20673458
Characterization and Tuning of A Microwave Gun Cavity
A microwave electron gun system is being constructed to evaluate the feasibility of using such system as the electron source for the linac pre-injector in storage ring synchrotron radiation sources and for novel linac-based light source R&D at NSRRC. A 2856 MHz SSRL-type microwave gun cavity has been fabricated in house for this purpose. Properties of the cavity resonant modes have been characterized as a function of side-coupled cell plunger position. Special tuning plunger design for this cell allows re-adjustment of field ratio even after brazing. Field amplitude ratio of the cavity full cell to half cell has now been tuned to 2:1. That is the optimized ratio for low energy bunch compression by an alpha magnet.
121866403
GENERATION OF ULTRA-SHORT ELECTRON BUNCHES FOR LIGHT SOURCE RESEARCH
An S-band thermionic 1.5-cell rf gun injector system is being built at NSRRC for Taiwan Photon Source (TPS) booster. At optimized field ratio, an electron beam with linear energy chirp can be generated by the rf gun. The beam is then compressed by an alpha magnet such that ultra-short electron bunches at femto-second bunch length can be obtained. Particle dynamics has been studied for an rf gun with nose cone at the cathode, simulation results show that 74 pC bunches at about 97 fs is achievable. Some of the critical components such as the rf gun and alpha magnet have been fabricated and being tested in house. Experiments for intense coherent THz radiations and tunable femto-second X-ray from ultra-short bunches are being proposed as future applications.
123472634
Unnatural parity resonances in the positron-excited hydrogen system
We present an investigation of resonances with unnatural parities in positron scattering by excited hydrogen. The momentum space coupled channels optical potential method has been used. Positronium formation channels have been included via a complex equivalent local potential. States with angular momenta L = 1 to L = 2 and parity (−1)L+1 are calculated.
119450128
Anti-d / anti-u asymmetry and the origin of the nucleon sea
The Drell-Yan cross section ratios, {sigma}(p+d)/{sigma}(p+p), measured in Fermilab E866, have led to the first determination of {bar d}(x)/{bar u}(x), {bar d}(x){minus}{bar u}(x), and the integral of {bar d}(x){minus}{bar u}(x) for the proton over the range 0.02{le}x{le}0.345. The E866 results are compared with predictions based on parton distribution functions and various theoretical models. The relationship between the E866 results and the NMC measurement of the Gottfried integral is discussed. The agreement between the E866 results and models employing virtual mesons indicates that these non-perturbative processes play an important role in the origin of the {bar d},{bar u} asymmetry in the nucleon sea. {copyright} {ital 1998} {ital The American Physical Society}
125960882
Measurement of Drell-Yan cross sections and flavor asymmetry in the nucleon sea
Measurements of Drell-Yan cross sections from the bombardment of liquid deuterium and hydrogen with an 800 GeV proton beam are reported. The relative cross section (σpd/2σpp) directly probes the ratio of anti-down (d) to anti-up (ū) quarks in the nucleon sea, while absolute measurement of the deuterium cross section constrain d+ū. Results are compared with previous experiments and next-to-leading order calculations based on current sets of parton distribution functions.
54921026
Measurement of the light antiquark flavor asymmetry in the nucleon sea
A precise measurement of the ratio of Drell-Yan yields from an 800 GeV/c proton beam incident on hydrogen and deuterium targets is reported. Over 140000 Drell-Yan muon pairs with dimuon mass M{sub {mu}{sup +}{mu}{sup {minus}}}{ge}4.5 GeV/c{sup 2} were recorded. From these data, the ratio of antidown ({bar d} ) to antiup ({bar u} ) quark distributions in the proton sea is determined over a wide range in Bjorken x . A strong x dependence is observed in the ratio {bar d}/{bar u} , showing substantial enhancement of {bar d} with respect to {bar u} for x{lt}0.2 . This result is in fair agreement with recent parton distribution parametrizations of the sea. For x{gt}0.2 , the observed {bar d}/{bar u} ratio is much nearer unity than given by the parametrizations. {copyright} {ital 1998} {ital The American Physical Society}
43062196
Development of thermionic-cathode RF electron gun at IHEP
A thermionic cathode RF electron gun has been developed at the Institute of High Energy Physics, Academia Sinica, China. The gun will accelerate and prebunch electrons emitted from a L/sub a/B/sub 6/ cathode using a high electric field in a resonant cavity. The gun was fabricated and tested, and used in the Beijing free-electron laser project. Results of experimental measurements of the injector performance of a prototype gun are also presented.<<ETX>>
14445704
The Palo Verde reactor neutrino experiment a test for long baseline neutrino oscillations
Our collaboration has installed a long baseline neutrino oscillation experiment at the Palo Verde Nuclear Generating Station in Arizona. 12 tons of Gd loaded liquid scintillator, in a segmented detector, are used to search for νe ↔ νx oscillations at 740 m distance to three reactors. The anti-neutrino capture on the proton serves as detection reaction. The experiment is expected to reach a sensitivity of Δm2 > 1.3 · 10−3 eV2 and sin22Θ > 0.1. Our range of sensitivity is tuned to test the νμ ↔ νe solution of the atmospheric neutrino anomaly.
49387747
PROGRESS IN RAISING THE ENERGY OF THE CAMD LINAC TO 300 MEV *
Technical design details are presented of the proposed upgrade to 300 MeV of the linac at the Center for Advanced Microstructures & Devices (CAMD). The key parameters of the linac are listed and the benefits of 300 MeV injection to the CAMD synchrotron radiation light source are explained. The optimum placement of the 300MeV linac in the existing tunnel has been established and the upgrades and locations of ancillary sub-systems are being prepared. Simulations of the electron beam trajectory by a MATLAB based linear accelerator program are ongoing.
108903001
Test results of heavily irradiated Si detectors
Abstract A large use of silicon microstrip detectors is foreseen for the intermediate part of the CMS tracker. A specific research and development program has been carried out with the aim of finding design layouts and technological solutions for allowing silicon microstrip detectors to be reliably used on a high radiation level environment. As a result of this work single sided, AC-coupled, polysilicon biased, 300 μ m thick, p + on n substrate detectors were chosen. Irradiation tests have been performed on prototypes up to fluence 2×10 14  n/cm 2 . The detector performances do not significantly change if the detectors are biased well above the depletion voltage. S / N is reduced by less than 20%, still enough to insure a good efficiency and space resolution. Multiguard structures has been developed in order to reach high voltage operation (above 500 V).
118398040
Multi-stream inflation
We propose a ``multi-stream'' inflation model, which is a double field model with spontaneous breaking and restoration of an approximate symmetry. We calculate the density perturbation and non-Gaussianity in this model. We find that this model can have large, scale dependent, and probably oscillating non-Gaussianity. We also note that our model can produce features in the CMB power spectrum and hemispherical power asymmetry.