First experiment with decelerated bare uranium ions conducted at the ESR storage ring

The deceleration capabilities of the ESR have been used for the first time in a dedicated ground state QED experiment conducted at the gasjet target of the ring. By decelerating bare uranium ions from 358 MeV/u down to energies of as low as 49 MeV/u, X-ray spectra have been obtained which provide an abundant yield of characteristic X-ray transitions. The experiment demonstrates that, by choosing the appropriate beam energy and gasjet target, almost all excited projectile states can be selectively populated. Moreover, the experiment provides the first data for beam lifetimes of stored decelerated high-Z ions. Such data are essential for the design of future experiments dealing with decelerated ion beams far below 50 MeV/u. This revised version was published online in August 2006 with corrections to the Cover Date.     

Photodissociation spectroscopy of OH+ molecular ions at the TSR storage ring

When infrared active molecular ions are stored in a heavy ion storage ring, a fast beam of vibrationally and rotationally relaxed molecules can be obtained. This opens up new opportunities for various experimental studies in molecular ion physics, particularly those involved with spectroscopy and dissociation dynamics of excited states. The analysis of such experiments is facilitated by the fact that the information on the initial states is able to identify and, therefore, eliminate them from the assignment problem. Moreover, when the intensity of the measured transitions is monitored as a function of storage time, the dependence of these processes on the degree of internal relaxation is revealed. We demonstrate these general principles by application to near threshold dissociation spectroscopy of the OH⁺ molecular ion. The structure of quasibound levels near the dissociation limit of OH⁺ and its dissociation energy are deduced. This revised version was published online in August 2006 with corrections to the Cover Date.     

Study of electron bremsstrahlung in strong Coulomb fields at the ESR storage ring

Electron bremsstrahlung has been investigated for collisions of 223.2 MeV/amu He-like uranium ions with N₂ and Ar gaseous targets. The doubly differential cross-sections for bremsstrahlung are compared to the predictions of relativistic first order Born calculations (Bethe-Heitler formula with Elwert correction factor) and to the calculations based on the exact wavefunctions for electrons moving in the external point-Coulomb potential of the projectile. Whereas the “exact” IPA calculations give an improved agreement with experimental data, as compared to the Bethe-Heitler theory, in particular at the end-point region of the bremsstrahlung spectra, discrepancies still remain at lower photon energies. This revised version was published online in July 2006 with corrections to the Cover Date.     

Longitudinal phase-space coating of beam in a storage ring

In this Letter, I report on a novel scheme for beam stacking without any beam emittance dilution using a barrier rf system in synchrotrons. The general principle of the scheme called longitudinal phase-space coating, validation of the concept via multi-particle beam dynamics simulations applied to the Fermilab Recycler, and its experimental demonstration are presented. In addition, it has been shown and illustrated that the rf gymnastics involved in this scheme can be used in measuring the incoherent synchrotron tune spectrum of the beam in barrier buckets and in producing a clean hollow beam in longitudinal phase space. The method of beam stacking in synchrotrons presented here is the first of its kind.     

White-light laser cooling of ions in a storage ring

We propose the use of a white laser for laser cooling of ions in a storage ring. The use of a broad-band laser provides a radiation pressure force with wide velocity capture range and high magnitude, which is promising to improve the performance of both longitudinal and indirect transverse cooling. This wide-range force could also be suitable for direct transverse cooling of low-density beams.     

Laser spectroscopy of optical centers in borosilicophosphate glass, coactivated by erbium and ytterbium ions

Based on analysis of the laser emission spectra of borosilicophosphate glass, coactivated by Er³⁺ and Yb³⁺ ions, we have determined the structure of the Stark splitting of the luminescence band for the erbium ion in the 1.5 μm region (the transition ⁴I_13/2 → ⁴I_15/2). In the wavelength interval 1532–1547 nm, we identified 12 sets of lines belonging to different types of optical centers of predominantly cubic symmetry. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 4, pp. 483–487, July–August, 2006.     

Longitudinal momentum mining of beam particles in a storage ring

I describe a scheme for selectively isolating high density low longitudinal emittance beam particles in a storage ring from the rest of the beam without emittance dilution. I discuss the general principle of the method, called longitudinal momentum mining, beam dynamics simulations and results of beam experiments. Multi-particle beam dynamics simulations applied to the Fermilab 8 GeV Recycler (a storage ring) convincingly validate the concepts and feasibility of the method, which I have demonstrated with beam experiments in the Recycler. The method presented here is the first of its kind.     

Mass measurements of relativistic projectile fragments in the storage ring ESR

Two experimental methods of measuring masses of exotic nuclei in the storage ring ESR are presented. Bismuth and nickel fragments were produced via projectile fragmentation, separated and investigated with the combination of the fragment separator FRS and the ESR: (i) Direct mass measurements of relativistic projectile fragments were performed using Schottky mass spectrometry (SMS), i.e., exotic nuclei were stored and cooled in the ESR. Applying electron cooling, the relative velocity spread of circulating low intensity beams can be reduced below 10⁻⁶. Under this condition a mass resolving power of up to m/Δm=6.5·10⁵ (FWHM) was achieved in a recent measurement. Previously unknown masses of more than 100 neutron-deficient isotopes have been measured in the range of 60≤Z≤84. Using known Q _α values the area of known masses could be extended to more exotic nuclei and to higher proton numbers. The results are compared with mass models and extrapolations of experimental values. In a second experiment with ²⁰⁹Bi projectiles the area of the measured masses was extended to lower proton numbers. Due to various improvements at the ESR the precision of the measurements could be raised. (ii) Exotic nuclei with half-lives shorter than the time needed for SMS (present limit: T _1/2 ≈ 5 sec) can be investigated by time-of-flight measurements whereby the ESR is operated in the isochronous mode. This novel experimental technique has been successfully applied in first measurements with nickel and neon fragments where a mass resolving power of m/Δm=1.5·10⁵ (FWHM) was achieved.     

