the strengths of the chicanes. Experimental studies for both these two schemes have been carried out at the SDUV-FEL to demonstrate the theoretical predictions.
120931097
Stripline beam position monitor for the MIT-Bates South Hall Ring
The MIT-Bates South Hall Ring (SHR) is an electron storage ring currently being commissioned. It is designed to operate at an RF frequency of 2856 MHz with all of the 1812 buckets filled and a circulating current of 80 mA or greater. This leads to a small charge per bunch and the requirement for beam position monitors. Since there will be 31 such monitors in the vacuum system, it is important to suppress trapped modes which may excite coupled bunch instabilities. The stripline monitor built for the SHR is a stainless steel structure, designed to be manufactured using standard machining techniques and commercial feedthroughs. With proper 50 Ohm matching and a geometry derived from insight from MAFIA calculations, the monitor was constructed having a nearly flat RF response up through 10 GHz over the range of measurement. The stripline electronics allows the measurements with 0.1 mm resolution, maintains orbital harmonics information past the 10th harmonic, and operates over a dynamic range of 1 mA to greater than 80 mA of beam current.<<ETX>>
124623797
HESYRL 200 MeV linac single bunch energy spectrum measurement
The HESYRL 200-MeV electron linac was completed in December 1987, and has been running well. A careful study of the single-bunch energy spectrum for the linac was done. The measurement shows that the energy spread of the linac is +or-0.4%. The energy spectrum is quite stable and repeatable, and the resolution and accuracy are found to be satisfactory.<<ETX>>
322774
INFLUENCE OF THE MAGNETIC COUPLING PROCESS ON ADVECTION-DOMINATED ACCRETION FLOWS AROUND BLACK HOLES
A large-scale closed magnetic field can transfer angular momentum and energy between a black hole (BH) and its surrounding accretion flow. We investigate the effects of this magnetic coupling (MC) process on the dynamics of a hot accretion flow (e. g., an advection-dominated accretion flow). The energy and angular momentum fluxes transported by the magnetic field are derived with an equivalent-circuit approach. For a rapidly rotating BH, it is found that the radial velocity and the electron temperature of the accretion flow decrease, whereas the ion temperature and the surface density increase. The significance of the MC effects depends on the value of the viscosity parameter alpha. The effects are obvious for alpha = 0.3 but nearly ignorable for alpha = 0.1. For a BH with specific angular momentum a(*) = 0.9 and alpha = 0.3, we find that for reasonable parameters the radiative efficiency of a hot accretion flow can be increased by similar to 30%.
120250349
Momentum space Z2 number, quantized Berry phase and the quantum phase transitions in spin chain systems
We characterize the quantum phase transitions of gapped time-reversal invariant spin chain systems by nontrivial Z2 numbers derived from a quantized Berry phase in a (1?+?1)-dimensional Bloch momentum space. We study this approach analytically in a general two-band model and give a concrete example in a transverse field XY spin chain system. In our scheme, an extra local gauge transformation is performed to the spin system by a time-dependent twist operator, which endows the Hamiltonian of the system with the topology of a torus without changing its energy spectrum. The Z2 number is obtained by a loop integral of the Berry gauge potential along a quarter of the Brillouin zone. We show that the different phases of the XY spin chain system are distinguished by the Z2 topological order in momentum space.
121216453
Heavy quark effective theory sum rules for higher excited charmed mesons: With a view on D(sJ)(2632)
Mass of the excited (1{sup -},2{sup -}) (2{sup -},3{sup -}) and (2{sup +},3{sup +}) cs states is calculated to the 1/m{sub Q} order within the framework of the heavy quark effective theory using QCD sum rule method. The obtained kinetic energy is comparable to the c-quark mass, thus results in large 1/m{sub Q} correction for the c-quark case. With the sum rules for the chromomagnetic interaction term, the mass splitting for the three doublets is presented. Based on the predicted mass spectrum the exotic D{sub sJ}(2632) state, if really exists, is unlikely to be a conventional orbitally higher excited cs state, although the experimental center lies within the range for the mass of the 1{sup -} meson.
122673118
Coherent synchrotron radiation effects in the electron cooler for RHIC
The Coherent Synchrotron Radiation (CSR) could be a concern in many modern accelerator projects. In the proposed electron-cooling project for the Relativistic Heavy Ion Collider (RHIC), the electron cooler is designed to cool 100 GeV/nucleon bunched ion-beam using 55 MeV electrons. The electron bunch length will be on the order of cm, and the charge per bunch would be around 5-10 nC. We study the CSR effect in this paper.
55527280
Electron beam instrumentation techniques using coherent radiation
Much progress has been made on coherent radiation research since coherent synchrotron radiation was first observed in 1989. The use of coherent radiation as a bunch length diagnostic tool has been studied by several groups. In this paper, brief introductions to coherent radiation and far-infrared measurement are given, the progress and status of their beam diagnostic application are reviewed, different techniques are described, and their advantages and limitations are discussed.