M Kikuchi’s research while affiliated with High Energy Accelerator Research Organization and other places

What is this page?


This page lists works of an author who doesn't have a ResearchGate profile or hasn't added the works to their profile yet. It is automatically generated from public (personal) data to further our legitimate goal of comprehensive and accurate scientific recordkeeping. If you are this author and want this page removed, please let us know.

Publications (453)


Beam injection and beam quality in injector LINAC and in beam transport lines at SuperKEKB
  • Article

February 2024

·

6 Reads

·

1 Citation

Journal of Instrumentation

·

N. Iida

·

M. Kikuchi

·

[...]

·

T. Yoshimoto

At SuperKEKB, the maximum beam currents and the luminosity could be limited by the beam injection in the near future. We estimated requirements to the beam injection to achieve the next target luminosity of 1 × 10 ³⁵ cm ⁻² s ⁻¹ . Two cases of β y * = 1 mm and 0.8 mm are considered. A simulation shows that we need to suppress the emittance growth of the injecting positron beam in the beam transport (BT) line down to its design value to meet the requirement with β y * = 1 mm. In the case of β y * = 0.8 mm, we need to improve dynamic aperture of LER in addition to the suppression of the emittance growth. Efforts to improve the beam quantity and quality in LINAC and in BT are summarized. The present most serious problem concerning quality of the injecting beams is emittance growth in the BT lines for both electron and positron beams. Simulations and experiments show that the effects of ISR and CSR in the BT lines cause a large horizontal emittance growth of the electron beam. Several measures to suppress the emittance growth are under considerations.


Figure 1. The effect of nonuniformity of transverse fringe field in septum core has been investigated with a tracking simulation of the beam transportation (BT) line. The upper(lower) row represents the horizontal(vertical) plane. The first (or the left) column represents the distributions in real coordinates, including the 1σ-ellipses of the lattices with (magenta) and without (lightgray) including just the linear part of the fringe field. The second column represent the distributions in normal coordinates, which are converted with Twiss parameters of the magenta ellipse.
Figure 4. The magnetic field distributions with different shim shapes for entire gap (left) and close-up near to the septum (right) are shown. The blue open circle stands for the scaled measurement result, colored lines stands for the simulation results. The three numbers in the legend show the values of τ [µs], h [mm] and w top [mm].
Figure 5. The plotted curves indicate B ′ L as functions of x inj with the different shim shapes. The horizontal and vertical axes represent x inj and B ′ L. The three numbers in the legend show the values of τ [µs], h [mm] and w top [mm]. The blue curve in the whole view (left) is for the present configuration. The right figure shows the detail of B ′ L around zero, where the color definition is same as that in left figure.
Figure 6. Decided shim shape (blue), the septum conductor (lightblue) and the gap of core (gray) are shown.
Field Quality Improvement of Septum Magnets for SuperKEKB Injection System
  • Article
  • Full-text available

January 2024

·

15 Reads

Journal of Physics Conference Series

The SuperKEKB accelerator is a electron-positron collider consisting of the 7 GeV electron ring (high energy ring or HER) and the 4 GeV positron ring (low energy ring or LER). The commissioning of the SuperKEKB accelerator is underway, aiming to supply a great number of interaction events of electrons and positrons to the Belle II detector which is used for discovering the new physics beyond the standard model. The important milestone is to obtain integrated luminosity of 15 ab –1 in the next decade, so that the luminosity should exceed 2 × 10 ³⁵ cm –2 s –1 in several years. To achieve the goal, both rings have to be filled with high current beam of a few amperes, where the high injection efficiency is vitally important because lifetime is expected to be very short. One of the key components of the injection system is the septum magnet. It has been found that a transverse fringe field near the septum plate has sizable multipole components. A tracking simulation shows such fringe fields generate a vertical non-Gaussian tail, which could cause a beam background as well as a bad injection efficiency. Though quadrupole component in the multipoles could be, in principle, cancelled by adjusting the quadrupole magnets in the upstream of the beam line, it turned out to be difficult in actual operation. Even the quadrupole component was perfectly cancelled, components higher than quadrupole would be still harmful, since it generates a beam halo in the ring after injection, which increases the beam backgrounds to the Belle II detector. This paper describes about improvement of the field quality of the septum magnet.

