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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.

An angle sensor can be used to evaluate profiles without any shape references. We regard it suitable for evaluating a large profile and consider a gyro as an angle sensor for evaluating a profile larger than 100 m with an accuracy of better than 1 mm. A gyro can evaluate profiles without restrictions in span or direction; however, angles detected by a gyro typically fluctuate unacceptably for our purpose. We demonstrate that periodical reversal measurement by flipping a gyro is effective in reducing the effect of the fluctuation. Then, we rotate the gyro for continuously realizing the reversal, where the angles of the gyro’s rotating axis against the earth’s rotating axis can be derived without being affected by the fluctuation, and can be used as an angle sensor. Here, we consider a new method using gyro signals rotating around four orthogonally aligned axes. This can improve the accuracy of the derived angles by eliminating the effects of the gyro’s scale factor as well as the fluctuations.

A new field-programmable gate array (FPGA)-based time-to-digital converter (TDC) with a wide dynamic range greater than 20 ms has been developed to monitor the timing of various pulsed devices in the trigger timing distribution system of the KEKB injector linac for the Super KEK B-factory project. The pulsed devices are driven by feeding regular as well as any irregular (or event-based) timing pulses. The timing pulses are distributed to these pulsed devices along the linac beam line with fiber-optic links on the basis of the parameters to be set pulse-by-pulse in the event-based timing and control system within 20 ms. For monitoring the timing as precisely as possible, a 16-ch FPGA-based TDC has been developed on a Xilinx Spartan-6 FPGA equipped on VME board with a resolution of 1 ns. The resolution was achieved by applying a multisampling technique, and the accuracies were 2.6 ns (rms) and less than 1 ns (rms) within the dynamic ranges of 20 ms and 7.5 ms, respectively. The various nonlinear effects were improved by implementing a high-precision external clock with a built-in temperature-compensated crystal oscillator.

To evaluate the straightness of large objects, the use of an inclinometer is advantageous because it requires neither straight shape references nor transferring mechanisms. Herein, we consider adopting it for precise (with greater accuracy than 1 mm) evaluation of the straightness of linear particle accelerators (linacs) that are several hundred meters long or longer. In this study, the straightness evaluation of a 206-m-long part of the KEK injector linac was demonstrated using inclinometers with a pair of cantilevers called offset bars. The offset bars were adopted to extend the evaluation length by avoiding obstacles that block the evaluation path. Errors caused by the offset bars can be eliminated by reversal measurement considering the slope angles of the offset bars. The derived straightness corresponded with those derived by an alignment telescope and a laser-based alignment system within several millimeters and partly within several hundred micrometers. The reproducibility of slope angles for an arbitrary measurement point was 15 μrad at standard deviation. This corresponds to a standard deviation of 0.47 mm for straightness, with a total evaluation length of 500 m and measurement intervals of 2 m. The results indicate that our newly devised method is applicable for evaluating the straightness.

A new beam-timing monitor (BTM) has been developed to analyze the longitudinal beam dynamics and bunching characteristics at the pre-injector of the KEKB injector linear accelerator (linac). The BTM is a conventional stripline-type beam monitor with two pickup electrodes. It measures the relative time delay between the arrival time of the beam signal and 1st-zero-cross time of the fundamental accelerating radio frequency (rf) signal (2856 MHz) immediately after the detection of the beam signal. The beam tests were performed to evaluate the performance and characteristics of the BTM for primary single-bunched electron beams with high bunch charges of ∼ 8 nC for positron production. It was found that the results show that the resolution in the delay-time measurement is σ ∼ 1.2 ps in one standard deviation. This report describes the basic design of the BTM system, the beam tests, and results in detail, to investigate the sensitivity and stability of the beam timing based on the longitudinal phase-space parameters at the pre-injector and location A1 of the injector linac, along with the calibration method in the pulse-height variation of the BTM signal.

A precise inclinometer (Talyvel 4) was adopted for evaluating aligning straightness of the first 71 m of the KEK electron/positron injector linear accelerator (linac). The straightness could be evaluated with a standard deviation of less than 49 μm. It is in good agreement with those obtained using a conventional alignment telescope and our laser-based alignment system. Error estimation based on the rules of error propagation shows that shape evaluation with a standard deviation of 0.3 mm for a distance of 500 m can be achieved using the proposed method. It indicates that this method is suitable for evaluating straightness of several hundred meters of linacs with sub-millimeter of accuracy.

Signal transmission characteristics in stripline electrodes of a stripline-type beam position monitor (BPM) are discussed on the basis of a coupled-mode analysis in electromagnetically coupled transmission lines. The physical prospect in the calibration procedure of stripline electrodes is improved in terms of signal transmission characteristics in the frequency domain. It is demonstrated that in the signal transmission with electromagnetic coupling between the stripline electrodes, the magnetic- and electric-coupling parameters play an important role depending upon the spatial configuration and mechanical structure of the stripline electrodes. In this report, a theoretical analysis, and experimental investigation into signal transmission characteristics and performance in a standard stripline-type BPM are described in detail on the basis of a coupled-mode analysis in uniform transmission lines.

