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Researchers report sub-angstrom fundamental-wavelength lasing at the SPring-8 Angstrom Compact Free-Electron Laser in Japan. The output has a maximum power of more than 10 GW, a pulse duration of 10−14 s and a lasing wavelength of 0.634 A.

Top-up operation allows SPring-8 to provide highly stable X-ray beams with arbitrary filling patterns. The implementation of top-up operation is described, with a focus on the simultaneous achievement of stability of stored current, beam orbit, purity of an isolated single bunch, and beam injection efficiency. Stored-current fluctuations have been routinely reduced to a level of 10(-3). Stored-beam oscillation on frequent beam injection, which was originally regarded as the most serious problem, has been successfully suppressed to a sufficiently low level that it never perturbs imaging experiments. Current impurities in nominally empty buckets have been reduced to a level of 10(-9) over more than one week of operation, making possible the measurement of time-resolved spectra using high-current bunches. Finally, excellent injection efficiency, higher than 80%, is routinely obtained, even for small undulator gaps, which is critical for preventing radiation damage to insertion-device magnets and to reduce leakage radiation. The process of achieving highly stabilized top-up operation at SPring-8 and its utility for user experiments are described.

Femtosecond electron beams are novel tool for pump-probe analysis of condensed matter. Progress in developing femtosecond electron beams with the use of both conventional accelerators and laser-plasma accelerators is discussed. In conventional accelerators, the critical issue is timing jitter and drift of the linac-laser synchronization system. Sophisticated electronic devices are developed to reduce the jitter to 330 fs (rms); the precise control of temperature at several parts of the accelerator lessens the drift to 1 ps (rms). We also report on a full-optical X-ray and e-beam system based on the laser-plasma cathode by using a 12 TW 50 fs laser, which enables 40 MeV (at maximum), 40 fs (cal.), 100 pC and quasi-monochromatic single electron bunches. Since the synchronization is done by a passive optical beam-splitter, this system intrinsically has no jitter and drift. It could achieve tens of femtoseconds time-resolved analysis in the near future.

The 10-T superconducting wiggler at SPring-8 is an ideal photon source for nuclear astrophysics experiments because it produces high-energy synchrotron radiations with equivalent blackbody temperatures being billions of Kelvin. We discuss the characteristics of the high-energy radiation from the superconducting wiggler and its applications to ( γ ,n) measurements.

We fabricated improved DC septum magnets that have smaller leakage fields for continuous beam injection. We changed the shape of the coil and placed field clamps at both ends of the magnets. We increased the thickness of the septum-plane shields and extended them to the field clamps. Leakage fields were measured and the effect they had on an electron beam during injection was studied. After reducing the leakage fields, the orbit changes during injection were less than the beam sizes, which satisfied the requirements for continuous beam injection.

The fluctuation spectrum of the electron beam orbit in the SPring-8 storage ring had broad peaks at approximately 40 Hz vertically and from 80 to 100 Hz horizontally. Fourier analysis of orbit fluctuation identified these fluctuation sources not as magnet vibration but as chamber one due to the disturbance of the cooling water. When the chamber vibration was reduced by fixing the chamber rigidly, the orbit fluctuation was reduced in the same way. An eddy current induced in the vibrating thick chamber in quadrupole magnets produces a bending field, which kicks the electron beam. This field is equivalent to the vibration field of a quadrupole magnet with the same vibration amplitude. The calculated orbit fluctuation based on this model agrees with the measured one.

We had installed four magnet-free long straight sections (LSSs) of 27 m in the SPring-8 storage ring in the summer 2000 in spite that a lattice modification breaks high symmetry of the ring optics. This is because by the potentiality of the LSSs we can not only increase the brilliance of photon beams but also develop innovative light sources. The most serious problem for introducing the LSSs was that the lattice modification markedly deteriorates the stability of electron beams at a large amplitude or a large momentum deviation. To overcome this, a concept of “Quasi-Transparent Matching of sextupole fields” was proposed. This concept simultaneously manages both the symmetry restoration of sextupole fields and the local compensation of chromaticities. Owing to the reasonable lattice design and to the preparation with the precise ring model, the beam commissioning was successfully accomplished for about 3 weeks, achieving the beam performance which almost equals to that in the phase-1 lattice without the LSSs. A long undulator was also installed and it has been used in routine user operation. This success is the first step to challenge the new ideas growing up into future synchrotron radiation sources in the SPring-8 storage ring.

