55635310
Study of Beam Diagnostics with Trapped Modes in Third Harmonic Superconducting Cavities at FLASH
Off-axis beams passing through an accelerating cavity excite dipole modes among other higher order modes (HOMs). These modes have linear dependence on the transverse beam offset from the cavity axis. Therefore they can be used to monitor the beam position within the cavity. The fifth dipole passband of the third harmonic superconducting cavities at FLASH has modes trapped within each cavity and do not propagate through the adjacent beam pipes, while most other cavity modes do. This could enable the beam position measurement in individual cavities. This paper investigates the possibility to use the fifth dipole band for beam alignment in the third harmonic cavity module. Simulations and measurements both with and without beam-excitations are presented. Various analysis methods are used and compared. A good correlation of HOM signals to the beam position is observed.
7866182
Higher Order Modes for Beam Diagnostics in Third Harmonic 3.9 GHz Accelerating Module
An international team is currently investigating the best way to use Higher Order Modes (HOM) for beam diagnostics in 3.9 GHz cavities. HOMs are excited by charged particles when passing through an accelerating structure. Third harmonic cavities working at 3.9 GHz have been installed in FLASH to linearize the bunch energy profile. A proof-of-principle of using HOMs for beam monitoring has been made at FLASH in the TESLA 1.3 GHz cavities. Since the wakefields generated in the 3.9 GHz cavities are significantly larger, their impact on the beam should be carefully minimized. Therefore our target is to monitor HOMs and minimize them by aligning the beam on the cavity axis. The difficulty is that, in comparison to the 1.3 GHz cavities, the HOM-spectrum is dense, making it difficult to identify individual modes. Also, most modes propagate through the whole cryomodule containing several cavities, making it difficult to measure local beam properties. In this paper the options for the HOM-based beam position monitors are discussed.
116900231
Higher order mode spectra and the dependence of localized dipole modes on the transverse beam position in third harmonic superconducting cavities at FLASH
An electron beam entering an accelerating cavity excites a wakefield. This wakefield can be decomposed into a series of multi-poles or modes. The dominant component of the transverse wakefield is dipole. This report summarizes the higher order mode (HOM) signals of the third harmonic cavities of FLASH measured at various stages: transmission measurements in the single cavity test stand at Fermilab, at CMTB (Cryo-Module Test Bench) and at FLASH, and beam-excited measurements at FLASH. Modes in the first two dipole bands and the fifth dipole band have been identified using a global Lorentzian fit technique. The beam-pipe modes at approximately 4 GHz and some modes in the fifth dipole band have been observed as localized modes, while the first two dipole bands, containing some strong coupling cavity modes, propagate. This report also presents the dependence of the localized dipole modes on the transverse beam position. Linear dependence for various modes has been observed. This makes them suitable for beam position diagnostics. These modes, together with some propagating, strong coupling modes, have been considered in the design of a dedicated electronics for beam diagnostics with HOMs for the third harmonic cavities.
16733931
Cross correlations of the cosmic infrared background
The cosmic infrared background (CIB) is a sensitive measure of the star formation history. But this background is overwhelmed by foregrounds, which bias the CIB mean flux and auto correlation measurement severely. Since dominant foregrounds do not correlate with the large scale structure, the cross correlation of CIB with galaxies is free of such foregrounds and presents as an unbiased measure of the star formation history. This also allows the measurement of CIB based on integrated intensity, whose theoretical prediction is based on energy conservation, thus is fairly model independent and robust. The redshift information of CIB sources can be directly recovered with the aid of galaxy photometric redshifts. In the far IR region, correlation signal is around 10% at degree scale. Combining FIRAS and SDSS, the cross correlation can be measured with 20% accuracy (statistical and systematics errors) at $l\sim 40$. Such measurement would allow the measurement of star formation rate with comparable accuracies to $z\sim 1$. Future CIB experiments with $1^{\circ}$ resolution are able to measure the star formation rate with 10% accuracy to $z\sim 1.5$. Secondary CMB anisotropies arising from the large scale structure correlate with CIB. The correlation strength is about $0.5\mu$K at $\sim 10^{\circ}$ (the integrated Sachs-Wolfe effect) and $\sim -0.3\mu$K at $\sim 1^{\circ}$ (the Sunyaev Zeldovich effect, Rayleigh-Jeans regime). FIRAS+WMAP would allow the measurement of the ISW effect with $\ga 5\sigma$ confidence. Its detection helps to constrain the amount of dark energy and far IR emissivity bias.
119121382
Transverse shifts in paraxial spinoptics
The paraxial approximation of a classical spinning photon is shown to yield an "exotic particle" in the plane transverse to the propagation. The previously proposed and observed position shift between media with different refractive indices is modified when the interface is curved, and there also appears a novel, momentum [direction] shift. The laws of thin lenses are modified accordingly.
9177547
TOPOLOGICAL STRUCTURE OF THE MANY VORTICES SOLUTION IN JACKIW–PI MODEL
By using the gauge potential decomposition, we discuss the self-dual equation and its solution in Jackiw–Pi model. We obtain a new concrete self-dual equation and find relationship between Chern–Simons vortices solution and topological number which is determined by Hopf indices and Brouwer degrees of Ψ-mapping. To show the meaning of topological number we give several figures with different topological numbers. In order to investigate the topological properties of many vortices, we use five parameters (two positions, one scale, one phase per vortex and one charge of each vortex) to describe each vortex in many vortices solutions in Jackiw–Pi model. For many vortices, we give three figures with different topological numbers to show the effect of the charge on the many vortices solutions. We also study the quantization of flux of those vortices related to the topological numbers in this case.
119681568
Topology, and (in)stability of non-Abelian monopoles
The stability problem of non-Abelian monopoles with respect to "Brandt-Neri-Coleman type" variations reduces to that of a pure gauge theory on the two-sphere. Each topological sector admits exactly one stable monopole charge, and each unstable monopole admits 2 Sigma(2 vertical bar q vertical bar - 1) negative modes, where the sum goes over the negative eigenvalues q of an operator related to the non-Abelian charge Q of Goddard, Nuyts and Olive. An explicit construction for the [up-to-conjugation] unique stable charge, as well as the negative modes of the Hessian at any other charge is given. The relation to loops in the residual group is explained. From the global point of view, the instability is associated with energy-reducing two-spheres, which, consistently with the Morse theory, generate the homology of the configuration space. Our spheres are tangent to the negative modes at the considered critical point, and may indicate possible decay routes of an unstable monopole as a cascade into lower lying critical points. (C) 2011 Elsevier Inc. All rights reserved.
15003877
SELF-CALIBRATION OF GRAVITATIONAL SHEAR-GALAXY INTRINSIC ELLIPTICITY CORRELATION IN WEAK LENSING SURVEYS
The galaxy intrinsic alignment is a severe challenge to precision cosmic shear measurement. We propose self-calibrating the induced gravitational shear-galaxy intrinsic ellipticity correlation (the GI correlation) in weak lensing surveys with photometric redshift measurements. (1) We propose a method to extract the intrinsic ellipticity-galaxy density cross-correlation (I-g) from the galaxy ellipticity-density measurement in the same redshift bin. (2) We also find a generic scaling relation to convert the extracted I-g correlation to the necessary GI correlation. We perform a concept study under simplified conditions and demonstrate its capability to significantly reduce GI contamination. We discuss the impact of various complexities on the two key ingredients of the self-calibration technique, namely the method for extracting the I-g correlation and the scaling relation between the I-g and the GI correlation. We expect that none of them will likely be able to completely invalidate the proposed self-calibration technique.