123590995
Influence of fabrication errors on wake function suppression in NC X-band accelerating structures for linear colliders
Wake function suppression is effected by ensuring that the mode frequencies of an X-band normal conducting (NC) accelerating structure of multiple cells are detuned and moderately damped by waveguide manifolds attached to the outer wall of the accelerator. We report on the dilution in the wake function suppression that occurs due to errors resulting from the fabrication process. After diffusion bonding 206 cells a non-uniform expansion in the cell geometry forces a substantial shift in the frequencies of select cells. We remap all circuit parameters to these shifted cell frequencies to predict the wake function. Experiments performed on the SLC at the SLAC National Accelerator Laboratory indicate that the wake function is well predicted by the circuit model.
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.
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.
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.
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.
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.
13432743
Search for lepton-flavor-violating decays of the neutral kaon.
The Fermilab KTeV experiment has searched for lepton-flavor-violating decays of the K(L) meson in three decay modes. We observe no events in the signal region for any of the modes studied, and we set the following upper limits for their branching ratios at the 90% C.L.: BR(K(L) --> pi(0) micro(+/-) e(-/+)) <7.6 x 10(-11); BR(K(L) --> pi(0)pi(0) micro(+/-) e(-/+)) <1.7 x 10(-10); BR(pi(0) --> micro(+/-) e(-/+)) <3.6 x 10(-10). This result represents a factor of 82 improvement in the branching ratio limit for K(L) --> pi(0) micro(+/-) e(-/+) and is the first reported limit for K(L) --> pi(0)pi(0) micro(+/-) e(-/+).
119245573
Observational constraints on unified dark matter including Hubble parameter data
Abstract We constrain a unified dark matter (UDM) model from the latest observational data. This model assumes that the dark sector is degenerate. Dark energy and dark matter are the same component. It can be described by an affine equation of state P X = p 0 + α ρ X . Our data set contains the newly revised H ( z ) data, type Ia supernovae (SNe Ia) from Union2 set, baryonic acoustic oscillation (BAO) observation from the spectroscopic Sloan Digital Sky Survey (SDSS) data release 7 (DR7) galaxy sample, as well as the cosmic microwave background (CMB) observation from the 7-year Wilkinson Microwave Anisotropy Probe (WMAP7) results. By using the Markov Chain Monte Carlo (MCMC) method, we obtain the results in a flat universe: Ω Λ = 0.719 − 0.0305 + 0.0264 ( 1 σ ) − 0.0458 + 0.0380 ( 2 σ ) , α = 1.72 − 4.79 + 3.92 ( 1 σ ) − 7.30 + 5.47 ( 2 σ ) ( × 10 − 3 ) , Ω b h 2 = 0.0226 − 0.0011 + 0.0011 ( 1 σ ) − 0.0015 + 0.0016 ( 2 σ ) . Moreover, when considering a non-flat universe, Ω Λ = 0.722 − 0.0447 + 0.0362 ( 1 σ ) − 0.0634 + 0.0479 ( 2 σ ) , α = 0.242 − 0.775 + 0.787 ( 1 σ ) − 1.03 + 1.10 ( 2 σ ) ( × 10 − 2 ) , Ω b h 2 = 0.0227 − 0.0014 + 0.0015 ( 1 σ ) − 0.0018 + 0.0021 ( 2 σ ) , Ω k = − 0.194 − 1.85 + 2.02 ( 1 σ ) − 2.57 + 2.75 ( 2 σ ) ( × 10 − 2 ) . These give a more stringent results than before. We also give the results from other combinations of these data for comparison. The observational Hubble parameter data can give a more stringent constraint than SNe Ia. From the constraint results, we can see the parameters α and Ω k are very close to zero, which means a flat universe is strongly supported and the speed of sound of the dark sector seems to be zero.
55420796
FABRICATION TECHNOLOGIES OF THE HIGH GRADIENT ACCELERATOR STRUCTURES AT 100MV/m RANGE
A CERN-SLAC-KEK collaboration on high gradient X-band structure research has been established in order to demonstrate the feasibility of the CLIC baseline design for the main linac stably operating at more than 100 MV/m loaded accelerating gradient. Several prototype CLIC structures were successfully fabricated and high power tested. They operated at 105 MV/m with a breakdown rate that meets the CLIC linear collider specifications of < 5 x 10{sup -7}/pulse/m. This paper summarizes the fabrication technologies including the mechanical design, precision machining, chemical cleaning, diffusion bonding as well as vacuum baking and all related assembly technologies. Also, the tolerances control, tuning and RF characterization will be discussed.
17930160
DAMPING EFFECT STUDIES FOR X-BAND NORMAL CONDUCTING HIGH GRADIENT STANDING WAVE STRUCTURES*
The Multi-TeV colliders should have the capability to accelerate low emittance beam with high rf efficiency, X-band normal conducting high gradient accelerating structure is one of the promising candidate. However, the long range transverse wake field which can cause beam emittance dilution is one of the critical issues. We examined effectiveness of dipole mode damping in three kinds of X-band, {pi}-mode standing wave structures at 11.424GHz with no detuning considered. They represent three damping schemes: damping with cylindrical iris slot, damping with choke cavity and damping with waveguide coupler. We try to reduce external Q factor below 20 in the first two dipole bands, which usually have very high (R{sub T}/Q){sub T}. The effect of damping on the acceleration mode is also discussed.
17717493
Slim disks with transition regions and applications to microquasars and narrow-line Seyfert 1 galaxies
Slim disks have been received much attention because of the increasing evidence of supercritical accreting objects. In this paper, we make an attempt to construct a unified model in which the viscosity and the dimensionless accretion rate can span rather wide ranges. We replace blackbody radiation under the diffusion approximation with a bridged formula that accounts for both blackbody radiation and thermal bremsstrahlung in optically thick and thin cases, respectively. Thus this allows us to investigate the structures of and the emergent spectra from slim disks in a wider parameter space covering transition regions from optically thick to optically thin. We show that there is a maximum transition radius, roughly R-tr,R-max/R-g similar to 50 when (M)(C) similar to 15. The emergent spectra from the unified model of the accretion disk have been calculated. A simple model of the hot corona above the slim disk is taken into account for the hard X-ray spectrum in this paper based on the work of Wang and Netzer. We have applied the present model to the microquasar GRS 1915+105 and the narrow-line Seyfert 1 galaxies RE J1034+396 and Ark 564. Our model can explain well the broadband X-ray spectra of narrow-line Seyfert 1 galaxies, microquasars, and possible ultraluminous compact X-ray sources. The present model can be widely applied to candidates for supercritical accreting objects.