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A new remote-controllable sensing system for a laser-based alignment system is in development to measure slow dynamic displacements of the tunnel floor in real time at the KEKB injector linac. Although the injector linac had initially been aligned with a laser-based alignment system, we have found that, based on recent real-time observations, the transverse displacements of the tunnel floor to the laser axis caused by dynamic ground motion are not negligibly small compared with the required alignment tolerance, in terms of the straightness of the beam line. Based on spatial and temporal cross-correlation analyses performed using displacement vectors from data recorded during a nearly eight-month period, it was found that the tunnel floor moves coherently in space and time domains over the entire length of the linac on average over long periods of time, while the cross-correlation function varies irregularly and complexly over shorter periods of time. This report describes in detail the basic design, experimental results, and present status of the new remote-sensing system for real-time alignment observations at the KEKB injector linac.

A new tungsten single-crystal target has been successfully employed at the positron source of the KEKB injector linac. The crystal thickness was determined to be 10.5 mm based on previous systematic measurements of the positron-production efficiency. The crystal axis, ⟨111⟩, was precisely aligned to the direction of the 4-GeV primary electron beam. The positron yield increased by ∼25% compared to that for a conventional tungsten plate with a thickness of 14 mm. On the contrary, the steady-state heat load on the crystal target decreased by ∼20%. After a two-month operation, no degradation of the positron-production efficiency was observed, and the crystal target has been stably operating at the KEK B factory.

A new energy-spread feedback control system using nondestructive energy-spread monitors has been developed in order to control and stabilize the energy spreads of single-bunch electron and positron beams in the KEKB injector linac. A well-controlled feedback system has been successfully working in daily operation not only for keeping the injection rate higher along with the beam-orbit and energy-feedback control system, but also for reducing the background level to the KEKB collider experiment. The energy spreads of the injection beams have been well stabilized within 0.33±0.01% and 0.50±0.02% (0.55±0.06%) for the electron beam and the first (second) bunch of the high-current primary electron beam for positron production at the 180° arc, respectively, and within 0.39±0.01% (0.36±0.03%) for the first (second) bunch of the positron beam at the end of the injector linac through the energy-spread feedback control system under the nominal operation condition. In this report we describe in detail the energy-spread feedback control system using nondestructive energy-spread monitors with multi–strip-line electrodes and their performance in KEKB operation.

A nondestructive beam energy-spread monitor using multi-strip-line electrodes has been newly developed in order to measure and control the energy spread of a single-bunch electron beam at an 180° arc with a beam energy of 1.7 GeV in the KEKB injector linac. The detection principle is described based on a multipole-moment analysis of an electromagnetic field generated by a charged beam. A proof-of-principle experiment was performed to verify the analysis. The result shows that taking into account the second-order moment derived from the multipole-moment analysis, the analyzed transverse beamwidths are consistent with those measured by a screen monitor, and the energy spreads are estimated to be 0.150%±0.007% and 0.264%±0.004% for electron beams with charges of 0.9 and 8 nC/bunch at the rf phase of the energy-spread minimum, respectively. In this report we describe in detail the experimental result using the beam energy-spread monitor along with a theoretical multipole-moment analysis.

A control survey technique using a laser tracker and a digital level was introduced to the KEK e-/e+ injector linac in 2020. Control surveys are continuously demonstrated during the machine's downtimes every summer. Analysis of the two-year data reproduces their trends in terms of the fiducial points on the beam line. In our paper, we report on systematic coordinates and their error distributions evaluated by a control survey, compare them with a numerical survey simulation, and discuss newly encountered issues., (© 2023 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).)

A direct simultaneous detection of electron ([Formula: see text]) and positron ([Formula: see text]) bunches was successfully performed using wideband beam monitors and a detection system at the [Formula: see text] capture section of the SuperKEKB B-factory. The time intervals between the secondary-generated [Formula: see text] and [Formula: see text] bunches were measured to investigate their dynamical capture process. The results show that the time intervals were measured in the range of 20-280 ps on average, and the line-order switch of the [Formula: see text] and [Formula: see text] bunches and their dynamical phase-slip process in the axial direction were clearly observed as a function of the capture phase of accelerating structures. In this report, the dynamical capture and phase-slip process for the [Formula: see text] and [Formula: see text] bunches under the two-bunch acceleration scheme is described in detail. This study opens up a new window for direct observation of the [Formula: see text] and [Formula: see text] capture process at any present and future [Formula: see text] sources., (© 2022. The Author(s).)

