Seiji Asaoka

Synchrotron radiation beamline to study radioactive materials at the Photon factory

Abstract Design and construction of a new beamline have been described. The beamline is housed in a specially designed area controlled for radioactive materials at the Photon Factory (PF) in the National Laboratory for High Energy Physics (KEK). The beamline system consists of a front-end and two branchlines. One of the branchlines is used for X-ray photoelectron spectroscopy and radiation biology in the energy range of 1.8-6 keV and the other for X-ray diffractometry and XAFS studies as well as radiation biology in the range of 4–20 keV. The former was particularly equipped for the protection against accidental scattering of radioactive materials both inside and outside of the vacuum system.

Design and construction of beamline‐NE1 for circularly polarized synchrotron radiation from the 6‐GeV TRISTAN Accumulation Ring

The beamline for the circularly polarized synchrotron radiation at the 6‐GeV Accumulation Ring for the TRISTAN project is now under construction. The insertion device of this beamline was designed to produce circularly polarized x rays at the photon energy range of 200 eV∼100 keV. The beamline is divided into the following three branches: (1) High resolution Compton scattering and magnetic Compton scattering experiments; (2) multipurpose experiments such as magnetic x‐ray scattering and magnetic x‐ray absorption; and (3) completely circularly polarized soft x rays.

Fluorescence lifetimes and excitation spectra of liquid alkanes measured by means of synchrotron radiation

Fluorescence lifetimes of liquid cyclohexane, bicyclohexyl, cis‐decalin, trans‐decalin, n‐decane, and n‐dodecane have been measured at 25 °C by a delayed coincidence single photon counting technique at several excitation wavelengths of SR (synchrotron radiation) pulse between 120 and 180 nm. Excitation spectra of these liquids have been also examined at the wavelength region between 120 and 300 nm. The lifetimes show no dependence on the excitation wavelength of SR used in the experiment. The lifetimes determined are as follows: 1.1±0.1 ns (cyclohexane), 1.8±0.3 ns (bicyclohexyl), 2.4±0.1 ns (cis‐decalin), 3.0±0.1 ns (trans‐decalin), 3.0±0.1 ns (n‐decane), and 4.2±0.2 ns (n‐dodecane). Each of excitation spectra of these liquids shows a single broad peak with FWHM of (5–23)×103 cm−1 at the excitation wavelengths between 163 and 185 nm. There is no increase of fluorescence yield in the excitation spectrum with increasing the excitation energy across the ionization potential of each of the liquids. Fluoresce...

Observation of Undulator Radiation. : I. Operation Studies and Visual Observation

A 19-pole permanent magnet undulator has been tested by inserting it into a straight section from outside the vacuum chamber of the SOR-RING, a dedicated synchrotron radiation source operated between 0.2 and 0.38 GeV. It was confirmed that the undulator field did not seriously disturb stable operation by observing the shift of the closed orbit and the shift of the betatron numbers. Some results of visual observation of the radiation are presented. The polarization character was studied on the rainbow circle with a polarizer and some theoretical results by Kitamura were confirmed. It was found that the interfering synchrotron radiations along the straight section of the storage ring make a series of rainbows even without the undulator field.

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.

Equilibrium phase instability in the double RF system for Landau damping

Abstract A longitudinal coupled bunch instability in an electron storage ring was suppressed by the Landau damping in a double rf system composed of a second harmonic rf cavity. The damping became ineffective, however, above a beam current of 30 mA; the beam bunch slipped out of the optimum phase of the total rf voltage for the damping, which accompanied a simultaneous deformation of the total voltage. The unexpected phenomenon of the phase slip is explained by the concept of equilibrium phase instability of the beam bunch based on a rigid bunch model. The phase slip of the bunch was suppressed by introducing a phase feedback loop, resulting in an improvement of the maximum beam current for the damping. Discussions are made on various conditions of the equilibrium phase instability, including another possibility for avoiding the phase slip.

Present Status of SOR

Recent progress and investigations of an electron storage ring, SOCR, are presented. Stored current and beam life time increased considerably. Injection efficiency and the life time were studied critically. Especially the life time was found to depend on the pressure of the ring and effective momentum aperture related to betatron resonance as well as the Touschek effect.

New multipole wiggler/undulator beamline (BL‐16) at the Photon Factory

Design and experience of the initial operation of a new beamline (BL‐16) for a 3.6‐m‐long, 53‐pole wiggler/undulator constructed at the Photon Factory are described. The insertion device has hybrid permanent magnets with a period of 12 cm and a maximum magnetic field of 1.47 T. In the undulator mode, the energy of the fundamental peak can be varied from 40 to 400 eV. In the wiggler mode, an x‐ray beam (critical energy of 6 keV) 50–100 times more intense than that from the bending magnets is obtained. The beamline consists of two time‐shared branch lines: a side beamline for soft x‐rays in the undulator operation, to which photon beams are deflected sideways by a cylindrical SiC mirror, and a straight line for hard x rays under the wiggler operation. On the hard x‐ray line, a fixed‐exit sagittal‐focusing double‐crystal monochromator has been installed and commissioned. Collimating and refocusing mirrors will be installed in 1989. On the undulator beamline, a soft x‐ray monochromator utilizing sophisticated...

Slow fluctuation of synchrotron radiation and bunch lengthening in SOR

Abstract Slow fluctuation of synchrotron radiation and bunch lengthening of the stored beam current in SOR, a 400 MeV electron storage ring for synchrotron radiation, were studied experimentally and theoretically and found to be induced by a longitudinal coupled-bunch instability. The lengthening which follows a 1/5.8 power dependence on the beam current is explained well as an equilibrium state with a balance of the growth and damping rates of the instability. The damping is brought about by the frequency spread of synchrotron oscillations. The radiation fluctuation is due to a weak disturbance of the bunch length about the equilibrium state and a simple relation was found between the fluctuation frequency and the growth rate of the instability. Horizontal bunch widening is clearly related to the bunch lengthening. A quadratic frequency dependence of coupling impedance is derived from the data on bunch lengthening.

Vacuum protection system using an interlocked fast-closing valve for a high-power wiggler beam line

The finite-element method was used to calculate a rise in temperature at a fast-closing valve (FCV) blade during exposure to intense synchrotron radiation from a 53-pole wiggler at the 2.5-GeV Photon Factory storage ring. The results indicate a possible meltdown of the titanium-alloy blade within 0.1 s at a maximum beam current of 500 mA, making the vacuum protection function of the FCV ineffective for an instantaneous vacuum failure downstream of the wiggler beam line. In order to prevent the blade from melting, the FCV control system has been interlocked with RF klystrons so as to initiate blade closure after dumping the electron beam by turning off the RF power. Performance tests have shown that the system could dump the electron beam within 95 mu s and then close the blade within 12.4 ms after being triggered. >