Beam Dynamics Studies for the HIE-ISOLDE Linac at CERN

The upgrade of the normal conducting (NC) Radioactive Ion Beam EXperiment (REX)-ISOLDE heavy ion accelerator at CERN, under the High Intensity and Energy (HIE)-ISOLDE framework, proposes the use of superconducting (SC) quarter-wave resonators (QWRs) to increase the energy capability of the facility from 3 MeV/u to beyond 10 MeV/u. A beam dynamics study of a lattice design comprising SC QWRs and SC solenoids has confirmed the design's ability to accelerate ions, with a mass-to-charge ratio in the range 2.5 < A/q < 4.5, to the target energy with a minimal emittance increase. We report on the development of this study to include the implementation of realistic fields within the QWRs and solenoids. A preliminary error study is presented in order to constrain tolerances on the manufacturing and alignment of the linac.Comment: 3 pages, 8 figures, 1 table, submitted to the Particle Accelerator Conference (PAC) 2009 in Vancouver. Page formatting changed to US letter siz

Future plans at ISOLDE

The CERN ISOLDE facility has operated for over 30 years delivering beams of exotic ions to an ever-growing user community. The facility went through a major up-grade in the early 1990s with the move from the 600 MeV synchrocyclotron to the 1 GeV PS-Booster proton synchrotron. This was followed by a primary proton beam energy up grade to 1.4 GeV in 1999. Lately, an important step forward was taken with the start of the REX-ISOLDE experiment for charge breeding and post acceleration of exotic ions. CERN has recently decided on a consolidation project for the facility to assure that the required number of shifts can be delivered in the future. An overview will be given of the on-going consolidation and development programme and its implications on the physics programme, in particular the REX-ISOLDE post accelerator experiment. An important parameter for a better yield of very exotic elements is the primary proton beam intensity, beam energy and time structure. The possible short-term improvements of, in particular, beam intensity will be discussed in some detail. While the main effort at CERN today goes towards the completion of the LHC, some resources have been found for accelerator R&D. A possible project is a new high intensity proton source at CERN, the Superconducting Proton Linac (SPL), which could open the door to the construction of a next-generation radioactive beam facility. The possible primary beam characteristics and some design considerations and their implications for such a facility will be discussed. Some ideas for the facility itself, such as the use of antiprotons and muons as new probes, production of a neutrino beam from stored radioactive ions and a preliminary design for a low energy storage ring, will be presented

On the absence of appreciable half-life changes in alpha emitters cooled in metals to 1 Kelvin and below

The recent suggestion that dramatic changes may occur in the lifetime of alpha and beta decay when the activity, in a pure metal host, is cooled to a few Kelvin, is examined in the light of published low temperature nuclear orientation (LTNO) experiments, with emphasis here on alpha decay. In LTNO observations are made of the anisotropy of radioactive emissions with respect to an axis of orientation. Correction of data for decay of metallic samples held at temperatures at and below 1 Kelvin for periods of days and longer has been a routine element of LTNO experiments for many years. No evidence for any change of half life on cooling, with an upper level of less than 1%, has been found, in striking contrast to the predicted changes, for alpha decay, of several orders of magnitude. The proposal that such dramatic changes might alleviate problems of disposal of long-lived radioactive waste is shown to be unrealistic.Comment: 27 pages, 12 figures, accepted for publication in Nucl.Phys.A. Revised version, including quantitative analysis of the sensitivity of nuclear orientation experiments, discussed in this work, to changes of alpha-decay lifetimes in metals at low temperatures. Conclusions remain unchange

Evolution of Mid-gap States and Residual 3-Dimensionality in La2−x_{2-x}Srx_xCuO4_4

We have carried out extensive first principles doping-dependent computations of angle-resolved photoemission (ARPES) intensities in La$_{2-x}$Sr$_x$CuO$_4$ (LSCO) over a wide range of binding energies. Intercell hopping and the associated 3-dimensionality, which is usually neglected in discussing cuprate physics, is shown to play a key role in shaping the ARPES spectra. Despite the obvious importance of strong coupling effects (e.g. the presence of a lower Hubbard band coexisting with mid-gap states in the doped insulator), we show that a number of salient features of the experimental ARPES spectra are captured to a surprisingly large extent when effects of $k_z$-dispersion are properly included in the analysis.Comment: 5 pages, 4 figure

Matrix Element and Strong Electron Correlation Effects in ARPES from Cuprates

We discuss selected results from our recent work concerning the ARPES (angle-resolved photoemission) spectra from the cuprates. Our focus is on developing an understanding of the effects of the ARPES matrix element and those of strong electron correlations in analyzing photointensities. With simulations on Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$ (Bi2212), we show that the ARPES matrix element possesses remarkable selectivity properties, such that by tuning the photon energy and polarization, emission from the bonding or the antibonding states can be enhanced. Moreover, at low photon energies (below 25 eV), the Fermi surface (FS) emission is dominated by transitions from just the O-atoms in the CuO$_2$ planes. In connection with strong correlation effects, we consider the evolution with doping of the FS of Nd$_{2-x}$Ce$_x$CuO$_{4\pm\delta}$ (NCCO) in terms of the $t$-$t'$-$U$ Hubbard model Hamiltonian. We thus delineate how the FS evolves on electron doping from the insulating state in NCCO. The Mott pseudogap is found to collapse around optimal doping suggesting the existence of an associated quantum critical point.Comment: 5 pages, 4 figures, accepted to be published in Journal of Physics and Chemistry of Solid

Reply to Comment on Circular Dichroism in the Angle-Resolved Photoemission Spectrum of the High-Temperature Bi2Sr2CaCu2O8 Superconductor http://arxiv.org/abs/1004.1648

We conclude that arguments of Norman et al. in their Comment do not provide a significant basis for their claim that the geometric mechanism for explaining the observations reported by them is not viable. More generally, our study highlights the importance of assessing structural issues before invoking exotic mechanisms for explaining unusual spectroscopic observations, especially in complex materia