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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.

Profile evaluation by detecting tangential angles of the profile is competent for large objects because it inherently requires no reference, which is difficult to define with sufficient accuracy as the object becomes larger. We considered using a gyro for detecting the angles instead of an inclinometer or an autocollimator, which are conventionally used as angle detectors. A gyro can detect angles without angular reference; therefore, profiles can be evaluated without the limitation of a reference. However, angles detected by a gyro generally have considerable fluctuations to ensure accuracy in the μrad range, which is the same level as a highly precise inclinometer. In this work, we adopted a periodic reversal measurement using a rotating mechanism to eliminate fluctuations. Analysis and experimental results show that the angles of the gyro’s rotating axis against the earth’s rotating axis can be derived from the angular signals of two gyros rotating in counter directions, and that this method is effective for reducing the influences of fluctuations.

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 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 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 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 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.

International audience; The hybrid positron source made of a crystal-radiator, as a source of channeling radiation, and an amorphous converter is briefly described. Optimization of the heating effects and thermal shocks led to a granular converter made of small tungsten spheres. Simulation results with application to two linear collider projects CLIC and ILC are presented. A test operated with this kind of source at KEK is described and the results gathered last year, reported. Plans for the future are briefly described.

The spatiotemporal diffusive evolution and fractal structure of ground motion have been investigated at the in-ground tunnel of the KEK B-Factory (KEKB) injector linear accelerator (linac). The slow dynamic fluctuating displacements of the tunnel floor are measured in real time with a new remote-controllable sensing system based on a laser-based alignment system. Based on spatiotemporal analyses with linear-regression models, which were applied in both the time and frequency domains to time-series data recorded over a period of approximately 8 months, both coherent and stochastic components in the displacements of the tunnel floor were clearly observed along the entire length of the linac. In particular, it was clearly observed that the stochastic components exhibited characteristic spatiotemporal diffusive evolution with the fractal structure and fractional dimension. This report describes in detail the experimental techniques and analyses of the spatiotemporal diffusive evolution of ground motion observ...

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.

About 90 stripline-type beam-position monitors have been newly installed in the KEKB injector linac. These monitors easily reinforce the handling of beam orbits and measure the amount of beam charge for single-bunch electron and positron beams which are injected to the KEKB rings. The design value of the beam-position resolution is expected to be less than 0.1 mm. A new data-acquisition system based on VME/OS-9 computers has been developed in order to control the monitors in real time. A hardware and software system which includes 18 front-end computers was tuned for the linac commissioning. This report describes the hardware and software system, the monitor calibration, and the beam-test results in detail.

A new wall-current monitor has been developed in order to reinforce the beam-monitoring system in the PF 2.5-GeV linac for the KEK B-Factory. A prototype monitor was tested for its performance and characteristics. The experimental results in terms of both bench tests and beam tests by single-bunch electron beams were analyzed on the basis of equivalent-circuit models. The frequency response of the monitor agreed well with a lumped equivalent-circuit model for both time- and frequency-domain measurements. The position dependence and its frequency characteristics of the monitor also agreed well with a distributed equivalent-circuit model for both time- and frequency-domain measurements. The rise time of the monitor was about 3 ns, which indicated a poor response for short-pulse beams (

A new energy-spread monitor is under development in order to control the transverse positions and energy spread of a single-bunch positron beam with charges of 4 nC. This monitor is to be installed at a dispersion section of the beam transport line (E = 1.1 GeV) for the positron beam transporting from the linac to a damping ring towards the Super KEK B-factory. The author proposes the use of this new monitor consisting of multi-stripline electrodes in order to simultaneously measure not only the transverse beam positions but also the energy spread pulse-by-pulse. This report describes in detail the basic design of the energy-spread monitor, its detection sensitivity and its characteristics depending on the transverse positions and energy spread of the positron beam based on numerical simulations.

