Ring Facility Research Articles

The operation of a superconducting wiggler at TERAS.

A superconducting wiggler has been successfully installed at the ETL 800 MeV electron storage ring facility (TERAS). The operation of the wiggler at magnetic field strengths of 5 T with electron beam energy of 750 MeV has been accomplished. The wiggler has been designed and constructed to produce synchrotron radiation with critical photon energy around 3 keV for scientific, industrial and medical applications. We report here experiments that demonstrate the possibility of stable operation of a superconducting wiggler in a small storage ring.

High-pressure solid-state spectroscopy at UVSOR by Infrared Synchrotron Radiation

Solid-state spectroscopy by infrared synchrotron radiation (IRSR) has been in use since 1985 at the beamline BL6A1 of UVSOR, the electron storage ring facility of the Institute for Molecular Science at Okazaki in Japan. The wavelength region covered by BL6A1 extends from the near-infrared to the millimeter wave region (1 µm to 3 mm). Up to now, many types of experiments have been done there. In the present article, after a description of the optics of BL6A1 and of the time-resolved infrared spectrum of the source, I discuss the use of that beamline for spectroscopy with diamond anvil cells (DAC) in the far-infrared region. Spectroscopy under high pressure, based either on transmission and on reflection measurements, has been carried out in order to show the advantage of the utilization of the infrared synchrotron radiation with respect to conventional sources. In the former type of experiment, the bulk TO phonon spectra of alkali halide thin films have been measured in order to observe the change in the phonon spectrum due to the phase transition under pressure. The transmission spectrum on the surface phonon state of CuBr microcrystals has also been measured in order to study the response of the surface phonon state to a pressure up to 20 GPa. The reflectivity spectra under pressure have been done instead on a single crystal of KCl, where a change in the rest-strahlen band of KCl due to the phase transition has been observed. Through these measurements one has confirmed that infrared synchrotron radiation is a powerful light source, particularly for those experiments where the acceptance angle of the sample surface with respect to the incident light beam is very small. This is indeed the case of spectroscopy under high pressure in a diamond anvil cell. Finally, a proposal is presented for realizing an even more intense infrared radiation source on a storage ring, with particular regard to the spectroscopic investigation of solid specimens.

Recent dielectronic recombination experiments

New recombination experiments with merged cold beams of electrons and atomic ions have been carried out at the storage ring facilities TSR in Heidelberg, ESR in Darmstadt, and CRYRING in Stockholm. A brief overview is given on the recent activities in which the Giessen group was engaged. Topics of this research were dielectronic recombination (DR) of astrophysically relevant ions, recombination of highly charged ions with respect to cooling losses in storage rings, field effects on DR, search for interference effects in photorecombination of ions, correlation effects in DR of low-Z ions, spectroscopy of high-Z ions by DR, and lifetimes of metastable states deduced from DR experiments.

Planned storage ring facilities in Japan and in China

Two accumulators are proposed in Asia. One is the MUSES in the RI Beam Factory in RIKEN and the other is the CSR at HIRFL in Lanzhou. Both of them aim at storing heavy-ions and radioactive nuclear beams. In this paper, a brief introduction to the two facilities is presented and then the planned nuclear physics experiments are introduced based on the proposal of the RI Beam Factory.

Pionic Fusion Study of the halo analogue state6Li

The isobaric analogue state of the ground state of the halo nucleus6He,6Li* has been studied in a pionic fusion experiment at the CELSIUS storage ring facility in Uppsala, Sweden. This was the first of two proposed experiments with the aim to study the high momentum part of the wave functions of the halo nuclei6He and6Li (0+, T=1). The Li nuclei were produced in inverse kinematics reactions with alpha particles incident on a deuterium cluster jet target. The6Li ions were detected in a zero-degree spectrometer situated in the fourth quadrant of the CELSIUS ring. The measurement was done for three different beam energies corresponding to 5.4, 2.2 and 1.5 MeV above threshold in the c.m. The cross-sections slowly increase with beam energy from 95 nb at the lowest energy to about 250 nb at 5.4 MeV above threshold.

