120739371
High gradient test at Nextef and high-power long-term operation of devices
Abstract The X-band high gradient studies at Nextef, the 100 MW X-Band test station in KEK operated since 2008, is reviewed. Recent high power test results of TD18#2, an 18-cell CLIC prototype structure with HOM damping slots, are given. The measured breakdown rate is ∼10 −5 /pulse/m under the operation at 100 MV/m gradient with 250 ns rf pulse width. The rate is higher by one- to two-order compared with that of the T18 structure, which is a disk loaded structure without the HOM slots. The recent performance of the station is also reviewed, especially that of PPM klystrons is discussed. An overview of our on-going programs such as the pulse compression system of Nextef as well as the future plans of X-band study is given.
121413098
Multipactoring suppression by fine grooving of conductor surfaces of coaxial-line input couplers for high beam current storage rings
123321012
Performance and operation results of the RF systems at the KEK B-Factory
KEK B-Factory (KEKB) was terminated in 2010 after achieving the world record luminosity of 2.11 × 1034 cm−2s−1. This paper describes the design features, performance, and operation results of the KEKB RF systems, which include a lot of original RF technologies and methods to store an electron/positron beam over 1 A stably. To cope with beam instabilities caused by large beam currents, two new types of normal and superconducting (SC) cavities with large stored energy were developed and successfully operated. For a new beam colliding scheme called crab crossing, two SC crab cavities were introduced and boosted the peak luminosity. Performance of these cavities is reported, along with the lowlevel and high-power RF systems, and the cryogenic system for the SC cavities. The status of the RF system upgrade towards SuperKEKB, which aims at a luminosity of 8.0 × 1035 cm−2s−1, is briefly described. © The Author(s) 2013. Published by Oxford University Press on behalf of the Physical Society of Japan. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Disclaimer: Please note that abstracts for content published before 1996 were created through digital scanning and may therefore not exactly replicate the text of the original print issues. All efforts have been made to ensure accuracy, but the Publisher will not be held responsible for any remaining inaccuracies. If you require any further clarification, please contact our Customer Services Department. Copyright © 2013 The Physical Society of Japan Other Oxford University Press sites: Oxford University Press
119017224
Estimation of synchrotron-radiation background based on a real beam orbit
Some high-energy experiments have suffered from synchrotron-radiation background. As a measure, we have developed a new calculation method of synchrotron radiation based on a real beam orbit, aiming at quantitative estimations and the construction of a possible alarm system for the background. An explanation and a demonstration of our method are given.
54944635
Various Observables of TW Accelerator Structures Operating 100MV/m or Higher at X-band Facility, Nextef of KEK
Under the CERN-SLAC-KEK collaboration, we have been developing the high gradient TW accelerator structures. One of the main focuses is the feasibility study of CLIC accelerator structure at X-band. A high power facility, Nextef, was established at KEK in 2007. A few structures have been tested, including an un-damped diskloaded structure successfully tested beyond 100 MV/m, a heavily damped structure being tested now and a structure made in a quadrant configuration. These structures follow the same accelerating-mode RF parameter profile of the CLIC design, called CLIC-C, but showed very different features at high gradient operation. Various observables, such as dark current, vacuum activity, light emission, breakdown rate, and so on, were measured. We discuss the high gradient phenomena related to these observables. INTRODUCTION The collaboration program of the feasibility study on CLIC [1] accelerator structure was started since 2007 mainly lead by CERN, SLAC and KEK. At test facility Nextef of KEK, we have been testing three prototype structures to date. Last year, we have proved the operation of 100 MV/m [2]. Since then, we have tested two more structures, both equipped with heavy damping feature with magnetically coupled damping waveguides facing the accelerator cell. The surface temperature rise within a pulse has been recognized as a possible cause of breakdown trigger, though the mechanism not understood. The two structures tested last year are classified in this group with high surface pulse temperature rise. In the present paper are described those structure test results in various aspects of the high gradient performance to understand the physics behind. TEST ACCELERATOR STRUCTURES The test structures were electrically designed by CERN [3]. All the structures are equipped with 18 accelerating cells. The information on fabrication is listed in the Table 1. The un-damped structure (T18) and damped structure (TD18) was made each as one of the twins through SLAC –KEK collaboration based on GLC/NLC technology [4]. Another structure, called Quad_#5, was made by KEK with CuZr material [5]. The structures were tested with 60Hz at NLCTA of SLAC and with 50Hz at Nextef of KEK. Each one of the twins (T18_Disk and TD18_Disk) was tested at each laboratory, while the quadrant Quad_#5 described in this paper was tested at KEK. HIGH GRADIENT TEST RESULTS The test results compiling all those from SLAC and KEK are discussed [6].
119235875
Does the three site Higgsless model survive the electroweak precision tests at loop
We complete the list of one-loop renormalization group equations and matching conditions relevant for the computation of the electroweak precision parameters $S$ and $T$ in the three site Higgsless model. We obtain one-loop formulas for $S$ and $T$ expressed in terms of physical observables such as the Kaluza-Klein (KK) gauge boson mass ${M}_{{W}^{\ensuremath{'}}}$, the KK fermion mass $M$, and the KK gauge boson (${W}^{\ensuremath{'}}$) couplings with light quarks and leptons ${g}_{{W}^{\ensuremath{'}}ff}$. It is shown that these physical observables, ${M}_{{W}^{\ensuremath{'}}}$, $M$, and ${g}_{{W}^{\ensuremath{'}}ff}$ are severely constrained by the electroweak precision data. Unlike the tree level analysis on the ideally delocalized fermion, we find that perfect fermiophobity of ${W}^{\ensuremath{'}}$ is ruled out by the precision data. We also study the cutoff dependence of our analysis. Although the model is nonrenormalizable, the dependence on the cutoff parameter $\ensuremath{\Lambda}$ is shown to be nonsignificant.
85538675
Phenomenology of Partially Composite Standard Model
We propose a model to describe the low energy physics of partially composite Standard Model, in which the electroweak sector in the Standard Model is weakly coupled to some strong dynamics. The vector resonances in the strong sector are introduced as the effective degrees of freedom, W' and Z', which mixes with the W and Z bosons through the electroweak symmetry breaking. Through the coupling to the strong sector, the Standard Model Higgs boson becomes partially composite, and its properties are modified. We study the constraints from the electroweak precision data and direct searches of W' and Z' at the LHC expriments, and discuss the effects on the production/decay properties of the Higgs boson.