The signal transmission characteristics of a wideband beam monitor (WBM) with feedthrough electrodes are discussed in the frequency region up to 13.5 GHz on the basis of a coupled-mode analysis using an equivalent circuit model with electromagnetically coupled transmission lines. It is demonstrated that in the signal transmission characteristics based on an electromagnetic induction method, electromagnetic couplings for fundamental and higher-order rf waves play an important role depending on the spatial configuration and geometrical structure of the electrodes mounted on the WBM with a cylindrical structure. The physical prospect in the calibration procedure of feedthrough electrodes is improved in terms of the signal transmission characteristics over the frequency region. In this report, the modal analyses and experimental investigations of the signal transmission characteristics in the WBM are described in detail. An alternative method of gain calibration for each electrode is also demonstrated.

The epigenetic regulatory system significant influences the fate determination of cells during developmental processes. Prdm12 is a transcriptional regulator that modulates gene expression epigenetically. The Prdm12 gene has been shown to be expressed in neural tissues, specifically during development, but its detailed function is not fully understood. This study investigated the function of the Prdm12 gene in P19 mouse embryonic tumor cells as a model for neural differentiation. A decrease in the expression of neuron-specific genes and the alterations of dendrites and axons morphology was confirmed in Prdm12-knockout P19 cells. In addition, almost no astrocytes were generated in Prdm12-knockout P19 cells. Comprehensive gene expression analysis revealed that there was a reduction in the expression of the inhibitory neuron-specific genes Gad1/2 and Glyt2 , but not the excitatory neuron-specific gene VGLUT2 , in Prdm12-knockout P19 cells. Furthermore, the expression of inhibitory neuron-related factors, Ptf1a , Dbx1 , and Gsx1/2 , decreased in Prdm12-knockout P19 cells. Gene expression analysis also revealed that the Ptf1a , Hic1 , and Foxa1 genes were candidate targets of Prdm12 during neurogenesis. These results suggest that Prdm12 regulates the differentiation of inhibitory neurons and astrocytes by controlling the expression of these genes during the neural differentiation of P19 cells., (© The Author(s), under exclusive licence to Springer Nature B.V. 2022.)

The direct simultaneous detection of electron and positron bunch signals was successfully performed for the first time with wideband pickups and a detection system at the positron capture section of the SuperKEKB factory. The time interval between the electron and positron bunches, their bunch lengths, and bunch intensities depending on the phase of accelerating structures were measured to investigate their capture process and to maximally optimize the positron intensity. The results show that the time intervals were measured in the range of 135-265 ps, and the line-order switch of the electron and positron bunches in the axial direction was clearly observed as a function of the phase. The positron (electron) intensity was maximized at the optimal phase (180[Formula: see text] shifted from the optimum). These series of measurements have never been experimentally conducted so far. It is demonstrated that the positron intensity can be systematically optimized with this system as functions of beam parameters in multidimensional spaces for any positron capture section.

A signal transmission line and its characteristics were analyzed in detail for a beam-current monitor (CM) for long-pulsed electron beams. The monitor was based on a conventional current transformer, which comprised an induction coil wound around a ferrite core. The signal transmission and noise generation mechanism were analyzed by theoretical models based on balanced and unbalanced coaxial transmission circuits to effectively reduce noises superimposed on the beam-current signal waveform. The results of numerical analyses based on the theoretical models were in good agreement with those of an experiment for verification. It was found that the noise signals were generated by a high-power klystron operation and they were mode-transformed on the way to the transmission line. These results show that the locations of the grounded points in the transmission line were important. Based on a symmetrically configured three-line circuit theory, a new highly symmetrically configured coaxial transmission line is proposed to effectively suppress noises generated in CM. This report describes in detail the numerical and experimental analysis of a signal transmission line with coaxial cables for CM where the noise generation mechanism and its reduction technique are deeply involved.