Recombination studies of highly charged ions in the cooler ring CRYRING

Cooler-storage ring facilities offer unique experimental possibilities for studies of electron-ion recombination processes at low relative energies by employing the electron cooler as a target. Through the use of an adiabatically expanded electron beam in the cooler of CRYRING, collisions down to 10−4 eV relative energies were measured with highly charged ions stored in the ring at around 15 MeV/amu energies. Examples of recombination measurements for C4+ and Ar15+ ions at an energy resolution of as low as 10−2 eV FWHM are presented and compared with calculations of the energies and resonance strength for dielectronic recombination using multiconfiguration Breit-Pauli approximations. They agree in spectral shape and absolute cross section but show some deviation for lower n in the Rydberg series.

Vacuum system of the Dubna heavy ion storage ring facility K4-K10

The complex K4-K10 of two storage rings is intended to provide the beams of exotic neutron deficient and neutron excess nuclei ranging from He to Ni. High momentum resolution of cooled exotic beams ( δp/ p = 10 −5 −10 −6) and maximum energy of 150–200 MeV amu −1 are the purpose of this project. Interactions of heavy ions with the molecules of the important constituents of the residual gas are analysed. For a successful operation of the ring complex, the pressure in the vacuum chambers must not be less than 1 × 10 −8 Pa. The gas load sources are analysed and the vacuum technology of the initial preparation of the vacuum chamber materials and the procedure of reaching the desirable vacuum are defined. The structures of the vacuum systems and their different parts are described. An ultra high vacuum test bench for modelling works and examination of individual parts of the vacuum system is created.

The combination of a VUV Fourier-transform spectrometer and synchrotron radiation

Current research on the Earth’s upper atmosphere requires molecular parameters of unprecedented detail and accuracy. For example, state-of-the-art models of the vacuum-ultraviolet (VUV) absorbing properties of the atmosphere call for absorption cross sections with details on the scale of the Doppler linewidths. As a consequence, spectroscopic data at resolving powers of the order of 106 are needed. Current particular needs are for ultra-high-resolution absorption cross-section data for some bands of NO and O2 in the 170–185 nm spectral region. To meet these requirements, an existing, portable, VUV Fourier-transform (FT) spectrometer will be moved to a synchrotron-radiation facility (Photon Factory, KEK, Japan) and VUV photoabsorption cross sections of NO and O2 will be measured. It has been demonstrated so far with emission line sources that the FT spectrometer will perform to ≤139 nm. Extension of work on absorption measurements to shorter wavelengths and with ultrahigh resolution requires an improved light source. Synchrotron radiation from a storage ring facility is the best alternative.

Radiometry at the NIST SURF II storage ring facility

The National Institute of Standards and Technology (NIST) in Gaithersburg, MD, is the site of the Synchrotron Ultraviolet Radiation Facility (SURF II). The synchrotron radiation from the 300 MeV electron storage ring is used for most of the NIST radiometry programs in the far ultraviolet. Continuum radiation from SURF II extends from the infrared to about 4 nm (310 eV) and is a standard source for the calibration of integrated optical systems, particularly space experiments. The SURF II facility is also used for a large portion of the NIST far ultraviolet transfer detector standards program, in which spectrally calibrated detector standards are available from 5 nm (248 eV) to 254 nm (4.9 eV). One of the most recent activities has been the development of a new apparatus designed to qualify working standards for calibration of the NIST MgF2 windowed far ultraviolet transfer standard detectors. Additionally, new radiometric quality silicon photodiodes have now been developed. These detectors offer many improvements onver NIST’s photoemissive standards.