Download

SuperKEKB operation using crab waist collision scheme

November 2021

·

194 Reads

The European Physical Journal Plus

SuperKEKB is an electron-positron asymmetric-energy double-ring collider, which was built in Japan. It has been operated to explore new phenomena in B-meson decays. Hence, extremely higher luminosity is required. A collision scheme of low emittance with a large Piwinski angle called a "nano-beam scheme" has been adopted to achieve higher luminosity by squeezing the vertical beta function at the interaction point to be smaller than the bunch length. A "crab waist collision scheme" proposed by P. Raimondi et al. has also been adopted to improve the luminosity performance. The article presents an overview of the operation of the nano-beam and crab waist collision schemes at SuperKEKB.


SuperKEKB operation using crab waist collision scheme

October 2021

·

71 Reads

·

15 Citations

The European Physical Journal Plus

SuperKEKB is an electron–positron asymmetric-energy double-ring collider, which was built in Japan. It has been operated to explore new phenomena in B-meson decays. Hence, extremely higher luminosity is required. A collision scheme of low emittance with a large Piwinski angle called a “nano-beam scheme” has been adopted to achieve higher luminosity by squeezing the vertical beta function at the interaction point to be smaller than the bunch length. A “crab waist collision scheme” proposed by P. Raimondi et al. has also been adopted to improve the luminosity performance. The article presents an overview of the operation of the nano-beam and crab waist collision schemes at SuperKEKB.


COMMISSIONING OF THE PHASE-1 SuperKEKB B-FACTORY AND UPDATE ON THE OVERALL STATUS

March 2016

·

151 Reads

·

7 Citations

The SuperKEKB B-Factory at KEK (Japan), after few years of shutdown for the construction and renovation, has finally come to the Phase-1 commissioning of the LER and HER rings, without the final focus system and the Belle II detector. Vacuum scrubbing, optics tuning, and beam related background measurements were performed in this phase. Low emittance tuning techniques have also been applied in order to set up the rings for Phase-2 with colliding beams next year. An update of the final focus system construction, as well as the status of the injection system with the new positron damping ring and high current/low emittance electron gun is also presented.


The negative triangularity tokamak: Stability limits and prospects as a fusion energy system

June 2015

·

959 Reads

·

79 Citations

The paper discusses edge stability, beta limits and power handling issues for negative triangularity tokamaks. The edge magnetohydrodynamic stability is the most crucial item for power handling. For the case of negative triangularity the edge stability picture is quite different from that for conventional positive triangularity tokamaks: the second stability access is closed for localized Mercier/ballooning modes due to the absence of a magnetic well, and nearly internal kink modes set the pedestal height limit to be weakly sensitive to diamagnetic stabilization just above the margin of the localized mode Mercier criterion violation. While a negative triangularity tokamak is thought to have a low beta limit with its magnetic hill property, it is found that plasmas with reactor-relevant values of normalized beta βN > 3 can be stable to global kink modes without wall stabilization with appropriate core pressure profile optimization against localized mode stability, and also with increased magnetic shear in the outer half-radius. The beta limit is set by the n = 1 mode for the resulting flat pressure profile. The wall stabilization is very inefficient due to strong coupling between external and internal modes. The n > 1 modes are increasingly internal when approaching the localized mode limit, and set a lower beta in the case of the peaked pressure profile leading to a Mercier unstable core. With the theoretical predictions supported by experiments, a negative triangularity tokamak would become a prospective fusion energy system with other advantages including a larger separatrix wetted area, more flexible divertor configuration design, wider trapped particle-free scrape-off layer, lower background magnetic field for internal poloidal field coils, and larger pumping conductance from the divertor room.


