55574230
CSR in the SuperKEKB Damping Ring
Coherent synchrotron radiation (CSR) is generated when a bunched beam traverses a dipole magnet or a wiggler/undulator. It can degrade the beam quality in both storage rings and linacs through enhancing the beam energy spread and lengthening the bunch length, even cause single-bunch microwave instabilities. Using several methods, CSR impedances in the positron damping ring (DR) of the SuperKEKB which is under design were calculated. From the impedances due to CSR, resistive wall and various vacuum components, quasi-Green function wake potentials were constructed and used in simulations of Particle-In-Cell (PIC) tracking. We present the CSR related results in this paper.
15081704
DESIGN OF POSITRON DAMPING RING FOR SUPER-KEKB
Super-KEKB, an upgrade plan of the present KEKB collider, has recently changed its baseline-design from “high current” option to “nano-beam” scheme. The current is relatively low(4A/2.3A for LER/HER ring) compared to that of the high-current option(9.4A/4.1A), while the vertical beam size is squeezed to 60 nm at the interaction point to get the high luminosity. Since the Tousheck lifetime of LER is very short(600 sec), the intensity of the positron beam is as high as 8 nC/pulse. The emittance of the injected positron beam should be small enough to be accepted in the aperture of the LER. A damping ring has been proposed for the high-current option[1]. In this paper an updated design optimized to the nano-beam scheme is presented.
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].
122906250
Accelerator design at SuperKEKB
Accelerator design at SuperKEKB Yukiyoshi Ohnishi∗, Tetsuo Abe, Toshikazu Adachi, Kazunori Akai, Yasushi Arimoto, Kiyokazu Ebihara, Kazumi Egawa, John Flanagan, Hitoshi Fukuma, Yoshihiro Funakoshi, Kazuro Furukawa, Takaaki Furuya, Naoko Iida, Hiromi Iinuma, Hoitomi Ikeda, Takuya Ishibashi, Masako Iwasaki, Tatsuya Kageyama, Susumu Kamada, Takuya Kamitani, Ken-ichi Kanazawa, Mitsuo Kikuchi, Haruyo Koiso, Mika Masuzawa, Toshihiro Mimashi, Takako Miura, Takashi Mori, Akio Morita, Tatsuro Nakamura, Kota Nakanishi, Hiroyuki Nakayama, Michiru Nishiwaki, Yujiro Ogawa, Kazuhito Ohmi, Norihito Ohuchi, Katsunobu Oide, Toshiyuki Oki, Masaaki Ono, Masanori Satoh, Kyo Shibata, Masaaki Suetake, Yusuke Suetsugu, Ryuhei Sugahara, Hiroshi Sugimoto, Tsuyoshi Suwada, Masafumi Tawada, Makoto Tobiyama, Noboru Tokuda, Kiyosumi Tsuchiya, Hiroshi Yamaoka, Yoshiharu Yano, Mitsuhiro Yoshida, Shin-ichi Yoshimoto, Demin Zhou, and Zhanguo Zong
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.
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.
206997263
Efficient computation of Hamiltonian matrix elements between non-orthogonal Slater determinants
Abstract We present an efficient numerical method for computing Hamiltonian matrix elements between non-orthogonal Slater determinants, focusing on the most time-consuming component of the calculation that involves a sparse array. In the usual case where many matrix elements should be calculated, this computation can be transformed into a multiplication of dense matrices. It is demonstrated that the present method based on the matrix–matrix multiplication attains ∼80% of the theoretical peak performance measured on systems equipped with modern microprocessors, a factor of 5–10 better than the normal method using indirectly indexed arrays to treat a sparse array. The reason for such different performances is discussed from the viewpoint of memory access.
119190303
Novel extrapolation method in the Monte Carlo shell model
We propose an extrapolation method utilizing energy variance in the Monte Carlo shell model to estimate the energy eigenvalue and observables accurately. We derive a formula for the energy variance with deformed Slater determinants, which enables us to calculate the energy variance efficiently. The feasibility of the method is demonstrated for the full pf-shell calculation of {sup 56}Ni, and the applicability of the method to a system beyond the current limit of exact diagonalization is shown for the pf+g{sub 9/2}-shell calculation of {sup 64}Ge.
125388267
Minimal dilaton model
Both the ATLAS and CMS experiments at the LHC have reported the observation of the particle of mass around 125 GeV which is consistent to the Standard Model (SM) Higgs boson, but with an excess of events beyond the SM expectation in the diphoton decay channel at each of them. There still remains room for a logical possibility that we are not seeing the SM Higgs but something else. Here we introduce the minimal dilaton model in which the LHC signals are explained by an extra singlet scalar of the mass around 125 GeV that slightly mixes with the SM Higgs heavier than 600 GeV. When this scalar has a vacuum expectation value well beyond the electroweak scale, it can be identified as a linearly realized version of a dilaton field. Though the current experimental constraints from the Higgs search disfavors such a region, the singlet scalar model itself still provides a viable alternative to the SM Higgs in interpreting its search results.
118433920
Drell-Yan production ofZ′in the three-site Higgsless model at the LHC
In the Higgsless models, there are extra gauge bosons which keep the perturbative unitarity of a longitudinally polarized gauge boson. The three-site Higgsless model is a minimal Higgsless model and contains three extra gauge bosons, $W^{\prime \pm}$ and Z'. In this paper, we report the discovery potential of the Z' gauge boson via Drell-Yan production with Z'(mass=380, 500, 600 GeV) $\rightarrow WW \rightarrow \ell\nu qq$ ($\ell=e$, $\mu$) at the LHC ($\sqrt{s}$=14 TeV).
118637766
Vector WIMP Miracle
Abstract Weakly interacting massive particle (WIMP) is well known to be a good candidate for dark matter, and it is also predicted by many new physics models beyond the standard model at the TeV scale. We found that, if the WIMP is a vector particle (spin-one particle) which is associated with some gauge symmetry broken at the TeV scale, the Higgs mass is often predicted to be 120–125 GeV, which is very consistent with the result of Higgs searches recently reported by ATLAS and CMS Collaborations at the Large Hadron Collider experiment. In this Letter, we consider the vector WIMP using a non-linear sigma model in order to confirm this result as general as possible in a bottom-up approach. Near-future prospects to detect the vector WIMP at both direct and indirect detection experiments of dark matter are also discussed.