111171338
DEVELOPMENT OF RADIO FREQUENCY GUNS AT NSRRC
Technologies for rf gun-based high brightness injector are being developed at NSRRC. An X-band photo-cathode rf gun has been constructed and operated successfully for coherent electromagnetic radiation research at U.C. Davis. Recent measurement of a 1.5-2 MeV beam from this gun with bunch charge at 25 pC showed that it has a normalized emittance at 1.65 mm-mrad. As a successive project, a 100 MeV electron beam injector system with a thermionic rf gun and a photo-cathode rf gun that share the same 2998 MHz rf linac is being designed as the pre-injector of the TPS (Taiwan Photon Source) booster as well as beam injector for novel light source research. For evaluation purposes, a prototype thermionic rf gun system is now under construction at NSRRC with the existing 2856 MHz high power microwave system as the driver source.
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.
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.
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}
118855433
Alternative Kondo breakdown mechanism: Orbital-selective orthogonal metal transition
In a recent paper of Nandkishore, Metlitski, and Senthil [Phys. Rev. B 86, 045128 (2012)], a concept of orthogonal metal has been introduced to reinterpret the disordered state of slave-spin representation in the Hubbard model as an exotic gapped metallic state. We extend this concept to study the corresponding quantum phase transition in the extended Anderson lattice model. It is found that the disordered state of slave spins in this model is an orbital-selective orthogonal metal, a generalization of the concept of the orthogonal metal in the Hubbard model. The quantum critical behaviors are multiscale and dominated by a z = 3 and z = 2 critical modes in the high-and low-temperature regime, respectively. Such behaviors are obviously in contrast to the naive expectation in the Hubbard model. The result provides alternative Kondo breakdown mechanism for heavy fermion compounds underlying the physics of the orbital-selective orthogonalmetal in the disordered state, which is different from the conventional Kondo breakdown mechanism with the fractionalized Fermi-liquid picture. This work is expected to be useful in understanding the quantum criticality happening in some heavy fermion materials and other related strongly correlated systems.
108773563
The silicon microstrip tracker for CMS
The CMS silicon strip tracker involves about 70 m2 of instrumented silicon, with approximately 18500 microstrip detectors read out by 5 × 106 electronics channels. It has to satisfy a set of stringent requirements imposed by the environment and by the physics expected at the LHC: low cell occupancy and good resolution, radiation hardness aided by adequate cooling, low mass combined with high stability. These conditions have been incorporated in a highly modular design of the detector modules and their support structures, chosen to facilitate construction and to allow for easy assembly and maintenance.
121941527
B∗ production in Z decays at LEP
Abstract The production of B ∗ mesons in Z decays has been measured at LEP with the L3 detector. A sample of Z → b b events was obtained by tagging muons in 1.6 million hadronic Z decays collected in 1991, 1992 and 1993. A signal with a peak value of E γ = 46.3 ± 1.9 (stat) MeV in the B rest frame energy spectrum was interpreted to come from the decay B ∗ → γB. The inclusive production ratio of B ∗ mesons relative to B mesons was determined from a fit to the spectrum to be N B ∗ (N B ∗ + N B ) = 0.76 ± 0.08 ± 0.06 , where the first error is statistical and the second is systematic.
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>>
110807481
Development of a high power 1.2 MW CW L-band klystron
The high power CW L-band klystron has been developed as the RF source of the PNC high power CW electron linac (10 MeV, 100 mA). CW power of 1.2 MW at 1.249135 GHz and efficiencies over 65% were the design goals. RF analysis of the windows using high-frequency simulation codes provided information about power loss distribution in the ceramic and optimizing properties of the RF structure. The prototype klystron window was replaced with a long pill-box type beryllia window as a result of the simulation and hardware tests. The klystron has reached CW power of 885 kW with efficiency above 45%. This paper describes key points of the designs and results of the high power RF tests.