High-accuracy mass measurements in ion traps and storage rings

High-accuracy mass measurements have recently been performed on radioactive isotopes produced by proton-induced spallation at the on-line isotope separator ISOLDE at CERN and by heavy-ion projectile fragmentation at the fragment separator FRS at GSI. At ISOLDE, singly charged ions were injected into the Penning trap mass spectrometer ISOLTRAP and their masses determined by observing their cyclotron frequencies in the homogeneous magnetic field of the ion trap. At GSI, bare, hydrogen, or helium-like ions were injected into the experimental storage ring ESR, electron-cooled to the same velocity, and their masses determined by observing their revolution frequencies in the ESR. With ISOLTRAP and ESR, resolving power in the range of 4 × 10⁵< = m/Δ m(FWHM)< = 10⁷ and an accuracy up to \delta m/m~ 10^-7 were achieved for radioactive isotopes. Mass measurements of highly charged ions of stable isotopes were performed at Stockholm by use of SMILETRAP. In this case, a resolving power of about 10⁸ and an accuracy close to 10^-9 were obtained. This revised version was published online in August 2006 with corrections to the Cover Date.     

Connection between beam polarization and systematical errors in storage ring electric-dipole-moment experiments

Analysis of spin dynamics in storage ring electric-dipole-moment (EDM) experiments ascertains that the use of initial vertical beam polarization allows the cancellation of spin-dependent systematical errors imitating the EDM effect. While the use of this polarization meets certain difficulties, it should be considered as an alternative or supplementary possibility of fulfilling the EDM experiment.     

New method of measuring electric dipole moments in storage rings

A new highly sensitive method of looking for electric dipole moments of charged particles in storage rings is described. The major systematic errors inherent in the method are addressed and ways to minimize them are suggested. It seems possible to measure the muon EDM to levels that test speculative theories beyond the standard model.     

Resonance backscattering in submicron rings

We discuss the rate of relaxation of the total spin in a two-electron droplet in the vicinity of the magnetic-field-driven singlet-triplet transition. The total spin relaxation is attributed to spin-orbit and electron-phonon interactions. The relaxation process is found to depend on the spin of ground and excited states. This asymmetry is used to explain puzzles in recent high source-drain transport experiments.     

New measurements of proton-proton total cross section at the CERN intersecting storage rings

Measurements of the proton-proton total cross section have been made with increased precision (±0.6%) over the ISR energy range $\text{s}\text{=23.5?62.7}\text{GeV}$. Two different experimental methods gave consistent results, showing that the total cross section increases 10% over the ISR range and in addition that the absolute value of the ISR luminosity can be measured to ±0.9%.     

A method to polarise antiprotons in storage rings and create polarised antineutrons

An intense circularly polarised g \gamma -beam interacts with a cooled antiproton beam in a storage ring. Due to spin-dependent absorption cross-sections for the reaction g+[`(p)]?p<sup>-</sup>+[`(n)]\ensuremath \gamma+\overline{p}\rightarrow\pi^{-}+\overline{n} a built-up of polarisation of the stored antiprotons takes place. Figures of merit around 0.1 can be reached in principle over a wide range of antiproton energies. In this process polarised antineutrons with polarisation P_[`(n)] \succ 70%\ensuremath P_{\overline{n}} \succ 70\% emerge. The method is presented for the case of a 300MeV/c cooled antiproton beam.     

Free electron lasers in storage rings

In this paper we briefly describe the principle of the free electron laser in a storage ring and the results obtained recently at Orsay. We also discuss the expected performances of such a device in more modern storage rings.     

Effect of fringing fields in storage rings

Electron beams in storage rings of third-generation synchrotron radiation sources feature a low emittance and extended lifetime. The provision of such characteristics requires a detailed study of higher order effects related to magnetic fields and cooperative effects associated with beam density. Fringing fields, being an unavoidable attribute of magnets of any type, may significantly affect the beam dynamics, since they appear in equations of particle motion of first and higher orders. A simple technique for evaluating the effect of fringing fields on the beam dynamics is suggested. Numerical results obtained with this technique for the quadrupoles of the CANDLE storage ring [1] are reported.     

Polarized beams at storage rings

This paper reviews modern techniques to accelerate polarized particles to high energy and to preserve their polarization in the storage rings. Possibilities of the bean polarization control are discussed for proton and electron machines.     

Beam lifetimes of low-charged ions in storage rings

The beam lifetimes and the charge-changing cross-sections for fast low-charged ions are calculated for the energy range of 1–100 MeV/u and compared with experimental data for Mg¹⁺ and U¹⁰⁺ ions recently measured at SIS GSI, Darmstadt. A moderate agreement of calculations with experiment was obtained. The results show that the heavy components of the residual gas (N₂ and Ar) play a key role for projectile charge-changing processes in the energy range considered. This revised version was published online in July 2006 with corrections to the Cover Date.     

Workshop on coherent synchrotron radiation in storage rings

The annual UK SR User meeting at Diamond Light Source welcomed 250 members of the international synchrotron community to the site in South Oxfordshire, UK. This is the first time that Diamond has hosted this event as an operational facility.     

Bunch transverse emittance increase in electron storage rings

In this paper a theoretical framework to estimate the bunch transverse emittance growing in electron storage rings due to short range transverse wakefield of the machine is established. New equilibrium emittance equations are derived and applied to explain the experimentally obtained results in ATF damping ring. This equation will be useful for linear collider damping ring design.     

Bunch transverse emittance increase in electron storage rings

In this paper a theoretical framework to estimate the bunch transverse emittance growing in electron storage rings due to short range transverse wakefield of the machine is established. New equilibrium emittance equations are derived and applied to explain the experimentally obtained results in ATF damping ring. This equation will be useful for linear collider damping ring design.     

Incoherent effects of electron clouds in proton storage rings

Electron clouds in the beam pipe of high-energy proton or positron storage rings can give rise to significant incoherent emittance growth, at densities far below the coherent-instability threshold. We identify two responsible mechanisms: namely, (1) a beam particle periodically crosses a resonance and (2) a beam particle periodically crosses a region of the bunch where its motion is linearly unstable. Formation of halo or beam-core blow up, respectively, are the result. Key ingredients for both processes are synchrotron motion and electron-induced tune shift. The mechanisms considered provide a possible explanation for reduced beam lifetime and emittance growth observed at several operating accelerators. Similar phenomena are likely to occur in other two-stream systems.     

Review of collective beam instabilities in electron-positron storage rings

The review of studies of collective beam instabilities in electron-positron storage rings is presented. The processes of excitation and suppression of the longitudinal microwave instability, transverse mode coupling instability, longitudinal and transverse multi-bunch instabilities, and instabilities induced by an interaction of a beam with ions or electron clouds are discussed. Important equations for estimation of the threshold beam currents and the rise time of instabilities, as well as the references to the major original works are given. The methods for diagnostics and suppression of instabilities are considered using specific examples.     

Landau damping and free-electron laser interaction in storage rings

In this paper we will discuss the conditions under which the free-electron laser interaction in a storage ring may reinforce the effect of the Landau damping, thus leading to the suppression of different types of instabilities. The problem will be discussed both by making use of general arguments and referring to the specific examples.     

Compton scattering with quasi-real photons in electron-positron storage rings

For electron-positron colliding-beam processes of the type e^?e⁺ → e^?e⁺, where one of the e^± particles and the photon are detected at large angle, a number of theoretical predictions are given and compared with some data of a recent experiment performed at Orsay.