In a conventional positron source driven by a few GeV electron beam, a high amount of heat is loaded into a positron converter target to generate intense positrons required by linear colliders, and which would eventually damage the converter target. A hybrid target, composed of a single crystal target as a radiator of intense gamma--rays, and an amorphous converter target placed downstream of the crystal, was proposed as a scheme which could overcome the problem.This paper describes the development of an intense positron source with the hybrid target. A series of experiments on positron generation with the hybrid target has been carried out with a 8--GeV electron beam at the KEKB linac. We observed that positron yield from the hybrid target increased when the incident electron beam was aligned to the crystal axis and exceeded the one from the conventional target with the converter target of the same thickness, when its thickness is less than about 2 radiation length. The measurements in the temperature rise of the amorphous converter target was successfully carried out by use of thermocouples. These results lead to establishment to the evaluation of the hybrid target as an intense positron source., 17pages, 10figures

An alternative way to the conventional positron source using intense electron beams, of some GeV, impinging on thick amorphous targets is presented. This source is using two successive targets: the first one is a tungsten crystal, which axis is aligned with the beam direction, and the second is an amorphous target put at some distance from the crystal. The enhanced radiation due to electron channelling produces a large amount of photons which, consecutively, create high quantity of e +- e - pairs in the amorphous target. Between the two targets a sweeping magnet takes off all or part of the charged particles coming out from the crystal. An optimization procedure is carried out based on two important parameters: a) the distance between the two targets; b) the minimum energy above which the charged particles coming out from the crystal are allowed to hit the amorphous target. This optimization, which first step is presented here, aims to obtain the highest accepted yield (> 1 e +/ e -) after the capture system and the minimum Peak Energy Density Distribution (PEDD) (PEDD < 35 J/g) in order to avoid thermal gradients, which are destructive for the target.

Beam injections to KEKB and Photon Factory are performed with pulse-to-pulse modulation at 50 Hz. Three very different beams are switched every 20 ms in order to inject those beams into KEKB HER, LER and Photon Factory (PF) simultaneously. Human operators work on one of those three virtual accelerators, which correspond to three-fold accelerator parameters. Beam charges for PF injection and the primary electron for positron generation are 50-times different, and beam energies for PF and HER injection are 3-times different. Thus, the beam stabilities are sensitive to operational parameters, and if any instability in accelerator equipment occurred, beam parameter adjustments for those virtual accelerators have to be performed. In order to cure such a situation, beam energy feedback system was installed that can respond to each of virtual accelerators independently., Comment: 3 pages, 2 figures, Contributed Talk at IPAC10, Kyoto, id:TUOCMH01

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 $\ensuremath{\sim}25%$ 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 $\ensuremath{\sim}20%$. 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.

An eccentric-fluted beam pipe was proposed to damp quadrupole modes. The eccentric-flute acts as a mode converter from quadrupole to dipole. Optimized parameters permit to damp both degenerate modes of the quadrupole with the eccentric-flute. External Q-values measured with a low power model agreed well with those calculated with MAFIA.

The energy recovery linac is a very promising synchrotron light source in future. We are contemplating to realize a ERL_based next generation light source in Japan, under a collaboration between KEK, JAEA, ISSP, and other SR institutes. To this end, we started R&D efforts on its key technologies, including a low-emittance photocathode gun and superconducting cavities. We also plan to assemble these technologies into a small test ERL, and to demonstrate their operations. We report our R&D status.

Some feedback loops are needed to perform the stable beam operation in the long term. The beam orbit and energy feedback loops are widely used for the linac beam operations of many facilities. In addition, the beam energy spread control is also effective for the stable beam operation. In order to realize the energy-spread feedback, the non-destructive beam-energy-spread monitor (ESM) has been developed for the KEKB injector linac. This monitor is an ordinary strip-line type beam monitor with eight electrodes instead of four electrodes. Three EMSs have been installed in the KEKB injector linac for a regular energy-spread measurement. One of them is used for the energy-spread feedback operation. This system works well. In this paper, we will present the energy-spread feedback system for the KEKB injector linac in detail.

We summarize the machine operation of KEKB during past one year focusing on progress for this period.

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 energyspread feedback control system using nondestructive energy-spread monitors with multi‐strip-line electrodes and their performance in KEKB operation.