Structure of very heavy few-electron ions—new results from the heavy ion storage ring, ESR

The heavy ion synchrotron/storage ring facility at GSI, SIS/ESR, provides intense beams of cooled, highly-charged ions up to naked uranium (U92+). By electron capture during ion-atom collisions in the gas target of the ESR or by recombination at ion-electron encounters in the "electron cooler" excited states are populated. The detailed structure of very heavy one-, two-and three-electron ions is studied. The different mechanisms leading to the excited states are described, as well as the new experimental tools now available for a detailed spectroscopy of these interesting systems. Special emphasis is given to x-ray transitions to the groundstates in H- and He-like systems. For the heaviest species the groundstate Lambshift can now be probed on an accuracy level of better than 10% using solid-state x-ray detectors. Applying dispersive x-ray analysing techniques, this accuracy will certainly be improved in future. However, utilizing the dielectronic recombination resonances for a spectroscopy, the structure in Li-like heavy ions can already be probed now on the sub eV level.

Antiproton-nucleus annihilation at rest

Cooled antiprotons from the LEAR storage ring facility have been stopped in targets from A = 6 to 238 to investigate the processes following annihilation at the nuclear surface. Among the recent results are the following: The measured spectra can be fitted to N(p2) = N0 exp (–p2/p02), where p is the momentum of the ejectiles and p0 ≈ 360MeV/c for all ejected particles from protons to alpha particles and for all 16 targets except 6Li. The proton spectra show an additional low-momentum component attributed to evaporation. The measured residual nucleus distribution from stopped p annihilation in Cu, when compared with INC calculations and with residual mass distributions from energetic π+, π- and proton interactions with Cu, indicate that the energy set free in the annihilation process is used only in part as excitation energy. The residual nucleus distribution from a 238U target shows that both symmetric and asymmetric fission take place. Detection and analysis of coincident fission products from 209Vi, 232Th and 238U enabled us to determine the individual and total mass and energy distributions of the fragments, their opening angle, the average excitation energy and momentum of the nucleus at scission, and the number of nucleons emitted before and after scission. We also found that the process is asymmetric for low excitation energies and symmetric for higher ones. INC calculations have reproduced the experimental results.

Cooler ring facilities

The principles and history of electron cooling and stochastic cooling are presented, and the characteristics of a number of existing storage rings, for antiproton accumulation and collection, for low energy antiproton physics, and for atomic and nuclear physics are discussed. Finally, three new proposals for the use of phase space cooling at higher energies are mentioned.

Experimental aspects and Z-dependent systematics in one- and two-electron ions and single vacancy systems

Some predominantly experimental considerations concerning both few electron highly charged ion spectra and inner-shell vacancy spectra are discussed in relation to the currently available theoretical approaches. For the cases of H-like and He-like spectra theoretical machinery appears to be well in hand particularly in comparison to the relatively sparse experimental database which is also of limited accuracy in most cases. Owing particularly to some impressive recent theoretical progress on the problem of nearly neutral ions containing inner-shell vacancies, the traditional x-ray data suitably filtered and strengthened by modern measurements, appear to offer some quite useful insights in spite of their formidable complexity. With the advent of new storage ring facilities and advanced technology ion sources as well as a new effort on transuranic x-ray spectra, one can reasonably foresee an upcoming period of fruitful activity.

Interaction of stopped antiprotons with copper.

A natural Cu target was irradiated with the antiproton beam from the Low Energy Antiproton Ring facility at CERN. The 105 MeV/[ital c] [ital [bar p]] beam was completely slowed down inside a thick target producing many radioactive products. Starting shortly after the irradiation and continuing for about one year, this residual activity was counted using off-line gamma-ray spectroscopy techniques. The yields of 40 radioactive reaction products were determined. The charge dispersion and complete mass yield distribution were deduced using a well-established fitting procedure. The shape of the mass yield and, in particular, the average number of removed nucleons, the dispersion of the mass distribution, and its logarithmic slope characterize the average energy deposited during the antiproton-nucleus interaction. We compare these quantities with similar data gathered for other projectiles interacting with natural Cu targets. These comparisons indicate that the average excitation energy of the system formed after the stopped antiproton annihilation is similar to the average excitation energy following 2-GeV proton interaction with Cu nuclei. The observed mass distribution is also compared with the intranuclear cascade calculations.

