Eur. Phys. J. A (2009) 42: 503-507
https://doi.org/10.1140/epja/i2009-10828-0

Regular Article - Experimental Physics

An ion cooler-buncher for high-sensitivity collinear laser spectroscopy at ISOLDE

¹ The University of Manchester, M13 9PL, Manchester, UK
² Max-Planck-Institute for Nuclear Physics, 69117, Heidelberg, Germany
³ ISOLDE-CERN, route de Meyrin, CH-1211, Geneva 23, Switzerland
⁴ IPN, IN2P3-CNRS, F-91406, Orsay Cedex, France
⁵ The University of Birmingham, B15 2TT, Birmingham, UK
⁶ Institute for Physics, Johannes Gutenberg University, 55099, Mainz, Germany
⁷ Department of Physics, University of Jyväskylä, P.O. Box 35 (YFL), FIN-40014, Jyväskylä, Finland
⁸ Helsinki Institute of Physics, University of Helsinki, P.O. Box 64, FIN-00014, Helsinki, Finland
⁹ K.U. Leuven, IKS, Celestijnenlaan 200 D, B-3001, Leuven, Belgium
¹⁰ Accelerator Group, CIEMAT, Avda. Complutense 22, 28040, Madrid, Spain

^* e-mail: Ernesto@cern.ch

Received: 27 November 2008
Revised: 15 May 2009
Accepted: 18 May 2009
Published online: 16 June 2009

Abstract

A gas-filled segmented linear Paul trap has been installed at the focal plane of the high-resolution separator (HRS) at CERN-ISOLDE. As well as providing beams with a reduced transverse emittance, this device is also able to accumulate the ions and release the sample in bunches with a well-defined time structure. This has recently permitted collinear laser spectroscopy with stable and radioactive bunched beams to be demonstrated at ISOLDE. Surface-ionized ^{39, 44, 46}K and ⁸⁵Rb beams were accelerated to 30keV, mass separated and injected into the trap for subsequent extraction and delivery to the laser setup. The ions were neutralized in a charge exchange cell and excited with a co-propagating laser. The small ion beam emittance allowed focussing in the ion-laser overlap region, which is essential to achieve the best experimental sensitivity. Fluorescent photons were detected by a photomultiplier tube as a frequency scan was taken. A gate (typically 7-12μs wide) was set on the photomultiplier signal to accept the fluorescent photons within the time window defined by the bunch. Thus, using accumulation times of 100ms, the dominant contribution to background due to continuous laser scattering could be reduced by a factor of up to 4×10⁴ .