The Physics of the B Factories

November 2014

·

102,747 Reads

·

456 Citations

The European Physical Journal C

This work is on the Physics of the B Factories. Part A of this book contains a brief description of the SLAC and KEK B Factories as well as their detectors, BaBar and Belle, and data taking related issues. Part B discusses tools and methods used by the experiments in order to obtain results. The results themselves can be found in Part C. Please note that version 3 on the archive is the auxiliary version of the Physics of the B Factories book. This uses the notation alpha, beta, gamma for the angles of the Unitarity Triangle. The nominal version uses the notation phi_1, phi_2 and phi_3. Please cite this work as Eur. Phys. J. C74 (2014) 3026.


Influence of scattered gamma rays by body trunk on image quality of Si/CdTe semiconductor compton camera for medical and biological applications

August 2014

·

30 Reads

We are currently developing a Compton camera apparatus for use as a novel imaging modality of nuclear medicine. It is based on the advanced technology used in Si/CdTe semiconductor Compton cameras developed by the Japan Aerospace Exploration Agency. In this study, the influence of scattered gamma rays by body trunk on image quality was evaluated using the developed Compton camera and a NEMA IEC body phantom. Na-22, Co-57 or Ba-133 gamma point source, which emit 511 keV, 122 keV or 356 keV respectively, was placed at the center of the body phantom. We compared the Compton images taken with the empty phantom and taken with the phantom filled with water. The image quality was degraded notably although the position resolution was not decreased. This is thought to be aftereffects of the reduction of the number of Compton events, broadening of the energy spectral region and the increase of the background. © 2014, Japan Soc. of Med. Electronics and Biol. Engineering. All rights reserved.


Electron beam injection system for SuperKEKB main ring

July 2014

·

30 Reads

·

1 Citation

The SuperKEKB project [1] is in progress toward the initial physics run in the year 2015. It assumes the nano-beam scheme, in which the horizontal emittance of the colliding beams is εx = 4.6[nm]. The horizontal emittance of the injected beam is εx = 1.46[nm]. To achieve such a low emittance, it is vitally important to preserve the emittance during the transport of the beam from the linac [2] to the main ring (MR). One of the most difficult sections is the injection system. It has been pointed out that the injected beam has possibility of leading to blowup in the ring, which is caused by a beam-beam interaction with the stored positron beam. To avoid the beam blowup, the synchrotron injection [3-5] is adopted as a backup option. The orbit of the electron injection beam has been designed and the septum magnet prototype has been constructed. The optics study for electron injection and the current R&D status for the septum magnet will be reported in this paper.


Development and operational status of PF-ring and PF-AR

July 2014

·

21 Reads

The Photon Factory storage ring (PF-ring) and the Photon Factory advanced ring (PF-AR) continue a stable user operation as a synchrotron radiation source. The MTBF of the PF-ring has been kept at high around 200 h. At the PF-ring, a top-up operation started in April 2009. A rapid-polarization-switching device consisting of tandem polarizing undulators and a new injection system using a pulsed sextupole magnet are being developed. In a dust trapping experiment at the PF-AR, visual observation of luminous trapped dust by using a CCD camera was accomplished recently.


Citations (57)


... A possible limitation of SuperKEKB maximum beam currents and luminosity could come by the beam injection in the near future. This problem is addressed in the paper by Y. Funakoshi et al. [4]. An estimation of beam injection requirements to achieve the next target luminosity with * = 1 mm and 0.8 mm was carried out. ...

Reference:

Editorial announcements and information — ICFA Beam Dynamics Newsletter No. 85
Beam injection and beam quality in injector LINAC and in beam transport lines at SuperKEKB
  • Citing Article
  • February 2024

Journal of Instrumentation

... † dmzhou@post.kek.jp the record luminosity with 4.71 · 10 34 cm −2 s −1 [22,23]. This achievement was made possible by various machine optimizations, such as the application of the crab-waist scheme since 2020 [24] based on a similar scheme initially designed for the FCC-ee [25][26][27], collisions with a large full crossing angle of 83 mrad and with a vertical spot size of the order of hundreds of nanometers. A significant challenge in crab-waist colliders is the coherent beam-beam-driven − instability, which becomes particularly severe near the resonance lines of 2 − = Integer [8], where = 2, 4, 6, . . . ...

