11870821
Analysis And Application Of Manifold Radiation In DDS 1 : First Experiences 1
The cells in the SLAC DDS are designed in such a way that the transverse modes excited by the beam are detuned in a Gaussian fashion so that destructive interference causes the wake function to decrease rapidly and smoothly. Moderate damping provided by four waveguide manifolds running along the outer wall of the accelerator is utilised to suppress the reappearance of the wake function at long ranges where the interference becomes constructive again. The newly developed spectral function method, involving a continuum of frequencies, is applied to analyze the wake function of the DDS 1 design and to study the dependence of the wake function on manifold termination. The wake function obtained with the actually realized manifold terminations is presented and compared to wake function measurements recently carried out at the ASSET facility installed in the SLAC LINAC. Paper presented at the 7 Workshop on Advanced Accelerator Concepts, Lake Tahoe, CA, October 13-19 1996 1 Supported by Department of Energy grant number DE-FG03-93ER40759 and DE-AC0376SF00515 Analysis And Application Of Manifold Radiation In DDS 1: First Experiences R.M. Jones , N.M. Kroll, M. Seidel , C. Adolphsen, K.L.F. Bane, W.R.Fowkes, K. Ko, R.H. Miller, R.D. Ruth, and J.W. Wang †Stanford Linear Accelerator Center, M/S 26, P.O Box 4349, Stanford, CA 94309 ‡ University of California, San Diego, La Jolla, CA 92093-0319 Abstract. The frequency spectrum of the manifold radiation resulting from a uniformly displaced drive beam in DDS 1 has been calculated utilising the spectral function theory and compared with observations in the ASSET experiment. They are found to be in good qualitative agreement. The bulk of the radiation, both measured and computed, is found to emerge from the downstream end of the manifolds. This is in conflict with perturbation theory predictions, and is thus one more indication of the unreliability of perturbation theory for estimating manifold effects for DDS 1. Beam centering as a function of frequency is accomplished by minimizing manifold radiation within a narrow frequency band. This procedure provides information on structure misalignment. While misalignments in DDS 1 degraded the precision of beam centering which could be achieved by minimizing manifold radiation, the results obtained are considered to be encouraging. The frequency spectrum of the manifold radiation resulting from a uniformly displaced drive beam in DDS 1 has been calculated utilising the spectral function theory and compared with observations in the ASSET experiment. They are found to be in good qualitative agreement. The bulk of the radiation, both measured and computed, is found to emerge from the downstream end of the manifolds. This is in conflict with perturbation theory predictions, and is thus one more indication of the unreliability of perturbation theory for estimating manifold effects for DDS 1. Beam centering as a function of frequency is accomplished by minimizing manifold radiation within a narrow frequency band. This procedure provides information on structure misalignment. While misalignments in DDS 1 degraded the precision of beam centering which could be achieved by minimizing manifold radiation, the results obtained are considered to be encouraging.
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.
36955336
Measurements of Ultimate Accelerating Gradients in the SLAC Disk-Loaded Structure
The work reported here describes measurements made to study the maximum attainable accelerating gradients in a conventional SLAC disk-loaded accelerator section of the constant-gradient type running at 2856 MHz. The objective was to reach an accelerating gradient of at least 100 MV/m. The accelerating gradient at which the SLAC disk-loaded waveguide runs routinely is approx. 9 MV/m (36 MW tubes without SLED) and approx. 12 MV/m with SLED I (2.5 ..mu..sec pulse). To reach 100 MV/m in a conventional 3 m constant-gradient section, one would need a klystron with a peak power output of 900 MW. since such a tube is not available, we decided to use a short standing-wave section in which the resonant fields would be allowed to build up. The design criteria for this section, the fabrication, matching and tuning, the experimental set-up and the results are described below.