In general, a closed orbit distortion is observed as the sum of beam orbit and various noises such as beam position monitor (BPM) setting errors, BPM's electric response errors, etc. In order to obtain a beam with high performance in a low emittance ring with strong sextupole magnets, it is important to pick up information only of the beam orbit and perform orbit corrections by using this information. For this purpose we developed a new method of estimating BPM offsets to suppress the noise in the orbit data, based on the concept of “two-stage magnet alignment with common girders”. This alignment scheme, adopted in an 8 GeV electron storage ring at SPring-8, reduces high harmonic Fourier components of the orbit which results from magnet misalignment. Then, the main part of high harmonic components of a measured closed orbit is the artificial noise, and these harmful high harmonic components can be extracted as “effective” BPM offsets by filtering a measured closed orbit. This method was applied to the SPring-8 storage ring and found to be effective for reducing residual orbit distortions and a leakage of the dispersion function. To check the reliability of the resulting effective offsets, a beam-based measurement was also carried out at some BPMs and the beam position was measured with respect to the center of a nearby quadrupole magnet. The results were compared with the effective offsets and a reasonable agreement was found.

The SPring-8 storage ring is under the operation dedicated to synchrotron light users. The stability of the electron beam orbit during long term operation is one of the main goals to be achieved. Data on the beam orbit taken for this purpose show variations in time including a very clear signature of an effect of the earth tide.

The 8 GeV electron beam stored on the SPring-8 storage ring finally hits the vacuum chamber wall, especially stainless steel chamber wall of 0.7 mm thickness in the injection section, when the operation is suddenly stopped by interlock system for safety. At that time the localized heat load is generated in the stainless steel material as a result of the dense electro-magnetic shower. Because of the several times such heat loads, the stainless steel chamber has been broken and vacuum also has. On the cross section of the broken stainless steel wall, one can see the evidence of the degeneration or melting down of the stainless steel which is well described by the cascade calculation for the high energy electro-magnetic events using GEANT31). To avoid such a vacuum break, a thicker stainless steel chamber has been installed and an Al damper, in which density of electro-magnetic shower is low because of its small atomic number, has been developed.

We developed a three-dimensional electron bunch charge distribution (3D-BCD) monitor with single-shot detection, and a spectral decoding based electro-optic (EO) sampling technique for a nondestructive monitor enables real-time reconstruction of the three-dimensional distribution of a bunch charge. We realized three goals by simultaneously probing a number of Pockels EO crystals that surround the electron beam axis with hollow and radial polarized laser pulses. First, we performed a feasibility test as a simple case of a 3D-BCD monitor probing two ZnTe crystals as EO detectors installed on the opposite angle to the electron beam axis and confirmed that we simultaneously obtained both EO signals. Since the adopted hollow probe laser pulse is not only radially polarized but also temporally shifted azimuthally, some disorders in the radial polarization distribution of such a laser pulse were numerically analyzed with a plane-wave expansion method. Based on the above investigations, the 3D-BCD monitor is feasible both in experimental and numerical estimations. Furthermore, we previously developed a femtosecond response organic crystal as a Pockels EO detector and a broadband probe laser ($\ensuremath{\ge}350\text{ }\text{ }\mathrm{nm}$ in FWHM); the 3D-BCD monitor realizes 30- to 40-fs (FWHM) temporal resolution. Eventually, the monitor is expected to be equipped in such advanced accelerators as XFEL to measure and adjust the electron bunch charge distribution in real time. The 3D-BCD measurement works as a critical tool to provide feedback to seeded FELs.

The 13th harmonic of a Ti:sapphire (Ti:S) laser in the plateau region was injected as a seeding source to a 250-MeV free-electron-laser (FEL) amplifier. When the amplification conditions were fulfilled, strong enhancement of the radiation intensity by a factor of 650 was observed. The random and uncontrollable spikes, which appeared in the spectra of the Self-Amplified Spontaneous Emission (SASE) based FEL radiation without the seeding source, were found to be suppressed drastically to form to a narrow-band, single peak profile at 61.2 nm. The properties of the seeded FEL radiation were well reproduced by numerical simulations. We discuss the future precept of the seeded FEL scheme to the shorter wavelength region.

We achieved stable operation of a free-electron laser (FEL) based on the self-amplified spontaneous-emission (SASE) scheme at the SPring-8 Compact SASE Source (SCSS) test accelerator in the extremely ultraviolet region. Saturation of the SASE FEL power has been achieved at wavelengths ranging from 50 to 60 nm. The pulse energy has reached $\ensuremath{\sim}30\text{ }\text{ }\ensuremath{\mu}\mathrm{J}$ at 60 nm. The observed fluctuation of the pulse energy is about 10% (standard deviation) for several hours, which agrees with the expectation from the SASE theory showing the stable operation of the accelerator. The SASE FEL has been routinely operated to provide photon beams for user experiments over a period of a few weeks. Analysis on the experimental data gave the normalized-slice emittance at the lasing part is around $0.7\ensuremath{\pi}\text{ }\mathrm{mm}\text{ }\mathrm{mrad}$. This result indicates that the normalized-slice emittance of the initial electron beam, $0.6\ensuremath{\pi}\text{ }\mathrm{mm}\text{ }\mathrm{mrad}$ in a 90% core part, is kept almost unchanged after the bunch compression process with a compression factor of approximately 300. The success of the SCSS test accelerator strongly encourages the realization of a compact XFEL source.