The lattice and beam optics of the arc section of the KEK-ERL test facility, having an energy of 200 MeV, were optimized to efficiently suppress emittance growth based on a simulation using a particle-tracking method taking coherent synchrotron radiation effects into account. The lattice optimization in the arc section was performed under two conditions: a high-current mode with a bunch charge of 76.9 pC without bunch compression, and a short-bunch mode with bunch compression, producing a final bunch length of around 0.1 ps. The simulation results showed that, in the high-current mode, emittance growth was efficiently suppressed by keeping a root-mean-square (rms) bunch length of 1 ps at a bunch charge of 76.9 pC, and in the short-bunch mode, emittance growth was kept within permissible limits with a maximum allowable bunch charge of 23.1 pC at an rms bunch length of 0.1 ps.

A conceptual design for a test accelerator based on an energy recovery scheme is under way in developing a next generation light source at KEK. A high bright electron beam will be delivered from the test accelerator with a maximum energy of 200 MeV using 1.3 GHz superconducting accelerating cavities installed in two cryomodules. It is of great importance to design a pre-injector that can generate an electron beam with exceptionally high brightness and low emittances. A new simulation code is being developed to simulate the beam dynamics of the electron beam and to optimize the beam characteristics at the pre-injector. The simulation code describes semi-analytically the two-dimensional (transverse and longitudinal) beam dynamics of the electron beam based on a well-known envelope equation taking into account the space charge effect. The purpose of this code is not to rigorously simulate the particle dynamics, as is done by the particle tracking code “Parmela”, but rather to quickly optimize the design parameters of the accelerator components and beam characteristics themselves. This code has been validated by comparison with the results obtained from the “Parmela” code using the pre-injector design parameters. In this report, the development and some numerical results obtained from this new simulation code are presented in detail.

We measured positron-production efficiency from an axially-oriented single crystal target by 8-GeV channeling electrons at the KEK electron/positron injector linac. The targets tested are silicon crystals with the thicknesses of 9.9, 29.9 and 48.15 mm, a diamond crystal with the thickness of 4.57 mm, and their combinations with amorphous tungsten plates. The crystal axis 〈1 1 0〉 has been aligned to the electron beam by a precise goniometer. The positron-production efficiency in the momentum range of 10–30 MeV/c was systematically investigated for each target by measuring the positron yield generated in the forward direction with a magnetic analyzer. The result shows that the maximum positron-production efficiency from the 29.9-mm-thick silicon and the 4.57-mm-thick diamond combined with amorphous tungsten are 6.1% and 2.9%, respectively, larger than that from amorphous tungsten at the momentum of 20 MeV/c. In such a light crystal target combined with amorphous tungsten, the total target thickness, which gives the maximum positron yield, is clearly reduced in comparison with that of the amorphous tungsten alone. The result is also compared with our previous experiments for tungsten crystal targets.

The KEK electron/positron injector linac provides a short-pulse electron beam with an energy of 2.5 GeV for the Photon Factory (PF) storage ring, that with an energy of 3 GeV for the Advanced Ring (PF–AR) for pulse X-rays, and single-bunch electron and positron beams with energies of 8 and 3.5 GeV respectively for the KEK B-Factory (KEKB) storage rings. A trigger-timing signal distribution system of the injector linac was newly developed and extended for stable injection to the KEKB rings with the required injection-timing accuracy highly stabilized to less than 30 ps in root mean square because the old trigger system distributed the trigger-timing signals for the injection to the PF ring and the PF–AR with an injection-timing accuracy of 300 ps . In this report the design and its performance of the new trigger-timing signal distribution system are described in detail.

An 8-GeV electron/3.5-GeV positron injector for KEKB was completed in 1998 by upgrading the existing 2.5-GeV electron/positron linac. The main goals were to upgrade its accelerating energy from 2.5 to 8 GeV and to increase the positron intensity by about 20 times. This article describes not only the composition and features of the upgraded linac, but also how these goals were achieved, by focusing on an optics design and commissioning issues concerning especially high-intensity single-bunch acceleration to produce positron beams.

KEKB has been operated since December, 1998, to deliver BB pairs for a physics detector. In this paper,we describe the commissioning procedure of KEKB.

We have measured the positron production efficiency from tungsten single-crystal targets using an 8 GeV electron beam. A single-bunch beam with a bunch width of 10 ps, a repetition rate of 2 Hz, and an intensity of 0.2 nC/bunch was incident on a target mounted on a precision goniometer. Positrons produced in the forward direction were detected by a magnetic spectrometer in the 10–20 MeV/c momentum range. Systematic data on the target-thickness dependence and the momentum distribution of the produced positrons were obtained for crystal targets. The results show that, when the crystal axis 〈1 1 1〉 is aligned to the electron beam direction, the positron yield increases compared to the amorphous case by factors of 6.5, 3.4 and 2.3 at 10 MeV/c for 2.2, 5.3 and 9.0 mm thick crystals, respectively. We observed that the positron yield from the 9.0 mm thick crystal is larger than the maximum yield attainable with 18–20 mm thick amorphous targets at 8 GeV.

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 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.