17263744
RF POWER SOURCES FOR LINEAR COLLIDERS
The next generation of linear colliders requires peak power sources of over 200 MW per meter at frequencies above 10 GHz at pulse widths of less than 100 nsec. Several power sources are under active development, including a conventional klystron with rf pulse compression, a relativistic klystron (RK) and a crossed-field amplifier. Power from one of these has energized a 0.5 meter two- section High Gradient Accelerator (HGA) and accelerated a beam at over 80 MeV meter. Results of tests with these experimental devices are presented here.
45575016
MANIFOLD DAMPING OF WAKEFIELDS IN HIGH PHASE ADVANCE LINACS FOR THE NLC
Earlier RDDS (Rounded Damped Detuned Structures) [1,2], designed, fabricated and tested at SLAC, in collaboration with KEK, have been shown to damp wakefields successfully. However, electrical breakdown has been found to occur in these structures and this makes them inoperable at the desired gradient. Recent results [3] indicate that lowering the group velocity of the accelerating mode reduces electrical breakdown events. In order to preserve the filling time of each structure a high synchronous phase advance (150 degrees as opposed to 120 used in previous NLC designs) has been chosen. Here, damping of the wakefield is analyzed. Manifold damping and interleaving of structure cell frequencies is discussed. These wakefields impose alignment tolerances on the cells and on the structure as a whole. Tolerance calculations are performed and these are compared with analytic estimations.
123848492
Modeling and design of an X-band rf photoinjector
A design for an X-band rf photoinjector that was developed jointly by SLAC National Accelerator Laboratory (SLAC) and Lawrence Livermore National Laboratory (LLNL) is presented. The photoinjector is based around a 5.59 cell rf gun that has state-of-the-art features including: elliptical contoured irises; improved mode separation; an optimized initial half cell length; a racetrack input coupler; and coupling that balances pulsed heating with cavity fill time. Radio-frequency and beam dynamics modeling have been done using a combination of codes including PARMELA, HFSS, IMPACT-T, ASTRA, and the ACE3P suite of codes developed at SLAC. The impact of lower gradient operation, magnet misalignment, solenoid multipole errors, beam offset, mode beating, wakefields, and beam line symmetry have been analyzed and are described. Fabrication and testing plans at both LLNL and SLAC are discussed.
118552734
Next-to-leading order QCD effect of $W'$ on top quark Forward-Backward Asymmetry
We present the calculations of the complete next-to-leading order (NLO) QCD corrections to the total cross section, invariant mass distribution and the forward-backward asymmetry ($\rm A_{FB}$) of top quark pair production mediated by $W'$ boson. Our results show that in the best fit point in the parameter space allowed by data at the Tevatron, the NLO corrections change the new physics contributions to the total cross section slightly, but increase the $\rm A_{FB}$ in the large invariant mass region by about 9%. Moreover, we evaluate the total cross section and charge asymmetry ($\rm{A}_{\rm{C}}$) of top pair production at the LHC, and find that both total cross section and $A_{\rm C}$ can be used to distinguish NP from SM with the integrated luminosity increasing.
