55717747
The drive laser system for dc-sc injector
PKU-SCAF has developed a photoinjector which adopt a 1+1/2 cell super conducting cavity and DC electron gun. We also developed a low cost drive laser system for the photocathode DC gun to provide high average beam current. This laser system include a commercial high repetition rate, ps, all solid-state laser, the home made SHG and FHG, Fourier relay optics and the uniform illumination optics. The test results shows the output power at 266 nm of the laser system is more than 1.2W and got more than 500 µA beam current from CsTe cathode from the DC gun.
125267189
Helium production from Kr-84- and Au-197-emulsion interactions at high energies
The properties of the relativistic helium fragments produced in interactions of Kr-84 at 1.8 A GeV and Au-197 at 1.7 A GeV in emulsion are investigated. The experimental results are compared with those obtained from various projectiles with emulsion collisions at different energies. It is found that the multiplicity distribution of helium projectile fragments (HPFs) is well described by the Koba-Nielsen-Olesen (KNO) scaling presentation. The second Mueller moment f(2) of the HPF multiplicity distribution is independent of the projectile energy for the same projectile, but it is dependent on the projectile mass number. The value of f(2) increases with the increase of projectile mass number A(p). The negative value of f(2), when A(p) 69, means that the emission of HPFs is anticorrelated, but positive value of f(2), when A(p) > 69, referes to that the emission of HPFs is corrleated. The non-zero f(2) moment in this experiment implies the strong correlation existing between the HPFs.
122621857
Cold RF test and associated mechanical features correlation of a TESLA-style 9-cell superconducting niobium cavity built in China
The RF performance of a 1.3 GHz 9-cell superconducting niobium cavity was evaluated at cryogenic temperatures following surface processing by using the standard ILC-style recipe. The cavity is a TESLA-style 9-cell superconducting niobium cavity, with complete end group components including a higher order mode coupler, built in China for practical applications. An accelerating gradient of 28.6 MV/m was achieved at an unloaded quality factor of 4 × 109. The morphological property of mechanical features on the RF surface of this cavity was characterized through optical inspection. Correlation between the observed mechanical features and the RF performance of the cavity is attempted.
121908829
Amplitude and phase stability studies in a DC superconducting injector
The DC superconducting injector will be used in the PKU-THz facility which consists of a DC-gun and a 3+1/2-cell superconducting cavity. The cavity must accelerate the electron beam to 5.82 MeV which is susceptible to perturbations because of its narrow bandwidth. In this paper, the sources and influences of the perturbations in the 3+1/2-cell cavity are discussed. It is shown that the control system is essential for the cavity. The design of a feedback based digital RF low level control system for the 3+1/2-cell cavity is accomplished.
89654095
The First Nine-Cell TESLA Cavity Made in China
A totally home-made 9-cell TESLA type superconducting cavity is made at Peking University. The cavity fabrication is according to DESY specification. The cavity is made of high purity niobium from OTIC, Ningxia. The electron beam welding is carried out at Harbin Institute of Technology, Harbin. By the cooperation, the cavity is tested at Thomas Jefferson National Accelerator Facility, USA. The preliminary result shows the acceleration gradient Eacc is 23MV/m without quench and has potential for improvement.
11226958
Constraining the cosmological parameters and transition redshift with gamma-ray bursts and supernovae
A new method of measuring cosmology with gamma-ray bursts (GRBs) has been proposed by Liang and Zhang recently. In this method, only observable quantities including the rest-frame peak energy of the νF ν spectrum (E' p ), the isotropic energy of GRB (E γ,iso ) and the break time of the optical afterglow light curves in the rest frame (t' b ) are used. By considering this method, we constrain the cosmological parameters and the redshift at which the Universe expanded from the deceleration to acceleration phase. We add five recently detected GRBs to the sample and derive E γ,iso /10 52 erg = (0.93 ± 0.25) (E' p /100 keV) 1.91±0.32 (t'b/1d) -0.93±0.38 for a flat universe with Ω M = 0.28 and H 0 = 71.0km s -1 Mpc -1 . This relation is independent of the medium density around bursts and the efficiency of conversion of the explosion energy to gamma-ray energy. We consider the E γ,iso (E' p , t' b ) relationship as a standard candle and find 0.05 < Ω M < 0.48 and Ω Λ < 1.15 (at the la confidence level). In a flat universe with the cosmological constant, we obtain 0.25 < Ω M < 0.46 and 0.54 < Ω Λ < 0.78 at the la confidence level. The transition redshift is z T = 0.69 +0.11 -0.12 . Combining 20 GRBs with 157 Type Ia supernovae (SNe Ia), we find Ω M = 0.29 ± 0.03 for a flat universe and the transition redshift is z T = 0.61 +0.06 -0.05 , which is slightly larger than the value found by considering SNe Ia alone. In particular, we also discuss several dark-energy models in which the equation of state w(z) is parametrized, and investigate constraints on the cosmological parameters in detail.