FELICITA II, a design study for a VUV-high-gain FEL at the storage ring DELTA

FELICITA II (free electron laser in a circular test accelerator) is the second FEL experiment planned at DELTA, the storage ring facility at the University of Dortmund, following a more conventional experiment in the visible and near UV [1]. It is designed to operate in the wavelength regime of 100 nm and considerably below. Due to the high losses of the optical cavity FELICITA II has to provide extremely high gain. This paper presents a design study of this FEL, giving preliminary parameters for the undulator, the ring resonator and the installation into the storage ring. Furthermore, simulation results concerning gain, susceptibility to energy spread and emittance, and the operation of FELICITA II in DELTA will be presented.

German heavy-ion ICF activities: Status and prospects

The main goals of the German program are the study of key issues of inertial fusion with intense beams of heavy ions. The completion of the new heavy-ion synchrotron and storage ring facility SIS/ESR at GSI opens new directions for experimental investigations on beam dynamics at high intensity and on beam/target interaction. In addition, new accelerator scenarios will be investigated based on non-Liouvillean beam-handling techniques.

Why study on nuclei?

A brief summary of the first elastic and inelastic scattering results obtained at the European low-energy antiproton ring facility is presented. The constraints thereby put on the antiproton–nucleus interaction are discussed, and the unique features of the antiproton as a probe of the nucleus are pointed out. In particular, it is stressed that the near blackness of the nucleus to antiprotons could be exploited in the [Formula: see text] reaction to specific states excited mainly by the long-range part of the nucleon–antinucleon interaction. The spin–isospin parts of the interaction as well as some isovector nuclear excitations could thus be studied.

Heavy ions in the CELSIUS storage ring in Uppsala

The CELSIUS storage ring facility will include electron cooling, acceleration and internal targets. It is presently under construction adjacent to its injector machine, the rebuilt synchrocyclotron of the Gustaf Werner Institute. The maximum energy for protons will be 1.16 GeV and for heavy ions 388 MeV/A for ions with Q/A=0.5.

Photoionization cross section of helium for photon energies 59-67 eV: The(sp,2n+)Po1Rydberg series of autoionizing resonances

The central position of the 2s2p /sup 1/P/sup o/ two-electron resonance of He at 206.21 A has been remeasured using the background continuum of the National Bureau of Standards storage ring facility. In addition, the line-shape parameter q and width GAMMA of the resonance have also been obtained. We obtained a value of 60.151 +- 0.010 eV for the resonance position, -2.6 +- 0.3 for the line-shape parameter, and 0.038 +- 0.002 eV for the width of the resonance. Our value for the resonance position is in good agreement with the theoretical calculation of 60.145 eV of Bhatia and Temkin and lies within the error budget of the previous experimental measurements of Madden and Codling. Parameter values for the other resonances have also been obtained and are in good agreement with the earlier measurements of Madden and Codling.

Extraction for ISABELLE

The design specifications for ISABELLE, a superconducting proton storage ring facility under construction at Brookhaven National Laboratory call for circulating beam intensities of up to 6 x 1014 protons at 400 GeV energy in each ring. The energy stored in the beam is 41 Megajoules, an order of magnitude more than what has been dealt with in the past. This beam energy cannot be safely disposed of within the confines of the ISABELLE lattice if damage to the dump or quenching of the superconducting magnets is to be avoided. Therefore the full intensity beam must be extracted from the storage rings under all circumstances of emergency or routine beam disposal. Beam losses in excess of 10-3 of the full beam can jeopardize the extraction components and lead to magnet quenching as well. In this note we summarize a conceptual design of the extraction system and discuss the major constraints which lead to the parameters chosen.