ISOLDE Seminar

"Characterization of very low intensity ion beam from REX/HIE-ISOLDE linear accelerator"

by Niels Killian Noal Bidault (CERN, INFN & Sapienza University of Rome)




We present instrumental methodologies that allow for the determination of radioactive ion beam properties from the REX/HIE-ISOLDE linear accelerator, at intensities often too weak to make use of conventional beam-line monitoring detectors (for instance, Faraday cups). By justifying the collisional aspects of the electron-ion plasma inside an EBIS, we infer a correlation between the measured axial energy distributions and the temperature of ions. Key indicators of the extracted beam's quality can then be deduced from the ion temperature using Boltzmann distributions, such as the emittance. We illustrate the studies related to the charge-state and the energy dynamics with the case of a multi-charged xenon beam. The question of beam purity is assessed by demonstrating the possibility to map a spectrum of the contamination from residual gas ions on a wide A/q-range.

Furthermore, we characterize the beam dynamics in the HEBT lines after acceleration through REX/HIE-ISOLDE linac. The principles behind the identification of the transverse and the longitudinal beam properties are mainly based on multiple acquisitions of the respective trace-space projections. In the case of transverse beam properties, we correlate measurements using the quadrupole-scan method and the double-slit method using a potassium beam of less than one femto-Ampere current, at an energy of 3.8 MeV/u. We show the uncertainties associated with the evaluation of the emittance and Twiss parameters for each method. We then explain the choice made for measuring the beam energy and the analysis of results using RIB. The complete longitudinal beam properties are measured using a superconducting quarter-wave resonator as a buncher, and measuring the beam energy and time-of-flight distributions.