206352395
The attachment of amino fragment to purine: inner-shell structures and spectra.
The impact of the amino fragment (-NH(2)) attachment on the inner-shell structures and spectra of unsubstituted purine and the purine ring of adenine are studied. Density functional theory calculations, using the LB94/TZ2P//B3LYP/TZVP model, reveal significant site-dependent electronic structural changes in the inner shell of the species. A condensed Fukui function indicates that all of the N and C sites, except for N((1)) and C((5)), demonstrate significant electrophilic reactivity (f(-) > 0.5 in |e|) in the unsubstituted purine. Once the amino fragment binds to the C((6)) position of purine to form adenine, the electrophilic reactivity of these N and C sites is greatly reduced. As expected, the C((6)) position experiences substantial changes in energy and charge transfer, owing to the formation of the C-NH(2) bond in adenine. The present study reveals that the N1s spectra of adenine inherit the N1s spectra of the unsubstituted purine, whereas the C1s spectra experience significant changes although purine and adenine have geometrically similar carbon frames. The findings also indicate that the attachment of the NH(2) fragment to purine exhibits deeply rooted influences to the inner-shell structures of DNA/RNA bases. The present study suggests that some fragment-based methods may not be applicable to spectral analyses in the inner shell.
110770779
Planned waveguide electric field breakdown studies
This paper presents an experimental setup for X-band rf breakdown studies. The setup is composed of a section of WR90 waveguide with a tapered pin located at the middle of the waveguide E-plane. Another pin is used to rf match the waveguide so it operates in a travelling wave mode. By adjusting the penetration depth of the tapered pin, different surface electric field enhancements can be obtained. The setup will be used to study the rf breakdown rate dependence on power flow in the waveguide for a constant maximum surface electric field on the pin. Two groups of pins have been designed. The Q of one group is different and very low. The other has a similar Q. With the test of the two groups of pins, we should be able to discern how the net power flow and Q affect the breakdown. Furthermore, we will apply an electron beam treatment to the pins to study its effect on breakdown. Overall, these experiments should be very helpful in understanding rf breakdown phenomena and could significantly benefit the design of high gradient accelerator structures.
118676242
Gravitational effects of condensate dark matter on compact stellar objects
We study the gravitational effect of non-self-annihilating dark matter on compact stellar objects. The self-interaction of condensate dark matter can give high accretion rate of dark matter onto stars. Phase transition to condensation state takes place when the dark matter density exceeds the critical value. A compact degenerate dark matter core is developed and alter the structure and stability of the stellar objects. Condensate dark matter admixed neutron stars is studied through the two-fluid TOV equation. The existence of condensate dark matter deforms the mass-radius relation of neutron stars and lower their maximum baryonic masses and radii. The possible effects on the Gamma-ray Burst rate in high redshift are discussed.
111221941
ASTROD and ASTROD I: Progress Report
Over the next decade the gravitational physics community will benefit from dramatic improvements in many technologies critical to the tests of gravity and gravitational-wave detection. The highly accurate deep space navigation, interplanetary laser ranging and communication, interferometry and metrology, high precision frequency standards, precise pointing and attitude control, together with the drag-free technologies will revolutionize the field of the experimental gravitational physics. Deep-space laser ranging will be ideal for gravitational-wave detection, and testing relativity and measuring solar-system parameter to an unprecedented accuracy. ASTROD I is such a mission with single spacecraft; it is the first step of ASTROD (Astrodynamical Space Test of Relativity using Optical Devices) with 3 spacecraft. In this paper, we will present the progress of ASTROD and ASTROD I with emphases on the acceleration noises, mission requirement, charging simulation, drag-free control and low-frequency gravitational-wave sensitivity.