A laser-based alignment system with a He-Ne laser has been newly developed in order to precisely align accelerator units at the KEKB injector linac. The laser beam was first implemented as a 500-m-long fiducial straight line for alignment measurements. We experimentally investigated the propagation and stability characteristics of the laser beam passing through laser pipes in vacuum. The pointing stability at the last fiducial point was successfully obtained with the transverse displacements of ±40 μm level in one standard deviation by applying a feedback control. This pointing stability corresponds to an angle of ±0.08 μrad. This report contains a detailed description of the experimental investigation for the propagation and stability characteristics of the laser beam in the laser-based alignment system for long-distance linear accelerators.

We experimentally investigate the focusing characteristics of a He-Ne laser at the focal region for the high-precision alignment of long-distance linear accelerators using a circular Fresnel zone plate. The laser wave passing through the Fresnel zone plate having a focal length of 66.7 m propagates for a 268-m-long distance at atmospheric pressure. A new laser-based alignment system using Fresnel zone plates as the alignment targets is discussed. The transverse displacement of the focused spot of the laser is measured as a function of the displacement of the target by a detector installed at the focal point. Systematic studies on the focusing characteristics and alignment precision have been successfully conducted in this experiment. The experimental results are in good agreement with theoretical calculations, and the alignment precision of the target is determined to be less than ±30 μm. In this study, we perform a detailed experimental investigation on the laser propagation and focusing characteristics using the circular Fresnel zone plate at the focal region along with theoretical calculations.

A new laser-based alignment system for the precise alignment of accelerator components along an ideal straight line at the KEK B-factory injector linear accelerator (linac) is under development. This system is strongly required in the next generation of B-factories for the stable acceleration of high-brightness electron and positron beams with high bunch charges and also for maintaining the stability of injection beams with high quality. A new laser optics for the generation of a so-called Airy beam has been developed for the laser-based alignment system. The laser propagation characteristics both in vacuum and at atmospheric pressure have been systematically investigated in an 82-m-long straight section of the injector linac. The laser-based alignment measurements based on the new laser optics have been carried out with a measurement resolution of ±0.1 mm level by using an existing laser detection electronics. The horizontal and vertical displacements from a reference laser line measured using this system are in good agreement with those measured using a standard telescope-based optical alignment technique. In this report, we describe the experimental study in detail along with the basic designs and the recent developments in the new laser-based alignment system.

A new beam-charge interlock system is under development for radiation safety and machine protection at the KEKB injector linac. A hardware-based interlock system is required instead of the present software-based interlock system in order to boost its reliability. This system restricts the integrated amount of beam charges delivered to four different storage rings. The beam charges are measured using wall-current monitors and detection electronics at six locations along the linac. The detection electronics independently transmits a beam-abort request through a twisted hardwire cable directly to the safety control system of the linac, when the integrated amount of beam charges exceeds a certain threshold level prescribed for each location. We describe the characteristics and performance of the new beam-charge interlock system along with the details of the experimental tests.

Intense positron sources are being widely investigated for the next-generation linear colliders and B factories. A new method utilizing an axially oriented crystal as a positron-production target is one of the bright schemes, since it provides a powerful photon source through channeling and coherent bremsstrahlung processes when high-energy electrons penetrate the target. A series of positron-production experiments with tungsten crystals hit by 4- and 8-GeV single-bunch electron beams were carried out at the KEKB 8-GeV injector linac. Three tungsten crystals with different thicknesses (2.2, 5.3, and 9.0 mm) and those combined with amorphous tungsten plates were tested on a precise goniometer. The positron-production yields were measured with a magnetic spectrometer in the positron momentum (P(e(+))) range from 5 to 20 MeV/c. The angle of the <111> crystal axis with respect to the electron-beam direction was controlled by measuring the relative intensities of the produced positrons as a function of the rotational angle of the goniometer. The results show that the enhancements of the positron yield from crystal targets compared to amorphous targets of the same thickness at P(e(+))=20 MeV/c are from 1.5 to 3.7 and from 1.8 to 5.1, depending upon the target thickness for 4- and 8-GeV electrons, respectively.