We have investigated quenching phenomena of channeling radiation through positron production from a silicon crystal hit by a single-bunch electron beam with high-bunch charge at the 8-GeV electron/positron injector linac. The crystal axis, left angle bracket1 1 0right-pointing angle bracket, was aligned to the electron beam with a precise goniometer, and positrons produced in the forward direction with a momentum of 20 MeV/c were detected with a magnetic spectrometer. Positron yields were measured by varying the charge in a bunch with a typical bunch length of not, vert, similar10 ps from 0.1 nC to 2 nC. The corresponding instantaneous current density ranged from 0.15 × 104 to 1.2 × 104 A/cm2. The results show that, at these current densities, the positron yield is proportional to the bunch charge within the experimental accuracy, which implies that no non-linear phenomena are observed in channeling radiation.

In an extensive luminosity upgrade of the KEK-B factory, considered as a future plan, the injector linac has to increase the positron acceleration energy from 3.5 GeV to 8.0 GeV. In order to double the acceleration field (from 21 to 42 MV/m), a design study of the C-band accelerating unit has been started. This paper reports on the R & D status of the C-band components for a high-power test and for a beam-acceleration test at the KEKB injector linac.

In the KEKB injector linac, a two-bunch acceleration scheme has been used for doubling the positron injection rate to the KEKB low-energy-ring (LER). In this operation mode, the multi-bunch transverse wake field caused by the first bunch affects the beam orbit of the second bunch. In the KEKB linac, an orbit correction method based on the average minimum of two-bunch orbits has been adopted, and has worked stably. However, a new two-bunch orbit correction method is strongly required to make the loss of charge less. We propose a new two-bunch orbit correction method based on a local bump method. In this scheme, some local bumps are intentionally constructed in a low-energy area. Adjusting the local bump height can control the wake field strength affecting the second bunch. In this paper, we report on the results of a preliminary beam test to confirm that this new method is useful

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 $180\ifmmode^\circ\else\textdegree\fi{}$ 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 $0.150%\ifmmode\pm\else\textpm\fi{}0.007%$ and $0.264%\ifmmode\pm\else\textpm\fi{}0.004%$ for electron beams with charges of 0.9 and $8\text{ }\text{ }\mathrm{nC}/\mathrm{bunch}$ 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.

We have measured beta functions using single kick closed orbit at KEKB. The measured beta functions were compared with the model lattice and gradient errors were extracted from the result in a beta beat. The gradient errors were also obtained by changing strength of steering magnets and measuring beam positions as the second method. The methods of the error estimation and preliminary results are reported.

An absolute beam-charge measurement of single-bunch electron beams with a pulse width of 10 ps and short-pulsed electron beams with a pulse width of 1 ns was performed by the beam test for the KEKB injector linac using a Faraday cup. A wall-current monitor was directly recalibrated by the beam test with an error of /spl plusmn/2%.

We have performed a simulation study on beam bunching in the KEK 2.5-GeV linac new pre-injector comprising double prebunchers and a buncher. The dependence of the bunching performance upon the rf power and the phases of the prebunchers is discussed. We obtained an optimum bunch length of 4 ps with the simulation. >

The injection system (pre-injector) of the KEK 2.5-GeV linac has been upgraded so that we can investigate intense beam acceleration for the KEK B-factory project. It requires intense beams to achieve a short injection time in practice. An outline of the new pre-injector and its performance is given. >

The first beam collision study was done in the KEKB double ring collider. Beam collision conditions were found by searching beam-beam deflection curves in a trial-and-error method. From these curves, beam sizes at IP and a luminosity was estimated.

In the beam transport lines from the injector linac to KEKB rings, four wire scanners were installed for each of positron and electron line. The vibrations and non-linearities of the wire holders were suppressed to be small enough for beam size measurements. Optics matchings were made wing the wire scanners. Better transmission from the linac to the rings was obtained. By detecting shower due to Bremsstrahlung near the detector, the beam sizes were successfully measured without any beam tunings dedicated for background.

The commissioning of the KEKB B-Factory storage rings started on Dec. 1, 1998. The two rings both achieved a stored current of over 0.5 A after operating for four months. The two beams were successfully collided several times. The commissioning stopped on Apr. 19, taking a 5-week break to install the Belle detector.