Eur. Phys. J. A (2019) 55: 101
https://doi.org/10.1140/epja/i2019-12777-3

Regular Article - Experimental Physics

The open LPC Paul trap for precision measurements in beta decay

¹ GANIL, CEA/DSM-CNRS/IN2P3, Bd Henri Becquerel, 14000, Caen, France
² Normandie Univ, ENSICAEN, UNICAEN, CNRS/IN2P3, LPC Caen, 14000, Caen, France
³ Institut de Physique nucléaire de Lyon, 4 rue Enrico Fermi, 69622, Villeurbanne, France
⁴ CIMAP, CEA/CNRS/ENSICAEN, Université de Caen, Caen, France
⁵ National Superconducting Cyclotron Laboratory and Department of Physics and Astronomy, Michigan State University, 48824, East Lansing, MI, USA
⁶ Departamento de Física Atómica Molecular y Nuclear, Universidad de Granada, Granada, Spain

^* e-mail: pierre.delahaye@ganil.fr

Received: 19 October 2018
Accepted: 21 May 2019
Published online: 28 June 2019

Abstract

The LPCTrap experiment uses an open Paul trap which was built to enable precision measurements in the beta decay of radioactive ions. The initial goal was the precise measurement of the beta-neutrino angular correlation coefficient in the decay of ⁶He . Its geometry results from a careful optimization of the harmonic potential created by cylindrical electrodes. It supersedes previously considered geometries that presented a smaller detection solid angle to the beta particle and the recoiling ion. We describe here the methods which were used for the potential optimization, and we present the measured performances in terms of trapping time, cloud size and temperature, and space charge related limits. The properties of the ion cloud at equilibrium are investigated by a simple numerical simulation using hard sphere collisions, which additionally gives insights on the trapping loss mechanism. The interpretation for the observed trapping lifetimes is further corroborated by a model recently developed for ion clouds in Paul traps. The open trap shall serve other projects. It is currently used for commissioning purpose in the TRAPSENSOR experiment and is also considered in tests of the Standard Model involving the beta decay of polarized ²³Mg and ³⁹Ca ion in the frame of the MORA experiment. The latter tests require in-trap polarization of the ions and further optimization of the trapping and detection setup. Based on the results of the simulations and of their interpretation, different improvements of the trapping setup are discussed.