54649249
ADVANCED X-BAND TEST ACCELERATOR FOR HIGH BRIGHTNESS ELECTRON AND GAMMA RAY BEAMS
In support of Compton scattering gamma-ray source efforts at LLNL, a multi-bunch test stand is being developed to investigate accelerator optimization for future upgrades. This test stand will enable work to explore the science and technology paths required to boost the current 10 Hz monoenergetic gamma-ray (MEGa-Ray) technology to an effective repetition rate exceeding 1 kHz, potentially increasing the average gamma-ray brightness by two orders of magnitude. Multiple bunches must be of exceedingly high quality to produce narrow-bandwidth gamma-rays. Modeling efforts will be presented, along with plans for a multi-bunch test stand at LLNL. The test stand will consist of a 5.5 cell X-band rf photoinjector, single accelerator section, and beam diagnostics. The photoinjector will be a high gradient standing wave structure, featuring a dual feed racetrack coupler. The accelerator will increase the electron energy so that the emittance can be measured using quadrupole scanning techniques. Multi-bunch diagnostics will be developed so that the beam quality can be measured and compared with theory. Design will be presented with modeling simulations, and layout plans.
119978196
Some aspects in accelerator structure studies at SLAC
Recent progress in the accelerator structure studies at SLAC is reported. This paper covers the room temperature accelerator structures for the ILC e+/e− sources; RF structures for some photon science projects including RF deflectors and the LCLS RF gun; the high gradient accelerator R&D in a global CLIC collaboration for the future multi-TeV linear colliders.
119247224
The Development of the Linac Coherent Light Source RF Gun
The Linac Coherent Light Source (LCLS) is the first x-ray laser user facility based upon a free electron laser (FEL). In addition to many other stringent requirements, the LCLS XFEL requires extraordinary beam quality to saturate at 1.5 angstroms within a 100 meter undulator.[1] This new light source is using the last kilometer of the three kilometer linac at SLAC to accelerate the beam to an energy as high as 13.6 GeV and required a new electron gun and injector to produce a very bright beam for acceleration. At the outset of the project it was recognized that existing RF guns had the potential to produce the desired beam but none had demonstrated it. This paper describes the analysis and design improvements of the BNL/SLAC/UCLA s-band gun leading to achievement of the LCLS performance goals.
13214805
Accelerator Structure Development for NLC / GLC *
The NLC (Next Linear Collider) and GLC (Global Linear Collider) [1,2] are e e linear collider proposals based on room-temperature accelerator technology – so called “warm machines” in comparison with the TESLA “cold machine” that is based on superconducting accelerator technology. There have been two major challenges in developing X-band (11.4 GHz) accelerator structures for the GLC/NLC. The first is to demonstrate stable, long-term operation at the high gradient (65 MV/m) that is required to optimize the machine cost. The second is to strongly suppress the beam induced long-range wakefields, which is required to achieve high luminosity. The development of high gradient structures has been a high priority in recent years. Nearly thirty X-band structures with various rf parameters, cavity shapes and coupler types have been fabricated and tested since 2000. This program has been a successful collaborative effort among groups at SLAC, KEK, FNAL and other labs. A summary of the main achievements and experiences are presented in this paper as well as a status report on the structure design, high power performance, manufacturing techniques, and other structure related issues.
55989671
Traveling wave structure optimization for the NLC
The JLC/NLC linac must accelerate multi-bunch beams in order to obtain a luminosity >3/spl times/10/sup 34/ cm/sup -2/ sec/sup -1/ at a center of mass energy of 1 TeV. It is essential for the structure design to minimize the long and short-range dipole wakefields to prevent emittance degradation and the beam breakup instability (BBU). In addition, the structures must operate at a high RF gradient to minimize the linac cost. High-power testing of prototype structures at SLAC has shown noticeable damage. The damage is largest in the front of the structure, where the group velocity is high, and there is minimal or no damage at the back end, where the group velocity is low. Theoretical analysis using a simple circuit model suggests using structures with a lower group velocity, on the order of a few percent, would be a way of avoiding damage. For the standard 2/spl pi//3 accelerating mode, it is difficult to lower the group velocity without losing efficiency or increasing the wakefields. With this in mind, we have taken the phase advance as an additional parameter in structure optimization. We found that a low group velocity structure at higher phase advance can maintain high RF efficiency and low wakefields. In this paper, we study the impact of phase advance on structure performance. We then optimize the NLC S-band and X-band structures to meet design requirements.
109333657
RF Design of X-Band RF Deflector for Femtosecond Diagnostics of LCLS Electron Beam
We designed a successful constant impedance traveling wave X-band rf deflector for electron beam diagnostics at the 14 GeV SLAC Linac Coherent Light Source (LCLS). This is the first practical deflector built with a waveguide coupler. The 1-meter rf deflector produces 24 MeV peak transverse kick when powered with 20 MW of 11.424 GHz rf. The design is based on our experience with high gradient X-band accelerating structures. Several deflectors of this design have been built at SLAC and are currently in use. Here we describe the design and distinguishing features of this device.
