16215815
Design of 2x2 DLDS RF Components for JLC
We have studied a multi-mode Delay Line Distribution System (DLDS)[1][2] as the RF power distribution system from klystrons to RF structures for linear colliders. In particular, a 2×2 DLDS has been proposed and studied at KEK for Japan Linear Collider(JLC). It has been proved that the 2×2 DLDS is simple, bus has good transmission efficiency. We have designed RF components of a basic unit of a DLDS using the High Frequency Structure Simulator (HFSS) code[3]. They include the TE01 extractor, the TE11 to TE01 converter, and the TE11 to TE12 converter for TE12 mode. HFSS calculation of the system, which consists of TE01 extractor and TE11 to TE01 converter, shows that the transmission efficiency of each mode is better than 95%. A low power test model for the mode stability experiment in 55m long wave guide in DLDS is also being developed. Further study is underway.
17279318
THE PROPOSED EXPERIMENTAL STUDY ON BEAM-PHOTOELECTRON INTERACTIONS IN BEPC
A vertical collective effect suspected as photoelectron instability (PEI) has been observed at Photon Factory (PF) of KEK in recent years. This phenomena may impose a limitation on the performance of the proposed B-Factories or T-c Factories. An experiment has been planned to test it using positron beam at Beijing Electron Positron Collider (BEPC) in 1996 under the cooperation between IHEP and KEK. Preliminary simulation results have shown that the PEI may occur in BEPC on the total beam current level of 40 mA over more than 20 bunches. The instrumentation for observation of PEI is jointly prepared by both sides of IHEP and KEK. The machine study has been scheduled and the experiment will progress under the conditions of the best machine performance.
119741336
Electron cloud instability studies in the Beijing Electron Positron Collider
The electron cloud instability (ECI) in the Beijing Electron Positron Collider (BEPC) was studied systematically with experiments and simulations in recent years. Several electron cloud detectors have been installed into the BEPC storage ring to measure the electron yield. The effects of solenoid, the clearing electrode, the chromaticity, and the octupole on ECI have been investigated in BEPC experimentally. To evaluate the ECI in BEPCII, the upgrade project of BEPC, a computer code has been developed to simulate the electron density in the antechamber under different conditions, as well as the progress of the single bunch and coupled-bunch instabilities caused by the electron cloud. The experimental and simulation results, as well as the activities, are reported in this paper.
16640761
Recent studies on beam-photoelectron instability in BEPC
An experiment investigating the photoelectron instability has been performed in BEPC at IHEP, China. The betatron oscillation of each bunch was observed and recorded by a single pass beam position monitor system which has a capability to measure the transverse position of every bunch over 16000 turns. The effect of an octupole magnet on the instability was also studied. This paper describes results of those observations and analyses.
54864896
BEAM INSTABILITIY STUDIES OF BEPC AND BEPCII
BEPC has been well operated for more than 15 years, and it will be upgraded to a double ring electron positron collider in the existing tunnel, namely BEPCII. This paper describes the recent studies on beam instabilities for the improvement of BEPC performance as well as for BEPCII. The instabilities caused by impedance and twostream effects are investigated. The experimental and simulation results are reported.
73585218
PRELIMINARY STUDY OF THE BEPCII IMPEDANCE
This paper summarizes the preliminary results on the impedance study of BEPCII, which is the upgrade of Beijing Electron Positron Collider (BEPC). Focus is on the longitudinal broadband impedance, which may lead to bunch lengthening and microwave instability. With the impedance of its main generating vacuum components being investigated, a primary impedance budget is obtained. The estimated impedance is below the impedance threshold of microwave instability.
118584432
Search for pair production of excited top quarks in the lepton + jets final state
A bstractA search is performed for pair-produced spin-3/2 excited top quarks t∗t¯∗$$ \left({\mathrm{t}}^{\ast }{\overline{\mathrm{t}}}^{\ast}\right) $$, each decaying to a top quark and a gluon. The search uses data collected with the CMS detector from pp collisions at a center-of-mass energy of s$$ \sqrt{s} $$ = 8 TeV, selecting events that have a single isolated muon or electron, an imbalance in transverse momentum, and at least six jets, of which one must be compatible with originating from the fragmentation of a b quark. The data, corresponding to an integrated luminosity of 19.5 fb−1, show no significant excess over standard model predictions, and provide a lower limit of 803 GeV at 95% confidence on the mass of the spin-3/2 t* quark in an extension of the Randall-Sundrum model, assuming a 100% branching fraction of its decay into a top quark and a gluon. This is the first search for a spin-3/2 excited top quark performed at the LHC.

9536870
SLAC high gradient testing of a KEK X-band accelerator structure
The high accelerating gradients required for future linear colliders demands a better study of field emission and RF breakdown in accelerator structures. Changes in structure geometry, vacuum pumping, fabrication methods, and surface finish can all potentially impact the conditioning process, dark current emission, and peak RF power handling capability. Recent tests at SLAC of KEK's "M2" travelling wave X-band accelerator section provides an opportunity to investigate some of these effects by comparing its performance to previously high power tested structures at SLAC. In addition to studying ultimate power limitations, this test also demonstrates the use of computer automated conditioning to reach practical, achievable gradients.
125677368
Observation of color suppressed anti-B0 ---> D(*)0 X0 decays
55601369
50 MW X-BAND RF SYSTEM FOR A PHOTOINJECTOR TEST STATION AT LLNL
In support of X-band photoinjector development efforts at LLNL, a 50 MW test station is being constructed to investigate structure and photocathode optimization for future upgrades. A SLAC XL-4 klystron capable of generating 50 MW, 1.5 microsecond pulses will be the high power RF source for the system. Timing of the laser pulse on the photocathode with the applied RF field places very stringent requirements on phase jitter and drift. To achieve these requirements, the klystron will be powered by a state of the art, solid-state, high voltage modulator. The 50 MW will be divided between the photoinjector and a traveling wave accelerator section. A high power phase shifter is located between the photoinjector and accelerator section to adjust the phasing of the electron bunches with respect to the accelerating field. A variable attenuator is included on the input of the photoinjector. The distribution system including the various x-band components is being designed and constructed. In this paper, we will present the design, layout, and status of the RF system.
111355896
GROUND VIBRATION MEASUREMENT AT NSRRC SITE
For the future TPS project in the NSRRC, ground vibration would be important for this new machine. We have monitored the ground vibration under various experimental conditions at NSRRC site. Sensors were installed in different sites, on the ground and underground in different depth up to 40 meters. From the collected data, we compare the effect of day and night, traffic effect, and internal machine vibration. Specific vibration sources and their propagations are also discussed.