Multiple Coulomb ordered strings of ions in a storage ring

We explain that the anomalous frequency shifts of very close masses obtained in the high precision mass measurement experiments in the ESR storage ring result from the locking of Coulomb interacting strings of ions. Here two concentric strings which run horizontally close to each other are captured into a single string if their thermal clouds overlap and give up their identity.     

Observation of beam instability in the SSRF storage ring

During the SSRF(Shanghai Synchrotron Radiation Facility) storage ring phase-I commissioning, some instabilities have been observed, and the broadband impedance has also been measured. The primary instabilities at present stage are vertical beam blow up and resistive wall instability.     

合肥储存环电子束流寿命分析

 电子束流寿命是个很重要的指标,直接影响合肥光源的正常运行,为此研究了影响束流寿命的因素,测量了高频腔压、耦合度以及束团长度对电子束流寿命的影响,研究显示合肥储存环的电子束流真空寿命和托歇克寿命相当;并且利用束损系统测量了因托歇克寿命的变化而造成束流损失的相对变化;通过增加耦合度增加束流的垂直发射度,有效地提高了束流的寿命,保证了合肥光源的正常运行。     

Observation of beam instability in the SSRF storage ring

During the SSRF(Shanghai Synchrotron Radiation Facility) storage ring phase-I commissioning, some instabilities have been observed, and the broadband impedance has also been measured. The primary instabilities at present stage are vertical beam blow up and resistive wall instability.     

Laser probing of ions in a storage ring: A method for selective determination of lifetimes of metastable states

A collinear laser probing technique is introduced for use in ion storage rings. This method can be used for high resolution studies of the decay properties of metastable states in ions. An experiment on singly charged xenon utilizing this technique is presented. By selective excitation of individual hyperfine states a drastic hyperfine induced quenching was observed. Systematic effects from ion beam neutralization in the rest gas and mixing effects occurring in the bending magnets are discussed. This revised version was published online in August 2006 with corrections to the Cover Date.     

Magnetic dipole transition rates in B-like and F-like titanium ions measured at a heavy-ion storage ring

The rates of the electric-dipole forbidden transitions between the fine structure levels of the ground state in B- and F-like ions of Ti have been measured optically at a heavy-ion storage ring. The lifetime results, (0.627±0.010) ms for Ti¹⁷⁺ and (0.513±0.010) ms for Ti¹³⁺, are the most precise for any such transition yet and are in reasonable agreement with theory. An isoelectronic comparison includes data from electron beam and Kingdon-type ion traps.     

Longitudinal Schottky spectra of a bunched Ne10+ ion beam at the CSRe

The longitudinal Schottky spectra of a radio-frequency (RF) bunched and electron cooled ²²Ne¹⁰⁺ ion beam at 70 MeV/u have been studied by a newly installed resonant Schottky pick-up at the experimental cooler storage ring (CSRe), at IMP. For an RF-bunched ion beam, a longitudinal momentum spread of Δp/p=1.6×10^-5 has been reached with less than 10⁷ stored ions. The reduction of momentum spread compared with a coasting ion beam was observed from Schottky noise signal of the bunched ion beam. In order to prepare the future laser cooling experiment at the CSRe, the RF-bunching power was modulated at 25^th, 50^th and 75^th harmonic of the revolution frequency, effective bunching amplitudes were extracted from the Schottky spectrum analysis. Applications of Schottky noise for measuring beam lifetime with ultra-low intensity of ion beams are presented, and it is relevant to upcoming experiments on laser cooling of relativistic heavy ion beams and nuclear physics at the CSRe.     

合肥电子储存环束流不稳定性的抑制

 合肥光源二期工程改造的电子储存环调试过程中,发现多束团存储和运行时存在耦合束团不稳定性,严重地限制了注入的最高流强,并且影响了光源运行的质量。通过过正地增大正色品以及在储存环上插入八极磁铁,基本上抑制了横向的耦合束团不稳定性,保证了稳定注入束流300 mA的技术指标。     

Realization of a locally-round beam in an ultimate storage ring using solenoids

"Ultimate" storage rings (USRs), with electron emittance smaller than 100 pm·rad and on the scale of the diffraction limit for hard X-rays in both transverse planes, have the potential to deliver photons with much higher brightness and higher transverse coherence than that projected for the rings currently operational or under construction. Worldwide efforts have been made to design and to build light sources based on USRs. How to obtain a round beam, i.e., a beam with equivalent transverse emittances, is an important topic in USR studies. In this paper, we show that a locally-round beam can be achieved by using a pair of solenoid and anti-solenoid with a circularly polarized undulator located in between. Theoretical analysis and application of this novel method, particularly to one of the Beijing Advanced Photon Source storage ring design having natural emittance of 75 pm·rad, are presented.     

合肥电子储存环束流不稳定性的抑制

合肥光源二期工程改造的电子储存环调试过程中,发现多束团存储和运行时存在耦合束团不稳定性,严重地限制了注入的最高流强,并且影响了光源运行的质量。通过过正地增大正色品以及在储存环上插入八极磁铁,基本上抑制了横向的耦合束团不稳定性,保证了稳定注入束流300 mA的技术指标。