125850686
Transverse Feedback System and Instability Analysis at HLS
In this paper, the BxB transverse feedback systems at Hefei Light Source (HLS) are introduced, which employ an analog system and a digital system. The experiment result of two systems. as well as the primary analysis of beam instability in HLS operation is also presented in this paper. INTRODUCTION HLS is a synchrotron light source,injecting in the energy of 200MeV and operating in the 800MeV. The multi-cycle multi-turn injection system is used for current accumulation. The range of horizontal tune of HLS is from 3.54 to 3.56, and the range of vertical tune is from 2.58 to 2.60 for user operation. The injecting beam current usually cannot exceed 120mA without octupole magnet, and the injecting accumulating beam current is about 250mA with octupole magnet because the beam often occur sudden lose due to CB instabilities in storage ring to limit injection further increase. Therefore the constructing beam feedback system began from 2006 year. The analog feedback system has been built and commissioned at 2007[1-3], At the same time, the development of digital transverse BxB feedback system began at 2007 and has commissioned since 2008[4]. THE ANALOG TFB SYSTEM AND EXPERIMENT RESULTS The diagram of analog TFB system is shown as Figure 1. The analog feedback system is made up of: 3tap filter at centre frequency 612MHz (3*fRF) , hybrid for obtaining beam position oscillation signal, vector algorithm for two BPMs to obtain feedback signal of independent adjustable gain, multiple frequency circuit for centre frequency 612MHz (3*fRF) and 1.2GHz (6*fRF), PXI digitizer for data acquisition modular, the fiber correlator filter for eliminate DC and revolution frequencies, the power amplifier and kicker for exciting beam current. Commissioning Results of Analog TFB at HLS During the commissioning, the damping time and betatron sidebands have been measured by Turn-by-Turn (TBT) [5].and bunch-by-bunch (BXB) [6]. measurement system at beam injecting is shown as Figure 1. Figure 1: Overview of HLS analog TFB after update
126420285
Table 55 ; Measurement of the pseudorapidity and transverse momentum dependence of the elliptic flow of charged particles in lead-lead collisions at $\sqrt{s_{NN}}=2.76$ TeV with the ATLAS detector
56206479
SOURCE OF MICROBUNCHING AT BNL NSLS SOURCE DEVELOPMENT LABORATORY
We report experimental studies of the origins of electron beam microbunching instability at BNL Source Development Laboratory (SDL). We eliminated laser-induced microbunching by utilizing an ultra-short photocathode laser. The measurements of the resulting electron beam led us to conclude that, at SDL, microbunching arising from shot noise is not amplified to any significant level. Our results demonstrated that the only source of microbunching instability at SDL is the longitudinal modulation of the photocathode laser pulse. Our work shows that assuring a longitudinally smoothed photocathode laser pulse allows mitigating microbunching instability at a typical FEL injector with a moderate microbunching gain. In this paper we investigated the source of microbunching instability at the SDL. To distinguish microbunching induced by shot noise from that arising from the longitudinal modulation of the photocathode laser, we studied the beam created by a very short laser pulse, thus eliminating the possibility of laser-induced microbunching. While the measured energy spectra of compressed beam did reveal severe longitudinal fragmentation, an analysis of the beam dynamics proved this to be due to self-fields acting on a beam with an initially smooth longitudinal profile, and not due to microbunching instability. Such fragmentation only was possible with the very short bunch chosen for these studies, and is absent in routine SDL operations. Our experiment shows that in the absence of the initial laser-induced beam modulation, microbunching instability at the SDL is not observed, and must be well below the levels that would limit the FEL performance. This result agrees with assumption of previous SDL studies that (when present under different machine conditions) microbunching instability at the SDL was laser-induced. Microbunching instability gain at the SDL is moderate. This is mainly because the SDL utilizes a single stage bunch compressor as well as due to the small compression ratio. Since the design of the SDL injector is typical of the majority of FEL injectors, our experiment proves that one possible way to control microbunching instability in such machines (that by design have a moderate microbunching gain) is to maintain a sufficiently smooth longitudinal profile of the photo-cathode laser. We note that the general principles for designing a machine with a moderate microbunching instability gain are presented in [12]. In conclusion, our experiment demonstrates that microbunching instability can be eliminated from a typical FEL injector with single stage bunch compressor (and operating without a laser heater) as long as the photocathode laser is longitudinally smooth. For machines with multi-stage bunch compressors, our results offer an important benchmark to establish a minimal laser heater power for instability-free operation.
53133059
Phenomenology of an extended Higgs portal inflation model after Planck 2013
We consider an extended inflation model in the frame of Higgs portal model, assuming a nonminimal coupling of the scalar field to the gravity. Using the new data from Planck $$2013$$2013 and other relevant astrophysical data, we obtain the relation between the nonminimal coupling $$\xi $$ξ and the self-coupling $$\lambda $$λ needed to drive the inflation, and find that this inflationary model is favored by the astrophysical data. Furthermore, we discuss the constraints on the model parameters from the experiments of particle physics, especially the recent Higgs data at the LHC.