119213652
Production of $B_c$ or $\bar{B}_c$ meson and its excited states via $\bar{t}$ quark or $t$ quark decays
The production of (bc)-quarkonium (B{sub c} meson and its excited states) or (cb)-quarkonium (B{sub c} meson and its excited states) via top quark t or top antiquark t decays, t{yields}(bc)+c+W{sup +} or t{yields}(cb)+c+W{sup -}, respectively, is studied within the framework of NRQCD. In addition to the production of the two color-singlet S-wave states |(bc)({sup 1}S{sub 0}){sub 1}> or |(cb)({sup 1}S{sub 0}){sub 1}> and |(bc)({sup 3}S{sub 1}){sub 1}> or |(cb)({sup 3}S{sub 1}){sub 1}>, the production of the P-wave excited (bc) or (cb) states, i.e. the four color-singlet P-wave states |(bc)({sup 1}P{sub 1}){sub 1}> or |(cb)({sup 1}P{sub 1}){sub 1}>, and (bc)({sup 3}P{sub J}){sub 1}> or (cb)({sup 3}P{sub J}){sub 1}> (with J=(1,2,3)), is also studied. According to the velocity scaling rule of NRQCD, for the production of P-wave excited states the contributions from the two color-octet components |(bc)({sup 1}S{sub 0}){sub 8}> or |(cb)({sup 1}S{sub 0}){sub 8}> and |(bc)({sup 3}S{sub 1}){sub 8}> or |(cb)({sup 3}S{sub 1}){sub 8}> are also taken into account. We quantitatively discuss the possibility and the advantages in experimental studies of B{sub c} or B{sub c} meson and its excited states via the indirect production at LHC in high luminosity runs and at LHC possible upgraded versions such as SLHC, DLHC,more » TLHC, etc. in the future.« less
110785158
Measurement of wakefields generated in accelerator test structures using the SLC
Research is underway at SLAC to develop accelerator structures for the next generation linear collider. An important feature of the design is a detuning of the dipole moddes -of the cells to suppress the long-range transverse wakefield bptwo orders of magnitude. This paper describes a facility, called ASSET, that will be incorporated into the SLAC Linear Collider (SLC) to test the long-range wakefield suppression and also to measure the other components of the wakefields generated in accelerator test structures. _- 1 INTRGDUCTION The-designs being considered at SLAC for the Next Linear Collider (NLC) employ multi-bunch operation in a high acceleration -gradient X-band linac. The limitations in this _ __ approach come in part from the transverse and longitudinal wakefields generated in the accelerator structures of the linac. A particularly troublesome problem is the long-range transverse wakefield, -which if not controlled, will produce a large growth in the transverse motion of the bunches. The .currently favored cure for this problem is to detune the dipole mode frequencies of the cells of the structures so the sum of the wakefields generated in each structure decohere (l). Since a two orders of magnitude reduction is required, and the theoretical calculations of the suppression (2) have some uncertainty, it is important that the performance of the structures be verified before they are produced for use in an accelerator. Thus far, measurements of the wakefield suppression have been made on short-length detuned structures at Argonne's Advanced Accelerator Test Facility (3). Although the results look promising, this facility currently does not have the measurement precision required for the NLC structures being developed, nor the capability of measuring the wakefields beyond a few ns compared to the few hundred ns needed. In the future, the plan is to do the measurements at SLAC with a dedicated facility called the Accelerator Structure SETup or ASSET (4). It exploits the "asset" of the-SLC in its capability to independently inject two low emittance bunches (electrons and positrons) into the linac with individual control of the bunch timing and intensity. The layout for. ASSET. is shown in figure 1. It is divided into two sect*3 that.will take the place of the first two 3
109163764
International X-Band Linear Collider Accelerator Structure R&D
For more than fifteen years before the International Technology Recommendation Panel (ITRP) decision in August, 2004, there were intensive R&D activities and broad international collaboration among the groups at SLAC, KEK, FNAL, LLNL and other labs for the room temperature X-Band accelerator structures. The goal was to provide an optimized design of the main linac structure for the NLC (Next Linear Collider) or GLC (Global Linear Collider). There have been two major challenges in developing X-band accelerator structures for the linear colliders. The first is to demonstrate stable, long-term operation at the high gradient (65 MV/m) that is required to optimize the machine cost. The second is to strongly suppress the beam induced long-range wakefields, which is required to achieve high luminosity. More than thirty X-band accelerator structures with various RF parameters, cavity shapes and coupler types have been fabricated and tested since 1989. A summary of the main achievements and experiences are presented in this talk including the structure design, manufacturing techniques, high power performance, and other structure related issues. Also, the new progress in collaborating with the CLIC, high gradient structures and X-Band structure applications for RF deflectors and others are briefly introduced.
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.
119287240
Searches for Majorana neutrinos in $B^-$ decays
Searches for heavy Majorana neutrinos in B- decays in final states containing hadrons plus a \mu- \mu- pair have been performed using 0.41/fb of data collected with the LHCb detector in proton-proton collisions at a center-of-mass energy of 7 TeV. The D+ \mu- \mu- and D*+ \mu- \mu- final states can arise from the presence of virtual Majorana neutrinos of any mass. Other final states containing \pi+, Ds+, or D0\pi+ can be mediated by an on-shell Majorana neutrino. No signals are found and upper limits are set on Majorana neutrino production as a function of mass, and also on the B- decay branching fractions.