High operation rate is required for synchrotron radiation sources for their many users. Keeping high operation rate, we need to maintain the equipments continually and raise the reliability of each component. To raise the reliability, it is important to clarify the cause of failure of equipments. In this paper, we describe the major magnet-related failure experiences of the past six years for the SPring-8 storage ring: failure of flow switch, dissolution of copper in water, and radiation damage of equipments.

By introducing 13th- (61.7?nm) and 15th-order harmonics (53.4?nm) of femtosecond laser pulses at 800?nm into an undulator of SCSS (SPring-8 Compact SASE Source) test accelerator at RIKEN, these harmonic pulses were amplified by a factor of more than 102?with a high contrast ratio through the interaction between accelerated electron bunches and the harmonic pulses. From numerical simulations of the amplification processes of high-order harmonic pulses in the undulator, optimum conditions of the electron bunch duration interacting with the high-order harmonic pulses were investigated for generating full-coherent and intense pulses in the extreme ultraviolet wavelength region.

We present an experimental verification of a bunch compression method named “velocity bunching”. Velocity bunching based on the rectilinear compression uses a traveling wave accelerating tube as a compressor. The experiment was performed using an S-band photoinjector and a linac at the Nuclear Engineering Research Laboratory, University of Tokyo. The shot-by-shot bunch length was measured to be 0.5±0.1 ps (rms) on average using a femtosecond streak camera at a bunch charge of 1 nC. The experimental result is in good agreement with the PARMELA simulation result.

The accelerator complex of the proposed IPCR heavy-ion facility consists of a separated-sector cyclotron (SSC), a variable frequency linac, and an AVF cyclotron. The linac and AVF cyclotron are used independently or serve as injectors for the SSC. The distance from linac to SSC is about 40 m. The beam lines of the accelerators are not in the same horizontal plane. The vertical distance between the two beam lines is about 7 m. The beam transfer system consists of a charge stripper, beam bunchers, conventional bending magnets, and quadrupoles. An apparatus which shifts the phase of beam bunch to much higher harmonic acceleration can be used for high intensity mode.

A new research facility including an accelerator complex to provide all heavy ions up to uranium has been proposed at the Institute of Physical and Chemical Research. A separated-sector cyclotron (SSC) with K=620 MeV is being designed as a booster accelerator for a variable-frequency heavy-ion linac now under construction. For the injection of relatively light ions up to neon into the above SSC, the existing ordinary cyclotron will be converted into an AVF machine with K=90 MeV to be used as another preaccelerator. The maximum beam energy provided by this accelerator system will range from 120 MeV/u for fully stripped ions to 15 MeV/u for very heavy ions such as uranium. Acceleration of light particles like deuterons and ? particles is also possible. The basic design and some model studies of the proposed machine are described.

In August 2002, a 10-T superconducting wiggler was installed in the 8-GeV electron storage ring at SPring-8. High-energy (/spl sim/3 MeV) and intense synchrotron radiation was produced from the wiggler, and scattered photons were generated by the interaction of synchrotron radiation with photon absorber materials. The intense radiation environment in the storage ring tunnel damages accelerator components, such as cable insulators and coils for electromagnets. To suppress such damage, it is necessary to understand the dose distribution and the spectrum of scattered photons near the wiggler. The dose distribution and the spectrum of scattered photons from the photon absorber was measured by thermoluminescent dosimeters (LiF TLD) with lead filters (0, 0.5, 1, 3, 6 mm in thickness). At the same time, alanine dosimeters and GafChromic film (made of polyethylene) were used to measure the dose of photons which exceeded the dynamic range of TLD dosimeters. The results of an experimental data analysis showed that, as expected, photons of energies of several hundred keV were scattered over a wide range.

We first generated seeded FEL radiation in the EUV region at 61.2 nm with the 13th harmonic of a Ti:sapphire laser. We observed single-peak spectra with drastic enhancements of intensity by nearly three-orders of magnitude.

The SPring-8 storage ring has improved its reliability and beam performance. At the beginning of year 2001, a project of beam orbit stabilization started aiming for the stability of sub-micron. By two years' activities, we have taken a remarkable progress on improvement of the orbit stability of the SPring-8 storage ring. Recently, optics of the ring was changed from the Double Bend Achromat type to new one with finite dispersion at the straight section for insertion devices. The horizontal emittance of 3 nm.rad was obtained which is close to the theoretical value. To increase time-averaged brilliance in several bunch operation, we have prepared a top-up operation in user time from September 2003. In this paper, the operational status and recent beam performance of the SPring-8 storage ring are presented.