SuperKEKB operation using crab waist collision scheme
  • Citing Article
  • October 2021

The European Physical Journal Plus

... An upgrade to the KEKB project, SuperKEKB [19], collides a positron beam of 4 GeV in its Low Energy Ring (LER) with an electron beam of 7 GeV in its High Energy Ring (HER). Since its first commissioning in 2016 [20,21], it has operated successfully through 3 phases and has entered its fourth phase, started in January 2024. Since 2022 it has been the holder of * peter.kicsiny@cern.ch ...

COMMISSIONING OF THE PHASE-1 SuperKEKB B-FACTORY AND UPDATE ON THE OVERALL STATUS

... This in turn demonstrates the benefi t of improving hemodynamic parameters after normalization of heart rate through cardiostumulation and the overall positive effect on quality of life and long-term prognosis in patients with bradycardia. Changes in the coagulation system as well as fi brinolytic activity in patients with placed endocardial electrodes were studied by T. Yaegashi et al. [9]. They looked for difference in the response of the coagulation system after implantation of high-voltage and low-voltage electrodes in the early post-established venous thrombosis (28 women, 43 man; mean age: 71.2±7.6 yr.), and group B -with established thrombosis (2 women, 8 man; mean age: 72.6 ± 7.2 g). ...

Poster Session 3

Europace

... However, to pursue such a precise measurement program that was initiated at the LHC, there is a consensus or need to build a clean environment electron-positron Higgs factory [14][15][16], which allows detailed studies of the novel SM-like Higgs boson. Several projects for e + e − machines are planned, including the Circular Electron Positron Collider (CEPC) [17], the Compact Linear Collider (CLIC) [18,19], the Future Circular Collider (FCC-ee) [20,21], and the International Linear Collider (ILC) [22,23]. ...

First look at the physics case of TLEP

Journal of High Energy Physics

... The septum field has been measured and the distortion of the injection beam by the horizontal kick in the septum magnet has been estimated and concluded to be negligible for injection [3]. Recently, it has been found that the vertical kick by the septum transverse fringe field affects the injection efficiency. ...

Electron beam injection system for SuperKEKB main ring
  • Citing Article
  • July 2014

... Depending on the rf voltage, the dispersion, β functions, and phase advance from the rf cavity to the observation point, the beam tilt can be as large as 40 mrad [1]. At KEK, crab cavities were used to generate xz beam tilt at the collision point so as to increase luminosity [2]. The crabbing angle is about 40mrad. ...

Performance of KEKB with crab cavities

... The crab-crossing operation in KEKB for physics experiments started in 2007 and continued until 2010, when the operation was terminated to upgrade KEKB to SuperKEKB. The luminosity record of KEKB was obtained by crab crossing [6,7]. Crab-crossing and related systems have been considered and are under development in a wide number of accelerators, including upgradation of LHC to HL-LHC, the Electron-Ion Collider, the linear colliders, and the generation of short-pulse x-rays in storage-ring-based light sources. ...

Commissioning of KEKB
  • Citing Article
  • March 2013

Progress of Theoretical and Experimental Physics

... The problem of proving D f (g) → 0 for fixed g as the parameters C and k of f grow is a natural analogue of the Rudnick-Sarnak quantum unique ergodicity (QUE) conjecture [33]. It was proved by Holowinsky and Soundararajan [13] that D f (g) → 0 for fixed C (= 1) and varying k → ∞; we refer to their paper and [37] for further historical background. The case of varying squarefree levels was addressed in [29], where it was shown that D f (g) → 0 as Ck → ∞ provided that C is squarefree. ...

Recent progress of KEKB
  • Citing Conference Paper
  • January 2007

... Recent experimental results obtained from DIII-D [8][9][10] and TCV [11][12][13][14][15], featuring negative triangularity shapes (neg-D), present a promising approach to address the aforementioned challenges associated with ETB in plasma [11,[16][17][18][19]. The absence of a strong ETB in neg-D plasmas allows access to an ELM-free regime but still with good confinement [20,21]. ...

The negative triangularity tokamak: Stability limits and prospects as a fusion energy system