K. Haga

Reconstruction for the brilliance-upgrading project of the Photon Factory storage ring

Reconstruction of the Photon Factory storage ring (PF ring; 2.5 GeV) is now in progress to provide very brilliant synchrotron radiation to users, i.e. the emittance is being reduced by a factor of five. Components, such as the quadrupole and sextupole magnets, vacuum chambers, beamlines and beam-position monitors, are being replaced by new ones in 16 normal-cell sections of the PF ring. The accelerating cavities, injection systems and control systems are also being replaced. Operation will commence when the improvements are completed on 1 October 1997.

Commissioning of the PF Ring after the Reconstruction for the Straight‐sections Upgrade

At the 2.5‐GeV ring of the Photon Factory, a large reconstruction of the lattice around the straight sections has been accomplished in 2005. Thus reconstruction is the main part of the straight‐sections upgrade project to rebuild existing undulators and to increase the number of undulator beamlines. As a result of the reconstruction, four short straight sections have been newly created and the lengths of the existing straight sections have been much extended. To exploit the new straight sections, short‐period narrow‐gap undulators which have a sufficiently high brilliance in hard x‐ray range have been developed. The reconstruction work of the ring was completed in a seven‐month shutdown from March to September, 2005. In the area over two thirds of the storage ring, all the quadrupole magnets and all the beam ducts have been renewed and rearranged to construct the new lattice. Recommissioning of the storage ring was finished at the end of October, 2005. Though we made no in‐situ baking for the beam ducts, ...

Collective effects in single bunch mode at the Photon factory storage ring

The bunch length and width in the single bunch mode were measured as a function of bunch current. Bunch lengthening and widening were observed and compared with theoretical models of potential-well distortion and microwave instability. The experimental data was found to agree with these theoretical models. At the same time, the longitudinal effective impedance was obtained. The coherent betatron tune shifts were also observed. The tune shifts were explained with the head-tail mode theory, which gave an estimate of the horizontal and vertical effective impedances.<<ETX>>

New Upgrade Project for the Photon Factory Storage Ring

A new project for upgrading the 2.5‐GeV Photon Factory (PF) storage ring is now being undertaken to create six new short‐straight sections and to lengthen the existing eight straight sections. The short‐straight sections will provide an opportunity to install short‐period narrow‐gap undulators, while the extensions of existing straight sections will be taken advantage of updating current insertion devices to the latest models in future. To this end, the lattice configuration around the straight sections is modified by replacing old quadrupole magnets with new shorter ones and placing them closer to the near‐by bending magnets. Necessary replacement of the vacuum ducts and the beamline front ends will be carried out together. This project will be completed by the end of September, 2005, after six months of shutdown.

Status of R&D efforts toward the ERL-based future light source in Japan

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.

PF-ring and PF-AR operational status

The present operational status of the Photon Factory storage ring (PF-ring) and the Photon Factory advanced ring (PF-AR) in KEK is reported. The scheduled user times of them were more than 4000 hours in FY2006. In the last summer shutdown, new undulators were installed in both of the rings and have been stably operated. A top-up operation in a single-bunch mode was demonstrated for six days in February 2007 druring the shutdown of KEKB at the PF-ring.

New beam-position monitor system for upgraded Photon Factory storage ring

Accompanying the brilliance-upgrading project at the Photon Factory storage ring, the beam-position monitor (BPM) system has been renovated. The new system was designed to enable precise and fast measurements to correct the closed-orbit distortion (COD), as well as to feed back the orbit position during user runs. There are 42 BPMs newly installed, amounting to a total of 65 BPMs. All of the BPMs are calibrated on the test bench using a coaxially strung metallic wire. The measured electrical offsets are typically 200 micro m in both directions, which is 1/2-1/3 of those of the old-type BPMs. In the signal-processing system, PIN diode switches are employed in order to improve reliability. In the fastest mode, this system is capable of measuring COD within about 10 ms; this fast acquisition will allow fast suppression of the beam movement for frequencies up to 50 Hz using a global feedback system.

Measurement and Control of Beam Losses Under High Average-current Operation of the Compact ERL at KEK

The compact ERL (cERL) [1, 2] at KEK is a superconducting accelerator aimed at demonstrating ERL technologies for the future light source. In cERL, low-emittance and high-average-current electron beams of up to 10 mA will be recirculated in future. Toward this goal, we studied high-average-current operations where the beam losses should be controlled to very-small fractions. We have so far succeeded in recirculating beams of up to 0.9 mA with very-small beam losses. We report our accelerator tuning method for high-average-current operation, and present measured radiation data showing very-small beam losses. INTRODUCTION In cERL, production and transportation of lowemittance (< 1 mmmrad) and high-average-current ( 10 mA) electron beams are primarily important. In highintensity linacs such as cERL, reduction of beam loss is essential in order to reduce the risk of radiation hazard as well as to avoid damages in accelerator components. Till June of 2015, electron beam having an average current of 80 A was successfully transported to the beam dump in cERL. Due to careful accelerator tuning and the use of beam collimators, beam losses along a recirculation loop were reduced to small amounts. At this time, we conducted radiation measurements with several methods, and estimated amounts of beam losses [3]. Based on these data, we installed some additional radiation shields, and applied an increase in our authorized beam current, that is, from 100 A to 1 mA. This application was approved by the government in January, 2016. Until March of 2016, we established high averagecurrent operations of cERL up to a maximum beam current of 1 mA. Typical operational parameters are given in Table 1. We can choose one of two repetition rates of bunches, 1.3 GHz or 162.5 MHz, by selecting one of the laser oscillators of a photocathode DC gun. First, we tuned the machine at a higher bunch-repetition rate (1.3 GHz) with lower bunch charge (0.7 pC/bunch). After this Table 1: Typical Operational Parameters of cERL Beam energy 19.9 MeV Injection energy 2.9 MeV Bunch repetition rate (usual) (for laser-Compton scattering) 1.3 GHz

Operational Status of PF-Ring and PF-AR after the Earthquake

In 2011, two SR sources of KEK, PF-ring and PF-AR, needed to change the operation schedule because of the unprecedented earthquake on March 11. Though the injector linac and the storage rings suffered a serious damage, temporary recovery was accomplished quickly and the trial operation started in May. The regular user operation could be resumed in October 2011. In the restoration work after the earthquake, some old vacuum components were removed from PF-ring. This work fortunately brought an effect of settling the quadrupole-mode longitudinal instability. For the top-up injection of PF-ring, the pulsed sextupole magnet has been used instead of the conventional kicker magnets since 2011. The hybrid-fill mode in place of the single-bunch mode has become available. Recently, the 10-Hz orbit switching for the tandem circularly polarized undulators has been developed for the user operation.

Status of the 6.5‐GeV Photon Factory Advanced Ring

The Photon Factory Advanced Ring (PF‐AR) is a 6.5‐GeV synchrotron light source at the High Energy Accelerator Research Organization (KEK). It can provide high‐flux hard X‐rays for such research as the materials science, structural biology and medical applications. The PF‐AR has five insertion devices including four in‐vacuum undulators. It is operated with a single bunch which fits for time‐resolved experiments. A special 5‐GeV operation is partly provided for a clinical application. An initial beam current and a beam lifetime are 60 mA and approximately 14 hours, respectively. Recent developments include an installation of a new in‐vacuum undulator (U♯NW14‐36) to the west rf section, which was accompanied by transferring two rf cavities to other section. The undulator has been successfully operated at a minimum magnetic gap of 10 mm. We also carried out such accelerator studies as a successful test of beam injection using a pulsed quadrupole magnet, a study of low emittance optics, an establishment of tw...