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.

title: Some aspects in accelerator structure studies at SLAC
abstract: 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.

title: Accelerator Structure Development for NLC / GLC *
abstract: The NLC (Next Linear Collider) and GLC (Global Linear Collider)  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.

title: The Development of the Linac Coherent Light Source RF Gun
abstract: 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.

title: Performance of a 1.3 GHz Normal-Conducting 5-Cell Standing-Wave Cavity
abstract: A 5-cell, normal-conducting, 1.3 GHz, standing-wave (SW) cavity was built as a prototype capture accelerator for the ILC positron source. Although the ILC uses predominantly superconducting cavities, the capture cavity location in both a high radiation environment and a solenoidal magnetic field requires it to be normal conducting. With the relatively high duty ILC beam pulses (1 msec at 5 Hz) and the high gradient required for efficient positron capture (15 MV/m), achieving adequate cavity cooling to prevent significant detuning is challenging. This paper presents the operational performance of this cavity including the processing history, characteristics of the breakdown events and the acceleration gradient witnessed by a single bunch at different injection times for different rf pulse lengths.

title: Traveling wave structure optimization for the NLC
abstract: 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.

title: ATF2 proposal. Vol. 2
abstract: The two major goals for this facility, called ATF2, are : (A) Achievement of a 37 nm beam size, and (B) control of beam position down to 2 nm level. The scientific justification for the ATF2 project and its technical design have been described in Volume 1 of the ATF2 Proposal. We present here Volume 2 of the ATF2 Proposal, in which we present specifics of the construction plans and the group organization to execute the research programs at ATF2.

title: Results of the SLAC LCLS gun high-power RF tests
abstract: The beam quality and operational requirements for the Linac coherent light source (LCLS) currently being constructed at SLAC are exceptional, requiring the design of a new RF photocathode gun for the electron source. Based on operational experience at SLAC's GTF and SDL and ATF at BNL as well as other laboratories, the 1.6 cell s-band (2856 MHz) gun was chosen to be the best electron source for the LCLS, however a significant re-design was necessary to achieve the challenging parameters. Detailed 3-D analysis and design was used to produce near-perfect rotationally symmetric rf fields to achieve the emittance requirement. In addition, the thermo-mechanical design allows the gun to operate at 120 Hz and a 140 MV/m cathode field, or to an average power dissipation of 4 kW. Both average and pulsed heating issues are addressed in the LCLS gun design. The first LCLS gun is now fabricated and has been operated with high-power RF. The results of these high-power tests are presented and discussed.

title: Magnetic tuning of the relativistic BCS-BEC crossover
abstract: The effect of an applied magnetic field in the crossover from Bose-Einstein condensate (BEC) to Bardeen-Cooper-Schrieffer (BCS) pairing regimes is investigated. We use a model of relativistic fermions and bosons inspired by those previously used in the context of cold fermionic atoms and in the magnetic-color-flavor-locking phase of color superconductivity. It turns out that as with cold atom systems, an applied magnetic field can also tune the BCS-BEC crossover in the relativistic case. We find that no matter what the initial state is at B=0, for large enough magnetic fields the system always settles into a pure BCS regime. In contrast to the atomic case, the magnetic field tuning of the crossover in the relativistic system is not connected to a Feshbach resonance, but to the relative numbers of Landau levels with either BEC or BCS type of dispersion relations that are occupied at each magnetic field strength.

title: X-ray absorption variability in NGC 4507
abstract: We present a complete spectral analysis of an XMM-Newton and Chandra campaign of the obscured AGN in NGC 4507, consisting of six observations spanning a period of six months, ranging from June 2010 to December 2010. We detect strong absorption variability on time scales between 1.5 and 4 months, suggesting that the obscuring material consists of gas clouds at parsec-scale distance. The lack of significant variability on shorter time scales suggests that this event is not due to absorption by broad line region clouds, which was instead found in other studies of similar sources. This shows that a single, universal structure of the absorber (either BLR clouds, or the parsec-scale torus) is not enough to reproduce the observed complexity of the X-ray absorption features of this AGN.

title: X-BAND TEST STATION AT LAWRENCE LIVERMORE NATIONAL LABORATORY ∗
abstract: An X-band multi-bunch test station is being built at LLNL to investigate the science and technology paths required to boost the current mono-energetic gamma-ray (MEGa-Ray) brightness by orders of magnitude. The test station will consist of a 5.5 cell X-band RF photoinjector, single accelerator section, and beam diagnostics. Beam quality must be exceedingly high in order to produce narrow-bandwidth gamma-rays, requiring a robust state of the art photoinjector. The photoinjector will be a high gradient (200 MV/m peak surface field on the cathode) standing wave structure, featuring a dual feed racetrack coupler, elliptical irises, and an optimized first cell length. A solidstate Scandinova modulator will power a single SLAC XL4 11.424 GHz 50 MW klystron. RF distribution will allow for full powering of the photoinjector with the balance of the RF powering a single accelerator section so that the electron parameters can be measured. The status of the facility will be presented including commissioning schedule and first experiment plans. Future experimental programs pertinent to Compton scattering R&D, high gradient structure testing, and light source development will be discussed.