The open LPC Paul trap for precision measurements in beta decay

The LPCTrap experiment uses an open Paul trapwhich was built to enable precision measurements in the beta decayof 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 angleto the beta particleand the recoiling ion. We describe here the methods which were used for the potential optimization, and we present the measured performances in terms of trappingtime, cloud size and temperature, and space charge related limits. The properties of the ion cloud at equilibrium are well reproduced by a simple numerical simulation using hard sphere collisions, which additionally gives insights on the trappingloss mechanism. The interpretation for the observed trappingliftetimes is further corroborated by a model recently developed for ion clouds in Paul traps. The open trapshall 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 decayof polarized $^{23}$Mg and $^{39}$Ca ion in the frame of the MORAexperiment. The latter tests require in- trappolarization of the ions and further optimization of the trappingand detection setup. Based on the results of the simulations and of their interpretations given by the model, different improvements of the trappingsetup are discussed.